Release v1.14.0-rc.1

Closes #12076

.cirrus.yml

@@ -23,10 +23,10 @@ test_freebsd_task:
   env:
     CHECK_REPRODUCIBLE: true
     LC_ALL: en_US.UTF-8
-    PATH: $PATH:/usr/local/lib/erlang22/bin
+    PATH: $PATH:/usr/local/lib/erlang24/bin
 
   install_script:
-    - pkg install -y erlang-runtime22 git gmake
+    - pkg install -y erlang-runtime24 git gmake
     - rm -rf .git
     - gmake compile
 

.formatter.exs

@@ -14,5 +14,6 @@
 
     # Errors tests
     assert_eval_raise: 3
-  ]
+  ],
+  normalize_bitstring_modifiers: false
 ]

.github/ISSUE_TEMPLATE.md

@@ -1,21 +0,0 @@
-### Precheck
-
-* For proposing a new feature, please start a discussion on the Elixir Core mailing list: https://groups.google.com/group/elixir-lang-core
-* For bugs, do a quick search and make sure the bug has not yet been reported
-* Please disclose security vulnerabilities privately at elixir-security@googlegroups.com
-* Do not use the issues tracker for guidance, questions or support (try Elixir Forum, Stack Overflow, Slack, etc. instead)
-* Finally, be nice and have fun!
-
-### Environment
-
-* Elixir & Erlang/OTP versions (elixir --version): 
-* Operating system: 
-
-### Current behavior
-
-Include code samples, errors and stacktraces if appropriate.
-If reporting a bug, please include the reproducing steps.
-
-### Expected behavior
-
-A short description on how you expect the code to behave.

.github/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,11 @@
+---
+blank_issues_enabled: true
+
+contact_links:
+  - name: Discuss proposals
+    url: https://groups.google.com/g/elixir-lang-core
+    about: Send proposals for new ideas to our mailing list
+
+  - name: Ask questions and support
+    url: https://elixirforum.com/
+    about: Ask questions, provide support and more on Elixir Forum

.github/ISSUE_TEMPLATE/issue.yml

@@ -0,0 +1,53 @@
+---
+name: Report an issue
+description:
+  Tell us about something that is not working the way we (probably) intend
+body:
+  - type: markdown
+    attributes:
+      value: >
+        Thank you for contributing to Elixir! :heart:
+
+
+        Please, do not use this form for guidance, questions or support.
+        Try instead in [Elixir Forum](https://elixirforum.com),
+        the [IRC Chat](https://web.libera.chat/#elixir),
+        [Stack Overflow](https://stackoverflow.com/questions/tagged/elixir),
+        [Slack](https://elixir-slackin.herokuapp.com),
+        [Discord](https://discord.gg/elixir) or in other online communities.
+
+  - type: textarea
+    id: elixir-and-otp-version
+    attributes:
+      label: Elixir and Erlang/OTP versions
+      description: Paste the output of `elixir --version` here.
+    validations:
+      required: true
+
+  - type: input
+    id: os
+    attributes:
+      label: Operating system
+      description: The operating system that this issue is happening on.
+    validations:
+      required: true
+
+  - type: textarea
+    id: current-behavior
+    attributes:
+      label: Current behavior
+      description: >
+        Include code samples, errors, and stacktraces if appropriate.
+
+
+        If reporting a bug, please include the reproducing steps.
+    validations:
+      required: true
+
+  - type: textarea
+    id: expected-behavior
+    attributes:
+      label: Expected behavior
+      description: A short description on how you expect the code to behave.
+    validations:
+      required: true

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"

.github/workflows/ci.yml

@@ -8,22 +8,29 @@ env:
   ERLC_OPTS: "warnings_as_errors"
   LANG: C.UTF-8
 
+permissions:
+  contents: read
+
 jobs:
   test_linux:
     name: Linux, ${{ matrix.otp_release }}, Ubuntu 18.04
     strategy:
       fail-fast: false
       matrix:
-        otp_release: ['OTP-24.0', 'OTP-23.3', 'OTP-23.0', 'OTP-22.3', 'OTP-22.0']
-        development: [false]
         include:
+          - otp_release: OTP-25.0
+            otp_latest: true
+          - otp_release: OTP-24.3
+          - otp_release: OTP-24.0
+          - otp_release: OTP-23.3
+          - otp_release: OTP-23.0
           - otp_release: master
             development: true
           - otp_release: maint
             development: true
     runs-on: ubuntu-18.04
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           fetch-depth: 50
       - name: Install Erlang/OTP
@@ -38,11 +45,12 @@ jobs:
         run: |
           rm -rf .git
           make compile
+          echo "$PWD/bin" >> $GITHUB_PATH
       - name: Build info
         run: bin/elixir --version
       - name: Check format
         run: make test_formatted && echo "All Elixir source code files are properly formatted."
-      - name: Dyalizer
+      - name: Run Dialyzer
         run: dialyzer -pa lib/elixir/ebin --build_plt --output_plt elixir.plt --apps lib/elixir/ebin/elixir.beam lib/elixir/ebin/Elixir.Kernel.beam
       - name: Erlang test suite
         run: make test_erlang
@@ -52,22 +60,37 @@ jobs:
         continue-on-error: ${{ matrix.development }}
       - name: Check reproducible builds
         run: taskset 1 make check_reproducible
-        if: matrix.otp_release == 'OTP-24.0'
+        if: ${{ matrix.otp_latest }}
+      - name: Build docs
+        if: ${{ matrix.otp_latest }}
+        run: |
+          git config --global advice.detachedHead false
+          EX_DOC_LATEST_STABLE_VERSION=$(curl -s https://hex.pm/api/packages/ex_doc | jq --raw-output '.latest_stable_version')
+          for branch in main v${EX_DOC_LATEST_STABLE_VERSION}; do
+            echo "Building docs with ExDoc ${branch}"
+            cd ..
+            git clone https://github.com/elixir-lang/ex_doc.git --branch ${branch} --depth 1
+            cd ex_doc
+            ../elixir/bin/mix do local.rebar --force + local.hex --force + deps.get + compile
+            cd ../elixir/
+            make docs
+            rm -rf ../ex_doc/
+          done
 
   test_windows:
     name: Windows, OTP-${{ matrix.otp_release }}, Windows Server 2019
     strategy:
       matrix:
-        otp_release: ['22.3']
+        otp_release: ['23.3']
     runs-on: windows-2019
     steps:
       - name: Configure Git
         run: git config --global core.autocrlf input
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           fetch-depth: 50
       - name: Cache Erlang/OTP package
-        uses: actions/cache@v2
+        uses: actions/cache@v3
         with:
           path: C:\Users\runneradmin\AppData\Local\Temp\chocolatey\erlang
           key: OTP-${{ matrix.otp_release }}-windows-2019
@@ -92,7 +115,7 @@ jobs:
     name: Check POSIX-compliant
     runs-on: ubuntu-18.04
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
         with:
           fetch-depth: 50
       - name: Install Shellcheck

.github/workflows/notify.exs

@@ -0,0 +1,72 @@
+# #!/usr/bin/env elixir
+[tag] = System.argv()
+
+Mix.install([
+  {:req, "~> 0.2.1"},
+  {:jason, "~> 1.0"}
+])
+
+%{status: 200, body: release} =
+  Req.get!("https://api.github.com/repos/elixir-lang/elixir/releases/tags/#{tag}")
+
+if release["draft"] do
+  raise "cannot notify a draft release"
+end
+
+## Notify on elixir-lang-ann
+
+names_and_checksums =
+  for asset <- release["assets"],
+      name = asset["name"],
+      name =~ ~r/.sha\d+sum$/,
+      do: {name, Req.get!(asset["browser_download_url"]).body}
+
+line_items =
+  for {name, checksum_and_name} <- Enum.sort(names_and_checksums) do
+    [checksum | _] = String.split(checksum_and_name, " ")
+    root = Path.rootname(name)
+    "." <> type = Path.extname(name)
+    "  * #{root} - #{type} - #{checksum}\n"
+  end
+
+mail = %{
+  "From" => "jose.valim@dashbit.co",
+  "To" => "elixir-lang-ann@googlegroups.com",
+  "Subject" => "Elixir #{tag} released",
+  "HtmlBody" => "https://github.com/elixir-lang/elixir/releases/tag/#{tag}\n\n#{line_items}",
+  "MessageStream" => "outbound"
+}
+
+if System.get_env("DRYRUN") do
+  IO.puts("MAIL")
+  IO.inspect(mail)
+else
+  headers = %{
+    "X-Postmark-Server-Token" => System.fetch_env!("ELIXIR_LANG_ANN_TOKEN")
+  }
+
+  resp = Req.post!("https://api.postmarkapp.com/email", {:json, mail}, headers: headers)
+  IO.puts("#{resp.status} elixir-lang-ann\n#{inspect(resp.body)}")
+end
+
+## Notify on Elixir Forum
+
+post = %{
+  "title" => "Elixir #{tag} released",
+  "raw" => "https://github.com/elixir-lang/elixir/releases/tag/#{tag}\n\n#{release["body"]}",
+  # Elixir News
+  "category" => 28
+}
+
+if System.get_env("DRYRUN") do
+  IO.puts("POST")
+  IO.inspect(post)
+else
+  headers = %{
+    "api-key" => System.fetch_env!("ELIXIR_FORUM_TOKEN"),
+    "api-username" => "Elixir"
+  }
+
+  resp = Req.post!("https://elixirforum.com/posts.json", {:json, post}, headers: headers)
+  IO.puts("#{resp.status} Elixir Forum\n#{inspect(resp.body)}")
+end

.github/workflows/notify.yml

@@ -0,0 +1,28 @@
+name: Notify
+
+on:
+  release:
+    types:
+      - published
+
+permissions:
+  contents: read
+
+jobs:
+  notify:
+    runs-on: ubuntu-18.04
+    name: Notify
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 50
+      - uses: erlef/setup-beam@v1
+        with:
+          otp-version: 24.3
+          elixir-version: 1.13.4
+      - name: Run Elixir script
+        env:
+          ELIXIR_FORUM_TOKEN: ${{ secrets.ELIXIR_FORUM_TOKEN }}
+          ELIXIR_LANG_ANN_TOKEN: ${{ secrets.ELIXIR_LANG_ANN_TOKEN }}
+        run: |
+          elixir .github./workflows/notify.exs ${{ github.ref_name }}

.github/workflows/release.yml

@@ -0,0 +1,96 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - v*
+
+env:
+  ELIXIR_OPTS: "--warnings-as-errors"
+  ERLC_OPTS: "warnings_as_errors"
+  LANG: C.UTF-8
+
+jobs:
+  create_draft_release:
+    permissions:
+      contents: write
+    runs-on: ubuntu-18.04
+    env:
+      GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+    steps:
+      - name: Create draft release
+        run: |
+          gh release create \
+            --repo ${{ github.repository }} \
+            --title ${{ github.ref_name }} \
+            --notes '' \
+            --draft \
+            ${{ github.ref_name }}
+  release_pre_built:
+    needs: create_draft_release
+    strategy:
+      fail-fast: true
+      matrix:
+        include:
+          - otp: 23
+            otp_version: 23.3
+          - otp: 24
+            otp_version: 24.3
+          - otp: 25
+            otp_version: 25.0
+            build_docs: build_docs
+    runs-on: ubuntu-18.04
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 50
+      - uses: erlef/setup-beam@v1
+        with:
+          otp-version: ${{ matrix.otp_version }}
+          version-type: strict
+      - name: Build Elixir Release
+        run: |
+          make Precompiled.zip
+          mv Precompiled.zip elixir-otp-${{ matrix.otp }}.zip
+          shasum -a 1 elixir-otp-${{ matrix.otp }}.zip > elixir-otp-${{ matrix.otp }}.zip.sha1sum
+          shasum -a 256 elixir-otp-${{ matrix.otp }}.zip > elixir-otp-${{ matrix.otp }}.zip.sha256sum
+          echo "$PWD/bin" >> $GITHUB_PATH
+      - name: Upload Pre-built
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          gh release upload --clobber "${{ github.ref_name }}" \
+            elixir-otp-${{ matrix.otp }}.zip \
+            elixir-otp-${{ matrix.otp }}.zip.sha{1,256}sum
+      - name: Get latest stable ExDoc version
+        if: ${{ matrix.build_docs }}
+        run: |
+          EX_DOC_LATEST_STABLE_VERSION=$(curl -s https://hex.pm/api/packages/ex_doc | jq --raw-output '.latest_stable_version')
+          echo "EX_DOC_LATEST_STABLE_VERSION=${EX_DOC_LATEST_STABLE_VERSION}" >> $GITHUB_ENV
+      - uses: actions/checkout@v3
+        if: ${{ matrix.build_docs }}
+        with:
+          repository: elixir-lang/ex_doc
+          ref: v${{ env.EX_DOC_LATEST_STABLE_VERSION }}
+          path: ex_doc
+      - name: Build ex_doc
+        if: ${{ matrix.build_docs }}
+        run: |
+          mv ex_doc ../ex_doc
+          cd ../ex_doc
+          ../elixir/bin/mix do local.rebar --force + local.hex --force + deps.get + compile
+          cd ../elixir
+      - name: Build Docs
+        if: ${{ matrix.build_docs }}
+        run: |
+          make Docs.zip
+          shasum -a 1 Docs.zip > Docs.zip.sha1sum
+          shasum -a 256 Docs.zip > Docs.zip.sha256sum
+      - name: Upload Docs
+        if: ${{ matrix.build_docs }}
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          gh release upload --clobber "${{ github.ref_name }}" \
+            Docs.zip \
+            Docs.zip.sha{1,256}sum

CHANGELOG.md

@@ -1,288 +1,464 @@
-# Changelog for Elixir v1.13
+# Changelog for Elixir v1.14
 
-The focus behind Elixir v1.13 has been on tooling, mainly tooling related to code formatting, code fragments, code reflection, and code recompilation. A lot of this functionality will directly impact developers working on large codebases and provide meaningful quality of life improvements for those working on Elixir tooling and environments, such as IDEs, notebooks, etc.
+Elixir v1.14 brings many improvements to the debugging experience in Elixir
+and data-type inspection. It also includes a new abstraction for easy
+partitioning of processes called `PartitionSupervisor`, as well as improved
+compilation times and error messages.
 
-## Semantic recompilation
+Elixir v1.14 is the last version to support Erlang/OTP 23. Consider updating
+to Erlang/OTP 24 or Erlang/OTP 25.
 
-Elixir v1.13 comes with many improvements to the compiler, so it recompiles your files less frequently. In particular:
+## `dbg`
 
-  * The digest of the files are considered in addition to their size. This avoids recompiling many files when switching or rebasing branches.
+`Kernel.dbg/2` is a new macro that's somewhat similar to `IO.inspect/2`, but
+specifically tailored for **debugging**.
 
-  * Changing your `mix.exs` will no longer trigger a full recompilation, unless you specifically change the configurations used by the Elixir compiler (`:elixirc_paths` and `:elixirc_options`).
-
-  * Changing compile-time configuration files (`config/config.exs` and any other file imported from it) now only recompiles the project files that depend on the reconfigured applications, instead of a full recompilation. However, if you change the configuration of your application itself, the whole project is still recompiled.
-
-  * Adding, updating or removing a dependency now only recompiles the project files that depend on the modified a dependency.
-
-  * If your project has both Erlang and Elixir files, changing an Erlang file will now recompile only the Elixir files that depend on it.
-
-In a nutshell, Elixir went from triggering full recompilations whenever any of `mix.exs`, `config/config.exs`, `src/*`, and `mix.lock` changed on disk to semantic recompilations. Now it only fully recompiles when:
-
-  * you change the compilation options in `mix.exs`
-  * you change the configuration for the current project in `config/config.exs`
-
-## mix xref
-
-`mix xref` is a tool that analyzes relationships between files. By analyzing the compile-time and runtime dependencies between files, it allows developers to understand what files have to be recompiled whenever a file changes.
-
-Elixir v1.13 comes with many improvements to `mix xref`, such as:
-
-  * `mix xref graph` now supports `--label` to be set to "compile-connected", which returns all compile-time dependencies that lead to additional transitive dependencies.
-
-  * A new `mix xref trace FILE` subcommand receives a file and returns all dependencies in said file, including the line and what caused said dependency (a function/macro call, an alias, a struct, etc).
-
-  * All `mix xref` subcommands support the `--fail-above` flag, which allows you to enforce your project has at most a certain number of compile-time cycles, transitive compile-time dependencies, etc.
-
-  * `mix xref graph` now supports multiple `--sink` and `--source` to be given.
-
-With these improvements, it has become simpler to understand the impact code recompilation has in our codebases and how to limit it.
-
-## Code fragments
-
-The `Code` module got a companion module called `Code.Fragment`, which hosts functions that work on incomplete code, as is often the scenario in editors, interactive shells, etc. The module contains different heuristics to analyze the source code and return context informational.
-
-Thanks to these improvements, `IEx`' autocomplete got several quality of life improvements, such as the autocompletion of sigils, structs, and paths. For example, typing `~<TAB>` now shows:
-
-```iex
-iex(1)> ~
-~C (sigil_C)    ~D (sigil_D)    ~N (sigil_N)    ~R (sigil_R)
-~S (sigil_S)    ~T (sigil_T)    ~U (sigil_U)    ~W (sigil_W)
-~c (sigil_c)    ~r (sigil_r)    ~s (sigil_s)    ~w (sigil_w)
-
-```
-
-Adding the sigil letter and pressing tab then shows the available delimiters:
-
-```iex
-iex(1)> ~r
-"      """    '      '''    (      /      <      [      {      |
-
-```
-
-Similarly, `%<TAB>` now shows only the available structs (exceptions excluded), instead of all modules:
+When called, it prints the value of whatever you pass to it, plus the debugged
+code itself as well as its location. This code:
 
 ```elixir
-iex(1)> %File.St
-File.Stat      File.Stream
+# In my_file.exs
+feature = %{name: :dbg, inspiration: "Rust"}
+dbg(feature)
+dbg(Map.put(feature, :in_version, "1.14.0"))
 ```
 
-Once you define the struct, you can hit `tab` to show all struct fields available:
+Prints this:
 
-```elixir
-iex(1)> %URI{
-authority:    fragment:     host:         path:         port:
-query:        scheme:       userinfo:
+```shell
+$ elixir my_file.exs
+[my_file.exs:2: (file)]
+feature #=> %{inspiration: "Rust", name: :dbg}
+
+[my_file.exs:3: (file)]
+Map.put(feature, :in_version, "1.14.0") #=> %{in_version: "1.14.0", inspiration: "Rust", name: :dbg}
 ```
 
-As you fill them in, the already filled structs no longer show up:
+`dbg/2` can do more. It's a macro, so it *understands Elixir code*. You can see
+that when you pass a series of `|>` pipes to it. `dbg/2` will print the value
+for every step of the pipeline. This code:
 
 ```elixir
-iex(1)> %URI{path: "/example",
-authority:    fragment:     host:         port:         query:
-scheme:       userinfo:
+# In dbg_pipes.exs
+__ENV__.file
+|> String.split("/", trim: true)
+|> List.last()
+|> File.exists?()
+|> dbg()
 ```
 
-Finally, new compilation tracers have been added, alongside a handful of functions in `Module` to retrieve module metadata, which can be used to enrich suggestions in programming environments.
+Prints this:
 
-## Extended code formatting
-
-The `mix format` task has been augmented with the notion of plugins. Plugins can teach the formatter how to format new files and how to format sigils, via the `Mix.Tasks.Format` behaviour.
-
-For example, imagine that your project uses Markdown in two distinct ways: via a custom `~M` sigil and via files with the `.md` and `.markdown` extensions. A custom plugin would look like this:
-
-```elixir
-defmodule MixMarkdownFormatter do
-  @behaviour Mix.Tasks.Format
-
-  def features(_opts) do
-    [sigils: [:M], extensions: [".md", ".markdown"]]
-  end
-
-  def format(contents, opts) do
-    # logic that formats markdown
-  end
-end
+```shell
+$ elixir dbg_pipes.exs
+[dbg_pipes.exs:5: (file)]
+__ENV__.file #=> "/home/myuser/dbg_pipes.exs"
+|> String.split("/", trim: true) #=> ["home", "myuser", "dbg_pipes.exs"]
+|> List.last() #=> "dbg_pipes.exs"
+|> File.exists?() #=> true
 ```
 
-Now any application can use your formatter as follows:
+### IEx and Prying
+
+`dbg/2` supports configurable backends. IEx automatically replaces the default
+backend by one that halts the code execution with `IEx.Pry`, giving developers
+the option to access local variables, imports, and more. This also works with
+pipelines: if you pass a series of `|>` pipe calls to `dbg` (or pipe into it at the
+end, like `|> dbg()`), you'll be able to step through every line in the pipeline.
+
+You can keep the default behaviour by passing the `--no-pry` option to IEx.
+
+## PartitionSupervisor
+
+`PartitionSupervisor` is a new module that implements a new supervisor type. The
+partition supervisor is designed to help with situations where you have a single
+supervised process that becomes a bottleneck. If that process's state can be
+easily partitioned, then you can use `PartitionSupervisor` to supervise multiple
+isolated copies of that process running concurrently, each assigned its own
+partition.
+
+For example, imagine you have an `ErrorReporter` process that you use to report
+errors to a monitoring service.
 
 ```elixir
-# .formatter.exs
-[
-  # Define the desired plugins
-  plugins: [MixMarkdownFormatter],
-  # Remember to update the inputs list to include the new extensions
-  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}", "posts/*.{md,markdown}"]
+# Application supervisor:
+children = [
+  # ...,
+  ErrorReporter
+]
+
+Supervisor.start_link(children, strategy: :one_for_one)
+```
+
+As the concurrency of your application goes up, the `ErrorReporter` process
+might receive requests from many other processes and eventually become a
+bottleneck. In a case like this, it could help to spin up multiple copies of the
+`ErrorReporter` process under a `PartitionSupervisor`.
+
+```elixir
+# Application supervisor
+children = [
+  {PartitionSupervisor, child_spec: ErrorReporter, name: Reporters}
 ]
 ```
 
-Finally, the `Code` module has also been augmented with two functions: `Code.string_to_quoted_with_comments/2` and `Code.quoted_to_algebra/2`. Those functions allow someone to retrieve the Elixir AST with their original source code comments, and then convert this AST to formatted code. In other words, those functions provide a wrapper around the Elixir Code Formatter, supporting developers who wish to create tools that directly manipulate and custom format Elixir source code.
+The `PartitionSupervisor` will spin up a number of processes equal to
+`System.schedulers_online()` by default (most often one per core). Now, when
+routing requests to `ErrorReporter` processes we can use a `:via` tuple and
+route the requests through the partition supervisor.
 
-## v1.13.0-dev
+```elixir
+partitioning_key = self()
+ErrorReporter.report({:via, PartitionSupervisor, {Reporters, partitioning_key}}, error)
+```
+
+Using `self()` as the partitioning key here means that the same process will
+always report errors to the same `ErrorReporter` process, ensuring a form of
+back-pressure. You can use any term as the partitioning key.
+
+### A Common Example
+
+A common and practical example of a good use case for `PartitionSupervisor` is
+partitioning something like a `DynamicSupervisor`. When starting many processes
+under it, a dynamic supervisor can be a bottleneck, especially if said processes
+take a long time to initialize. Instead of starting a single `DynamicSupervisor`,
+you can start multiple:
+
+```elixir
+children = [
+  {PartitionSupervisor, child_spec: DynamicSupervisor, name: MyApp.DynamicSupervisors}
+]
+
+Supervisor.start_link(children, strategy: :one_for_one)
+```
+
+Now you start processes on the dynamic supervisor for the right partition.
+For instance, you can partition by PID, like in the previous example:
+
+```elixir
+DynamicSupervisor.start_child(
+  {:via, PartitionSupervisor, {MyApp.DynamicSupervisors, self()}},
+  my_child_specification
+)
+```
+
+## Improved errors on binaries and evaluation
+
+Erlang/OTP 25 improved errors on binary construction and evaluation. These improvements
+apply to Elixir as well. Before v1.14, errors when constructing binaries would
+often be hard-to-debug generic "argument errors". With Erlang/OTP 25 and Elixir v1.14,
+more detail is provided for easier debugging. This work is part of [EEP
+54](https://www.erlang.org/eeps/eep-0054).
+
+Before:
+
+```elixir
+int = 1
+bin = "foo"
+int <> bin
+#=> ** (ArgumentError) argument error
+```
+
+Now:
+
+```elixir
+int = 1
+bin = "foo"
+int <> bin
+#=> ** (ArgumentError) construction of binary failed:
+#=>    segment 1 of type 'binary':
+#=>    expected a binary but got: 1
+```
+
+## Slicing with steps
+
+Elixir v1.12 introduced **stepped ranges**, which are ranges where you can
+specify the "step":
+
+```elixir
+Enum.to_list(1..10//3)
+#=> [1, 4, 7, 10]
+```
+
+Stepped ranges are particularly useful for numerical operations involving
+vectors and matrices (see [Nx](https://github.com/elixir-nx/nx), for example).
+However, the Elixir standard library was not making use of stepped ranges in its
+APIs. Elixir v1.14 starts to take advantage of steps with support for stepped
+ranges in a couple of functions. One of them is `Enum.slice/2`:
+
+```elixir
+letters = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j"]
+Enum.slice(letters, 0..5//2)
+#=> ["a", "c", "e"]
+```
+
+`binary_slice/2` (and `binary_slice/3` for completeness) has been added to the
+`Kernel` module, that works with bytes and also support stepped ranges:
+
+```elixir
+binary_slice("Elixir", 1..5//2)
+#=> "lx"
+```
+
+## Expression-based inspection and `Inspect` improvements
+
+In Elixir, it's conventional to implement the `Inspect` protocol for opaque
+structs so that they're inspected with a special notation, resembling this:
+
+```elixir
+MapSet.new([:apple, :banana])
+#MapSet<[:apple, :banana]>
+```
+
+This is generally done when the struct content or part of it is private and the
+`%name{...}` representation would reveal fields that are not part of the public
+API.
+
+The downside of the `#name<...>` convention is that *the inspected output is not
+valid Elixir code*. For example, you cannot copy the inspected output and paste
+it into an IEx session.
+
+Elixir v1.14 changes the convention for some of the standard-library structs.
+The `Inspect` implementation for those structs now returns a string with a valid
+Elixir expression that recreates the struct when evaluated. In the `MapSet`
+example above, this is what we have now:
+
+```elixir
+fruits = MapSet.new([:apple, :banana])
+MapSet.put(fruits, :pear)
+#=> MapSet.new([:apple, :banana, :pear])
+```
+
+The `MapSet.new/1` expression evaluates to exactly the struct that we're
+inspecting. This allows us to hide the internals of `MapSet`, while keeping
+it as valid Elixir code. This expression-based inspection has been
+implemented for `Version.Requirement`, `MapSet`, and `Date.Range`.
+
+Finally, we have improved the `Inspect` protocol for structs so that
+fields are inspected in the order they are declared in `defstruct`.
+The option `:optional` has also been added when deriving the `Inspect`
+protocol, giving developers more control over the struct representation.
+See the updated documentation for `Inspect` for a general rundown on
+the approaches and options available.
+
+## v1.14.0-rc.1 (2022-08-15)
+
+### 1. Enhancements
+
+#### IEx
+
+  * [IEx.Helpers] Support sigils in `h/1`
+
+#### Mix
+
+  * [Mix] Add `:config_path` and `:lockfile` options to `Mix.install/2`
+
+### 2. Bug fixes
+
+#### Elixir
+
+  * [Enum] Fix usage of range with `steps != 1` in a few functions (regression)
+  * [Kernel] Fix usage of range with `steps != 1` on `binary_slice/2` (regression)
+  * [Kernel] Recursively expand pipelines on right-hand side of `|>` (regression)
+  * [Kernel] Fix equality in guards for dynamic ranges without steps
+  * [Module] Fix loop while unifying type variables
+  * [System] Raise non-generic exception on missing env in `System.fetch_env!/1` to mirror map operations
+
+#### IEx
+
+  * [IEx] Continue parsing after `--no-pry` (regression)
+
+#### Mix
+
+  * [Mix] Properly compile-dependencies on `mix format`
+
+## v1.14.0-rc.0 (2022-08-01)
 
 ### 1. Enhancements
 
 #### EEx
 
-  * [EEx] Add `:parser_options` to EEx functions
+  * [EEx] Support multi-line comments to EEx via `<%!-- --%>`
+  * [EEx] Add `EEx.tokenize/2`
 
 #### Elixir
 
-  * [Calendar] Add `c:Calendar.year_of_era/3` to support calendars where the beginning of a new era does not align with the beginning of a new year
-  * [CLI] Support `--short-version` on the CLI that does not boot the VM
-  * [Code] Add `Code.string_to_quoted_with_comments/2` and `Code.quoted_to_algebra/2`
-  * [Code] Add more `:token_metadata` to aliases and remote calls when parsing strings
-  * [Code] Add `Code.Fragment` module to provide best-effort information from code fragments. The module currently provides an updated `Code.Fragment.cursor_context/2` with operator support and `Code.Fragment.surround_context/2` which looks at a given position in a fragment and find its surrounding delimiters
-  * [Code] Allow custom sigil formatting on `Code.format_string!/2`
-  * [Code] Add `{:on_module, bytecode, :none}` trace to compilation tracers
-  * [Enum] Optimize `Enum.concat/1` for lists of lists
-  * [Exception] Better format Elixir exceptions in Erlang
-  * [Inspect] Allow default inspect fun to be set globally with `Inspect.Opts.default_inspect_fun/1`
-  * [IO] Allow `:eof` to be given as limit to `IO.getn/2`
-  * [Kernel] Support the `:sigils` option in `import Mod, only: :sigils` and allow the sigil modifiers to be also digits
-  * [Kernel] Make `get_in` consistently abort when `nil` values are found
-  * [Kernel] Improve compilation times by reducing the amount of copies of the AST across compiler processes
-  * [Kernel] Raise if trying to define a module with a slash in its name
-  * [Kernel] Warn when `?\` is used and there is no need for a escape character
-  * [Kernel] Track structs in typespecs as export deps instead of compile-time deps
-  * [Kernel] Add power operator (`**/2`)
-  * [Keyword] Add `Keyword.validate/2`
-  * [Keyword] Implement `Keyword.filter/2` and `Keyword.map/2`
-  * [List] Add `List.keyfind!/3`
-  * [Macro] Add `Macro.prewalker/1` and `Macro.postwalker/1`
-  * [Macro.Env] Add the following reflection functions: `required?/2`, `lookup_import/2`, `fetch_alias/2`, and `fetch_macro_alias/2`
-  * [Map] Implement `Map.filter/2` and `Map.map/2`
-  * [Module] Support `:nillify_clauses` in `Module.get_definition/3`
-  * [Module] Add `Module.attributes_in/1` and `Module.overridables_in/1`
-  * [OptionParser] Add "did you mean?" suggestions to `OptionParser.ParseError` messages
-  * [Record] Add record reflection via `@__records__`
-  * [Task] Add `Task.completed/1`
-  * [Task] Add `Task.ignore/1` to keep a task running but ignoring all of its results
-  * [Task] Reduce the amount of copying `Task.async*` functions
+  * [Access] Add `Access.slice/1`
+  * [Application] Add `Application.compile_env/4` and `Application.compile_env!/3` to read the compile-time environment inside macros
+  * [Calendar] Support ISO8601 basic format parsing with `DateTime.from_iso8601/2`
+  * [Calendar] Add `day`/`hour`/`minute` on `add`/`diff` across different calendar modules
+  * [Code] Add `:normalize_bitstring_modifiers` to `Code.format_string!/2`
+  * [Code] Emit deprecation and type warnings for invalid options in on `Code.compile_string/2` and `Code.compile_quoted/2`
+  * [Code] Warn if an outdated lexical tracker is given on eval
+  * [Code] Add `Code.env_for_eval/1` and `Code.eval_quoted_with_env/3`
+  * [Code] Improve stacktraces from eval operations on Erlang/OTP 25+
+  * [Code.Fragment] Add support for `__MODULE__` in several functions
+  * [Code.Fragment] Support surround and context suggestions across multiple lines
+  * [Enum] Allow slicing with steps in `Enum.slice/2`
+  * [File] Support `dereference_symlinks: true` in `File.cp/3` and `File.cp_r/3`
+  * [Float] Do not show floats in scientific notation if below `1.0e16` and the fractional value is precisely zero
+  * [Float] Add `Float.min_finite/0` and `Float.max_finite/0`
+  * [Inspect] Improve error reporting when there is a faulty implementation of the `Inspect` protocol
+  * [Inspect] Allow `:optional` when deriving the Inspect protocol for hiding fields that match their default value
+  * [Inspect] Inspect struct fields in the order they are declared in `defstruct`
+  * [Inspect] Use expression-based inspection for `Date.Range`, `MapSet`, and `Version.Requirement`
+  * [IO] Support `Macro.Env` and keywords as stacktrace definitions in `IO.warn/2`
+  * [IO] Add `IO.ANSI.syntax_colors/0` and related configuration to be shared across IEx and `dbg`
+  * [Kernel] Add new `dbg/0-2` macro
+  * [Kernel] Allow any guard expression as the size of a bitstring in a pattern match
+  * [Kernel] Allow composite types with pins as the map key in a pattern match
+  * [Kernel] Print escaped version of control chars when they show up as unexpected tokens
+  * [Kernel] Warn on confusable non-ASCII identifiers
+  * [Kernel] Add `..` as a nullary operator that returns `0..-1//1`
+  * [Kernel] Implement Unicode Technical Standard #39 recommendations. In particular, we warn for confusable scripts and restrict identifiers to single-scripts or highly restrictive mixed-scripts
+  * [Kernel] Automatically perform NFC conversion of identifiers
+  * [Kernel] Add `binary_slice/2` and `binary_slice/3`
+  * [Kernel] Lazily expand module attributes to avoid compile-time deps
+  * [Kernel] Automatically cascade `generated: true` annotations on macro expansion
+  * [Keyword] Add `Keyword.from_keys/2` and `Keyword.replace_lazy/3`
+  * [List] Add `List.keysort/3` with support for a `sorter` function
+  * [Macro] Add `Macro.classify_atom/1` and `Macro.inspect_atom/2`
+  * [Macro] Add `Macro.expand_literal/2` and `Macro.path/2`
+  * [Macro.Env] Add `Macro.Env.prune_compile_info/1`
+  * [Map] Add `Map.from_keys/2` and `Map.replace_lazy/3`
+  * [MapSet] Add `MapSet.filter/2`, `MapSet.reject/2`, and `MapSet.symmetric_difference/2`
+  * [Node] Add `Node.spawn_monitor/2` and `Node.spawn_monitor/4`
+  * [Module] Support new `@after_verify` attribute for executing code whenever a module is verified
+  * [PartitionSupervisor] Add `PartitionSupervisor` that starts multiple isolated partitions of the same child for scalability
+  * [Path] Add `Path.safe_relative/1` and `Path.safe_relative_to/2`
+  * [Registry] Add `Registry.count_select/2`
+  * [Stream] Add `Stream.duplicate/2` and `Stream.transform/5`
+  * [String] Support empty lookup lists in `String.replace/3`, `String.split/3`, and `String.splitter/3`
+  * [String] Allow slicing with steps in `String.slice/2`
+  * [Task] Add `:zip_input_on_exit` option to `Task.async_stream/3`
+  * [Task] Store `:mfa` in the `Task` struct for reflection purposes
+  * [URI] Add `URI.append_query/2`
+  * [Version] Add `Version.to_string/1`
+  * [Version] Colorize `Version.Requirement` source in the `Inspect` protocol
 
 #### ExUnit
 
-  * [ExUnit.CaptureIO] Add `with_io/3` to return result with captured io
-  * [ExUnit.CaptureLog] Add `with_log/2` to return result with captured logs
+  * [ExUnit] Add `ExUnit.Callbacks.start_link_supervised!/2`
+  * [ExUnit] Add `ExUnit.run/1` to rerun test modules
+  * [ExUnit] Colorize summary in yellow with message when all tests are excluded
+  * [ExUnit] Display friendly error when test name is too long
 
 #### IEx
 
-  * [IEx.Autocomplete] Add path autocompletion whenever when the cursor follows `"./` or `"/` or `"DRIVER:` where `DRIVER` is a single letter
-  * [IEx.Autocomplete] Add autocompletion for sigils, struct names, and struct fields
-  * [IEx.Helpers] Allow multiple modules to be given to `r/1`
+  * [IEx] Evaluate `--dot-iex` line by line
+  * [IEx] Add line-by-line evaluation of IEx breakpoints
+  * [IEx.Autocomplete] Autocomplete bitstrings modifiers (after `::` inside `<<...>>`)
+  * [IEx.Helpers] Allow an atom to be given to `pid/1`
 
 #### Logger
 
-  * [Logger] Add `Logger.put_application_level/2`
+  * [Logger] Add `Logger.put_process_level/2`
 
 #### Mix
 
-  * [mix archive.install] Run `loadconfig` before building archive
-  * [mix compile] Move Elixir version check to before deps are compiled, in order to give feedback earlier
-  * [mix compile.elixir] Do not recompile files if their modification time change but their contents are still the same and the .beam files are still on disk
-  * [mix compile.elixir] Do not recompile all Elixir sources when Erlang modules change, only dependent ones
-  * [mix compile.elixir] Do not recompile Elixir files if `mix.exs` changes, instead recompile only files using `Mix.Project` or trigger a recompilation if a compiler option changes
-  * [mix compile.elixir] Only recompile needed files when a dependency is added, updated or removed
-  * [mix compile.elixir] Only recompile needed files when a dependency is configured
-  * [mix deps] Add `:subdir` option to git deps
-  * [mix escript.install] Run `loadconfig` before building escript
-  * [mix format] Support `:plugins` in `mix format` that can hook into custom extensions and sigils
-  * [mix format] Add `Mix.Tasks.Format.formatter_for_file/2`
-  * [mix local.rebar] No longer support `sub_dirs` in Rebar 2 to help migration towards Rebar 3
-  * [mix local.rebar] Support `--if-missing` option when installing Rebar
-  * [mix local.rebar] Set `REBAR_PROFILE=prod` when compiling Rebar dependencies
-  * [mix test] Support `--profile-require=time` to profile the time loading test files themselves
-  * [mix test] Allow filtering modules from coverage using regex
-  * [mix test] Allow the exit status of ExUnit to be configured and set the default to 2
-  * [mix test] Exit with a status of 3 when coverage falls below threshold
-  * [mix test] Write failed manifest when suite fails due to --warnings-as-errors
-  * [mix test] Ignore `MIX_TEST_PARTITION` when partitions set to 1
-  * [mix xref] Support multiple sinks and sources in `mix xref graph`
-  * [mix xref] Add `trace` subcommand to print compilation dependencies between files
-  * [mix xref] Add `--fail-above` option to `mix xref`
-  * [mix xref] Add `--label compile-connected` to `mix xref`
+  * [mix compile] Add `--no-optional-deps` to skip optional dependencies to test compilation works without optional dependencies
+  * [mix compile] Include column information on error diagnostics when possible
+  * [mix deps] `Mix.Dep.Converger` now tells which deps formed a cycle
+  * [mix do] Support `--app` option to restrict recursive tasks in umbrella projects
+  * [mix do] Allow using `+` as a task separator instead of comma
+  * [mix format] Support filename in `mix format -` when reading from stdin
+  * [mix format] Compile if `mix format` plugins are missing
+  * [mix new] Do not allow projects to be created with application names that conflict with multi-arg Erlang VM switches
+  * [mix profile] Return the return value of the profiled function
+  * [mix release] Make BEAM compression opt-in
+  * [mix release] Let `:runtime_config_path` accept `false` to skip the `config/runtime.exs`
+  * [mix test] Improve error message when suite fails due to coverage
+  * [mix test] Support `:test_elixirc_options` and default to not generating docs nor debug info chunk for tests
+  * [mix xref] Support `--group` flag in `mix xref graph`
 
 ### 2. Bug fixes
 
-#### EEx
-
-  * [EEx] Accept EEx expressions where `->` is followed by newline
-
 #### Elixir
 
-  * [Application] Warn if `Application.compile_env` or `Application.compile_env!` are called without a require
-  * [Code] Make sure `:static_atoms_encoder` in `Code.string_to_quoted/2` also applies to quoted keyword keys
-  * [Code] Ensure bindings with no context are returned as atoms instead of `{binding, nil}` in eval operations
-  * [Kernel] Raise if `__CALLER__` or `__ENV__` or `__STACKTRACE__` are used in match
-  * [Kernel] Improve error message on invalid argument for `byte_size` from binary concat
-  * [Kernel] Raise when aliasing non-Elixir modules without `:as`
-  * [Kernel] Allow `unquote_splicing` inside `%{...}` without parens
-  * [Kernel] Ensure that waiting on a struct expansion inside a typespec is correctly tracked as waiting time in the compiler
-  * [Kernel] Correctly parse the atom `.` as a keyword list key
-  * [Kernel] Do not leak variables from the first generator in `with` and `for` special forms
-  * [Kernel] Fix column number on strings with NFD characters
-  * [Kernel] Fix a bug where a combination of dynamic line in `quote` with `unquote` of remote calls would emit invalid AST metadata
-  * [OptionParser] Validate switch types/modifiers early on to give more precise feedback
-  * [Protocol] Add `defdelegate` to the list of unallowed macros inside protocols as protocols do not allow function definitions
-  * [Protocol] Warn if `@callback`, `@macrocallback` and `@optional_callbacks` are defined inside protocol
-  * [Protocol] Ensure protocol metadata is deterministic on consolidation
-  * [Range] Always show step when range is descending
-  * [String] Update Unicode database to version 14.0
-  * [URI] Only percent decode if followed by hex digits (according to https://url.spec.whatwg.org/#percent-decode)
-  * [Version] Ensure proper precedence of `and`/`or` in version requirements
+  * [Calendar] Handle widths with "0" in them in `Calendar.strftime/3`
+  * [CLI] Improve errors on incorrect `--rpc-eval` usage
+  * [CLI] Return proper exit code on Windows
+  * [Code] Do not emit warnings when formatting code
+  * [Enum] Allow slices to overflow on both starting and ending positions
+  * [Kernel] Do not allow restricted characters in identifiers according to UTS39
+  * [Kernel] Define `__exception__` field as `true` when expanding exceptions in typespecs
+  * [Kernel] Warn if any of `True`, `False`, and `Nil` aliases are used
+  * [Kernel] Warn on underived `@derive` attributes
+  * [Kernel] Remove compile-time dependency from `defimpl :for`
+  * [Kernel] Track all arities on imported functions
+  * [Protocol] Warn if a protocol has no definitions
+  * [Regex] Show list options when inspecting a Regex manually defined with `Regex.compile/2`
+  * [String] Allow slices to overflow on both starting and ending positions
 
 #### ExUnit
 
-  * [ExUnit] Fix formatter and counters from `ExUnit.run/0` to consider all tests in a module whenever if a module's `setup_all` fails
-  * [ExUnit] Allow doctests newlines to be terminated by CRLF
+  * [ExUnit] Do not crash when diffing unknown bindings in guards
+  * [ExUnit] Properly print diffs when comparing improper lists with strings at the tail position
+  * [ExUnit] Add short hash to `tmp_dir` in ExUnit to avoid test name collision
+  * [ExUnit] Do not store logs in the CLI formatter (this reduces memory usage for suites with `capture_log`)
+  * [ExUnit] Run `ExUnit.after_suite/1` callback even when no tests run
+  * [ExUnit] Fix scenario where `setup` with imported function from within `describe` failed to compile
 
 #### IEx
 
-  * [IEx] Fix the loss of `.iex.exs` context after a pry session
+  * [IEx] Disallow short-hand pipe after matches
+  * [IEx] Fix `exports/1` in IEx for long function names
+
+#### Mix
+
+  * [mix compile.elixir] Fix `--warnings-as-errors` when used with `--all-warnings`
+  * [mix compile.elixir] Ensure semantic recompilation cascades to path dependencies
+  * [mix compile.elixir] Lock the compiler to avoid concurrent usage
+  * [mix format] Do not add new lines if the formatted file is empty
+  * [mix release] Only set `RELEASE_MODE` after `env.{sh,bat}` are executed
+  * [mix release] Allow application mode configuration to cascade to dependencies
+  * [mix xref] Do not emit already consolidated warnings during `mix xref trace`
+  * [Mix] Do not start apps with `runtime: false` on `Mix.install/2`
+
+### 3. Soft deprecations (no warnings emitted)
+
+#### Elixir
+
+  * [File] Passing a callback as third argument to `File.cp/3` and `File.cp_r/3` is deprecated.
+    Instead pass the callback the `:on_conflict` key of a keyword list
+
+#### EEx
+
+  * [EEx] Using `<%# ... %>` for comments is deprecated. Please use `<% # ... %>` or the new multi-line comments with `<%!-- ... --%>`
 
 #### Logger
 
-  * [Logger] Raise clear error message for invalid `:compile_time_purge_matching` configuration
+  * [Logger] Deprecate `Logger.enable/1` and `Logger.disable/1` in favor of `Logger.put_process_level/2`
 
 #### Mix
 
-  * [mix compile.elixir] Recompile file if `@external_resource` is deleted
-  * [mix compile.elixir] Print number of compiling files on all compiler cycles. This will make the `Compiling N files (.ex)` show up multiple times if necessary
-  * [mix deps] Raise if local dep is unavailable while compiling
-  * [mix deps.unlock] Fix blank output when dependency is not locked
-  * [mix local.install] Do not respect `MIX_DEPS_PATH` for install commands
-  * [mix release] Improve release scripts to make sure shell errors cascade by avoiding exporting and defining variables at once
-  * [mix release] Do not boot release if RELEASE_COOKIE is empty
-  * [mix release] Allow release running as a daemon to be restarted
-  * [mix test] Allow coverage engine to also tag `case`, `cond`, and `receive` branches where the right side is a literal
-  * [Mix.Shell] Add `default` option to `Mix.Shell.yes?`
+  * [mix cmd] The `--app` option in `mix cmd CMD` is deprecated in favor of the more efficient `mix do --app app cmd CMD`
 
-### 3. Soft-deprecations (no warnings emitted)
+### 4. Hard deprecations
 
 #### Elixir
 
-  * [IO] `:all` on `IO.getn` is deprecated in favor of `:eof`
-  * [Code] Environment options in `Code.eval_quoted/3` and `Code.eval_string/3`, such as `:aliases` and `:tracers`, have been deprecated in favor of passing an environment
+  * [Application] Calling `Application.get_env/3` and friends in the module body is now discouraged, use `Application.compile_env/3` instead
+  * [Bitwise] `use Bitwise` is deprecated, use `import Bitwise` instead
+  * [Bitwise] `~~~` is deprecated in favor of `bnot` for clarity
+  * [Kernel.ParallelCompiler] Returning a list or two-element tuple from `:each_cycle` is deprecated, return a `{:compile | :runtime, modules, warnings}` tuple instead
+  * [Kernel] Deprecate the operator `<|>` to avoid ambiguity with upcoming extended numerical operators
+  * [String] Deprecate passing a binary compiled pattern to `String.starts_with?/2`
+
+#### Logger
+
+  * [Logger] Deprecate `$levelpad` on message formatting
 
 #### Mix
 
-  * [mix format] `Mix.Tasks.Format.formatter_opts_for_file/2` is deprecated in favor of `Mix.Tasks.Format.formatter_for_file/2`
+  * [Mix] `Mix.Tasks.Xref.calls/1` is deprecated in favor of compilation tracers
 
-### 4. Hard-deprecations
-
-#### Elixir
-
-  * [Code] `Code.cursor_context/2` is deprecated, use `Code.Fragment.cursor_context/2` instead
-  * [Macro] `Macro.to_string/2` is deprecated, use `Macro.to_string/1` instead
-  * [System] `System.get_pid/0` is deprecated, use `System.pid/0` instead
-  * [Version] Using `!` or `!=` in version requirements is deprecated, use `~>` or `>=` instead
+### 5. Backwards incompatible changes
 
 #### Mix
 
-  * [mix escript.build] `:strip_beam` option is deprecated in favor of `:strip_beams`
-  * [Mix] `:exit_code` in `Mix.raise/2` has been deprecated in favor of `:exit_status`
-  * [Mix.Config] `Mix.Config` is deprecated in favor of `Config` module
+  * [mix local.rebar] Remove support for rebar2, which has not been updated in 5 years, and is no longer supported on recent Erlang/OTP versions
 
-## v1.12
+## v1.13
 
-The CHANGELOG for v1.12 releases can be found [in the v1.12 branch](https://github.com/elixir-lang/elixir/blob/v1.12/CHANGELOG.md).
+The CHANGELOG for v1.13 releases can be found [in the v1.13 branch](https://github.com/elixir-lang/elixir/blob/v1.13/CHANGELOG.md).

Makefile

@@ -2,8 +2,9 @@ PREFIX ?= /usr/local
 TEST_FILES ?= "*_test.exs"
 SHARE_PREFIX ?= $(PREFIX)/share
 MAN_PREFIX ?= $(SHARE_PREFIX)/man
-#CANONICAL := MAJOR.MINOR/
-CANONICAL ?= master/
+CANONICAL := 1.14/
+CANONICAL ?= main/
+DOCS_FORMAT ?= html
 ELIXIRC := bin/elixirc --ignore-module-conflict $(ELIXIRC_OPTS)
 ERLC := erlc -I lib/elixir/include
 ERL_MAKE := if [ -n "$(ERLC_OPTS)" ]; then ERL_COMPILER_OPTIONS=$(ERLC_OPTS) erl -make; else erl -make; fi
@@ -28,9 +29,9 @@ SOURCE_DATE_EPOCH_FILE = $(SOURCE_DATE_EPOCH_PATH)/SOURCE_DATE_EPOCH
 #==> Functions
 
 define CHECK_ERLANG_RELEASE
-	erl -noshell -eval '{V,_} = string:to_integer(erlang:system_info(otp_release)), io:fwrite("~s", [is_integer(V) and (V >= 22)])' -s erlang halt | grep -q '^true'; \
+	erl -noshell -eval '{V,_} = string:to_integer(erlang:system_info(otp_release)), io:fwrite("~s", [is_integer(V) and (V >= 23)])' -s erlang halt | grep -q '^true'; \
 		if [ $$? != 0 ]; then \
-		  echo "At least Erlang/OTP 22.0 is required to build Elixir"; \
+		  echo "At least Erlang/OTP 23.0 is required to build Elixir"; \
 		  exit 1; \
 		fi
 endef
@@ -92,10 +93,10 @@ $(KERNEL): lib/elixir/lib/*.ex lib/elixir/lib/*/*.ex lib/elixir/lib/*/*/*.ex
 		echo "==> bootstrap (compile)"; \
 		$(ERL) -s elixir_compiler bootstrap -s erlang halt; \
 	fi
-	$(Q) $(MAKE) unicode
+	$(Q) "$(MAKE)" unicode
 	@ echo "==> elixir (compile)";
 	$(Q) cd lib/elixir && ../../$(ELIXIRC) "lib/**/*.ex" -o ebin;
-	$(Q) $(MAKE) app
+	$(Q) "$(MAKE)" app
 
 app: $(APP)
 $(APP): lib/elixir/src/elixir.app.src lib/elixir/ebin VERSION $(GENERATE_APP)
@@ -105,6 +106,7 @@ unicode: $(UNICODE)
 $(UNICODE): lib/elixir/unicode/*
 	@ echo "==> unicode (compile)";
 	$(Q) $(ELIXIRC) lib/elixir/unicode/unicode.ex -o lib/elixir/ebin;
+	$(Q) $(ELIXIRC) lib/elixir/unicode/security.ex -o lib/elixir/ebin;
 	$(Q) $(ELIXIRC) lib/elixir/unicode/tokenizer.ex -o lib/elixir/ebin;
 
 $(eval $(call APP_TEMPLATE,ex_unit,ExUnit))
@@ -126,7 +128,7 @@ install: compile
 	$(Q) for file in "$(DESTDIR)$(PREFIX)"/$(LIBDIR)/elixir/bin/*; do \
 		ln -sf "../$(LIBDIR)/elixir/bin/$${file##*/}" "$(DESTDIR)$(PREFIX)/$(BINDIR)/"; \
 	done
-	$(MAKE) install_man
+	"$(MAKE)" install_man
 
 check_reproducible: compile
 	$(Q) echo "==> Checking for reproducible builds..."
@@ -144,7 +146,7 @@ check_reproducible: compile
 	$(Q) mv lib/iex/ebin/* lib/iex/tmp/ebin_reproducible/
 	$(Q) mv lib/logger/ebin/* lib/logger/tmp/ebin_reproducible/
 	$(Q) mv lib/mix/ebin/* lib/mix/tmp/ebin_reproducible/
-	SOURCE_DATE_EPOCH=$(call READ_SOURCE_DATE_EPOCH) $(MAKE) compile
+	SOURCE_DATE_EPOCH=$(call READ_SOURCE_DATE_EPOCH) "$(MAKE)" compile
 	$(Q) echo "Diffing..."
 	$(Q) bin/elixir lib/elixir/diff.exs lib/elixir/ebin/ lib/elixir/tmp/ebin_reproducible/
 	$(Q) bin/elixir lib/elixir/diff.exs lib/eex/ebin/ lib/eex/tmp/ebin_reproducible/
@@ -158,7 +160,7 @@ clean:
 	rm -rf ebin
 	rm -rf lib/*/ebin
 	rm -rf $(PARSER)
-	$(Q) $(MAKE) clean_residual_files
+	$(Q) "$(MAKE)" clean_residual_files
 
 clean_elixir:
 	$(Q) rm -f lib/*/ebin/Elixir.*.beam
@@ -171,14 +173,14 @@ clean_residual_files:
 	rm -rf lib/mix/test/fixtures/git_rebar/
 	rm -rf lib/mix/test/fixtures/git_repo/
 	rm -rf lib/mix/test/fixtures/git_sparse_repo/
+	rm -rf lib/mix/test/fixtures/archive/ebin/
 	rm -f erl_crash.dump
-	$(Q) $(MAKE) clean_man
+	$(Q) "$(MAKE)" clean_man
 
 #==> Documentation tasks
 
 LOGO_PATH = $(shell test -f ../docs/logo.png && echo "--logo ../docs/logo.png")
 SOURCE_REF = $(shell tag="$(call GIT_TAG)" revision="$(call GIT_REVISION)"; echo "$${tag:-$$revision}")
-DOCS_FORMAT = html
 COMPILE_DOCS = CANONICAL=$(CANONICAL) bin/elixir ../ex_doc/bin/ex_doc "$(1)" "$(VERSION)" "lib/$(2)/ebin" --main "$(3)" --source-url "https://github.com/elixir-lang/elixir" --source-ref "$(call SOURCE_REF)" $(call LOGO_PATH) --output doc/$(2) --canonical "https://hexdocs.pm/$(2)/$(CANONICAL)" --homepage-url "https://elixir-lang.org/docs.html" --formatter "$(DOCS_FORMAT)" $(4)
 
 docs: compile ../ex_doc/bin/ex_doc docs_elixir docs_eex docs_mix docs_iex docs_ex_unit docs_logger
@@ -220,24 +222,14 @@ docs_logger: compile ../ex_doc/bin/ex_doc
 #==> Zip tasks
 
 Docs.zip: docs
-	rm -f Docs-v$(VERSION).zip
-	zip -9 -r Docs-v$(VERSION).zip CHANGELOG.md doc NOTICE LICENSE README.md
-	@ echo "Docs file created $(CURDIR)/Docs-v$(VERSION).zip"
+	rm -f Docs.zip
+	zip -9 -r Docs.zip CHANGELOG.md doc NOTICE LICENSE README.md
+	@ echo "Docs file created $(CURDIR)/Docs.zip"
 
 Precompiled.zip: build_man compile
-	rm -f Precompiled-v$(VERSION).zip
-	zip -9 -r Precompiled-v$(VERSION).zip bin CHANGELOG.md lib/*/ebin lib/*/lib LICENSE man NOTICE README.md VERSION
-	@ echo "Precompiled file created $(CURDIR)/Precompiled-v$(VERSION).zip"
-
-zips: Precompiled.zip Docs.zip
-	@ echo ""
-	@ echo "### Checksums"
-	@ echo ""
-	@ shasum -a 1 < Precompiled-v$(VERSION).zip | sed -e "s/-//" | xargs echo "  * Precompiled.zip SHA1:"
-	@ shasum -a 512 < Precompiled-v$(VERSION).zip | sed -e "s/-//" | xargs echo "  * Precompiled.zip SHA512:"
-	@ shasum -a 1 < Docs-v$(VERSION).zip | sed -e "s/-//" | xargs echo "  * Docs.zip SHA1:"
-	@ shasum -a 512 < Docs-v$(VERSION).zip | sed -e "s/-//" | xargs echo "  * Docs.zip SHA512:"
-	@ echo ""
+	rm -f Precompiled.zip
+	zip -9 -r Precompiled.zip bin CHANGELOG.md lib/*/ebin lib/*/lib LICENSE man NOTICE README.md VERSION
+	@ echo "Precompiled file created $(CURDIR)/Precompiled.zip"
 
 #==> Test tasks
 
@@ -295,7 +287,7 @@ PLT = .elixir.plt
 
 $(PLT):
 	@ echo "==> Building PLT with Elixir's dependencies..."
-	$(Q) dialyzer --output_plt $(PLT) --build_plt --apps erts kernel stdlib compiler syntax_tools parsetools tools ssl inets crypto runtime_tools ftp tftp mnesia public_key asn1 hipe sasl
+	$(Q) dialyzer --output_plt $(PLT) --build_plt --apps erts kernel stdlib compiler syntax_tools parsetools tools ssl inets crypto runtime_tools ftp tftp mnesia public_key asn1 sasl
 
 clean_plt:
 	$(Q) rm -f $(PLT)
@@ -334,4 +326,4 @@ install_man: build_man
 	$(Q) $(INSTALL_DATA) man/elixirc.1 $(DESTDIR)$(MAN_PREFIX)/man1
 	$(Q) $(INSTALL_DATA) man/iex.1     $(DESTDIR)$(MAN_PREFIX)/man1
 	$(Q) $(INSTALL_DATA) man/mix.1     $(DESTDIR)$(MAN_PREFIX)/man1
-	$(MAKE) clean_man
+	"$(MAKE)" clean_man

README.md

@@ -1,6 +1,7 @@
-<img src="https://github.com/elixir-lang/elixir-lang.github.com/raw/master/images/logo/logo.png" width="200" alt="Elixir">
+<img src="https://github.com/elixir-lang/elixir-lang.github.com/raw/main/images/logo/logo.png#gh-light-mode-only" width="200" alt="Elixir">
+<img src="https://github.com/elixir-lang/elixir-lang.github.com/raw/main/images/logo/logo-dark.png#gh-dark-mode-only" width="200" alt="Elixir">
 
-[![CI](https://github.com/elixir-lang/elixir/workflows/CI/badge.svg?branch=master)](https://github.com/elixir-lang/elixir/actions?query=branch%3Amaster+workflow%3ACI) [![Build status](https://api.cirrus-ci.com/github/elixir-lang/elixir.svg?branch=master)](https://cirrus-ci.com/github/elixir-lang/elixir)
+[![CI](https://github.com/elixir-lang/elixir/workflows/CI/badge.svg?branch=main)](https://github.com/elixir-lang/elixir/actions?query=branch%3Amain+workflow%3ACI) [![Build status](https://api.cirrus-ci.com/github/elixir-lang/elixir.svg?branch=main)](https://cirrus-ci.com/github/elixir-lang/elixir)
 
 Elixir is a dynamic, functional language designed for building scalable
 and maintainable applications.
@@ -114,7 +115,7 @@ in applications inside the `lib` folder:
 
 You can run all tests in the root directory with `make test` and you can
 also run tests for a specific framework `make test_#{APPLICATION}`, for example,
-`make test_ex_unit`. If you just changed something in the Elixir's standard
+`make test_ex_unit`. If you just changed something in Elixir's standard
 library, you can run only that portion through `make test_stdlib`.
 
 If you are changing just one file, you can choose to compile and run tests only
@@ -126,6 +127,12 @@ bin/elixirc lib/elixir/lib/string.ex -o lib/elixir/ebin
 bin/elixir lib/elixir/test/elixir/string_test.exs
 ```
 
+You can also use the `LINE` env var to run a single test:
+
+```sh
+LINE=123 bin/elixir lib/elixir/test/elixir/string_test.exs
+````
+
 To recompile (including Erlang modules):
 
 ```sh
@@ -164,12 +171,12 @@ We outline our process below to clarify the roles of everyone involved.
 
 All pull requests must be approved by two committers before being merged into
 the repository. If any changes are necessary, the team will leave appropriate
-comments requesting changes to the code. Unfortunately we cannot guarantee a
+comments requesting changes to the code. Unfortunately, we cannot guarantee a
 pull request will be merged, even when modifications are requested, as the Elixir
 team will re-evaluate the contribution as it changes.
 
 Committers may also push style changes directly to your branch. If you would
-rather manage all changes yourself, you can disable "Allow edits from maintainers"
+rather manage all changes yourself, you can disable the "Allow edits from maintainers"
 feature when submitting your pull request.
 
 The Elixir team may optionally assign someone to review a pull request.
@@ -188,8 +195,8 @@ to be installed and built alongside Elixir:
 
 ```sh
 # After cloning and compiling Elixir, in its parent directory:
-git clone git://github.com/elixir-lang/ex_doc.git
-cd ex_doc && ../elixir/bin/mix do deps.get, compile
+git clone https://github.com/elixir-lang/ex_doc.git
+cd ex_doc && ../elixir/bin/mix do deps.get + compile
 ```
 
 Now go back to Elixir's root directory and run:

RELEASE.md

@@ -10,19 +10,13 @@
 
 4. Update "Compatibility and Deprecations" if a new OTP version is supported
 
-5. Commit changes above with title "Release vVERSION" and generate a new tag
+5. Commit changes above with title "Release vVERSION", generate a new tag, and push it
 
-6. Run `make clean test` to ensure all tests pass from scratch and the CI is green
+6. Wait until GitHub Actions publish artifacts to the draft release and the CI is green
 
-7. Recompile an existing project (for example, Ecto) to ensure manifests can be upgraded
+7. Copy the relevant bits from /CHANGELOG.md to the GitHub release and publish it
 
-8. Push branch and the new tag
-
-9. Publish new zips with `make zips`, upload `Precompiled.zip` and `Docs.zip` to GitHub Releases, and include SHAs+CHANGELOG
-
-10. Add the release to `elixir.csv` (all releases), update `erlang.csv` to the precompiled OTP version, and `_data/elixir-versions.yml` (except for RCs) files in `elixir-lang/elixir-lang.github.com`
-
-11. Send an e-mail to elixir-lang-ann@googlegroups.com with title "Elixir vVERSION released". The body should be a link to the Release page on GitHub and the checksums. If it is a security release, prefix the title with the `[security]` tag
+8. Add the release to `elixir.csv` with the minimum supported OTP version (all releases), update `erlang.csv` to the latest supported OTP version, and `_data/elixir-versions.yml` (except for RCs) files in `elixir-lang/elixir-lang.github.com`
 
 ## Creating a new vMAJOR.MINOR branch
 
@@ -32,14 +26,24 @@
 
 2. Update tables in /SECURITY.md and "Compatibility and Deprecations"
 
-3. Commit "Prepare vMAJOR.MINOR for release"
+3. Commit "Branch out vMAJOR.MINOR"
 
-### Back in master
+### Back in main
 
 1. Bump /VERSION file, bin/elixir and bin/elixir.bat
 
 2. Start new /CHANGELOG.md
 
-3. Update tables in /SECURITY.md in "Compatibility and Deprecations"
+3. Update tables in /SECURITY.md and in "Compatibility and Deprecations"
 
 4. Commit "Start vMAJOR.MINOR+1"
+
+## Changing supported Erlang/OTP versions
+
+1. Update the table in Compatibility and Deprecations
+
+2. Update `otp_release` checks in /Makefile and `/lib/elixir/src/elixir.erl`
+
+3. Update CI workflows in `/.cirrus.yml`, `/.github/workflows/ci.yml`, and `/.github/workflows/releases.yml`
+
+4. Remove `otp_release` version checks that are no longer needed

SECURITY.md

@@ -6,18 +6,17 @@ Elixir applies bug fixes only to the latest minor branch. Security patches are a
 
 Elixir version | Support
 :------------- | :-----------------------------
-1.13           | Development
-1.12           | Bug fixes and security patches
+1.14           | Bug fixes and security patches
+1.13           | Security patches only
+1.12           | Security patches only
 1.11           | Security patches only
 1.10           | Security patches only
-1.9            | Security patches only
-1.8            | Security patches only
 
 ## Announcements
 
 New releases are announced in the read-only [announcements mailing list](https://groups.google.com/group/elixir-lang-ann). You can subscribe by sending an email to elixir-lang-ann+subscribe@googlegroups.com and replying to the confirmation email.
 
-All security releases [will be tagged with `[security]`](https://groups.google.com/forum/#!searchin/elixir-lang-ann/%5Bsecurity%5D%7Csort:date).
+Security notifications [will be tagged with `[security]`](https://groups.google.com/forum/#!searchin/elixir-lang-ann/%5Bsecurity%5D%7Csort:date).
 
 ## Reporting a vulnerability
 

VERSION

@@ -1 +1 @@
-1.13.0-dev
+1.14.0-rc.1

bin/elixir

@@ -1,7 +1,7 @@
 #!/bin/sh
 set -e
 
-ELIXIR_VERSION=1.13.0-dev
+ELIXIR_VERSION=1.14.0-rc.1
 
 if [ $# -eq 0 ] || { [ $# -eq 1 ] && { [ "$1" = "--help" ] || [ "$1" = "-h" ]; }; }; then
   cat <<USAGE >&2
@@ -16,7 +16,7 @@ Usage: $(basename "$0") [options] [.exs file] [data]
   -pr "FILE"                   Requires the given files/patterns in parallel (*)
   -pa "PATH"                   Prepends the given path to Erlang code path (*)
   -pz "PATH"                   Appends the given path to Erlang code path (*)
-  -v, --version                Prints Erlang/OTP and Elixir versions
+  -v, --version                Prints Erlang/OTP and Elixir versions (standalone)
 
   --app APP                    Starts the given app and its dependencies (*)
   --erl "SWITCHES"             Switches to be passed down to Erlang (*)
@@ -100,32 +100,29 @@ LENGTH=$#
 set -- "$@" -extra
 
 while [ $I -le $LENGTH ]; do
-  S=1
+  # S counts to be shifted, C counts to be copied
+  S=0
+  C=0
   case "$1" in
     +iex)
-        set -- "$@" "$1"
+        C=1
         MODE="iex"
         ;;
     +elixirc)
-        set -- "$@" "$1"
+        C=1
         MODE="elixirc"
         ;;
     -v|--no-halt)
-        set -- "$@" "$1"
+        C=1
         ;;
-    -e|-r|-pr|-pa|-pz|--app|--eval|--remsh|--dot-iex)
-        S=2
-        set -- "$@" "$1" "$2"
+    -e|-r|-pr|-pa|-pz|--app|--eval|--remsh|--dot-iex|--no-pry)
+        C=2
         ;;
     --rpc-eval)
-        S=3
-        set -- "$@" "$1" "$2" "$3"
-        ;;
-    --detached)
-        echo "warning: the --detached option is deprecated" >&2
-        ERL="$ERL -detached"
+        C=3
         ;;
     --hidden)
+        S=1
         ERL="$ERL -hidden"
         ;;
     --logger-otp-reports)
@@ -186,6 +183,7 @@ while [ $I -le $LENGTH ]; do
         fi
         ;;
     --werl)
+        S=1
         if [ "$OS" = "Windows_NT" ]; then ERL_EXEC="werl"; fi
         ;;
     *)
@@ -198,6 +196,13 @@ while [ $I -le $LENGTH ]; do
         ;;
   esac
 
+  while [ $I -le $LENGTH ] && [ $C -gt 0 ]; do
+    C=$((C - 1))
+    I=$((I + 1))
+    set -- "$@" "$1"
+    shift
+  done
+
   I=$((I + S))
   shift $S
 done

bin/elixir.bat

@@ -1,6 +1,6 @@
 @if defined ELIXIR_CLI_ECHO (@echo on) else (@echo off)
 
-set ELIXIR_VERSION=1.13.0-dev
+set ELIXIR_VERSION=1.14.0-rc.1
 
 setlocal enabledelayedexpansion
 if    ""%1""==""""                if ""%2""=="""" goto documentation
@@ -23,7 +23,7 @@ echo   -S SCRIPT                    Finds and executes the given script in $PATH
 echo   -pr "FILE"                   Requires the given files/patterns in parallel (*)
 echo   -pa "PATH"                   Prepends the given path to Erlang code path (*)
 echo   -pz "PATH"                   Appends the given path to Erlang code path (*)
-echo   -v, --version                Prints Erlang/OTP and Elixir versions
+echo   -v, --version                Prints Erlang/OTP and Elixir versions (standalone)
 echo.
 echo   --app APP                    Starts the given app and its dependencies (*)
 echo   --erl "SWITCHES"             Switches to be passed down to Erlang (*)
@@ -141,6 +141,7 @@ if ""==!par:--app=!       (set "parsElixir=!parsElixir! --app %1" && shift && go
 if ""==!par:--no-halt=!   (set "parsElixir=!parsElixir! --no-halt" && goto startloop)
 if ""==!par:--remsh=!     (set "parsElixir=!parsElixir! --remsh %1" && shift && goto startloop)
 if ""==!par:--dot-iex=!   (set "parsElixir=!parsElixir! --dot-iex %1" && shift && goto startloop)
+if ""==!par:--no-pry=!    (set "parsElixir=!parsElixir! --no-pry" && goto startloop)
 rem ******* ERLANG PARAMETERS **********************
 if ""==!par:--boot=!                (set "parsErlang=!parsErlang! -boot %1" && shift && goto startloop)
 if ""==!par:--boot-var=!            (set "parsErlang=!parsErlang! -boot_var %1 %2" && shift && shift && goto startloop)
@@ -174,10 +175,19 @@ if %errorlevel% == 0 (
 if not !runMode! == "iex" (
   set beforeExtra=-noshell -s elixir start_cli !beforeExtra!
 )
-if defined useWerl (
-  start "" "!ERTS_BIN!werl.exe" !ext_libs! !ELIXIR_ERL_OPTIONS! !parsErlang! !beforeExtra! -extra !parsElixir!
+if defined ELIXIR_CLI_DRY_RUN (
+   if defined useWerl (
+     echo start "" "!ERTS_BIN!werl.exe" !ext_libs! !ELIXIR_ERL_OPTIONS! !parsErlang! !beforeExtra! -extra !parsElixir!
+   ) else (
+     echo "!ERTS_BIN!erl.exe" !ext_libs! !ELIXIR_ERL_OPTIONS! !parsErlang! !beforeExtra! -extra !parsElixir!
+   )
 ) else (
-  "!ERTS_BIN!erl.exe" !ext_libs! !ELIXIR_ERL_OPTIONS! !parsErlang! !beforeExtra! -extra !parsElixir!
+  if defined useWerl (
+    start "" "!ERTS_BIN!werl.exe" !ext_libs! !ELIXIR_ERL_OPTIONS! !parsErlang! !beforeExtra! -extra !parsElixir!
+  ) else (
+    "!ERTS_BIN!erl.exe" !ext_libs! !ELIXIR_ERL_OPTIONS! !parsErlang! !beforeExtra! -extra !parsElixir!
+  )
 )
+exit /B %ERRORLEVEL%
 :end
 endlocal

bin/elixirc

@@ -7,7 +7,7 @@ Usage: $(basename "$0") [elixir switches] [compiler switches] [.ex files]
 
   -h, --help                Prints this message and exits
   -o                        The directory to output compiled files
-  -v, --version             Prints Elixir version and exits
+  -v, --version             Prints Elixir version and exits (standalone)
 
   --ignore-module-conflict  Does not emit warnings if a module was previously defined
   --no-debug-info           Does not attach debug info to compiled modules

bin/elixirc.bat

@@ -16,7 +16,7 @@ echo Usage: %~nx0 [elixir switches] [compiler switches] [.ex files]
 echo.
 echo   -h, --help                Prints this message and exits
 echo   -o                        The directory to output compiled files
-echo   -v, --version             Prints Elixir version and exits
+echo   -v, --version             Prints Elixir version and exits (standalone)
 echo.
 echo   --ignore-module-conflict  Does not emit warnings if a module was previously defined
 echo   --no-debug-info           Does not attach debug info to compiled modules

bin/iex

@@ -7,9 +7,11 @@ Usage: $(basename "$0") [options] [.exs file] [data]
 
 The following options are exclusive to IEx:
 
-  --dot-iex "PATH"    Overrides default .iex.exs file and uses path instead;
-                      path can be empty, then no file will be loaded
-  --remsh NAME        Connects to a node using a remote shell
+  --dot-iex "FILE"    Evaluates FILE, line by line, to set up IEx' environment.
+                      Defaults to evaluating .iex.exs or ~/.iex.exs, if any exists.
+                      If FILE is empty, then no file will be loaded.
+  --remsh NAME        Connects to a node using a remote shell.
+  --no-pry            Doesn't start pry sessions when dbg/2 is called.
 
 It accepts all other options listed by "elixir --help".
 USAGE

bin/iex.bat

@@ -11,17 +11,19 @@ echo Usage: %~nx0 [options] [.exs file] [data]
 echo.
 echo The following options are exclusive to IEx:
 echo.
-echo   --dot-iex "PATH"    Overrides default .iex.exs file and uses path instead;
-echo                       path can be empty, then no file will be loaded
+echo   --dot-iex "FILE"    Evaluates FILE, line by line, to set up IEx' environment.
+echo                       Defaults to evaluating .iex.exs or ~/.iex.exs, if any exists.
+echo                       If FILE is empty, then no file will be loaded.
 echo   --remsh NAME        Connects to a node using a remote shell
 echo   --werl              Uses Erlang's Windows shell GUI (Windows only)
+echo   --no-pry            Doesn't start pry sessions when dbg/2 is called.
 echo.
 echo Set the IEX_WITH_WERL environment variable to always use werl.
 echo It accepts all other options listed by "elixir --help".
 goto end
 
 :run
-if defined IEX_WITH_WERL (@set __ELIXIR_IEX_FLAGS=--werl) else (set __ELIXIR_IEX_FLAGS=)
+if defined IEX_WITH_WERL (set __ELIXIR_IEX_FLAGS=--werl) else (set __ELIXIR_IEX_FLAGS=)
 call "%~dp0\elixir.bat" --no-halt --erl "-noshell -user Elixir.IEx.CLI" +iex %__ELIXIR_IEX_FLAGS% %*
 :end
 endlocal

lib/eex/lib/eex.ex

@@ -9,14 +9,14 @@ end
 
 defmodule EEx do
   @moduledoc ~S"""
-  EEx stands for Embedded Elixir. It allows you to embed
-  Elixir code inside a string in a robust way.
+  EEx stands for Embedded Elixir.
+
+  Embedded Elixir allows you to embed Elixir code inside a string
+  in a robust way.
 
       iex> EEx.eval_string("foo <%= bar %>", bar: "baz")
       "foo baz"
 
-  ## API
-
   This module provides three main APIs for you to use:
 
     1. Evaluate a string (`eval_string/3`) or a file (`eval_file/3`)
@@ -34,24 +34,48 @@ defmodule EEx do
        above and is available to you if you want to provide your own
        ways of handling the compiled template.
 
+  The APIs above support several options, documented below. You may
+  also pass an engine which customizes how the EEx code is compiled.
+
   ## Options
 
-  All functions in this module accept EEx-related options.
-  They are:
+  All functions in this module, unless otherwise noted, accept EEx-related
+  options. They are:
 
     * `:file` - the file to be used in the template. Defaults to the given
       file the template is read from or to `"nofile"` when compiling from a string.
+
     * `:line` - the line to be used as the template start. Defaults to `1`.
+
     * `:indentation` - (since v1.11.0) an integer added to the column after every
       new line. Defaults to `0`.
+
     * `:engine` - the EEx engine to be used for compilation.
+
     * `:trim` - if `true`, trims whitespace left and right of quotation as
       long as at least one newline is present. All subsequent newlines and
       spaces are removed but one newline is retained. Defaults to `false`.
-    * `:parser_options` - (since: 1.13.0) allow customizing the parsed code that is generated.
-      See `Code.string_to_quoted/2` for available options. Note that the options
-      `:file`, `:line` and `:column` are ignored if passed in.
-      Defaults to `Code.get_compiler_option(:parser_options)` (which defaults to `[]` if not set).
+
+    * `:parser_options` - (since: 1.13.0) allow customizing the parsed code
+      that is generated. See `Code.string_to_quoted/2` for available options.
+      Note that the options `:file`, `:line` and `:column` are ignored if
+      passed in. Defaults to `Code.get_compiler_option(:parser_options)`
+      (which defaults to `[]` if not set).
+
+  ## Tags
+
+  EEx supports multiple tags, declared below:
+
+      <% Elixir expression: executes code but discards output %>
+      <%= Elixir expression: executes code and prints result %>
+      <%% EEx quotation: returns the contents inside the tag as is %>
+      <%!-- Comments: they are discarded from source --%>
+
+  EEx supports additional tags, that may be used by some engines,
+  but they do not have a meaning by default:
+
+      <%| ... %>
+      <%/ ... %>
 
   ## Engine
 
@@ -61,42 +85,10 @@ defmodule EEx do
   By default, `EEx` uses the `EEx.SmartEngine` that provides some
   conveniences on top of the simple `EEx.Engine`.
 
-  ### Tags
+  ### `EEx.SmartEngine`
 
-  `EEx.SmartEngine` supports the following tags:
-
-      <% Elixir expression - inline with output %>
-      <%= Elixir expression - replace with result %>
-      <%% EEx quotation - returns the contents inside %>
-      <%# Comments - they are discarded from source %>
-
-  All expressions that output something to the template
-  **must** use the equals sign (`=`). Since everything in
-  Elixir is an expression, there are no exceptions for this rule.
-  For example, while some template languages would special-case
-  `if` clauses, they are treated the same in EEx and
-  also require `=` in order to have their result printed:
-
-      <%= if true do %>
-        It is obviously true
-      <% else %>
-        This will never appear
-      <% end %>
-
-  To escape an EEx expression in EEx use `<%% content %>`. For example:
-
-      <%%= x + 3 %>
-
-  will be rendered as `<%= x + 3 %>`.
-
-  Note that different engines may have different rules
-  for each tag. Other tags may be added in future versions.
-
-  ### Macros
-
-  `EEx.SmartEngine` also adds some macros to your template.
-  An example is the `@` macro which allows easy data access
-  in a template:
+  The smart engine uses EEx default rules and adds the `@` construct
+  for reading template assigns:
 
       iex> EEx.eval_string("<%= @foo %>", assigns: [foo: 1])
       "1"
@@ -109,6 +101,16 @@ defmodule EEx do
   required by the template is not specified at compilation time.
   """
 
+  @type line :: non_neg_integer
+  @type column :: non_neg_integer
+  @type marker :: '=' | '/' | '|' | ''
+  @type metadata :: %{column: column, line: line}
+  @type token ::
+          {:comment, charlist, metadata}
+          | {:text, charlist, metadata}
+          | {:expr | :start_expr | :middle_expr | :end_expr, marker, charlist, metadata}
+          | {:eof, metadata}
+
   @doc """
   Generates a function definition from the given string.
 
@@ -116,7 +118,9 @@ defmodule EEx do
   The `name` argument is the name that the generated function will have.
   `template` is the string containing the EEx template. `args` is a list of arguments
   that the generated function will accept. They will be available inside the EEx
-  template. `options` is a list of EEx compilation options (see the module documentation).
+  template.
+
+  The supported `options` are described [in the module docs](#module-options).
 
   ## Examples
 
@@ -148,11 +152,13 @@ defmodule EEx do
   The `name` argument is the name that the generated function will have.
   `file` is the path to the EEx template file. `args` is a list of arguments
   that the generated function will accept. They will be available inside the EEx
-  template. `options` is a list of EEx compilation options (see the module documentation).
+  template.
 
   This function is useful in case you have templates but
   you want to precompile inside a module for speed.
 
+  The supported `options` are described [in the module docs](#module-options).
+
   ## Examples
 
       # sample.eex
@@ -197,6 +203,8 @@ defmodule EEx do
   will use the `a` and `b` variables in the context where it's evaluated. See
   examples below.
 
+  The supported `options` are described [in the module docs](#module-options).
+
   ## Examples
 
       iex> quoted = EEx.compile_string("<%= a + b %>")
@@ -207,7 +215,14 @@ defmodule EEx do
   """
   @spec compile_string(String.t(), keyword) :: Macro.t()
   def compile_string(source, options \\ []) when is_binary(source) and is_list(options) do
-    EEx.Compiler.compile(source, options)
+    case tokenize(source, options) do
+      {:ok, tokens} ->
+        EEx.Compiler.compile(tokens, options)
+
+      {:error, message, %{column: column, line: line}} ->
+        file = options[:file] || "nofile"
+        raise EEx.SyntaxError, file: file, line: line, column: column, message: message
+    end
   end
 
   @doc """
@@ -223,6 +238,8 @@ defmodule EEx do
   will use the `a` and `b` variables in the context where it's evaluated. See
   examples below.
 
+  The supported `options` are described [in the module docs](#module-options).
+
   ## Examples
 
       # sample.eex
@@ -245,6 +262,8 @@ defmodule EEx do
   @doc """
   Gets a string `source` and evaluate the values using the `bindings`.
 
+  The supported `options` are described [in the module docs](#module-options).
+
   ## Examples
 
       iex> EEx.eval_string("foo <%= bar %>", bar: "baz")
@@ -261,6 +280,8 @@ defmodule EEx do
   @doc """
   Gets a `filename` and evaluate the values using the `bindings`.
 
+  The supported `options` are described [in the module docs](#module-options).
+
   ## Examples
 
       # sample.eex
@@ -280,6 +301,43 @@ defmodule EEx do
     do_eval(compiled, bindings, options)
   end
 
+  @doc """
+  Tokenize the given contents according to the given options.
+
+  ## Options
+
+    * `:line` - An integer to start as line. Default is 1.
+    * `:column` - An integer to start as column. Default is 1.
+    * `:indentation` - An integer that indicates the indentation. Default is 0.
+    * `:trim` - Tells the tokenizer to either trim the content or not. Default is false.
+    * `:file` - Can be either a file or a string "nofile".
+
+  ## Examples
+
+      iex> EEx.tokenize('foo', line: 1, column: 1)
+      {:ok, [{:text, 'foo', %{column: 1, line: 1}}, {:eof, %{column: 4, line: 1}}]}
+
+  ## Result
+
+  It returns `{:ok, [token]}` where a token is one of:
+
+    * `{:text, content, %{column: column, line: line}}`
+    * `{:expr, marker, content, %{column: column, line: line}}`
+    * `{:start_expr, marker, content, %{column: column, line: line}}`
+    * `{:middle_expr, marker, content, %{column: column, line: line}}`
+    * `{:end_expr, marker, content, %{column: column, line: line}}`
+    * `{:eof, %{column: column, line: line}}`
+
+  Or `{:error, message, %{column: column, line: line}}` in case of errors.
+  Note new tokens may be added in the future.
+  """
+  @doc since: "1.14.0"
+  @spec tokenize(IO.chardata(), opts :: keyword) ::
+          {:ok, [token()]} | {:error, String.t(), metadata()}
+  def tokenize(contents, opts \\ []) do
+    EEx.Compiler.tokenize(contents, opts)
+  end
+
   ### Helpers
 
   defp do_eval(compiled, bindings, options) do

lib/eex/lib/eex/compiler.ex

@@ -3,80 +3,345 @@ defmodule EEx.Compiler do
 
   # When changing this setting, don't forget to update the docs for EEx
   @default_engine EEx.SmartEngine
+  @h_spaces [?\s, ?\t]
+  @all_spaces [?\s, ?\t, ?\n, ?\r]
+
+  @doc """
+  Tokenize EEx contents.
+  """
+  def tokenize(contents, opts) when is_binary(contents) do
+    tokenize(String.to_charlist(contents), opts)
+  end
+
+  def tokenize(contents, opts) when is_list(contents) do
+    file = opts[:file] || "nofile"
+    line = opts[:line] || 1
+    trim = opts[:trim] || false
+    indentation = opts[:indentation] || 0
+    column = indentation + (opts[:column] || 1)
+
+    state = %{trim: trim, indentation: indentation, file: file}
+
+    {contents, line, column} =
+      (trim && trim_init(contents, line, column, state)) || {contents, line, column}
+
+    tokenize(contents, line, column, state, [{line, column}], [])
+  end
+
+  defp tokenize('<%%' ++ t, line, column, state, buffer, acc) do
+    tokenize(t, line, column + 3, state, [?%, ?< | buffer], acc)
+  end
+
+  defp tokenize('<%!--' ++ t, line, column, state, buffer, acc) do
+    case comment(t, line, column + 5, state, []) do
+      {:error, line, column, message} ->
+        {:error, message, %{line: line, column: column}}
+
+      {:ok, new_line, new_column, rest, comments} ->
+        token = {:comment, Enum.reverse(comments), %{line: line, column: column}}
+        trim_and_tokenize(rest, new_line, new_column, state, buffer, acc, &[token | &1])
+    end
+  end
+
+  # TODO: Deprecate this on Elixir v1.18
+  defp tokenize('<%#' ++ t, line, column, state, buffer, acc) do
+    case expr(t, line, column + 3, state, []) do
+      {:error, line, column, message} ->
+        {:error, message, %{line: line, column: column}}
+
+      {:ok, _, new_line, new_column, rest} ->
+        trim_and_tokenize(rest, new_line, new_column, state, buffer, acc, & &1)
+    end
+  end
+
+  defp tokenize('<%' ++ t, line, column, state, buffer, acc) do
+    {marker, t} = retrieve_marker(t)
+
+    case expr(t, line, column + 2 + length(marker), state, []) do
+      {:error, line, column, message} ->
+        {:error, message, %{line: line, column: column}}
+
+      {:ok, expr, new_line, new_column, rest} ->
+        {key, expr} =
+          case :elixir_tokenizer.tokenize(expr, 1, file: "eex", check_terminators: false) do
+            {:ok, _line, _column, warnings, tokens} ->
+              Enum.each(Enum.reverse(warnings), fn {location, file, msg} ->
+                :elixir_errors.erl_warn(location, file, msg)
+              end)
+
+              token_key(tokens, expr)
+
+            {:error, _, _, _, _} ->
+              {:expr, expr}
+          end
+
+        marker =
+          if key in [:middle_expr, :end_expr] and marker != '' do
+            message =
+              "unexpected beginning of EEx tag \"<%#{marker}\" on \"<%#{marker}#{expr}%>\", " <>
+                "please remove \"#{marker}\""
+
+            :elixir_errors.erl_warn({line, column}, state.file, message)
+            ''
+          else
+            marker
+          end
+
+        token = {key, marker, expr, %{line: line, column: column}}
+        trim_and_tokenize(rest, new_line, new_column, state, buffer, acc, &[token | &1])
+    end
+  end
+
+  defp tokenize('\n' ++ t, line, _column, state, buffer, acc) do
+    tokenize(t, line + 1, state.indentation + 1, state, [?\n | buffer], acc)
+  end
+
+  defp tokenize([h | t], line, column, state, buffer, acc) do
+    tokenize(t, line, column + 1, state, [h | buffer], acc)
+  end
+
+  defp tokenize([], line, column, _state, buffer, acc) do
+    eof = {:eof, %{line: line, column: column}}
+    {:ok, Enum.reverse([eof | tokenize_text(buffer, acc)])}
+  end
+
+  defp trim_and_tokenize(rest, line, column, state, buffer, acc, fun) do
+    {rest, line, column, buffer} = trim_if_needed(rest, line, column, state, buffer)
+
+    acc = tokenize_text(buffer, acc)
+    tokenize(rest, line, column, state, [{line, column}], fun.(acc))
+  end
+
+  # Retrieve marker for <%
+
+  defp retrieve_marker([marker | t]) when marker in [?=, ?/, ?|] do
+    {[marker], t}
+  end
+
+  defp retrieve_marker(t) do
+    {'', t}
+  end
+
+  # Tokenize a multi-line comment until we find --%>
+
+  defp comment([?-, ?-, ?%, ?> | t], line, column, _state, buffer) do
+    {:ok, line, column + 4, t, buffer}
+  end
+
+  defp comment('\n' ++ t, line, _column, state, buffer) do
+    comment(t, line + 1, state.indentation + 1, state, '\n' ++ buffer)
+  end
+
+  defp comment([head | t], line, column, state, buffer) do
+    comment(t, line, column + 1, state, [head | buffer])
+  end
+
+  defp comment([], line, column, _state, _buffer) do
+    {:error, line, column, "missing token '--%>'"}
+  end
+
+  # Tokenize an expression until we find %>
+
+  defp expr([?%, ?> | t], line, column, _state, buffer) do
+    {:ok, Enum.reverse(buffer), line, column + 2, t}
+  end
+
+  defp expr('\n' ++ t, line, _column, state, buffer) do
+    expr(t, line + 1, state.indentation + 1, state, [?\n | buffer])
+  end
+
+  defp expr([h | t], line, column, state, buffer) do
+    expr(t, line, column + 1, state, [h | buffer])
+  end
+
+  defp expr([], line, column, _state, _buffer) do
+    {:error, line, column, "missing token '%>'"}
+  end
+
+  # Receives tokens and check if it is a start, middle or an end token.
+  defp token_key(tokens, expr) do
+    case {tokens, tokens |> Enum.reverse() |> drop_eol()} do
+      {[{:end, _} | _], [{:do, _} | _]} ->
+        {:middle_expr, expr}
+
+      {_, [{:do, _} | _]} ->
+        {:start_expr, maybe_append_space(expr)}
+
+      {_, [{:block_identifier, _, _} | _]} ->
+        {:middle_expr, maybe_append_space(expr)}
+
+      {[{:end, _} | _], [{:stab_op, _, _} | _]} ->
+        {:middle_expr, expr}
+
+      {_, [{:stab_op, _, _} | reverse_tokens]} ->
+        fn_index = Enum.find_index(reverse_tokens, &match?({:fn, _}, &1)) || :infinity
+        end_index = Enum.find_index(reverse_tokens, &match?({:end, _}, &1)) || :infinity
+
+        if end_index > fn_index do
+          {:start_expr, expr}
+        else
+          {:middle_expr, expr}
+        end
+
+      {tokens, _} ->
+        case Enum.drop_while(tokens, &closing_bracket?/1) do
+          [{:end, _} | _] -> {:end_expr, expr}
+          _ -> {:expr, expr}
+        end
+    end
+  end
+
+  defp drop_eol([{:eol, _} | rest]), do: drop_eol(rest)
+  defp drop_eol(rest), do: rest
+
+  defp maybe_append_space([?\s]), do: [?\s]
+  defp maybe_append_space([h]), do: [h, ?\s]
+  defp maybe_append_space([h | t]), do: [h | maybe_append_space(t)]
+
+  defp closing_bracket?({closing, _}) when closing in ~w"( [ {"a, do: true
+  defp closing_bracket?(_), do: false
+
+  # Tokenize the buffered text by appending
+  # it to the given accumulator.
+
+  defp tokenize_text([{_line, _column}], acc) do
+    acc
+  end
+
+  defp tokenize_text(buffer, acc) do
+    [{line, column} | buffer] = Enum.reverse(buffer)
+    [{:text, buffer, %{line: line, column: column}} | acc]
+  end
+
+  ## Trim
+
+  defp trim_if_needed(rest, line, column, state, buffer) do
+    if state.trim do
+      buffer = trim_left(buffer, 0)
+      {rest, line, column} = trim_right(rest, line, column, 0, state)
+      {rest, line, column, buffer}
+    else
+      {rest, line, column, buffer}
+    end
+  end
+
+  defp trim_init([h | t], line, column, state) when h in @h_spaces,
+    do: trim_init(t, line, column + 1, state)
+
+  defp trim_init([?\r, ?\n | t], line, _column, state),
+    do: trim_init(t, line + 1, state.indentation + 1, state)
+
+  defp trim_init([?\n | t], line, _column, state),
+    do: trim_init(t, line + 1, state.indentation + 1, state)
+
+  defp trim_init([?<, ?% | _] = rest, line, column, _state),
+    do: {rest, line, column}
+
+  defp trim_init(_, _, _, _), do: false
+
+  defp trim_left(buffer, count) do
+    case trim_whitespace(buffer, 0) do
+      {[?\n, ?\r | rest], _} -> trim_left(rest, count + 1)
+      {[?\n | rest], _} -> trim_left(rest, count + 1)
+      _ when count > 0 -> [?\n | buffer]
+      _ -> buffer
+    end
+  end
+
+  defp trim_right(rest, line, column, last_column, state) do
+    case trim_whitespace(rest, column) do
+      {[?\r, ?\n | rest], column} ->
+        trim_right(rest, line + 1, state.indentation + 1, column + 1, state)
+
+      {[?\n | rest], column} ->
+        trim_right(rest, line + 1, state.indentation + 1, column, state)
+
+      {[], column} ->
+        {[], line, column}
+
+      _ when last_column > 0 ->
+        {[?\n | rest], line - 1, last_column}
+
+      _ ->
+        {rest, line, column}
+    end
+  end
+
+  defp trim_whitespace([h | t], column) when h in @h_spaces, do: trim_whitespace(t, column + 1)
+  defp trim_whitespace(list, column), do: {list, column}
 
   @doc """
   This is the compilation entry point. It glues the tokenizer
   and the engine together by handling the tokens and invoking
   the engine every time a full expression or text is received.
   """
-  @spec compile(String.t(), keyword) :: Macro.t()
-  def compile(source, opts) when is_binary(source) and is_list(opts) do
+  @spec compile([EEx.token()], keyword) :: Macro.t()
+  def compile(tokens, opts) do
     file = opts[:file] || "nofile"
     line = opts[:line] || 1
-    column = 1
-    indentation = opts[:indentation] || 0
-    trim = opts[:trim] || false
     parser_options = opts[:parser_options] || Code.get_compiler_option(:parser_options)
-    tokenizer_options = %{trim: trim, indentation: indentation}
+    engine = opts[:engine] || @default_engine
 
-    case EEx.Tokenizer.tokenize(source, line, column, tokenizer_options) do
-      {:ok, tokens} ->
-        state = %{
-          engine: opts[:engine] || @default_engine,
-          file: file,
-          line: line,
-          quoted: [],
-          start_line: nil,
-          start_column: nil,
-          parser_options: parser_options
-        }
+    state = %{
+      engine: engine,
+      file: file,
+      line: line,
+      quoted: [],
+      start_line: nil,
+      start_column: nil,
+      parser_options: parser_options
+    }
 
-        init = state.engine.init(opts)
-        generate_buffer(tokens, init, [], state)
+    init = state.engine.init(opts)
+    generate_buffer(tokens, init, [], state)
+  end
 
-      {:error, line, column, message} ->
-        raise EEx.SyntaxError, file: file, line: line, column: column, message: message
-    end
+  # Ignore tokens related to comment.
+  defp generate_buffer([{:comment, _chars, _meta} | rest], buffer, scope, state) do
+    generate_buffer(rest, buffer, scope, state)
   end
 
   # Generates the buffers by handling each expression from the tokenizer.
   # It returns Macro.t/0 or it raises.
 
-  defp generate_buffer([{:text, line, column, chars} | rest], buffer, scope, state) do
+  defp generate_buffer([{:text, chars, meta} | rest], buffer, scope, state) do
     buffer =
       if function_exported?(state.engine, :handle_text, 3) do
-        meta = [line: line, column: column]
+        meta = [line: meta.line, column: meta.column]
         state.engine.handle_text(buffer, meta, IO.chardata_to_string(chars))
       else
-        # TODO: Remove this branch on Elixir v2.0
+        # TODO: Deprecate this branch on Elixir v1.18.
+        # We should most likely move this check to init to emit the deprecation once.
         state.engine.handle_text(buffer, IO.chardata_to_string(chars))
       end
 
     generate_buffer(rest, buffer, scope, state)
   end
 
-  defp generate_buffer([{:expr, line, column, mark, chars} | rest], buffer, scope, state) do
-    options = [file: state.file, line: line, column: column(column, mark)] ++ state.parser_options
+  defp generate_buffer([{:expr, mark, chars, meta} | rest], buffer, scope, state) do
+    options =
+      [file: state.file, line: meta.line, column: column(meta.column, mark)] ++
+        state.parser_options
+
     expr = Code.string_to_quoted!(chars, options)
     buffer = state.engine.handle_expr(buffer, IO.chardata_to_string(mark), expr)
     generate_buffer(rest, buffer, scope, state)
   end
 
   defp generate_buffer(
-         [{:start_expr, start_line, start_column, mark, chars} | rest],
+         [{:start_expr, mark, chars, meta} | rest],
          buffer,
          scope,
          state
        ) do
-    if mark != '=' do
+    if mark == '' do
       message =
         "the contents of this expression won't be output unless the EEx block starts with \"<%=\""
 
-      :elixir_errors.erl_warn({start_line, start_column}, state.file, message)
+      :elixir_errors.erl_warn({meta.line, meta.column}, state.file, message)
     end
 
-    {rest, line, contents} =
-      look_ahead_middle(rest, start_line, chars) || {rest, start_line, chars}
+    {rest, line, contents} = look_ahead_middle(rest, meta.line, chars) || {rest, meta.line, chars}
 
     {contents, rest} =
       generate_buffer(
@@ -87,8 +352,8 @@ defmodule EEx.Compiler do
           state
           | quoted: [],
             line: line,
-            start_line: start_line,
-            start_column: column(start_column, mark)
+            start_line: meta.line,
+            start_column: column(meta.column, mark)
         }
       )
 
@@ -97,47 +362,31 @@ defmodule EEx.Compiler do
   end
 
   defp generate_buffer(
-         [{:middle_expr, line, _column, '', chars} | rest],
+         [{:middle_expr, '', chars, meta} | rest],
          buffer,
          [current | scope],
          state
        ) do
-    {wrapped, state} = wrap_expr(current, line, buffer, chars, state)
-    state = %{state | line: line}
+    {wrapped, state} = wrap_expr(current, meta.line, buffer, chars, state)
+    state = %{state | line: meta.line}
     generate_buffer(rest, state.engine.handle_begin(buffer), [wrapped | scope], state)
   end
 
-  defp generate_buffer(
-         [{:middle_expr, line, column, modifier, chars} | t],
-         buffer,
-         [_ | _] = scope,
-         state
-       ) do
-    message =
-      "unexpected beginning of EEx tag \"<%#{modifier}\" on \"<%#{modifier}#{chars}%>\", " <>
-        "please remove \"#{modifier}\" accordingly"
-
-    :elixir_errors.erl_warn({line, column}, state.file, message)
-    generate_buffer([{:middle_expr, line, column, '', chars} | t], buffer, scope, state)
-    # TODO: Make this an error on Elixir v2.0 since it accidentally worked previously.
-    # raise EEx.SyntaxError, message: message, file: state.file, line: line
-  end
-
-  defp generate_buffer([{:middle_expr, line, column, _, chars} | _], _buffer, [], state) do
+  defp generate_buffer([{:middle_expr, _, chars, meta} | _], _buffer, [], state) do
     raise EEx.SyntaxError,
       message: "unexpected middle of expression <%#{chars}%>",
       file: state.file,
-      line: line,
-      column: column
+      line: meta.line,
+      column: meta.column
   end
 
   defp generate_buffer(
-         [{:end_expr, line, _column, '', chars} | rest],
+         [{:end_expr, '', chars, meta} | rest],
          buffer,
          [current | _],
          state
        ) do
-    {wrapped, state} = wrap_expr(current, line, buffer, chars, state)
+    {wrapped, state} = wrap_expr(current, meta.line, buffer, chars, state)
     column = state.start_column
     options = [file: state.file, line: state.start_line, column: column] ++ state.parser_options
     tuples = Code.string_to_quoted!(wrapped, options)
@@ -145,40 +394,24 @@ defmodule EEx.Compiler do
     {buffer, rest}
   end
 
-  defp generate_buffer(
-         [{:end_expr, line, column, modifier, chars} | t],
-         buffer,
-         [_ | _] = scope,
-         state
-       ) do
-    message =
-      "unexpected beginning of EEx tag \"<%#{modifier}\" on end of " <>
-        "expression \"<%#{modifier}#{chars}%>\", please remove \"#{modifier}\" accordingly"
-
-    :elixir_errors.erl_warn({line, column}, state.file, message)
-    generate_buffer([{:end_expr, line, column, '', chars} | t], buffer, scope, state)
-    # TODO: Make this an error on Elixir v2.0 since it accidentally worked previously.
-    # raise EEx.SyntaxError, message: message, file: state.file, line: line, column: column
-  end
-
-  defp generate_buffer([{:end_expr, line, column, _, chars} | _], _buffer, [], state) do
+  defp generate_buffer([{:end_expr, _, chars, meta} | _], _buffer, [], state) do
     raise EEx.SyntaxError,
       message: "unexpected end of expression <%#{chars}%>",
       file: state.file,
-      line: line,
-      column: column
+      line: meta.line,
+      column: meta.column
   end
 
-  defp generate_buffer([{:eof, _, _}], buffer, [], state) do
+  defp generate_buffer([{:eof, _meta}], buffer, [], state) do
     state.engine.handle_body(buffer)
   end
 
-  defp generate_buffer([{:eof, line, column}], _buffer, _scope, state) do
+  defp generate_buffer([{:eof, meta}], _buffer, _scope, state) do
     raise EEx.SyntaxError,
       message: "unexpected end of string, expected a closing '<% end %>'",
       file: state.file,
-      line: line,
-      column: column
+      line: meta.line,
+      column: meta.column
   end
 
   # Creates a placeholder and wrap it inside the expression block
@@ -195,7 +428,10 @@ defmodule EEx.Compiler do
 
   # Look middle expressions that immediately follow a start_expr
 
-  defp look_ahead_middle([{:text, _, _, text} | rest], start, contents) do
+  defp look_ahead_middle([{:comment, _comment, _meta} | rest], start, contents),
+    do: look_ahead_middle(rest, start, contents)
+
+  defp look_ahead_middle([{:text, text, _meta} | rest], start, contents) do
     if only_spaces?(text) do
       look_ahead_middle(rest, start, contents ++ text)
     else
@@ -203,8 +439,8 @@ defmodule EEx.Compiler do
     end
   end
 
-  defp look_ahead_middle([{:middle_expr, line, _column, _, chars} | rest], _start, contents) do
-    {rest, line, contents ++ chars}
+  defp look_ahead_middle([{:middle_expr, _, chars, meta} | rest], _start, contents) do
+    {rest, meta.line, contents ++ chars}
   end
 
   defp look_ahead_middle(_tokens, _start, _contents) do
@@ -212,7 +448,7 @@ defmodule EEx.Compiler do
   end
 
   defp only_spaces?(chars) do
-    Enum.all?(chars, &(&1 in [?\s, ?\t, ?\r, ?\n]))
+    Enum.all?(chars, &(&1 in @all_spaces))
   end
 
   # Changes placeholder to real expression

lib/eex/lib/eex/tokenizer.ex

@@ -1,244 +0,0 @@
-defmodule EEx.Tokenizer do
-  @moduledoc false
-
-  @type content :: IO.chardata()
-  @type line :: non_neg_integer
-  @type column :: non_neg_integer
-  @type marker :: '=' | '/' | '|' | ''
-  @type token ::
-          {:text, line, column, content}
-          | {:expr | :start_expr | :middle_expr | :end_expr, line, column, marker, content}
-          | {:eof, line, column}
-
-  @spaces [?\s, ?\t]
-
-  @doc """
-  Tokenizes the given charlist or binary.
-
-  It returns {:ok, list} with the following tokens:
-
-    * `{:text, line, column, content}`
-    * `{:expr, line, column, marker, content}`
-    * `{:start_expr, line, column, marker, content}`
-    * `{:middle_expr, line, column, marker, content}`
-    * `{:end_expr, line, column, marker, content}`
-    * `{:eof, line, column}`
-
-  Or `{:error, line, column, message}` in case of errors.
-  """
-  @spec tokenize(binary | charlist, line, column, map) ::
-          {:ok, [token]} | {:error, line, column, String.t()}
-
-  def tokenize(bin, line, column, opts) when is_binary(bin) do
-    tokenize(String.to_charlist(bin), line, column, opts)
-  end
-
-  def tokenize(list, line, column, opts)
-      when is_list(list) and is_integer(line) and line >= 0 and is_integer(column) and column >= 0 do
-    column = opts.indentation + column
-
-    {list, line, column} =
-      (opts.trim && trim_init(list, line, column, opts)) || {list, line, column}
-
-    tokenize(list, line, column, opts, [{line, column}], [])
-  end
-
-  defp tokenize('<%%' ++ t, line, column, opts, buffer, acc) do
-    tokenize(t, line, column + 3, opts, [?%, ?< | buffer], acc)
-  end
-
-  defp tokenize('<%#' ++ t, line, column, opts, buffer, acc) do
-    case expr(t, line, column + 3, opts, []) do
-      {:error, _, _, _} = error ->
-        error
-
-      {:ok, _, new_line, new_column, rest} ->
-        {rest, new_line, new_column, buffer} =
-          trim_if_needed(rest, new_line, new_column, opts, buffer)
-
-        acc = tokenize_text(buffer, acc)
-        tokenize(rest, new_line, new_column, opts, [{new_line, new_column}], acc)
-    end
-  end
-
-  defp tokenize('<%' ++ t, line, column, opts, buffer, acc) do
-    {marker, t} = retrieve_marker(t)
-
-    case expr(t, line, column + 2 + length(marker), opts, []) do
-      {:error, _, _, _} = error ->
-        error
-
-      {:ok, expr, new_line, new_column, rest} ->
-        {key, expr} =
-          case :elixir_tokenizer.tokenize(expr, 1, file: "eex", check_terminators: false) do
-            {:ok, _line, _column, warnings, tokens} ->
-              Enum.each(Enum.reverse(warnings), fn {location, file, msg} ->
-                :elixir_errors.erl_warn(location, file, msg)
-              end)
-
-              token_key(tokens, expr)
-
-            {:error, _, _, _, _} ->
-              {:expr, expr}
-          end
-
-        {rest, new_line, new_column, buffer} =
-          trim_if_needed(rest, new_line, new_column, opts, buffer)
-
-        acc = tokenize_text(buffer, acc)
-        final = {key, line, column, marker, expr}
-        tokenize(rest, new_line, new_column, opts, [{new_line, new_column}], [final | acc])
-    end
-  end
-
-  defp tokenize('\n' ++ t, line, _column, opts, buffer, acc) do
-    tokenize(t, line + 1, opts.indentation + 1, opts, [?\n | buffer], acc)
-  end
-
-  defp tokenize([h | t], line, column, opts, buffer, acc) do
-    tokenize(t, line, column + 1, opts, [h | buffer], acc)
-  end
-
-  defp tokenize([], line, column, _opts, buffer, acc) do
-    eof = {:eof, line, column}
-    {:ok, Enum.reverse([eof | tokenize_text(buffer, acc)])}
-  end
-
-  # Retrieve marker for <%
-
-  defp retrieve_marker([marker | t]) when marker in [?=, ?/, ?|] do
-    {[marker], t}
-  end
-
-  defp retrieve_marker(t) do
-    {'', t}
-  end
-
-  # Tokenize an expression until we find %>
-
-  defp expr([?%, ?> | t], line, column, _opts, buffer) do
-    {:ok, Enum.reverse(buffer), line, column + 2, t}
-  end
-
-  defp expr('\n' ++ t, line, _column, opts, buffer) do
-    expr(t, line + 1, opts.indentation + 1, opts, [?\n | buffer])
-  end
-
-  defp expr([h | t], line, column, opts, buffer) do
-    expr(t, line, column + 1, opts, [h | buffer])
-  end
-
-  defp expr([], line, column, _opts, _buffer) do
-    {:error, line, column, "missing token '%>'"}
-  end
-
-  # Receives tokens and check if it is a start, middle or an end token.
-  defp token_key(tokens, expr) do
-    case {tokens, tokens |> Enum.reverse() |> drop_eol()} do
-      {[{:end, _} | _], [{:do, _} | _]} ->
-        {:middle_expr, expr}
-
-      {_, [{:do, _} | _]} ->
-        {:start_expr, maybe_append_space(expr)}
-
-      {_, [{:block_identifier, _, _} | _]} ->
-        {:middle_expr, maybe_append_space(expr)}
-
-      {[{:end, _} | _], [{:stab_op, _, _} | _]} ->
-        {:middle_expr, expr}
-
-      {_, [{:stab_op, _, _} | reverse_tokens]} ->
-        fn_index = Enum.find_index(reverse_tokens, &match?({:fn, _}, &1)) || :infinity
-        end_index = Enum.find_index(reverse_tokens, &match?({:end, _}, &1)) || :infinity
-
-        if end_index > fn_index do
-          {:start_expr, expr}
-        else
-          {:middle_expr, expr}
-        end
-
-      {tokens, _} ->
-        case Enum.drop_while(tokens, &closing_bracket?/1) do
-          [{:end, _} | _] -> {:end_expr, expr}
-          _ -> {:expr, expr}
-        end
-    end
-  end
-
-  defp drop_eol([{:eol, _} | rest]), do: drop_eol(rest)
-  defp drop_eol(rest), do: rest
-
-  defp maybe_append_space([?\s]), do: [?\s]
-  defp maybe_append_space([h]), do: [h, ?\s]
-  defp maybe_append_space([h | t]), do: [h | maybe_append_space(t)]
-
-  defp closing_bracket?({closing, _}) when closing in ~w"( [ {"a, do: true
-  defp closing_bracket?(_), do: false
-
-  # Tokenize the buffered text by appending
-  # it to the given accumulator.
-
-  defp tokenize_text([{_line, _column}], acc) do
-    acc
-  end
-
-  defp tokenize_text(buffer, acc) do
-    [{line, column} | buffer] = Enum.reverse(buffer)
-    [{:text, line, column, buffer} | acc]
-  end
-
-  defp trim_if_needed(rest, line, column, opts, buffer) do
-    if opts.trim do
-      buffer = trim_left(buffer, 0)
-      {rest, line, column} = trim_right(rest, line, column, 0, opts)
-      {rest, line, column, buffer}
-    else
-      {rest, line, column, buffer}
-    end
-  end
-
-  defp trim_init([h | t], line, column, opts) when h in @spaces,
-    do: trim_init(t, line, column + 1, opts)
-
-  defp trim_init([?\r, ?\n | t], line, _column, opts),
-    do: trim_init(t, line + 1, opts.indentation + 1, opts)
-
-  defp trim_init([?\n | t], line, _column, opts),
-    do: trim_init(t, line + 1, opts.indentation + 1, opts)
-
-  defp trim_init([?<, ?% | _] = rest, line, column, _opts),
-    do: {rest, line, column}
-
-  defp trim_init(_, _, _, _), do: false
-
-  defp trim_left(buffer, count) do
-    case trim_whitespace(buffer, 0) do
-      {[?\n, ?\r | rest], _} -> trim_left(rest, count + 1)
-      {[?\n | rest], _} -> trim_left(rest, count + 1)
-      _ when count > 0 -> [?\n | buffer]
-      _ -> buffer
-    end
-  end
-
-  defp trim_right(rest, line, column, last_column, opts) do
-    case trim_whitespace(rest, column) do
-      {[?\r, ?\n | rest], column} ->
-        trim_right(rest, line + 1, opts.indentation + 1, column + 1, opts)
-
-      {[?\n | rest], column} ->
-        trim_right(rest, line + 1, opts.indentation + 1, column, opts)
-
-      {[], column} ->
-        {[], line, column}
-
-      _ when last_column > 0 ->
-        {[?\n | rest], line - 1, last_column}
-
-      _ ->
-        {rest, line, column}
-    end
-  end
-
-  defp trim_whitespace([h | t], column) when h in @spaces, do: trim_whitespace(t, column + 1)
-  defp trim_whitespace(list, column), do: {list, column}
-end

lib/eex/test/eex/tokenizer_test.exs

@@ -2,41 +2,67 @@ Code.require_file("../test_helper.exs", __DIR__)
 
 defmodule EEx.TokenizerTest do
   use ExUnit.Case, async: true
-  require EEx.Tokenizer, as: T
 
-  @opts %{indentation: 0, trim: false}
+  @opts [indentation: 0, trim: false]
 
   test "simple chars lists" do
-    assert T.tokenize('foo', 1, 1, @opts) == {:ok, [{:text, 1, 1, 'foo'}, {:eof, 1, 4}]}
+    assert EEx.tokenize('foo', @opts) ==
+             {:ok, [{:text, 'foo', %{column: 1, line: 1}}, {:eof, %{column: 4, line: 1}}]}
   end
 
   test "simple strings" do
-    assert T.tokenize("foo", 1, 1, @opts) == {:ok, [{:text, 1, 1, 'foo'}, {:eof, 1, 4}]}
+    assert EEx.tokenize("foo", @opts) ==
+             {:ok, [{:text, 'foo', %{column: 1, line: 1}}, {:eof, %{column: 4, line: 1}}]}
   end
 
   test "strings with embedded code" do
-    assert T.tokenize('foo <% bar %>', 1, 1, @opts) ==
-             {:ok, [{:text, 1, 1, 'foo '}, {:expr, 1, 5, '', ' bar '}, {:eof, 1, 14}]}
+    assert EEx.tokenize('foo <% bar %>', @opts) ==
+             {:ok,
+              [
+                {:text, 'foo ', %{column: 1, line: 1}},
+                {:expr, '', ' bar ', %{column: 5, line: 1}},
+                {:eof, %{column: 14, line: 1}}
+              ]}
   end
 
   test "strings with embedded equals code" do
-    assert T.tokenize('foo <%= bar %>', 1, 1, @opts) ==
-             {:ok, [{:text, 1, 1, 'foo '}, {:expr, 1, 5, '=', ' bar '}, {:eof, 1, 15}]}
+    assert EEx.tokenize('foo <%= bar %>', @opts) ==
+             {:ok,
+              [
+                {:text, 'foo ', %{column: 1, line: 1}},
+                {:expr, '=', ' bar ', %{column: 5, line: 1}},
+                {:eof, %{column: 15, line: 1}}
+              ]}
   end
 
   test "strings with embedded slash code" do
-    assert T.tokenize('foo <%/ bar %>', 1, 1, @opts) ==
-             {:ok, [{:text, 1, 1, 'foo '}, {:expr, 1, 5, '/', ' bar '}, {:eof, 1, 15}]}
+    assert EEx.tokenize('foo <%/ bar %>', @opts) ==
+             {:ok,
+              [
+                {:text, 'foo ', %{column: 1, line: 1}},
+                {:expr, '/', ' bar ', %{column: 5, line: 1}},
+                {:eof, %{column: 15, line: 1}}
+              ]}
   end
 
   test "strings with embedded pipe code" do
-    assert T.tokenize('foo <%| bar %>', 1, 1, @opts) ==
-             {:ok, [{:text, 1, 1, 'foo '}, {:expr, 1, 5, '|', ' bar '}, {:eof, 1, 15}]}
+    assert EEx.tokenize('foo <%| bar %>', @opts) ==
+             {:ok,
+              [
+                {:text, 'foo ', %{column: 1, line: 1}},
+                {:expr, '|', ' bar ', %{column: 5, line: 1}},
+                {:eof, %{column: 15, line: 1}}
+              ]}
   end
 
   test "strings with more than one line" do
-    assert T.tokenize('foo\n<%= bar %>', 1, 1, @opts) ==
-             {:ok, [{:text, 1, 1, 'foo\n'}, {:expr, 2, 1, '=', ' bar '}, {:eof, 2, 11}]}
+    assert EEx.tokenize('foo\n<%= bar %>', @opts) ==
+             {:ok,
+              [
+                {:text, 'foo\n', %{column: 1, line: 1}},
+                {:expr, '=', ' bar ', %{column: 1, line: 2}},
+                {:eof, %{column: 11, line: 2}}
+              ]}
   end
 
   test "strings with more than one line and expression with more than one line" do
@@ -48,191 +74,235 @@ defmodule EEx.TokenizerTest do
     '''
 
     exprs = [
-      {:text, 1, 1, 'foo '},
-      {:expr, 1, 5, '=', ' bar\n\nbaz '},
-      {:text, 3, 7, '\n'},
-      {:expr, 4, 1, '', ' foo '},
-      {:text, 4, 10, '\n'},
-      {:eof, 5, 1}
+      {:text, 'foo ', %{column: 1, line: 1}},
+      {:expr, '=', ' bar\n\nbaz ', %{column: 5, line: 1}},
+      {:text, '\n', %{column: 7, line: 3}},
+      {:expr, '', ' foo ', %{column: 1, line: 4}},
+      {:text, '\n', %{column: 10, line: 4}},
+      {:eof, %{column: 1, line: 5}}
     ]
 
-    assert T.tokenize(string, 1, 1, @opts) == {:ok, exprs}
+    assert EEx.tokenize(string, @opts) == {:ok, exprs}
   end
 
   test "quotation" do
-    assert T.tokenize('foo <%% true %>', 1, 1, @opts) ==
-             {:ok, [{:text, 1, 1, 'foo <% true %>'}, {:eof, 1, 16}]}
+    assert EEx.tokenize('foo <%% true %>', @opts) ==
+             {:ok,
+              [
+                {:text, 'foo <% true %>', %{column: 1, line: 1}},
+                {:eof, %{column: 16, line: 1}}
+              ]}
   end
 
   test "quotation with do-end" do
-    assert T.tokenize('foo <%% true do %>bar<%% end %>', 1, 1, @opts) ==
-             {:ok, [{:text, 1, 1, 'foo <% true do %>bar<% end %>'}, {:eof, 1, 32}]}
+    assert EEx.tokenize('foo <%% true do %>bar<%% end %>', @opts) ==
+             {:ok,
+              [
+                {:text, 'foo <% true do %>bar<% end %>', %{column: 1, line: 1}},
+                {:eof, %{column: 32, line: 1}}
+              ]}
   end
 
   test "quotation with interpolation" do
     exprs = [
-      {:text, 1, 1, 'a <% b '},
-      {:expr, 1, 9, '=', ' c '},
-      {:text, 1, 17, ' '},
-      {:expr, 1, 18, '=', ' d '},
-      {:text, 1, 26, ' e %> f'},
-      {:eof, 1, 33}
+      {:text, 'a <% b ', %{column: 1, line: 1}},
+      {:expr, '=', ' c ', %{column: 9, line: 1}},
+      {:text, ' ', %{column: 17, line: 1}},
+      {:expr, '=', ' d ', %{column: 18, line: 1}},
+      {:text, ' e %> f', %{column: 26, line: 1}},
+      {:eof, %{column: 33, line: 1}}
     ]
 
-    assert T.tokenize('a <%% b <%= c %> <%= d %> e %> f', 1, 1, @opts) == {:ok, exprs}
+    assert EEx.tokenize('a <%% b <%= c %> <%= d %> e %> f', @opts) == {:ok, exprs}
   end
 
   test "improperly formatted quotation with interpolation" do
     exprs = [
-      {:text, 1, 1, '<%% a <%= b %> c %>'},
-      {:eof, 1, 22}
+      {:text, '<%% a <%= b %> c %>', %{column: 1, line: 1}},
+      {:eof, %{column: 22, line: 1}}
     ]
 
-    assert T.tokenize('<%%% a <%%= b %> c %>', 1, 1, @opts) == {:ok, exprs}
+    assert EEx.tokenize('<%%% a <%%= b %> c %>', @opts) == {:ok, exprs}
   end
 
   test "EEx comments" do
     exprs = [
-      {:text, 1, 1, 'foo '},
-      {:eof, 1, 16}
+      {:text, 'foo ', %{column: 1, line: 1}},
+      {:eof, %{column: 16, line: 1}}
     ]
 
-    assert T.tokenize('foo <%# true %>', 1, 1, @opts) == {:ok, exprs}
+    assert EEx.tokenize('foo <%# true %>', @opts) == {:ok, exprs}
+
+    exprs = [
+      {:text, 'foo ', %{column: 1, line: 1}},
+      {:eof, %{column: 8, line: 2}}
+    ]
+
+    assert EEx.tokenize('foo <%#\ntrue %>', @opts) == {:ok, exprs}
   end
 
   test "EEx comments with do-end" do
     exprs = [
-      {:text, 1, 1, 'foo '},
-      {:text, 1, 19, 'bar'},
-      {:eof, 1, 32}
+      {:text, 'foo ', %{column: 1, line: 1}},
+      {:text, 'bar', %{column: 19, line: 1}},
+      {:eof, %{column: 32, line: 1}}
     ]
 
-    assert T.tokenize('foo <%# true do %>bar<%# end %>', 1, 1, @opts) == {:ok, exprs}
+    assert EEx.tokenize('foo <%# true do %>bar<%# end %>', @opts) == {:ok, exprs}
   end
 
   test "EEx comments inside do-end" do
     exprs = [
-      {:start_expr, 1, 1, '', ' if true do '},
-      {:text, 1, 31, 'bar'},
-      {:end_expr, 1, 34, [], ' end '},
-      {:eof, 1, 43}
+      {:start_expr, '', ' if true do ', %{column: 1, line: 1}},
+      {:text, 'bar', %{column: 31, line: 1}},
+      {:end_expr, [], ' end ', %{column: 34, line: 1}},
+      {:eof, %{column: 43, line: 1}}
     ]
 
-    assert T.tokenize('<% if true do %><%# comment %>bar<% end %>', 1, 1, @opts) == {:ok, exprs}
+    assert EEx.tokenize('<% if true do %><%# comment %>bar<% end %>', @opts) == {:ok, exprs}
 
     exprs = [
-      {:start_expr, 1, 1, [], ' case true do '},
-      {:middle_expr, 1, 33, '', ' true -> '},
-      {:text, 1, 46, 'bar'},
-      {:end_expr, 1, 49, [], ' end '},
-      {:eof, 1, 58}
+      {:start_expr, [], ' case true do ', %{column: 1, line: 1}},
+      {:middle_expr, '', ' true -> ', %{column: 33, line: 1}},
+      {:text, 'bar', %{column: 46, line: 1}},
+      {:end_expr, [], ' end ', %{column: 49, line: 1}},
+      {:eof, %{column: 58, line: 1}}
     ]
 
-    assert T.tokenize('<% case true do %><%# comment %><% true -> %>bar<% end %>', 1, 1, @opts) ==
+    assert EEx.tokenize('<% case true do %><%# comment %><% true -> %>bar<% end %>', @opts) ==
              {:ok, exprs}
   end
 
+  test "EEx multi-line comments" do
+    exprs = [
+      {:text, 'foo ', %{column: 1, line: 1}},
+      {:comment, ' true ', %{column: 5, line: 1}},
+      {:text, ' bar', %{column: 20, line: 1}},
+      {:eof, %{column: 24, line: 1}}
+    ]
+
+    assert EEx.tokenize('foo <%!-- true --%> bar', @opts) == {:ok, exprs}
+
+    exprs = [
+      {:text, 'foo ', %{column: 1, line: 1}},
+      {:comment, ' \ntrue\n ', %{column: 5, line: 1}},
+      {:text, ' bar', %{column: 6, line: 3}},
+      {:eof, %{column: 10, line: 3}}
+    ]
+
+    assert EEx.tokenize('foo <%!-- \ntrue\n --%> bar', @opts) == {:ok, exprs}
+
+    exprs = [
+      {:text, 'foo ', %{column: 1, line: 1}},
+      {:comment, ' <%= true %> ', %{column: 5, line: 1}},
+      {:text, ' bar', %{column: 27, line: 1}},
+      {:eof, %{column: 31, line: 1}}
+    ]
+
+    assert EEx.tokenize('foo <%!-- <%= true %> --%> bar', @opts) == {:ok, exprs}
+  end
+
   test "Elixir comments" do
     exprs = [
-      {:text, 1, 1, 'foo '},
-      {:expr, 1, 5, [], ' true # this is a boolean '},
-      {:eof, 1, 35}
+      {:text, 'foo ', %{column: 1, line: 1}},
+      {:expr, [], ' true # this is a boolean ', %{column: 5, line: 1}},
+      {:eof, %{column: 35, line: 1}}
     ]
 
-    assert T.tokenize('foo <% true # this is a boolean %>', 1, 1, @opts) == {:ok, exprs}
+    assert EEx.tokenize('foo <% true # this is a boolean %>', @opts) == {:ok, exprs}
   end
 
   test "Elixir comments with do-end" do
     exprs = [
-      {:start_expr, 1, 1, [], ' if true do # startif '},
-      {:text, 1, 27, 'text'},
-      {:end_expr, 1, 31, [], ' end # closeif '},
-      {:eof, 1, 50}
+      {:start_expr, [], ' if true do # startif ', %{column: 1, line: 1}},
+      {:text, 'text', %{column: 27, line: 1}},
+      {:end_expr, [], ' end # closeif ', %{column: 31, line: 1}},
+      {:eof, %{column: 50, line: 1}}
     ]
 
-    assert T.tokenize('<% if true do # startif %>text<% end # closeif %>', 1, 1, @opts) ==
+    assert EEx.tokenize('<% if true do # startif %>text<% end # closeif %>', @opts) ==
              {:ok, exprs}
   end
 
   test "strings with embedded do end" do
     exprs = [
-      {:text, 1, 1, 'foo '},
-      {:start_expr, 1, 5, '', ' if true do '},
-      {:text, 1, 21, 'bar'},
-      {:end_expr, 1, 24, '', ' end '},
-      {:eof, 1, 33}
+      {:text, 'foo ', %{column: 1, line: 1}},
+      {:start_expr, '', ' if true do ', %{column: 5, line: 1}},
+      {:text, 'bar', %{column: 21, line: 1}},
+      {:end_expr, '', ' end ', %{column: 24, line: 1}},
+      {:eof, %{column: 33, line: 1}}
     ]
 
-    assert T.tokenize('foo <% if true do %>bar<% end %>', 1, 1, @opts) == {:ok, exprs}
+    assert EEx.tokenize('foo <% if true do %>bar<% end %>', @opts) == {:ok, exprs}
   end
 
   test "strings with embedded -> end" do
     exprs = [
-      {:text, 1, 1, 'foo '},
-      {:start_expr, 1, 5, '', ' cond do '},
-      {:middle_expr, 1, 18, '', ' false -> '},
-      {:text, 1, 32, 'bar'},
-      {:middle_expr, 1, 35, '', ' true -> '},
-      {:text, 1, 48, 'baz'},
-      {:end_expr, 1, 51, '', ' end '},
-      {:eof, 1, 60}
+      {:text, 'foo ', %{column: 1, line: 1}},
+      {:start_expr, '', ' cond do ', %{column: 5, line: 1}},
+      {:middle_expr, '', ' false -> ', %{column: 18, line: 1}},
+      {:text, 'bar', %{column: 32, line: 1}},
+      {:middle_expr, '', ' true -> ', %{column: 35, line: 1}},
+      {:text, 'baz', %{column: 48, line: 1}},
+      {:end_expr, '', ' end ', %{column: 51, line: 1}},
+      {:eof, %{column: 60, line: 1}}
     ]
 
-    assert T.tokenize('foo <% cond do %><% false -> %>bar<% true -> %>baz<% end %>', 1, 1, @opts) ==
+    assert EEx.tokenize('foo <% cond do %><% false -> %>bar<% true -> %>baz<% end %>', @opts) ==
              {:ok, exprs}
   end
 
   test "strings with fn-end with newline" do
     exprs = [
-      {:start_expr, 1, 1, '=', ' a fn ->\n'},
-      {:text, 2, 3, 'foo'},
-      {:end_expr, 2, 6, [], ' end '},
-      {:eof, 2, 15}
+      {:start_expr, '=', ' a fn ->\n', %{column: 1, line: 1}},
+      {:text, 'foo', %{column: 3, line: 2}},
+      {:end_expr, [], ' end ', %{column: 6, line: 2}},
+      {:eof, %{column: 15, line: 2}}
     ]
 
-    assert T.tokenize('<%= a fn ->\n%>foo<% end %>', 1, 1, @opts) ==
+    assert EEx.tokenize('<%= a fn ->\n%>foo<% end %>', @opts) ==
              {:ok, exprs}
   end
 
   test "strings with multiple fn-end" do
     exprs = [
-      {:start_expr, 1, 1, '=', ' a fn -> '},
-      {:text, 1, 15, 'foo'},
-      {:middle_expr, 1, 18, '', ' end, fn -> '},
-      {:text, 1, 34, 'bar'},
-      {:end_expr, 1, 37, '', ' end '},
-      {:eof, 1, 46}
+      {:start_expr, '=', ' a fn -> ', %{column: 1, line: 1}},
+      {:text, 'foo', %{column: 15, line: 1}},
+      {:middle_expr, '', ' end, fn -> ', %{column: 18, line: 1}},
+      {:text, 'bar', %{column: 34, line: 1}},
+      {:end_expr, '', ' end ', %{column: 37, line: 1}},
+      {:eof, %{column: 46, line: 1}}
     ]
 
-    assert T.tokenize('<%= a fn -> %>foo<% end, fn -> %>bar<% end %>', 1, 1, @opts) ==
+    assert EEx.tokenize('<%= a fn -> %>foo<% end, fn -> %>bar<% end %>', @opts) ==
              {:ok, exprs}
   end
 
   test "strings with fn-end followed by do block" do
     exprs = [
-      {:start_expr, 1, 1, '=', ' a fn -> '},
-      {:text, 1, 15, 'foo'},
-      {:middle_expr, 1, 18, '', ' end do '},
-      {:text, 1, 30, 'bar'},
-      {:end_expr, 1, 33, '', ' end '},
-      {:eof, 1, 42}
+      {:start_expr, '=', ' a fn -> ', %{column: 1, line: 1}},
+      {:text, 'foo', %{column: 15, line: 1}},
+      {:middle_expr, '', ' end do ', %{column: 18, line: 1}},
+      {:text, 'bar', %{column: 30, line: 1}},
+      {:end_expr, '', ' end ', %{column: 33, line: 1}},
+      {:eof, %{column: 42, line: 1}}
     ]
 
-    assert T.tokenize('<%= a fn -> %>foo<% end do %>bar<% end %>', 1, 1, @opts) == {:ok, exprs}
+    assert EEx.tokenize('<%= a fn -> %>foo<% end do %>bar<% end %>', @opts) == {:ok, exprs}
   end
 
   test "strings with embedded keywords blocks" do
     exprs = [
-      {:text, 1, 1, 'foo '},
-      {:start_expr, 1, 5, '', ' if true do '},
-      {:text, 1, 21, 'bar'},
-      {:middle_expr, 1, 24, '', ' else '},
-      {:text, 1, 34, 'baz'},
-      {:end_expr, 1, 37, '', ' end '},
-      {:eof, 1, 46}
+      {:text, 'foo ', %{column: 1, line: 1}},
+      {:start_expr, '', ' if true do ', %{column: 5, line: 1}},
+      {:text, 'bar', %{column: 21, line: 1}},
+      {:middle_expr, '', ' else ', %{column: 24, line: 1}},
+      {:text, 'baz', %{column: 34, line: 1}},
+      {:end_expr, '', ' end ', %{column: 37, line: 1}},
+      {:eof, %{column: 46, line: 1}}
     ]
 
-    assert T.tokenize('foo <% if true do %>bar<% else %>baz<% end %>', 1, 1, @opts) ==
+    assert EEx.tokenize('foo <% if true do %>bar<% else %>baz<% end %>', @opts) ==
              {:ok, exprs}
   end
 
@@ -240,51 +310,61 @@ defmodule EEx.TokenizerTest do
     template = '\t<%= if true do %> \n TRUE \n  <% else %>\n FALSE \n  <% end %>  \n\n  '
 
     exprs = [
-      {:start_expr, 1, 2, '=', ' if true do '},
-      {:text, 1, 20, '\n TRUE \n'},
-      {:middle_expr, 3, 3, '', ' else '},
-      {:text, 3, 13, '\n FALSE \n'},
-      {:end_expr, 5, 3, '', ' end '},
-      {:eof, 7, 3}
+      {:start_expr, '=', ' if true do ', %{column: 2, line: 1}},
+      {:text, '\n TRUE \n', %{column: 20, line: 1}},
+      {:middle_expr, '', ' else ', %{column: 3, line: 3}},
+      {:text, '\n FALSE \n', %{column: 13, line: 3}},
+      {:end_expr, '', ' end ', %{column: 3, line: 5}},
+      {:eof, %{column: 3, line: 7}}
     ]
 
-    assert T.tokenize(template, 1, 1, %{@opts | trim: true}) == {:ok, exprs}
+    assert EEx.tokenize(template, [trim: true] ++ @opts) == {:ok, exprs}
   end
 
   test "trim mode with comment" do
     exprs = [
-      {:text, 1, 19, '\n123'},
-      {:eof, 2, 4}
+      {:text, '\n123', %{column: 19, line: 1}},
+      {:eof, %{column: 4, line: 2}}
     ]
 
-    assert T.tokenize('  <%# comment %>  \n123', 1, 1, %{@opts | trim: true}) == {:ok, exprs}
+    assert EEx.tokenize('  <%# comment %>  \n123', [trim: true] ++ @opts) == {:ok, exprs}
+  end
+
+  test "trim mode with multi-line comment" do
+    exprs = [
+      {:comment, ' comment ', %{column: 3, line: 1}},
+      {:text, '\n123', %{column: 23, line: 1}},
+      {:eof, %{column: 4, line: 2}}
+    ]
+
+    assert EEx.tokenize('  <%!-- comment --%>  \n123', [trim: true] ++ @opts) == {:ok, exprs}
   end
 
   test "trim mode with CRLF" do
     exprs = [
-      {:text, 1, 1, '0\n'},
-      {:expr, 2, 3, '=', ' 12 '},
-      {:text, 2, 15, '\n34'},
-      {:eof, 3, 3}
+      {:text, '0\n', %{column: 1, line: 1}},
+      {:expr, '=', ' 12 ', %{column: 3, line: 2}},
+      {:text, '\n34', %{column: 15, line: 2}},
+      {:eof, %{column: 3, line: 3}}
     ]
 
-    assert T.tokenize('0\r\n  <%= 12 %>  \r\n34', 1, 1, %{@opts | trim: true}) == {:ok, exprs}
+    assert EEx.tokenize('0\r\n  <%= 12 %>  \r\n34', [trim: true] ++ @opts) == {:ok, exprs}
   end
 
   test "trim mode set to false" do
     exprs = [
-      {:text, 1, 1, ' '},
-      {:expr, 1, 2, '=', ' 12 '},
-      {:text, 1, 11, ' \n'},
-      {:eof, 2, 1}
+      {:text, ' ', %{column: 1, line: 1}},
+      {:expr, '=', ' 12 ', %{column: 2, line: 1}},
+      {:text, ' \n', %{column: 11, line: 1}},
+      {:eof, %{column: 1, line: 2}}
     ]
 
-    assert T.tokenize(' <%= 12 %> \n', 1, 1, %{@opts | trim: false}) == {:ok, exprs}
+    assert EEx.tokenize(' <%= 12 %> \n', [trim: false] ++ @opts) == {:ok, exprs}
   end
 
   test "trim mode no false positives" do
     assert_not_trimmed = fn x ->
-      assert T.tokenize(x, 1, 1, %{@opts | trim: false}) == T.tokenize(x, 1, 1, @opts)
+      assert EEx.tokenize(x, [trim: false] ++ @opts) == EEx.tokenize(x, @opts)
     end
 
     assert_not_trimmed.('foo <%= "bar" %>  ')
@@ -294,12 +374,22 @@ defmodule EEx.TokenizerTest do
   end
 
   test "returns error when there is start mark and no end mark" do
-    assert T.tokenize('foo <% :bar', 1, 1, @opts) == {:error, 1, 12, "missing token '%>'"}
-    assert T.tokenize('<%# true ', 1, 1, @opts) == {:error, 1, 10, "missing token '%>'"}
+    assert EEx.tokenize('foo <% :bar', @opts) ==
+             {:error, "missing token '%>'", %{column: 12, line: 1}}
+
+    assert EEx.tokenize('<%# true ', @opts) ==
+             {:error, "missing token '%>'", %{column: 10, line: 1}}
+
+    assert EEx.tokenize('<%!-- foo ', @opts) ==
+             {:error, "missing token '--%>'", %{column: 11, line: 1}}
   end
 
   test "marks invalid expressions as regular expressions" do
-    assert T.tokenize('<% 1 $ 2 %>', 1, 1, @opts) ==
-             {:ok, [{:expr, 1, 1, [], ' 1 $ 2 '}, {:eof, 1, 12}]}
+    assert EEx.tokenize('<% 1 $ 2 %>', @opts) ==
+             {:ok,
+              [
+                {:expr, [], ' 1 $ 2 ', %{column: 1, line: 1}},
+                {:eof, %{column: 12, line: 1}}
+              ]}
   end
 end

lib/eex/test/eex_test.exs

@@ -207,6 +207,15 @@ defmodule EExTest do
       )
     end
 
+    test "embedded code with multi-line comments in do end" do
+      assert_eval("foo bar", "foo <%= case true do %><%!-- comment --%><% true -> %>bar<% end %>")
+
+      assert_eval(
+        "foo\n\nbar\n",
+        "foo\n<%= case true do %>\n<%!-- comment --%>\n<% true -> %>\nbar\n<% end %>"
+      )
+    end
+
     test "embedded code with nested do end" do
       assert_eval("foo bar", "foo <%= if true do %><%= if true do %>bar<% end %><% end %>")
     end
@@ -308,7 +317,7 @@ defmodule EExTest do
       assert ExUnit.CaptureIO.capture_io(:stderr, fn ->
                EEx.compile_string("foo <%= if true do %>true<% else %>false<%= end %>")
              end) =~
-               ~s[unexpected beginning of EEx tag \"<%=\" on end of expression \"<%= end %>\"]
+               ~s[unexpected beginning of EEx tag \"<%=\" on \"<%= end %>\"]
     end
 
     test "when trying to use marker '/' without implementation" do

lib/eex/test/test_helper.exs

@@ -1 +1,8 @@
-ExUnit.start(trace: "--trace" in System.argv())
+{line_exclude, line_include} =
+  if line = System.get_env("LINE"), do: {[:test], [line: line]}, else: {[], []}
+
+ExUnit.start(
+  trace: !!System.get_env("TRACE"),
+  include: line_include,
+  exclude: line_exclude
+)

lib/elixir/docs.exs

@@ -78,6 +78,7 @@ canonical = System.fetch_env!("CANONICAL")
       DynamicSupervisor,
       GenServer,
       Node,
+      PartitionSupervisor,
       Process,
       Registry,
       Supervisor,

lib/elixir/lib/access.ex

@@ -94,8 +94,7 @@ defmodule Access do
 
   @type container :: keyword | struct | map
   @type nil_container :: nil
-  @type any_container :: any
-  @type t :: container | nil_container | any_container
+  @type t :: container | nil_container | any
   @type key :: any
   @type value :: any
 
@@ -153,7 +152,7 @@ defmodule Access do
   """
   @callback get_and_update(data, key, (value | nil -> {current_value, new_value :: value} | :pop)) ::
               {current_value, new_data :: data}
-            when current_value: value, data: container | any_container
+            when current_value: value, data: container
 
   @doc """
   Invoked to "pop" the value under `key` out of the given data structure.
@@ -167,14 +166,18 @@ defmodule Access do
 
   See the implementations for `Map.pop/3` or `Keyword.pop/3` for more examples.
   """
-  @callback pop(data, key) :: {value, data} when data: container | any_container
+  @callback pop(data, key) :: {value, data} when data: container
 
   defmacrop raise_undefined_behaviour(exception, module, top) do
     quote do
       exception =
         case __STACKTRACE__ do
           [unquote(top) | _] ->
-            reason = "#{inspect(unquote(module))} does not implement the Access behaviour"
+            reason =
+              "#{inspect(unquote(module))} does not implement the Access behaviour. " <>
+                "If you are using get_in/put_in/update_in, you can specify the field " <>
+                "to be accessed using Access.key!/1"
+
             %{unquote(exception) | reason: reason}
 
           _ ->
@@ -826,4 +829,118 @@ defmodule Access do
   defp get_and_update_filter([], _func, _next, updates, gets) do
     {:lists.reverse(gets), :lists.reverse(updates)}
   end
+
+  @doc ~S"""
+  Returns a function that accesses all items of a list that are within the provided range.
+
+  The range will be normalized following the same rules from `Enum.slice/2`.
+
+  The returned function is typically passed as an accessor to `Kernel.get_in/2`,
+  `Kernel.get_and_update_in/3`, and friends.
+
+  ## Examples
+
+      iex> list = [%{name: "john", salary: 10}, %{name: "francine", salary: 30}, %{name: "vitor", salary: 25}]
+      iex> get_in(list, [Access.slice(1..2), :name])
+      ["francine", "vitor"]
+      iex> get_and_update_in(list, [Access.slice(1..3//2), :name], fn prev ->
+      ...>   {prev, String.upcase(prev)}
+      ...> end)
+      {["francine"], [%{name: "john", salary: 10}, %{name: "FRANCINE", salary: 30}, %{name: "vitor", salary: 25}]}
+
+  `slice/1` can also be used to pop elements out of a list or
+  a key inside of a list:
+
+      iex> list = [%{name: "john", salary: 10}, %{name: "francine", salary: 30}, %{name: "vitor", salary: 25}]
+      iex> pop_in(list, [Access.slice(-2..-1)])
+      {[%{name: "francine", salary: 30}, %{name: "vitor", salary: 25}], [%{name: "john", salary: 10}]}
+      iex> pop_in(list, [Access.slice(-2..-1), :name])
+      {["francine", "vitor"], [%{name: "john", salary: 10}, %{salary: 30}, %{salary: 25}]}
+
+  When no match is found, an empty list is returned and the update function is never called
+
+      iex> list = [%{name: "john", salary: 10}, %{name: "francine", salary: 30}, %{name: "vitor", salary: 25}]
+      iex> get_in(list, [Access.slice(5..10//2), :name])
+      []
+      iex> get_and_update_in(list, [Access.slice(5..10//2), :name], fn prev ->
+      ...>   {prev, String.upcase(prev)}
+      ...> end)
+      {[], [%{name: "john", salary: 10}, %{name: "francine", salary: 30}, %{name: "vitor", salary: 25}]}
+
+  An error is raised if the accessed structure is not a list:
+
+      iex> get_in(%{}, [Access.slice(2..10//3)])
+      ** (ArgumentError) Access.slice/1 expected a list, got: %{}
+
+  An error is raised if the step of the range is negative:
+
+      iex> get_in([], [Access.slice(2..10//-1)])
+      ** (ArgumentError) Access.slice/1 does not accept ranges with negative steps, got: 2..10//-1
+
+  """
+  @doc since: "1.14"
+  @spec slice(Range.t()) :: access_fun(data :: list, current_value :: list)
+  def slice(%Range{} = range) do
+    if range.step > 0 do
+      fn op, data, next -> slice(op, data, range, next) end
+    else
+      raise ArgumentError,
+            "Access.slice/1 does not accept ranges with negative steps, got: #{inspect(range)}"
+    end
+  end
+
+  defp slice(:get, data, %Range{} = range, next) when is_list(data) do
+    data
+    |> Enum.slice(range)
+    |> Enum.map(next)
+  end
+
+  defp slice(:get_and_update, data, range, next) when is_list(data) do
+    range = normalize_range(range, data)
+
+    if range.first > range.last do
+      {[], data}
+    else
+      get_and_update_slice(data, range, next, [], [], 0)
+    end
+  end
+
+  defp slice(_op, data, _range, _next) do
+    raise ArgumentError, "Access.slice/1 expected a list, got: #{inspect(data)}"
+  end
+
+  defp normalize_range(%Range{first: first, last: last, step: step}, list)
+       when first < 0 or last < 0 do
+    count = length(list)
+    first = if first >= 0, do: first, else: Kernel.max(first + count, 0)
+    last = if last >= 0, do: last, else: last + count
+    Range.new(first, last, step)
+  end
+
+  defp normalize_range(range, _list), do: range
+
+  defp get_and_update_slice([head | rest], range, next, updates, gets, index) do
+    if index in range do
+      case next.(head) do
+        :pop ->
+          get_and_update_slice(rest, range, next, updates, [head | gets], index + 1)
+
+        {get, update} ->
+          get_and_update_slice(
+            rest,
+            range,
+            next,
+            [update | updates],
+            [get | gets],
+            index + 1
+          )
+      end
+    else
+      get_and_update_slice(rest, range, next, [head | updates], gets, index + 1)
+    end
+  end
+
+  defp get_and_update_slice([], _range, _next, updates, gets, _index) do
+    {:lists.reverse(gets), :lists.reverse(updates)}
+  end
 end

lib/elixir/lib/application.ex

@@ -51,13 +51,23 @@ defmodule Application do
       config :my_app, :db_host, "db.local"
 
   See the "Configuration" section in the `Mix` module for more information.
-
   You can also change the application environment dynamically by using functions
-  such as `put_env/3` and `delete_env/2`. However, as a rule of thumb, each application
-  is responsible for its own environment. Please do not use the functions in this
-  module for directly accessing or modifying the environment of other applications.
+  such as `put_env/3` and `delete_env/2`.
 
-  ### Compile-time environment
+  > Note: The config files `config/config.exs` and `config/runtime.exs`
+  > are rarely used by libraries. Libraries typically define their environment
+  > in the `def application` function of their `mix.exs`. Configuration files
+  > are rather used by applications to configure their libraries.
+
+  > Note: Each application is responsible for its own environment. Do not
+  > use the functions in this module for directly accessing or modifying
+  > the environment of other applications. Whenever you change the application
+  > environment, Elixir's build tool will only recompile the files that
+  > belong to that application. So if you read the application environment
+  > of another application, there is a chance you will be depending on
+  > outdated configuration, as your file won't be recompiled as it changes.
+
+  ## Compile-time environment
 
   In the previous example, we read the application environment at runtime:
 
@@ -75,37 +85,48 @@ defmodule Application do
   will only be read when `MyApp.DBClient` effectively starts. While reading
   the application environment at runtime is the preferred approach, in some
   rare occasions you may want to use the application environment to configure
-  the compilation of a certain project. This is often done by calling `get_env/3`
-  outside of a function:
+  the compilation of a certain project. However, if you try to access
+  `Application.fetch_env!/2` outside of a function:
 
       defmodule MyApp.DBClient do
-        @db_host Application.get_env(:my_app, :db_host, "db.local")
+        @db_host Application.fetch_env!(:my_app, :db_host)
 
         def start_link() do
           SomeLib.DBClient.start_link(host: @db_host)
         end
       end
 
-  This approach has one big limitation: if you change the value of the
-  application environment after the code is compiled, the value used at
-  runtime is not going to change! For example, if your `config/runtime.exs`
-  has:
+  You might see warnings and errors:
 
-      config :my_app, :db_host, "db.production"
+      warning: Application.fetch_env!/2 is discouraged in the module body,
+      use Application.compile_env/3 instead
+        iex:3: MyApp.DBClient
 
-  This value will have no effect as the code was compiled to connect to "db.local",
-  which is mostly likely unavailable in the production environment.
+      ** (ArgumentError) could not fetch application environment :db_host
+      for application :my_app because the application was not loaded nor
+      configured
 
-  For those reasons, reading the application environment at runtime should be the
-  first choice. However, if you really have to read the application environment
-  during compilation, we recommend you to use `compile_env/3` instead:
+  This happens because, when defining modules, the application environment
+  is not yet available. Luckily, the warning tells us how to solve this
+  issue, by using `Application.compile_env/3` instead:
 
-      require Application
-      @db_host Application.compile_env(:my_app, :db_host, "db.local")
+      defmodule MyApp.DBClient do
+        @db_host Application.compile_env(:my_app, :db_host, "db.local")
 
-  By using `compile_env/3`, tools like Mix will store the values used during
-  compilation and compare the compilation values with the runtime values whenever
-  your system starts, raising an error in case they differ.
+        def start_link() do
+          SomeLib.DBClient.start_link(host: @db_host)
+        end
+      end
+
+  The difference here is that `compile_env` expects the default value to be
+  given as an argument, instead of using the `def application` function of
+  your `mix.exs`. Furthermore, by using `compile_env/3`, tools like Mix will
+  store the values used during compilation and compare the compilation values
+  with the runtime values whenever your system starts, raising an error in
+  case they differ.
+
+  In any case, compile-time environments should be avoided. Whenever possible,
+  reading the application environment at runtime should be the first choice.
 
   ## The application callback module
 
@@ -168,7 +189,7 @@ defmodule Application do
   In the sections above, we have configured an application in the
   `application/0` section of the `mix.exs` file. Ultimately, Mix will use
   this configuration to create an [*application resource
-  file*](https://erlang.org/doc/man/application.html), which is a file called
+  file*](https://www.erlang.org/doc/man/application.html), which is a file called
   `APP_NAME.app`. For example, the application resource file of the OTP
   application `ex_unit` is called `ex_unit.app`.
 
@@ -273,9 +294,9 @@ defmodule Application do
 
   For further details on applications please check the documentation of the
   [`:application` Erlang module](`:application`), and the
-  [Applications](https://erlang.org/doc/design_principles/applications.html)
+  [Applications](https://www.erlang.org/doc/design_principles/applications.html)
   section of the [OTP Design Principles User's
-  Guide](https://erlang.org/doc/design_principles/users_guide.html).
+  Guide](https://www.erlang.org/doc/design_principles/users_guide.html).
   """
 
   @doc """
@@ -504,33 +525,34 @@ defmodule Application do
   Giving a path is useful to let Elixir know that only certain paths
   in a large configuration are compile time dependent.
   """
-  # TODO: Warn on v1.14 if get_env/fetch_env/fetch_env! is used at
-  # compile time instead of compile_env
   @doc since: "1.10.0"
   @spec compile_env(app, key | list, value) :: value
-  defmacro compile_env(app, key_or_path, default \\ nil) when is_atom(app) do
+  defmacro compile_env(app, key_or_path, default \\ nil) do
     if __CALLER__.function do
       raise "Application.compile_env/3 cannot be called inside functions, only in the module body"
     end
 
-    key_or_path = expand_key_or_path(key_or_path, __CALLER__)
+    key_or_path = Macro.expand_literal(key_or_path, %{__CALLER__ | function: {:__info__, 1}})
 
     quote do
-      Application.__compile_env__(unquote(app), unquote(key_or_path), unquote(default), __ENV__)
+      Application.compile_env(__ENV__, unquote(app), unquote(key_or_path), unquote(default))
     end
   end
 
-  defp expand_key_or_path({:__aliases__, _, _} = alias, env),
-    do: Macro.expand(alias, %{env | function: {:__info__, 1}})
+  @doc """
+  Reads the application environment at compilation time from a macro.
 
-  defp expand_key_or_path(list, env) when is_list(list),
-    do: Enum.map(list, &expand_key_or_path(&1, env))
+  Typically, developers will use `compile_env/3`. This function must
+  only be invoked from macros which aim to read the compilation environment
+  dynamically.
 
-  defp expand_key_or_path(other, _env),
-    do: other
-
-  @doc false
-  def __compile_env__(app, key_or_path, default, env) do
+  It expects a `Macro.Env` as first argument, where the `Macro.Env` is
+  typically the `__CALLER__` in a macro. It raises if `Macro.Env` comes
+  from a function.
+  """
+  @doc since: "1.14.0"
+  @spec compile_env(Macro.Env.t(), app, key | list, value) :: value
+  def compile_env(%Macro.Env{} = env, app, key_or_path, default) do
     case fetch_compile_env(app, key_or_path, env) do
       {:ok, value} -> value
       :error -> default
@@ -545,20 +567,33 @@ defmodule Application do
   """
   @doc since: "1.10.0"
   @spec compile_env!(app, key | list) :: value
-  defmacro compile_env!(app, key_or_path) when is_atom(app) do
+  defmacro compile_env!(app, key_or_path) do
     if __CALLER__.function do
       raise "Application.compile_env!/2 cannot be called inside functions, only in the module body"
     end
 
-    key_or_path = expand_key_or_path(key_or_path, __CALLER__)
+    key_or_path = Macro.expand_literal(key_or_path, %{__CALLER__ | function: {:__info__, 1}})
 
     quote do
-      Application.__compile_env__!(unquote(app), unquote(key_or_path), __ENV__)
+      Application.compile_env!(__ENV__, unquote(app), unquote(key_or_path))
     end
   end
 
-  @doc false
-  def __compile_env__!(app, key_or_path, env) do
+  @doc """
+  Reads the application environment at compilation time from a macro
+  or raises.
+
+  Typically, developers will use `compile_env!/2`. This function must
+  only be invoked from macros which aim to read the compilation environment
+  dynamically.
+
+  It expects a `Macro.Env` as first argument, where the `Macro.Env` is
+  typically the `__CALLER__` in a macro. It raises if `Macro.Env` comes
+  from a function.
+  """
+  @doc since: "1.14.0"
+  @spec compile_env!(Macro.Env.t(), app, key | list) :: value
+  def compile_env!(%Macro.Env{} = env, app, key_or_path) do
     case fetch_compile_env(app, key_or_path, env) do
       {:ok, value} ->
         value
@@ -570,8 +605,9 @@ defmodule Application do
     end
   end
 
-  defp fetch_compile_env(app, key, env) when is_atom(key),
-    do: fetch_compile_env(app, key, [], env)
+  defp fetch_compile_env(app, key, env) when is_atom(key) do
+    fetch_compile_env(app, key, [], env)
+  end
 
   defp fetch_compile_env(app, [key | paths], env) when is_atom(key),
     do: fetch_compile_env(app, key, paths, env)
@@ -596,14 +632,13 @@ defmodule Application do
   If the configuration parameter does not exist, the function returns the
   `default` value.
 
-  **Important:** if you are reading the application environment at compilation
-  time, for example, inside the module definition instead of inside of a
-  function, see `compile_env/3` instead.
+  > **Important:** you must use this function to read only your own application
+  > environment. Do not read the environment of other applications.
 
-  **Important:** if you are writing a library to be used by other developers,
-  it is generally recommended to avoid the application environment, as the
-  application environment is effectively a global storage. For more information,
-  read our [library guidelines](library-guidelines.md).
+  > **Important:** if you are writing a library to be used by other developers,
+  > it is generally recommended to avoid the application environment, as the
+  > application environment is effectively a global storage. For more information,
+  > read our [library guidelines](library-guidelines.md).
 
   ## Examples
 
@@ -653,6 +688,14 @@ defmodule Application do
   Returns the value for `key` in `app`'s environment in a tuple.
 
   If the configuration parameter does not exist, the function returns `:error`.
+
+  > **Important:** you must use this function to read only your own application
+  > environment. Do not read the environment of other applications.
+
+  > **Important:** if you are writing a library to be used by other developers,
+  > it is generally recommended to avoid the application environment, as the
+  > application environment is effectively a global storage. For more information,
+  > read our [library guidelines](library-guidelines.md).
   """
   @spec fetch_env(app, key) :: {:ok, value} | :error
   def fetch_env(app, key) when is_atom(app) do
@@ -669,9 +712,13 @@ defmodule Application do
 
   If the configuration parameter does not exist, raises `ArgumentError`.
 
-  **Important:** if you are reading the application environment at compilation
-  time, for example, inside the module definition instead of inside of a
-  function, see `compile_env!/2` instead.
+  > **Important:** you must use this function to read only your own application
+  > environment. Do not read the environment of other applications.
+
+  > **Important:** if you are writing a library to be used by other developers,
+  > it is generally recommended to avoid the application environment, as the
+  > application environment is effectively a global storage. For more information,
+  > read our [library guidelines](library-guidelines.md).
   """
   @spec fetch_env!(app, key) :: value
   def fetch_env!(app, key) when is_atom(app) do
@@ -777,7 +824,7 @@ defmodule Application do
   @doc """
   Ensures the given `app` is loaded.
 
-  Same as `load/2` but returns `:ok` if the application was already
+  Same as `load/1` but returns `:ok` if the application was already
   loaded.
   """
   @doc since: "1.10.0"

lib/elixir/lib/atom.ex

@@ -56,7 +56,7 @@ defmodule Atom do
   """
   @spec to_string(atom) :: String.t()
   def to_string(atom) do
-    :erlang.atom_to_binary(atom, :utf8)
+    :erlang.atom_to_binary(atom)
   end
 
   @doc """

lib/elixir/lib/bitwise.ex

@@ -3,31 +3,11 @@ defmodule Bitwise do
   A set of functions that perform calculations on bits.
 
   All bitwise functions work only on integers; otherwise an
-  `ArithmeticError` is raised.
+  `ArithmeticError` is raised. The functions `band/2`,
+  `bor/2`, `bsl/2`, and `bsr/2` also have operators,
+  respectively: `&&&/2`, `|||/2`, `<<</2`, and `>>>/2`.
 
-  The functions in this module come in two flavors: named or
-  operators. For example:
-
-      iex> use Bitwise
-      iex> bnot(1) # named
-      -2
-      iex> 1 &&& 1 # operator
-      1
-
-  If you prefer to use only operators or skip them, you can
-  pass the following options:
-
-    * `:only_operators` - includes only operators
-    * `:skip_operators` - skips operators
-
-  For example:
-
-      iex> use Bitwise, only_operators: true
-      iex> 1 &&& 1
-      1
-
-  When invoked with no options, `use Bitwise` is equivalent
-  to `import Bitwise`.
+  ## Guards
 
   All bitwise functions can be used in guards:
 
@@ -42,6 +22,7 @@ defmodule Bitwise do
   """
 
   @doc false
+  @deprecated "import Bitwise instead"
   defmacro __using__(options) do
     except =
       cond do
@@ -49,7 +30,7 @@ defmodule Bitwise do
           [bnot: 1, band: 2, bor: 2, bxor: 2, bsl: 2, bsr: 2]
 
         Keyword.get(options, :skip_operators) ->
-          [~~~: 1, &&&: 2, |||: 2, ^^^: 2, <<<: 2, >>>: 2]
+          ["~~~": 1, &&&: 2, |||: 2, "^^^": 2, <<<: 2, >>>: 2]
 
         true ->
           []
@@ -80,25 +61,8 @@ defmodule Bitwise do
     :erlang.bnot(expr)
   end
 
-  @doc """
-  Bitwise NOT unary operator.
-
-  Calculates the bitwise NOT of the argument.
-
-  Allowed in guard tests. Inlined by the compiler.
-
-  ## Examples
-
-      iex> ~~~2
-      -3
-
-      iex> ~~~2 &&& 3
-      1
-
-  """
-  @doc guard: true
-  @spec ~~~integer :: integer
-  def ~~~expr do
+  @doc false
+  def unquote(:"~~~")(expr) do
     :erlang.bnot(expr)
   end
 
@@ -192,7 +156,7 @@ defmodule Bitwise do
   end
 
   @doc false
-  def unquote(:^^^)(left, right) do
+  def unquote(:"^^^")(left, right) do
     :erlang.bxor(left, right)
   end
 

lib/elixir/lib/calendar.ex

@@ -57,7 +57,7 @@ defmodule Calendar do
   representing the microseconds to external format. If the precision is 0,
   it means microseconds must be skipped.
   """
-  @type microsecond :: {non_neg_integer, non_neg_integer}
+  @type microsecond :: {value :: non_neg_integer, precision :: non_neg_integer}
 
   @typedoc "A calendar implementation"
   @type calendar :: module
@@ -365,7 +365,7 @@ defmodule Calendar do
   """
   @doc since: "1.8.0"
   @spec put_time_zone_database(time_zone_database()) :: :ok
-  def put_time_zone_database(database) do
+  def put_time_zone_database(database) when is_atom(database) do
     Application.put_env(:elixir, :time_zone_database, database)
   end
 
@@ -375,7 +375,7 @@ defmodule Calendar do
   @doc since: "1.8.0"
   @spec get_time_zone_database() :: time_zone_database()
   def get_time_zone_database() do
-    Application.get_env(:elixir, :time_zone_database, Calendar.UTCOnlyTimeZoneDatabase)
+    Application.fetch_env!(:elixir, :time_zone_database)
   end
 
   @doc """
@@ -544,8 +544,8 @@ defmodule Calendar do
     parse_modifiers(rest, width, "", parser_data)
   end
 
-  defp parse_modifiers("0" <> rest, width, nil, parser_data) do
-    parse_modifiers(rest, width, ?0, parser_data)
+  defp parse_modifiers("0" <> rest, nil, nil, parser_data) do
+    parse_modifiers(rest, nil, ?0, parser_data)
   end
 
   defp parse_modifiers("_" <> rest, width, nil, parser_data) do

lib/elixir/lib/calendar/date.ex

@@ -4,7 +4,7 @@ defmodule Date do
 
   The Date struct contains the fields year, month, day and calendar.
   New dates can be built with the `new/3` function or using the
-  `~D` (see `Kernel.sigil_D/2`) sigil:
+  `~D` (see `sigil_D/2`) sigil:
 
       iex> ~D[2000-01-01]
       ~D[2000-01-01]
@@ -31,7 +31,12 @@ defmodule Date do
 
   Comparisons in Elixir using `==/2`, `>/2`, `</2` and similar are structural
   and based on the `Date` struct fields. For proper comparison between
-  dates, use the `compare/2` function.
+  dates, use the `compare/2` function. The existence of the `compare/2`
+  function in this module also allows using `Enum.min/2` and `Enum.max/2`
+  functions to get the minimum and maximum date of an `Enum`. For example:
+
+      iex>  Enum.min([~D[2017-03-31], ~D[2017-04-01]], Date)
+      ~D[2017-03-31]
 
   ## Using epochs
 
@@ -72,16 +77,18 @@ defmodule Date do
   ## Examples
 
       iex> Date.range(~D[1999-01-01], ~D[2000-01-01])
-      #DateRange<~D[1999-01-01], ~D[2000-01-01]>
+      Date.range(~D[1999-01-01], ~D[2000-01-01])
 
   A range of dates implements the `Enumerable` protocol, which means
   functions in the `Enum` module can be used to work with
   ranges:
 
       iex> range = Date.range(~D[2001-01-01], ~D[2002-01-01])
+      iex> range
+      Date.range(~D[2001-01-01], ~D[2002-01-01])
       iex> Enum.count(range)
       366
-      iex> Enum.member?(range, ~D[2001-02-01])
+      iex> ~D[2001-02-01] in range
       true
       iex> Enum.take(range, 3)
       [~D[2001-01-01], ~D[2001-01-02], ~D[2001-01-03]]
@@ -108,10 +115,10 @@ defmodule Date do
 
       iex> range = Date.range(~D[2001-01-01], ~D[2002-01-01], 2)
       iex> range
-      #DateRange<~D[2001-01-01], ~D[2002-01-01], 2>
+      Date.range(~D[2001-01-01], ~D[2002-01-01], 2)
       iex> Enum.count(range)
       183
-      iex> Enum.member?(range, ~D[2001-01-03])
+      iex> ~D[2001-01-03] in range
       true
       iex> Enum.take(range, 3)
       [~D[2001-01-01], ~D[2001-01-03], ~D[2001-01-05]]
@@ -830,8 +837,6 @@ defmodule Date do
       ~D[2020-07-05]
       iex> Date.end_of_week(~D[2020-07-06], :sunday)
       ~D[2020-07-11]
-      iex> Date.end_of_week(~D[2020-07-06], :sunday)
-      ~D[2020-07-11]
       iex> Date.end_of_week(~D[2020-07-06], :saturday)
       ~D[2020-07-10]
       iex> Date.end_of_week(~N[2020-07-11 01:23:45])
@@ -992,6 +997,8 @@ defmodule Date do
   """
   @doc since: "1.11.0"
   @spec beginning_of_month(Calendar.date()) :: t()
+  def beginning_of_month(date)
+
   def beginning_of_month(%{year: year, month: month, calendar: calendar}) do
     %Date{year: year, month: month, day: 1, calendar: calendar}
   end
@@ -1011,6 +1018,8 @@ defmodule Date do
   """
   @doc since: "1.11.0"
   @spec end_of_month(Calendar.date()) :: t()
+  def end_of_month(date)
+
   def end_of_month(%{year: year, month: month, calendar: calendar} = date) do
     day = Date.days_in_month(date)
     %Date{year: year, month: month, day: day, calendar: calendar}

lib/elixir/lib/calendar/date_range.ex

@@ -16,12 +16,12 @@ defmodule Date.Range do
   @type t :: %__MODULE__{
           first: Date.t(),
           last: Date.t(),
-          first_in_iso_days: iso_days(),
-          last_in_iso_days: iso_days(),
+          first_in_iso_days: days(),
+          last_in_iso_days: days(),
           step: pos_integer | neg_integer
         }
 
-  @typep iso_days() :: Calendar.iso_days()
+  @typep days() :: integer()
 
   @enforce_keys [:first, :last, :first_in_iso_days, :last_in_iso_days, :step]
   defstruct [:first, :last, :first_in_iso_days, :last_in_iso_days, :step]
@@ -75,7 +75,7 @@ defmodule Date.Range do
             step: step
           } = range
         ) do
-      {:ok, size(range), &slice(first + &1 * step, step, &2, calendar)}
+      {:ok, size(range), &slice(first + &1 * step, step + &3 - 1, &2, calendar)}
     end
 
     # TODO: Remove me on v2.0
@@ -211,11 +211,11 @@ defmodule Date.Range do
     import Kernel, except: [inspect: 2]
 
     def inspect(%Date.Range{first: first, last: last, step: 1}, _) do
-      "#DateRange<" <> inspect(first) <> ", " <> inspect(last) <> ">"
+      "Date.range(" <> inspect(first) <> ", " <> inspect(last) <> ")"
     end
 
     def inspect(%Date.Range{first: first, last: last, step: step}, _) do
-      "#DateRange<" <> inspect(first) <> ", " <> inspect(last) <> ", #{step}>"
+      "Date.range(" <> inspect(first) <> ", " <> inspect(last) <> ", #{step})"
     end
 
     # TODO: Remove me on v2.0

lib/elixir/lib/calendar/datetime.ex

@@ -2,15 +2,24 @@ defmodule DateTime do
   @moduledoc """
   A datetime implementation with a time zone.
 
-  This datetime can be seen as an ephemeral snapshot
-  of a datetime at a given time zone. For such purposes,
-  it also includes both UTC and Standard offsets, as
-  well as the zone abbreviation field used exclusively
-  for formatting purposes.
+  This datetime can be seen as a snapshot of a date and time
+  at a given time zone. For such purposes, it also includes both
+  UTC and Standard offsets, as well as the zone abbreviation
+  field used exclusively for formatting purposes. Note future
+  datetimes are not necessarily guaranteed to exist, as time
+  zones may change any time in the future due to geopolitical
+  reasons. See the "Datetimes as snapshots" section for more
+  information.
 
   Remember, comparisons in Elixir using `==/2`, `>/2`, `</2` and friends
   are structural and based on the DateTime struct fields. For proper
-  comparison between datetimes, use the `compare/2` function.
+  comparison between datetimes, use the `compare/2` function. The
+  existence of the `compare/2` function in this module also allows
+  using `Enum.min/2` and `Enum.max/2` functions to get the minimum and
+  maximum datetime of an `Enum`. For example:
+
+      iex> Enum.min([~U[2022-01-12 00:01:00.00Z], ~U[2021-01-12 00:01:00.00Z]], DateTime)
+      ~U[2021-01-12 00:01:00.00Z]
 
   Developers should avoid creating the `DateTime` struct directly
   and instead rely on the functions provided by this module as
@@ -25,22 +34,74 @@ defmodule DateTime do
   datetimes and returns `{:error, :utc_only_time_zone_database}`
   for any other time zone.
 
-  Other time zone databases can also be configured. For example,
-  two of the available options are:
+  Other time zone databases can also be configured. Here are some
+  available options and libraries:
 
-    * [`tz`](https://hexdocs.pm/tz/)
-    * [`tzdata`](https://hexdocs.pm/tzdata/)
+    * [`tz`](https://github.com/mathieuprog/tz)
+    * [`tzdata`](https://github.com/lau/tzdata)
+    * [`zoneinfo`](https://github.com/smartrent/zoneinfo) -
+      recommended for embedded devices
 
   To use them, first make sure it is added as a dependency in `mix.exs`.
   It can then be configured either via configuration:
 
-      config :elixir, :time_zone_database, Tzdata.TimeZoneDatabase
+      config :elixir, :time_zone_database, Tz.TimeZoneDatabase
 
   or by calling `Calendar.put_time_zone_database/1`:
 
-      Calendar.put_time_zone_database(Tzdata.TimeZoneDatabase)
+      Calendar.put_time_zone_database(Tz.TimeZoneDatabase)
 
   See the proper names in the library installation instructions.
+
+  ## Datetimes as snapshots
+
+  In the first section, we described datetimes as a "snapshot of
+  a date and time at a given time zone". To understand precisely
+  what we mean, let's see an example.
+
+  Imagine someone in Poland wants to schedule a meeting with someone
+  in Brazil in the next year. The meeting will happen at 2:30 AM
+  in the Polish time zone. At what time will the meeting happen in
+  Brazil?
+
+  You can consult the time zone database today, one year before,
+  using the API in this module and it will give you an answer that
+  is valid right now. However, this answer may not be valid in the
+  future. Why? Because both Brazil and Poland may change their timezone
+  rules, ultimately affecting the result. For example, a country may
+  choose to enter or abandon "Daylight Saving Time", which is a
+  process where we adjust the clock one hour forward or one hour
+  back once per year. Whenener the rules change, the exact instant
+  that 2:30 AM in Polish time will be in Brazil may change.
+
+  In other words, whenever working with future DateTimes, there is
+  no guarantee the results you get will always be correct, until
+  the event actually happens. Therefore, when you ask for a future
+  time, the answers you get are a snapshot that reflects the current
+  state of the time zone rules. For datetimes in the past, this is
+  not a problem, because time zone rules do not change for past
+  events.
+
+  To make matters worse, it may be that the 2:30 AM in Polish time
+  does not actually even exist or it is ambiguous. If a certain
+  time zone observes "Daylight Saving Time", they will move their
+  clock forward once a year. When this happens, there is a whole
+  hour that does not exist. Then, when they move the clock back,
+  there is a certain hour that will happen twice. So if you want
+  to schedule a meeting when this shift back happens, you would
+  need to explicitly say which of the 2:30 AM you precisely mean.
+  Applications that are date and time sensitive, need to take
+  these scenarios into account and correctly communicate them to
+  users.
+
+  The good news is: Elixir contains all of the building blocks
+  necessary to tackle those problems. The default timezone database
+  used by Elixir, `Calendar.UTCOnlyTimeZoneDatabase`, only works
+  with UTC, which does not observe those issues. Once you bring
+  a proper time zone database, the functions in this module will
+  query the database and return the relevant information. For
+  example, look at how `DateTime.new/4` returns different results
+  based on the scenarios described in this section.
   """
 
   @enforce_keys [:year, :month, :day, :hour, :minute, :second] ++
@@ -82,6 +143,9 @@ defmodule DateTime do
   @doc """
   Returns the current datetime in UTC.
 
+  If you want the current time in Unix seconds,
+  use `System.os_time/1` instead.
+
   ## Examples
 
       iex> datetime = DateTime.utc_now()
@@ -753,10 +817,6 @@ defmodule DateTime do
   It will return the integer with the given unit,
   according to `System.convert_time_unit/3`.
 
-  If you want to get the current time in Unix seconds,
-  do not do `DateTime.utc_now() |> DateTime.to_unix()`.
-  Simply call `System.os_time(:second)` instead.
-
   ## Examples
 
       iex> 1_464_096_368 |> DateTime.from_unix!() |> DateTime.to_unix()
@@ -801,6 +861,8 @@ defmodule DateTime do
 
   """
   @spec to_naive(Calendar.datetime()) :: NaiveDateTime.t()
+  def to_naive(datetime)
+
   def to_naive(%{
         calendar: calendar,
         year: year,
@@ -840,6 +902,8 @@ defmodule DateTime do
 
   """
   @spec to_date(Calendar.datetime()) :: Date.t()
+  def to_date(datetime)
+
   def to_date(%{
         year: year,
         month: month,
@@ -870,6 +934,8 @@ defmodule DateTime do
 
   """
   @spec to_time(Calendar.datetime()) :: Time.t()
+  def to_time(datetime)
+
   def to_time(%{
         year: _,
         month: _,
@@ -1053,6 +1119,10 @@ defmodule DateTime do
       iex> datetime
       ~U[-2015-01-23 21:20:07.123Z]
 
+      iex> {:ok, datetime, 9000} = DateTime.from_iso8601("20150123T235007.123+0230", :basic)
+      iex> datetime
+      ~U[2015-01-23 21:20:07.123Z]
+
       iex> DateTime.from_iso8601("2015-01-23P23:50:07")
       {:error, :invalid_format}
       iex> DateTime.from_iso8601("2015-01-23T23:50:07")
@@ -1066,11 +1136,37 @@ defmodule DateTime do
 
   """
   @doc since: "1.4.0"
-  @spec from_iso8601(String.t(), Calendar.calendar()) ::
+  @spec from_iso8601(String.t(), Calendar.calendar(), :extended | :basic) ::
           {:ok, t, Calendar.utc_offset()} | {:error, atom}
-  def from_iso8601(string, calendar \\ Calendar.ISO) do
+
+  def from_iso8601(string, format_or_calendar \\ Calendar.ISO)
+
+  def from_iso8601(string, format) when format in [:basic, :extended] do
+    from_iso8601(string, Calendar.ISO, format)
+  end
+
+  def from_iso8601(string, calendar) when is_atom(calendar) do
+    from_iso8601(string, calendar, :extended)
+  end
+
+  @doc """
+  Converts to ISO8601 specifying both a calendar and a mode.
+
+  See `from_iso8601/2` for more information.
+
+  ## Examples
+
+      iex> {:ok, datetime, 9000} = DateTime.from_iso8601("2015-01-23T23:50:07,123+02:30", Calendar.ISO, :extended)
+      iex> datetime
+      ~U[2015-01-23 21:20:07.123Z]
+
+      iex> {:ok, datetime, 9000} = DateTime.from_iso8601("20150123T235007.123+0230", Calendar.ISO, :basic)
+      iex> datetime
+      ~U[2015-01-23 21:20:07.123Z]
+  """
+  def from_iso8601(string, calendar, format) do
     with {:ok, {year, month, day, hour, minute, second, microsecond}, offset} <-
-           Calendar.ISO.parse_utc_datetime(string) do
+           Calendar.ISO.parse_utc_datetime(string, format) do
       datetime = %DateTime{
         year: year,
         month: month,
@@ -1291,12 +1387,11 @@ defmodule DateTime do
   @doc """
   Subtracts `datetime2` from `datetime1`.
 
-  The answer can be returned in any `unit` available from `t:System.time_unit/0`.
+  The answer can be returned in any `:day`, `:hour`, `:minute`, or any `unit`
+  available from `t:System.time_unit/0`. The unit is measured according to
+  `Calendar.ISO` and defaults to `:second`.
 
-  Leap seconds are not taken into account.
-
-  This function returns the difference in seconds where seconds are measured
-  according to `Calendar.ISO`.
+  Fractional results are not supported and are truncated.
 
   ## Examples
 
@@ -1310,14 +1405,36 @@ defmodule DateTime do
       18000
       iex> DateTime.diff(dt2, dt1)
       -18000
+      iex> DateTime.diff(dt1, dt2, :hour)
+      5
+      iex> DateTime.diff(dt2, dt1, :hour)
+      -5
 
   """
   @doc since: "1.5.0"
-  @spec diff(Calendar.datetime(), Calendar.datetime(), System.time_unit()) :: integer()
+  @spec diff(
+          Calendar.datetime(),
+          Calendar.datetime(),
+          :day | :hour | :minute | System.time_unit()
+        ) :: integer()
+  def diff(datetime1, datetime2, unit \\ :second)
+
+  def diff(datetime1, datetime2, :day) do
+    diff(datetime1, datetime2, :second) |> div(86400)
+  end
+
+  def diff(datetime1, datetime2, :hour) do
+    diff(datetime1, datetime2, :second) |> div(3600)
+  end
+
+  def diff(datetime1, datetime2, :minute) do
+    diff(datetime1, datetime2, :second) |> div(60)
+  end
+
   def diff(
         %{utc_offset: utc_offset1, std_offset: std_offset1} = datetime1,
         %{utc_offset: utc_offset2, std_offset: std_offset2} = datetime2,
-        unit \\ :second
+        unit
       ) do
     naive_diff =
       (datetime1 |> to_iso_days() |> Calendar.ISO.iso_days_to_unit(unit)) -
@@ -1330,15 +1447,30 @@ defmodule DateTime do
   @doc """
   Adds a specified amount of time to a `DateTime`.
 
-  Accepts an `amount_to_add` in any `unit` available from `t:System.time_unit/0`.
-  Negative values will move backwards in time.
+  Accepts an `amount_to_add` in any `unit`. `unit` can be `:day`,
+  `:hour`, `:minute`, `:second` or any subsecond precision from
+  `t:System.time_unit/0`. It defaults to `:second`. Negative values
+  will move backwards in time.
 
-  Takes changes such as summer time/DST into account. This means that adding time
-  can cause the wall time to "go backwards" during "fall back" during autumn.
-  Adding just a few seconds to a datetime just before "spring forward" can cause wall
-  time to increase by more than an hour.
+  This function always consider the unit to be computed according
+  to the `Calendar.ISO`.
 
-  Fractional second precision stays the same in a similar way to `NaiveDateTime.add/2`.
+  This function uses relies on a contiguous representation of time,
+  ignoring the wall time and timezone changes. For example, if you add
+  one day when there are summer time/daylight saving time changes,
+  it will also change the time forward or backward by one hour,
+  so the ellapsed time is precisely 24 hours. Similarly, adding just
+  a few seconds to a datetime just before "spring forward" can cause
+  wall time to increase by more than an hour.
+
+  While this means this function is precise in terms of ellapsed time,
+  its result may be misleading in certain use cases. For example, if a
+  user requests a meeting to happen every day at 15:00 and you use this
+  function to compute all future meetings by adding day after day, this
+  function may change the meeting time to 14:00 or 16:00 if there are
+  changes to the current timezone. Computing of recurring datetimes is
+  not currently supported in Elixir's standard library but it is available
+  by third-party libraries.
 
   ### Examples
 
@@ -1349,15 +1481,26 @@ defmodule DateTime do
       iex> DateTime.add(~U[2018-11-15 10:00:00Z], 3600, :second)
       ~U[2018-11-15 11:00:00Z]
 
-  When adding 3 seconds just before "spring forward" we go from 1:59:59 to 3:00:02
+  When adding 3 seconds just before "spring forward" we go from 1:59:59 to 3:00:02:
 
       iex> dt = DateTime.from_naive!(~N[2019-03-31 01:59:59.123], "Europe/Copenhagen", FakeTimeZoneDatabase)
       iex> dt |> DateTime.add(3, :second, FakeTimeZoneDatabase)
       #DateTime<2019-03-31 03:00:02.123+02:00 CEST Europe/Copenhagen>
 
+  When adding 1 day during "spring forward", the hour also changes:
+
+      iex> dt = DateTime.from_naive!(~N[2019-03-31 01:00:00], "Europe/Copenhagen", FakeTimeZoneDatabase)
+      iex> dt |> DateTime.add(1, :day, FakeTimeZoneDatabase)
+      #DateTime<2019-04-01 02:00:00+02:00 CEST Europe/Copenhagen>
+
   """
   @doc since: "1.8.0"
-  @spec add(Calendar.datetime(), integer, System.time_unit(), Calendar.time_zone_database()) ::
+  @spec add(
+          Calendar.datetime(),
+          integer,
+          :day | :hour | :minute | System.time_unit(),
+          Calendar.time_zone_database()
+        ) ::
           t()
   def add(
         datetime,
@@ -1365,7 +1508,20 @@ defmodule DateTime do
         unit \\ :second,
         time_zone_database \\ Calendar.get_time_zone_database()
       )
-      when is_integer(amount_to_add) do
+
+  def add(datetime, amount_to_add, :day, time_zone_database) when is_integer(amount_to_add) do
+    add(datetime, amount_to_add * 86400, :second, time_zone_database)
+  end
+
+  def add(datetime, amount_to_add, :hour, time_zone_database) when is_integer(amount_to_add) do
+    add(datetime, amount_to_add * 3600, :second, time_zone_database)
+  end
+
+  def add(datetime, amount_to_add, :minute, time_zone_database) when is_integer(amount_to_add) do
+    add(datetime, amount_to_add * 60, :second, time_zone_database)
+  end
+
+  def add(datetime, amount_to_add, unit, time_zone_database) when is_integer(amount_to_add) do
     %{
       utc_offset: utc_offset,
       std_offset: std_offset,

lib/elixir/lib/calendar/naive_datetime.ex

@@ -5,7 +5,7 @@ defmodule NaiveDateTime do
   The NaiveDateTime struct contains the fields year, month, day, hour,
   minute, second, microsecond and calendar. New naive datetimes can be
   built with the `new/2` and `new/8` functions or using the
-  `~N` (see `Kernel.sigil_N/2`) sigil:
+  `~N` (see `sigil_N/2`) sigil:
 
       iex> ~N[2000-01-01 23:00:07]
       ~N[2000-01-01 23:00:07]
@@ -36,12 +36,18 @@ defmodule NaiveDateTime do
 
   Comparisons in Elixir using `==/2`, `>/2`, `</2` and similar are structural
   and based on the `NaiveDateTime` struct fields. For proper comparison
-  between naive datetimes, use the `compare/2` function.
+  between naive datetimes, use the `compare/2` function. The existence of the
+  `compare/2` function in this module also allows using `Enum.min/2` and
+  `Enum.max/2` functions to get the minimum and maximum naive datetime of an
+  `Enum`. For example:
+
+      iex> Enum.min([~N[2020-01-01 23:00:07], ~N[2000-01-01 23:00:07]], NaiveDateTime)
+      ~N[2000-01-01 23:00:07]
 
   ## Using epochs
 
-  The `add/3` and `diff/3` functions can be used for computing with
-  date times or retrieving the number of seconds between instants.
+  The `add/3` and `diff/3` functions can be used for computing date
+  times or retrieving the number of seconds between instants.
   For example, if there is an interest in computing the number of
   seconds from the Unix epoch (1970-01-01 00:00:00):
 
@@ -350,11 +356,18 @@ defmodule NaiveDateTime do
   @doc """
   Adds a specified amount of time to a `NaiveDateTime`.
 
-  Accepts an `amount_to_add` in any `unit` available from `t:System.time_unit/0`.
-  Negative values will move backwards in time.
+  Accepts an `amount_to_add` in any `unit`. `unit` can be `:day`,
+  `:hour`, `:minute`, `:second` or any subsecond precision from
+  `t:System.time_unit/0`. It defaults to `:second`. Negative values
+  will move backwards in time.
+
+  This function always consider the unit to be computed according
+  to the `Calendar.ISO`.
 
   ## Examples
 
+  It uses seconds by default:
+
       # adds seconds by default
       iex> NaiveDateTime.add(~N[2014-10-02 00:29:10], 2)
       ~N[2014-10-02 00:29:12]
@@ -363,19 +376,33 @@ defmodule NaiveDateTime do
       iex> NaiveDateTime.add(~N[2014-10-02 00:29:10], -2)
       ~N[2014-10-02 00:29:08]
 
-      # can work with other units
+  It can also work with subsecond precisions:
+
       iex> NaiveDateTime.add(~N[2014-10-02 00:29:10], 2_000, :millisecond)
       ~N[2014-10-02 00:29:12]
 
-      # keeps the same precision
+  As well as days/hours/minutes:
+
+      iex> NaiveDateTime.add(~N[2015-02-28 00:29:10], 2, :day)
+      ~N[2015-03-02 00:29:10]
+      iex> NaiveDateTime.add(~N[2015-02-28 00:29:10], 36, :hour)
+      ~N[2015-03-01 12:29:10]
+      iex> NaiveDateTime.add(~N[2015-02-28 00:29:10], 60, :minute)
+      ~N[2015-02-28 01:29:10]
+
+  This operation keeps the precision of the naive date time:
+
       iex> NaiveDateTime.add(~N[2014-10-02 00:29:10.021], 21, :second)
       ~N[2014-10-02 00:29:31.021]
 
-      # changes below the precision will not be visible
+  And ignores any changes below the precision:
+
       iex> hidden = NaiveDateTime.add(~N[2014-10-02 00:29:10], 21, :millisecond)
       iex> hidden.microsecond # ~N[2014-10-02 00:29:10]
       {21000, 0}
 
+  Operations on top of gregorian seconds or the Unix epoch are optimized:
+
       # from Gregorian seconds
       iex> NaiveDateTime.add(~N[0000-01-01 00:00:00], 63_579_428_950)
       ~N[2014-10-02 00:29:10]
@@ -391,11 +418,25 @@ defmodule NaiveDateTime do
 
   """
   @doc since: "1.4.0"
-  @spec add(Calendar.naive_datetime(), integer, System.time_unit()) :: t
+  @spec add(Calendar.naive_datetime(), integer, :day | :hour | :minute | System.time_unit()) :: t
+  def add(naive_datetime, amount_to_add, unit \\ :second)
+
+  def add(naive_datetime, amount_to_add, :day) when is_integer(amount_to_add) do
+    add(naive_datetime, amount_to_add * 86400, :second)
+  end
+
+  def add(naive_datetime, amount_to_add, :hour) when is_integer(amount_to_add) do
+    add(naive_datetime, amount_to_add * 3600, :second)
+  end
+
+  def add(naive_datetime, amount_to_add, :minute) when is_integer(amount_to_add) do
+    add(naive_datetime, amount_to_add * 60, :second)
+  end
+
   def add(
         %{microsecond: {_, precision}, calendar: calendar} = naive_datetime,
         amount_to_add,
-        unit \\ :second
+        unit
       )
       when is_integer(amount_to_add) do
     ppd = System.convert_time_unit(86400, :second, unit)
@@ -409,10 +450,11 @@ defmodule NaiveDateTime do
   @doc """
   Subtracts `naive_datetime2` from `naive_datetime1`.
 
-  The answer can be returned in any `unit` available from `t:System.time_unit/0`.
+  The answer can be returned in any `:day`, `:hour`, `:minute`, or any `unit`
+  available from `t:System.time_unit/0`. The unit is measured according to
+  `Calendar.ISO` and defaults to `:second`.
 
-  This function returns the difference in seconds where seconds are measured
-  according to `Calendar.ISO`.
+  Fractional results are not supported and are truncated.
 
   ## Examples
 
@@ -420,24 +462,57 @@ defmodule NaiveDateTime do
       2
       iex> NaiveDateTime.diff(~N[2014-10-02 00:29:12], ~N[2014-10-02 00:29:10], :microsecond)
       2_000_000
+
+      iex> NaiveDateTime.diff(~N[2014-10-02 00:29:10.042], ~N[2014-10-02 00:29:10.021])
+      0
       iex> NaiveDateTime.diff(~N[2014-10-02 00:29:10.042], ~N[2014-10-02 00:29:10.021], :millisecond)
       21
+
       iex> NaiveDateTime.diff(~N[2014-10-02 00:29:10], ~N[2014-10-02 00:29:12])
       -2
       iex> NaiveDateTime.diff(~N[-0001-10-02 00:29:10], ~N[-0001-10-02 00:29:12])
       -2
 
-      # to Gregorian seconds
-      iex> NaiveDateTime.diff(~N[2014-10-02 00:29:10], ~N[0000-01-01 00:00:00])
-      63579428950
+  It can also compute the difference in days, hours, or minutes:
+
+      iex> NaiveDateTime.diff(~N[2014-10-10 00:29:10], ~N[2014-10-02 00:29:10], :day)
+      8
+      iex> NaiveDateTime.diff(~N[2014-10-02 12:29:10], ~N[2014-10-02 00:29:10], :hour)
+      12
+      iex> NaiveDateTime.diff(~N[2014-10-02 00:39:10], ~N[2014-10-02 00:29:10], :minute)
+      10
+
+  But it also rounds incomplete days to zero:
+
+      iex> NaiveDateTime.diff(~N[2014-10-10 00:29:09], ~N[2014-10-02 00:29:10], :day)
+      7
 
   """
   @doc since: "1.4.0"
-  @spec diff(Calendar.naive_datetime(), Calendar.naive_datetime(), System.time_unit()) :: integer
+  @spec diff(
+          Calendar.naive_datetime(),
+          Calendar.naive_datetime(),
+          :day | :hour | :minute | System.time_unit()
+        ) :: integer
+
+  def diff(naive_datetime1, naive_datetime2, unit \\ :second)
+
+  def diff(naive_datetime1, naive_datetime2, :day) do
+    diff(naive_datetime1, naive_datetime2, :second) |> div(86400)
+  end
+
+  def diff(naive_datetime1, naive_datetime2, :hour) do
+    diff(naive_datetime1, naive_datetime2, :second) |> div(3600)
+  end
+
+  def diff(naive_datetime1, naive_datetime2, :minute) do
+    diff(naive_datetime1, naive_datetime2, :second) |> div(60)
+  end
+
   def diff(
         %{calendar: calendar1} = naive_datetime1,
         %{calendar: calendar2} = naive_datetime2,
-        unit \\ :second
+        unit
       ) do
     if not Calendar.compatible_calendars?(calendar1, calendar2) do
       raise ArgumentError,

lib/elixir/lib/calendar/time.ex

@@ -4,7 +4,7 @@ defmodule Time do
 
   The Time struct contains the fields hour, minute, second and microseconds.
   New times can be built with the `new/4` function or using the
-  `~T` (see `Kernel.sigil_T/2`) sigil:
+  `~T` (see `sigil_T/2`) sigil:
 
       iex> ~T[23:00:07.001]
       ~T[23:00:07.001]
@@ -31,7 +31,12 @@ defmodule Time do
 
   Comparisons in Elixir using `==/2`, `>/2`, `</2` and similar are structural
   and based on the `Time` struct fields. For proper comparison between
-  times, use the `compare/2` function.
+  times, use the `compare/2` function. The existence of the `compare/2`
+  function in this module also allows using `Enum.min/2` and `Enum.max/2`
+  functions to get the minimum and maximum time of an `Enum`. For example:
+
+      iex> Enum.min([~T[23:00:07.001], ~T[10:00:07.001]], Time)
+      ~T[10:00:07.001]
   """
 
   @enforce_keys [:hour, :minute, :second]
@@ -449,10 +454,15 @@ defmodule Time do
   end
 
   @doc """
-  Adds the `number` of `unit`s to the given `time`.
+  Adds the `amount_to_add` of `unit`s to the given `time`.
 
-  This function accepts the `number` measured according to `Calendar.ISO`.
-  The time is returned in the same calendar as it was given in.
+  Accepts an `amount_to_add` in any `unit`. `unit` can be `:day`,
+  `:hour`, `:minute`, `:second` or any subsecond precision from
+  `t:System.time_unit/0`. It defaults to `:second`. Negative values
+  will move backwards in time.
+
+  This function always consider the unit to be computed according
+  to the `Calendar.ISO`.
 
   Note the result value represents the time of day, meaning that it is cyclic,
   for instance, it will never go over 24 hours for the ISO calendar.
@@ -460,30 +470,56 @@ defmodule Time do
   ## Examples
 
       iex> Time.add(~T[10:00:00], 27000)
-      ~T[17:30:00.000000]
+      ~T[17:30:00]
       iex> Time.add(~T[11:00:00.005], 2400)
-      ~T[11:40:00.005000]
-      iex> Time.add(~T[00:00:00], 86_399_999, :millisecond)
-      ~T[23:59:59.999000]
-      iex> Time.add(~T[17:10:05], 86400)
-      ~T[17:10:05.000000]
+      ~T[11:40:00.005]
+      iex> Time.add(~T[00:00:00.000], 86_399_999, :millisecond)
+      ~T[23:59:59.999]
+
+  Negative values are allowed:
+
       iex> Time.add(~T[23:00:00], -60)
-      ~T[22:59:00.000000]
+      ~T[22:59:00]
+
+  Note that the time is cyclic:
+
+      iex> Time.add(~T[17:10:05], 86400)
+      ~T[17:10:05]
+
+  Hours and minutes are also supported:
+
+      iex> Time.add(~T[17:10:05], 2, :hour)
+      ~T[19:10:05]
+      iex> Time.add(~T[17:10:05], 30, :minute)
+      ~T[17:40:05]
 
   """
   @doc since: "1.6.0"
-  @spec add(Calendar.time(), integer, System.time_unit()) :: t
-  def add(%{calendar: calendar} = time, number, unit \\ :second) when is_integer(number) do
-    number = System.convert_time_unit(number, unit, :microsecond)
-    total = time_to_microseconds(time) + number
+  @spec add(Calendar.time(), integer, :hour | :minute | System.time_unit()) :: t
+  def add(time, amount_to_add, unit \\ :second)
+
+  def add(time, amount_to_add, :hour) when is_integer(amount_to_add) do
+    add(time, amount_to_add * 3600, :second)
+  end
+
+  def add(time, amount_to_add, :minute) when is_integer(amount_to_add) do
+    add(time, amount_to_add * 60, :second)
+  end
+
+  def add(%{calendar: calendar, microsecond: {_, precision}} = time, amount_to_add, unit)
+      when is_integer(amount_to_add) do
+    amount_to_add = System.convert_time_unit(amount_to_add, unit, :microsecond)
+    total = time_to_microseconds(time) + amount_to_add
     parts = Integer.mod(total, @parts_per_day)
-    {hour, minute, second, microsecond} = calendar.time_from_day_fraction({parts, @parts_per_day})
+
+    {hour, minute, second, {microsecond, _}} =
+      calendar.time_from_day_fraction({parts, @parts_per_day})
 
     %Time{
       hour: hour,
       minute: minute,
       second: second,
-      microsecond: microsecond,
+      microsecond: {microsecond, precision},
       calendar: calendar
     }
   end
@@ -650,12 +686,12 @@ defmodule Time do
   additional information about a date or time zone is ignored when calculating
   the difference.
 
-  The answer can be returned in any `unit` available from
-  `t:System.time_unit/0`. If the first time value is earlier than
-  the second, a negative number is returned.
+  The answer can be returned in any `:hour`, `:minute`, `:second` or any
+  subsecond `unit` available from `t:System.time_unit/0`. If the first time
+  value is earlier than the second, a negative number is returned.
 
-  This function returns the difference in seconds where seconds
-  are measured according to `Calendar.ISO`.
+  The unit is measured according to `Calendar.ISO` and defaults to `:second`.
+  Fractional results are not supported and are truncated.
 
   ## Examples
 
@@ -676,11 +712,24 @@ defmodule Time do
       iex> Time.diff(~T[00:29:10], ~T[00:29:12], :microsecond)
       -2_000_000
 
+      iex> Time.diff(~T[02:29:10], ~T[00:29:10], :hour)
+      2
+      iex> Time.diff(~T[02:29:10], ~T[00:29:11], :hour)
+      1
+
   """
   @doc since: "1.5.0"
-  @spec diff(Calendar.time(), Calendar.time(), System.time_unit()) :: integer
+  @spec diff(Calendar.time(), Calendar.time(), :hour | :minute | System.time_unit()) :: integer
   def diff(time1, time2, unit \\ :second)
 
+  def diff(time1, time2, :hour) do
+    diff(time1, time2, :second) |> div(3600)
+  end
+
+  def diff(time1, time2, :minute) do
+    diff(time1, time2, :second) |> div(60)
+  end
+
   def diff(
         %{
           calendar: Calendar.ISO,

lib/elixir/lib/code.ex

@@ -3,8 +3,9 @@ defmodule Code do
   Utilities for managing code compilation, code evaluation, and code loading.
 
   This module complements Erlang's [`:code` module](`:code`)
-  to add behaviour which is specific to Elixir. Almost all of the functions in this module
-  have global side effects on the behaviour of Elixir.
+  to add behaviour which is specific to Elixir. For functions to
+  manipulate Elixir's AST (rather than evaluating it), see the
+  `Macro` module.
 
   ## Working with files
 
@@ -129,6 +130,8 @@ defmodule Code do
 
     * `{:require, meta, module, opts}` - traced whenever `module` is required.
       `meta` is the require AST metadata and `opts` are the require options.
+      If the `meta` option contains the `:from_macro`, then `require` was called
+      from within a macro and therefore must be treated as a compile-time dependency.
 
     * `{:struct_expansion, meta, module, keys}` - traced whenever `module`'s struct
       is expanded. `meta` is the struct AST metadata and `keys` are the keys being
@@ -149,11 +152,13 @@ defmodule Code do
       of keys to traverse in the application environment and `return` is either
       `{:ok, value}` or `:error`.
 
-    * `{:on_module, bytecode, :none}` - (since v1.11.0) traced whenever a module
+    * `{:on_module, bytecode, _ignore}` - (since v1.11.0) traced whenever a module
       is defined. This is equivalent to the `@after_compile` callback and invoked
       after any `@after_compile` in the given module. The third element is currently
       `:none` but it may provide more metadata in the future. It is best to ignore
-      it at the moment.
+      it at the moment. Note that `Module` functions expecting not yet compiled modules
+      (such as `Module.definitions_in/1`) are still available at the time this event
+      is emitted.
 
   The `:tracers` compiler option can be combined with the `:parser_options`
   compiler option to enrich the metadata of the traced events above.
@@ -186,6 +191,7 @@ defmodule Code do
   @boolean_compiler_options [
     :docs,
     :debug_info,
+    :ignore_already_consolidated,
     :ignore_module_conflict,
     :relative_paths,
     :warnings_as_errors
@@ -230,6 +236,8 @@ defmodule Code do
   calling this function only removes them from the list,
   allowing them to be required again.
 
+  The list of files is managed per Erlang VM node.
+
   ## Examples
 
       # Require EEx test code
@@ -259,7 +267,8 @@ defmodule Code do
   Appends a path to the end of the Erlang VM code path list.
 
   This is the list of directories the Erlang VM uses for
-  finding module code.
+  finding module code. The list of files is managed per Erlang
+  VM node.
 
   The path is expanded with `Path.expand/1` before being appended.
   If this path does not exist, an error is returned.
@@ -282,7 +291,7 @@ defmodule Code do
   Prepends a path to the beginning of the Erlang VM code path list.
 
   This is the list of directories the Erlang VM uses for finding
-  module code.
+  module code. The list of files is managed per Erlang VM node.
 
   The path is expanded with `Path.expand/1` before being prepended.
   If this path does not exist, an error is returned.
@@ -302,8 +311,10 @@ defmodule Code do
   end
 
   @doc """
-  Deletes a path from the Erlang VM code path list. This is the list of
-  directories the Erlang VM uses for finding module code.
+  Deletes a path from the Erlang VM code path list.
+
+  This is the list of directories the Erlang VM uses for finding
+  module code. The list of files is managed per Erlang VM node.
 
   The path is expanded with `Path.expand/1` before being deleted. If the
   path does not exist, this function returns `false`.
@@ -320,7 +331,14 @@ defmodule Code do
   """
   @spec delete_path(Path.t()) :: boolean
   def delete_path(path) do
-    :code.del_path(to_charlist(Path.expand(path)))
+    case :code.del_path(to_charlist(Path.expand(path))) do
+      result when is_boolean(result) ->
+        result
+
+      {:error, :bad_name} ->
+        raise ArgumentError,
+              "invalid argument #{inspect(path)}"
+    end
   end
 
   @doc """
@@ -399,12 +417,18 @@ defmodule Code do
   end
 
   defp validated_eval_string(string, binding, opts_or_env) do
-    %{line: line, file: file} = env = :elixir.env_for_eval(opts_or_env)
+    %{line: line, file: file} = env = env_for_eval(opts_or_env)
     forms = :elixir.string_to_quoted!(to_charlist(string), line, 1, file, [])
-    {value, binding, _env} = :elixir.eval_forms(forms, binding, env)
+    {value, binding, _env} = eval_verify(:eval_forms, forms, binding, env)
     {value, binding}
   end
 
+  defp eval_verify(fun, forms, binding, env) do
+    Module.ParallelChecker.verify(fn ->
+      apply(:elixir, fun, [forms, binding, env])
+    end)
+  end
+
   @doc ~S"""
   Formats the given code `string`.
 
@@ -437,12 +461,23 @@ defmodule Code do
       If you set it to `false` later on, `do`-`end` blocks won't be
       converted back to keywords.
 
+    * `:normalize_bitstring_modifiers` (since v1.14.0) - when `true`,
+      removes unnecessary parentheses in known bitstring
+      [modifiers](`<<>>/1`), for example `<<foo::binary()>>`
+      becomes `<<foo::binary>>`, or adds parentheses for custom
+      modifiers, where `<<foo::custom_type>>` becomes `<<foo::custom_type()>>`.
+      Defaults to `true`. This option changes the AST.
+
   ## Design principles
 
   The formatter was designed under three principles.
 
-  First, the formatter never changes the semantics of the code by
-  default. This means the input AST and the output AST are equivalent.
+  First, the formatter never changes the semantics of the code.
+  This means the input AST and the output AST are almost always equivalent.
+  The only cases where the formatter will change the AST is when the input AST
+  would cause *compiler warnings* and the output AST won't. The cases where
+  the formatter changes the AST can be disabled through formatting options
+  if desired.
 
   The second principle is to provide as little configuration as possible.
   This eases the formatter adoption by removing contention points while
@@ -731,18 +766,13 @@ defmodule Code do
         unescape: false,
         warn_on_unnecessary_quotes: false,
         literal_encoder: &{:ok, {:__block__, &2, [&1]}},
-        token_metadata: true
+        token_metadata: true,
+        emit_warnings: false
       ] ++ opts
 
     {forms, comments} = string_to_quoted_with_comments!(string, to_quoted_opts)
-
-    to_algebra_opts =
-      [
-        comments: comments
-      ] ++ opts
-
+    to_algebra_opts = [comments: comments] ++ opts
     doc = Code.Formatter.to_algebra(forms, to_algebra_opts)
-
     Inspect.Algebra.format(doc, line_length)
   end
 
@@ -791,16 +821,48 @@ defmodule Code do
 
   """
   @spec eval_quoted(Macro.t(), binding, Macro.Env.t() | keyword) :: {term, binding}
-  def eval_quoted(quoted, binding \\ [], opts \\ [])
-
-  def eval_quoted(quoted, binding, %Macro.Env{} = env) do
-    {value, binding, _env} = :elixir.eval_quoted(quoted, binding, :elixir.env_for_eval(env))
+  def eval_quoted(quoted, binding \\ [], env_or_opts \\ []) do
+    {value, binding, _env} = eval_verify(:eval_quoted, quoted, binding, env_for_eval(env_or_opts))
     {value, binding}
   end
 
-  def eval_quoted(quoted, binding, opts) when is_list(opts) do
-    {value, binding, _env} = :elixir.eval_quoted(quoted, binding, :elixir.env_for_eval(opts))
-    {value, binding}
+  @doc """
+  Returns an environment for evaluation.
+
+  It accepts either a `Macro.Env`, that is then pruned and prepared,
+  or a list of options. It returns an environment that is ready for
+  evaluation.
+
+  Most functions in this module will automatically prepare the given
+  environment for evaluation, so you don't need to explicitly call
+  this function, with the exception of `eval_quoted_with_env/3`,
+  which was designed precisely to be called in a loop, to implement
+  features such as interactive shells or anything else with multiple
+  evaluations.
+
+  ## Options
+
+  If an env is not given, the options can be:
+
+    * `:file` - the file to be considered in the evaluation
+
+    * `:line` - the line on which the script starts
+  """
+  @doc since: "1.14.0"
+  def env_for_eval(env_or_opts), do: :elixir.env_for_eval(env_or_opts)
+
+  @doc """
+  Evaluates the given `quoted` contents with `binding` and `env`.
+
+  This function is meant to be called in a loop, to implement features
+  such as interactive shells or anything else with multiple evaluations.
+  Therefore, the first time you call this function, you must compute
+  the initial environment with `env_for_eval/1`. The remaining calls
+  must pass the environment that was returned by this function.
+  """
+  @doc since: "1.14.0"
+  def eval_quoted_with_env(quoted, binding, %Macro.Env{} = env) when is_list(binding) do
+    eval_verify(:eval_forms, quoted, binding, env)
   end
 
   @doc ~S"""
@@ -1119,19 +1181,19 @@ defmodule Code do
   """
   @spec eval_file(binary, nil | binary) :: {term, binding}
   def eval_file(file, relative_to \\ nil) when is_binary(file) do
-    file = find_file(file, relative_to)
-    eval_string(File.read!(file), [], file: file, line: 1)
+    {charlist, file} = find_file!(file, relative_to)
+    eval_string(charlist, [], file: file, line: 1)
   end
 
   @deprecated "Use Code.require_file/2 or Code.compile_file/2 instead"
   @doc false
   def load_file(file, relative_to \\ nil) when is_binary(file) do
-    file = find_file(file, relative_to)
+    {charlist, file} = find_file!(file, relative_to)
     :elixir_code_server.call({:acquire, file})
 
     loaded =
       Module.ParallelChecker.verify(fn ->
-        :elixir_compiler.file(file, fn _, _ -> :ok end)
+        :elixir_compiler.string(charlist, file, fn _, _ -> :ok end)
       end)
 
     :elixir_code_server.cast({:required, file})
@@ -1150,7 +1212,7 @@ defmodule Code do
   ones will block until the file is available. This means that if `require_file/2`
   is called more than once with a given file, that file will be compiled only once.
   The first process to call `require_file/2` will get the list of loaded modules,
-  others will get `nil`.
+  others will get `nil`. The list of required files is managed per Erlang VM node.
 
   See `compile_file/2` if you would like to compile a file without tracking its
   filenames. Finally, if you would like to get the result of evaluating a file rather
@@ -1172,7 +1234,7 @@ defmodule Code do
   """
   @spec require_file(binary, nil | binary) :: [{module, binary}] | nil
   def require_file(file, relative_to \\ nil) when is_binary(file) do
-    file = find_file(file, relative_to)
+    {charlist, file} = find_file!(file, relative_to)
 
     case :elixir_code_server.call({:acquire, file}) do
       :required ->
@@ -1181,7 +1243,7 @@ defmodule Code do
       :proceed ->
         loaded =
           Module.ParallelChecker.verify(fn ->
-            :elixir_compiler.file(file, fn _, _ -> :ok end)
+            :elixir_compiler.string(charlist, file, fn _, _ -> :ok end)
           end)
 
         :elixir_code_server.cast({:required, file})
@@ -1211,8 +1273,10 @@ defmodule Code do
   @doc """
   Stores all given compilation options.
 
-  To store individual options and for a description of all
-  options, see `put_compiler_option/2`.
+  Changing the compilation options affect all processes
+  running in a given Erlang VM node. To store individual
+  options and for a description of all options, see
+  `put_compiler_option/2`.
 
   ## Examples
 
@@ -1265,7 +1329,8 @@ defmodule Code do
   @doc """
   Stores a compilation option.
 
-  These options are global since they are stored by Elixir's code server.
+  Changing the compilation options affect all processes running in a
+  given Erlang VM node.
 
   Available options are:
 
@@ -1276,11 +1341,15 @@ defmodule Code do
       module. This allows a developer to reconstruct the original source
       code. Defaults to `true`.
 
-    * `:ignore_module_conflict` - when `true`, override modules that were
-      already defined without raising errors. Defaults to `false`.
+    * `:ignore_already_consolidated` - when `true`, does not warn when a protocol
+      has already been consolidated and a new implementation is added. Defaults
+      to `false`.
+
+    * `:ignore_module_conflict` - when `true`, does not warn when a module has
+      already been defined. Defaults to `false`.
 
     * `:relative_paths` - when `true`, use relative paths in quoted nodes,
-      warnings and errors generated by the compiler. Note disabling this option
+      warnings, and errors generated by the compiler. Note disabling this option
       won't affect runtime warnings and errors. Defaults to `true`.
 
     * `:warnings_as_errors` - causes compilation to fail when warnings are
@@ -1365,6 +1434,9 @@ defmodule Code do
   old compiler module names to be reused. If there are any processes running
   any code from such modules, they will be terminated too.
 
+  This function is only meant to be called if you have a long running node
+  that is constantly evaluating code.
+
   It returns `{:ok, number_of_modules_purged}`.
   """
   @doc since: "1.7.0"
@@ -1389,8 +1461,9 @@ defmodule Code do
   """
   @spec compile_string(List.Chars.t(), binary) :: [{module, binary}]
   def compile_string(string, file \\ "nofile") when is_binary(file) do
-    loaded = :elixir_compiler.string(to_charlist(string), file, fn _, _ -> :ok end)
-    Enum.map(loaded, &elem(&1, 0))
+    Module.ParallelChecker.verify(fn ->
+      :elixir_compiler.string(to_charlist(string), file, fn _, _ -> :ok end)
+    end)
   end
 
   @doc """
@@ -1403,8 +1476,9 @@ defmodule Code do
   """
   @spec compile_quoted(Macro.t(), binary) :: [{module, binary}]
   def compile_quoted(quoted, file \\ "nofile") when is_binary(file) do
-    loaded = :elixir_compiler.quoted(quoted, file, fn _, _ -> :ok end)
-    Enum.map(loaded, &elem(&1, 0))
+    Module.ParallelChecker.verify(fn ->
+      :elixir_compiler.quoted(quoted, file, fn _, _ -> :ok end)
+    end)
   end
 
   @doc """
@@ -1425,7 +1499,8 @@ defmodule Code do
   @spec compile_file(binary, nil | binary) :: [{module, binary}]
   def compile_file(file, relative_to \\ nil) when is_binary(file) do
     Module.ParallelChecker.verify(fn ->
-      :elixir_compiler.file(find_file(file, relative_to), fn _, _ -> :ok end)
+      {charlist, file} = find_file!(file, relative_to)
+      :elixir_compiler.string(charlist, file, fn _, _ -> :ok end)
     end)
   end
 
@@ -1599,7 +1674,7 @@ defmodule Code do
   file.
 
   It returns the term stored in the documentation chunk in the format defined by
-  [EEP 48](https://erlang.org/eep/eeps/eep-0048.html) or `{:error, reason}` if
+  [EEP 48](https://www.erlang.org/eeps/eep-0048.html) or `{:error, reason}` if
   the chunk is not available.
 
   ## Examples
@@ -1631,8 +1706,8 @@ defmodule Code do
   def fetch_docs(module_or_path)
 
   def fetch_docs(module) when is_atom(module) do
-    case :code.get_object_code(module) do
-      {_module, bin, beam_path} ->
+    case get_beam_and_path(module) do
+      {bin, beam_path} ->
         case fetch_docs_from_beam(bin) do
           {:error, :chunk_not_found} ->
             app_root = Path.expand(Path.join(["..", ".."]), beam_path)
@@ -1646,7 +1721,7 @@ defmodule Code do
       :error ->
         case :code.which(module) do
           :preloaded ->
-            # The erts directory is not necessarily included in releases
+            # The ERTS directory is not necessarily included in releases
             # unless it is listed as an extra application.
             case :code.lib_dir(:erts) do
               path when is_list(path) ->
@@ -1667,6 +1742,15 @@ defmodule Code do
     fetch_docs_from_beam(String.to_charlist(path))
   end
 
+  defp get_beam_and_path(module) do
+    with {^module, beam, filename} <- :code.get_object_code(module),
+         {:ok, ^module} <- beam |> :beam_lib.info() |> Keyword.fetch(:module) do
+      {beam, filename}
+    else
+      _ -> :error
+    end
+  end
+
   @docs_chunk 'Docs'
 
   defp fetch_docs_from_beam(bin_or_path) do
@@ -1699,17 +1783,8 @@ defmodule Code do
       {:error, {:invalid_chunk, bin}}
   end
 
-  @doc ~S"""
-  Deprecated function to retrieve old documentation format.
-
-  Elixir v1.7 adopts [EEP 48](https://erlang.org/eep/eeps/eep-0048.html)
-  which is a new documentation format meant to be shared across all
-  BEAM languages. The old format, used by `Code.get_docs/2`, is no
-  longer available, and therefore this function always returns `nil`.
-  Use `Code.fetch_docs/1` instead.
-  """
+  @doc false
   @deprecated "Code.get_docs/2 always returns nil as its outdated documentation is no longer stored on BEAM files. Use Code.fetch_docs/1 instead"
-  @spec get_docs(module, :moduledoc | :docs | :callback_docs | :type_docs | :all) :: nil
   def get_docs(_module, _kind) do
     nil
   end
@@ -1719,7 +1794,7 @@ defmodule Code do
   # Finds the file given the relative_to path.
   #
   # If the file is found, returns its path in binary, fails otherwise.
-  defp find_file(file, relative_to) do
+  defp find_file!(file, relative_to) do
     file =
       if relative_to do
         Path.expand(file, relative_to)
@@ -1727,10 +1802,9 @@ defmodule Code do
         Path.expand(file)
       end
 
-    if File.regular?(file) do
-      file
-    else
-      raise Code.LoadError, file: file
+    case File.read(file) do
+      {:ok, bin} -> {String.to_charlist(bin), file}
+      {:error, reason} -> raise Code.LoadError, file: file, reason: reason
     end
   end
 end

lib/elixir/lib/code/formatter.ex

@@ -22,7 +22,7 @@ defmodule Code.Formatter do
   @no_newline_binary_operators [:\\, :in]
 
   # Left associative operators that start on the next line in case of breaks (always pipes)
-  @pipeline_operators [:|>, :~>>, :<<~, :~>, :<~, :<~>, :<|>]
+  @pipeline_operators [:|>, :~>>, :<<~, :~>, :<~, :<~>, :"<|>"]
 
   # Right associative operators that start on the next line in case of breaks
   @right_new_line_before_binary_operators [:|, :when]
@@ -43,8 +43,8 @@ defmodule Code.Formatter do
     :<<~,
     :~>>,
     :<~>,
-    :<|>,
-    :^^^,
+    :"<|>",
+    :"^^^",
     :+++,
     :---,
     :in,
@@ -141,6 +141,24 @@ defmodule Code.Formatter do
 
   @do_end_keywords [:rescue, :catch, :else, :after]
 
+  @bitstring_modifiers [
+    :integer,
+    :float,
+    :bits,
+    :bitstring,
+    :binary,
+    :bytes,
+    :utf8,
+    :utf16,
+    :utf32,
+    :signed,
+    :unsigned,
+    :little,
+    :big,
+    :native,
+    :_
+  ]
+
   @doc """
   Converts the quoted expression into an algebra document.
   """
@@ -177,7 +195,9 @@ defmodule Code.Formatter do
   defp state(comments, opts) do
     force_do_end_blocks = Keyword.get(opts, :force_do_end_blocks, false)
     locals_without_parens = Keyword.get(opts, :locals_without_parens, [])
+    file = Keyword.get(opts, :file, nil)
     sigils = Keyword.get(opts, :sigils, [])
+    normalize_bitstring_modifiers = Keyword.get(opts, :normalize_bitstring_modifiers, true)
 
     sigils =
       Map.new(sigils, fn {key, value} ->
@@ -199,7 +219,9 @@ defmodule Code.Formatter do
       operand_nesting: 2,
       skip_eol: false,
       comments: comments,
-      sigils: sigils
+      sigils: sigils,
+      file: file,
+      normalize_bitstring_modifiers: normalize_bitstring_modifiers
     }
   end
 
@@ -270,7 +292,7 @@ defmodule Code.Formatter do
         {doc, state} =
           entries
           |> prepend_heredoc_line()
-          |> interpolation_to_algebra(:heredoc, state, @double_heredoc, @double_heredoc)
+          |> interpolation_to_algebra(~s["""], state, @double_heredoc, @double_heredoc)
 
         {force_unfit(doc), state}
 
@@ -292,7 +314,7 @@ defmodule Code.Formatter do
         {doc, state} =
           entries
           |> prepend_heredoc_line()
-          |> list_interpolation_to_algebra(:heredoc, state, @single_heredoc, @single_heredoc)
+          |> list_interpolation_to_algebra(~s['''], state, @single_heredoc, @single_heredoc)
 
         {force_unfit(doc), state}
 
@@ -355,7 +377,7 @@ defmodule Code.Formatter do
   defp quoted_to_algebra({:__block__, meta, [list]}, _context, state) when is_list(list) do
     case meta[:delimiter] do
       ~s['''] ->
-        string = list |> List.to_string() |> escape_heredoc()
+        string = list |> List.to_string() |> escape_heredoc(~s['''])
         {@single_heredoc |> concat(string) |> concat(@single_heredoc) |> force_unfit(), state}
 
       ~s['] ->
@@ -369,7 +391,7 @@ defmodule Code.Formatter do
 
   defp quoted_to_algebra({:__block__, meta, [string]}, _context, state) when is_binary(string) do
     if meta[:delimiter] == ~s["""] do
-      string = escape_heredoc(string)
+      string = escape_heredoc(string, ~s["""])
       {@double_heredoc |> concat(string) |> concat(@double_heredoc) |> force_unfit(), state}
     else
       string = escape_string(string, @double_quote)
@@ -377,8 +399,8 @@ defmodule Code.Formatter do
     end
   end
 
-  defp quoted_to_algebra({:__block__, _, [atom]}, _context, state) when is_atom(atom) do
-    {atom_to_algebra(atom), state}
+  defp quoted_to_algebra({:__block__, meta, [atom]}, _context, state) when is_atom(atom) do
+    {atom_to_algebra(atom, meta), state}
   end
 
   defp quoted_to_algebra({:__block__, meta, [integer]}, _context, state)
@@ -443,6 +465,15 @@ defmodule Code.Formatter do
     binary_op_to_algebra(:in, "not in", meta, left, right, context, state)
   end
 
+  # ..
+  defp quoted_to_algebra({:.., _meta, []}, context, state) do
+    if context in [:no_parens_arg, :no_parens_one_arg] do
+      {"(..)", state}
+    else
+      {"..", state}
+    end
+  end
+
   # 1..2//3
   defp quoted_to_algebra({:"..//", meta, [left, middle, right]}, context, state) do
     quoted_to_algebra({:"//", meta, [{:.., meta, [left, middle]}, right]}, context, state)
@@ -487,12 +518,10 @@ defmodule Code.Formatter do
 
             {:__block__, _, [atom]} when is_atom(atom) ->
               key =
-                case Code.Identifier.classify(atom) do
-                  type when type in [:callable_local, :callable_operator, :not_callable] ->
-                    IO.iodata_to_binary([Atom.to_string(atom), ?:])
-
-                  _ ->
-                    IO.iodata_to_binary([?", Atom.to_string(atom), ?", ?:])
+                if Macro.classify_atom(atom) in [:identifier, :unquoted] do
+                  IO.iodata_to_binary([Atom.to_string(atom), ?:])
+                else
+                  IO.iodata_to_binary([?", Atom.to_string(atom), ?", ?:])
                 end
 
               {string(key), state}
@@ -865,7 +894,7 @@ defmodule Code.Formatter do
   # @foo(bar)
   defp module_attribute_to_algebra(meta, {name, call_meta, [_] = args} = expr, context, state)
        when is_atom(name) and name not in [:__block__, :__aliases__] do
-    if Code.Identifier.classify(name) == :callable_local do
+    if Macro.classify_atom(name) == :identifier do
       {{call_doc, state}, wrap_in_parens?} =
         call_args_to_algebra(args, call_meta, context, :skip_unless_many_args, false, state)
 
@@ -910,7 +939,7 @@ defmodule Code.Formatter do
        )
        when is_atom(fun) and is_integer(arity) do
     {target_doc, state} = remote_target_to_algebra(target, state)
-    fun = Code.Identifier.inspect_as_function(fun)
+    fun = Macro.inspect_atom(:remote_call, fun)
     {target_doc |> nest(1) |> concat(string(".#{fun}/#{arity}")), state}
   end
 
@@ -955,7 +984,7 @@ defmodule Code.Formatter do
   defp remote_to_algebra({{:., _, [target, fun]}, meta, args}, context, state)
        when is_atom(fun) do
     {target_doc, state} = remote_target_to_algebra(target, state)
-    fun = Code.Identifier.inspect_as_function(fun)
+    fun = Macro.inspect_atom(:remote_call, fun)
     remote_doc = target_doc |> concat(".") |> concat(string(fun))
 
     if args == [] and not remote_target_is_a_module?(target) and not meta?(meta, :closing) do
@@ -1268,7 +1297,7 @@ defmodule Code.Formatter do
 
   defp list_interpolation_to_algebra([entry | entries], escape, state, acc, last) do
     {{:., _, [Kernel, :to_string]}, _meta, [quoted]} = entry
-    {doc, state} = interpolation_to_string(quoted, state)
+    {doc, state} = interpolation_to_algebra(quoted, state)
     list_interpolation_to_algebra(entries, escape, state, concat(acc, doc), last)
   end
 
@@ -1284,7 +1313,7 @@ defmodule Code.Formatter do
 
   defp interpolation_to_algebra([entry | entries], escape, state, acc, last) do
     {:"::", _, [{{:., _, [Kernel, :to_string]}, _meta, [quoted]}, {:binary, _, _}]} = entry
-    {doc, state} = interpolation_to_string(quoted, state)
+    {doc, state} = interpolation_to_algebra(quoted, state)
     interpolation_to_algebra(entries, escape, state, concat(acc, doc), last)
   end
 
@@ -1292,21 +1321,9 @@ defmodule Code.Formatter do
     {concat(acc, last), state}
   end
 
-  defp interpolation_to_string(quoted, %{skip_eol: skip_eol} = state) do
+  defp interpolation_to_algebra(quoted, %{skip_eol: skip_eol} = state) do
     {doc, state} = block_to_algebra(quoted, @max_line, @min_line, %{state | skip_eol: true})
-    doc = interpolation_to_string(surround("\#{", doc, "}"))
-    {doc, %{state | skip_eol: skip_eol}}
-  end
-
-  defp interpolation_to_string(doc) do
-    [head | tail] =
-      doc
-      |> format_to_string()
-      |> String.split("\n")
-
-    Enum.reduce(tail, string(head), fn line, acc ->
-      concat([acc, line(), string(line)])
-    end)
+    {no_limit(surround("\#{", doc, "}")), %{state | skip_eol: skip_eol}}
   end
 
   ## Sigils
@@ -1320,13 +1337,21 @@ defmodule Code.Formatter do
       entries =
         case state.sigils do
           %{^name => callback} ->
-            case callback.(hd(entries), sigil: List.to_atom([name]), modifiers: modifiers) do
-              binary when is_binary(binary) ->
-                [binary]
+            metadata = [
+              file: state.file,
+              line: meta[:line],
+              sigil: List.to_atom([name]),
+              modifiers: modifiers,
+              opening_delimiter: opening_delimiter
+            ]
+
+            case callback.(hd(entries), metadata) do
+              iodata when is_binary(iodata) or is_list(iodata) ->
+                [IO.iodata_to_binary(iodata)]
 
               other ->
                 raise ArgumentError,
-                      "expected sigil callback to return a binary, got: #{inspect(other)}"
+                      "expected sigil callback to return iodata, got: #{inspect(other)}"
             end
 
           %{} ->
@@ -1339,7 +1364,7 @@ defmodule Code.Formatter do
         {doc, state} =
           entries
           |> prepend_heredoc_line()
-          |> interpolation_to_algebra(:heredoc, state, doc, closing_delimiter)
+          |> interpolation_to_algebra(opening_delimiter, state, doc, closing_delimiter)
 
         {force_unfit(doc), state}
       else
@@ -1407,14 +1432,30 @@ defmodule Code.Formatter do
 
   defp bitstring_spec_to_algebra({op, _, [left, right]}, state) when op in [:-, :*] do
     {left, state} = bitstring_spec_to_algebra(left, state)
-    {right, state} = quoted_to_algebra_with_parens_if_operator(right, :parens_arg, state)
+    {right, state} = bitstring_spec_element_to_algebra(right, state)
     {concat(concat(left, Atom.to_string(op)), right), state}
   end
 
   defp bitstring_spec_to_algebra(spec, state) do
-    quoted_to_algebra_with_parens_if_operator(spec, :parens_arg, state)
+    bitstring_spec_element_to_algebra(spec, state)
   end
 
+  defp bitstring_spec_element_to_algebra(
+         {atom, meta, empty_args},
+         state = %{normalize_bitstring_modifiers: true}
+       )
+       when is_atom(atom) and empty_args in [nil, []] do
+    empty_args = bitstring_spec_normalize_empty_args(atom)
+    quoted_to_algebra_with_parens_if_operator({atom, meta, empty_args}, :parens_arg, state)
+  end
+
+  defp bitstring_spec_element_to_algebra(spec_element, state) do
+    quoted_to_algebra_with_parens_if_operator(spec_element, :parens_arg, state)
+  end
+
+  defp bitstring_spec_normalize_empty_args(atom) when atom in @bitstring_modifiers, do: nil
+  defp bitstring_spec_normalize_empty_args(_atom), do: []
+
   defp bitstring_wrap_parens(doc, i, last) when i == 0 or i == last do
     string = format_to_string(doc)
 
@@ -1482,25 +1523,36 @@ defmodule Code.Formatter do
     end
   end
 
-  defp atom_to_algebra(atom) when atom in [nil, true, false] do
+  defp atom_to_algebra(atom, _) when atom in [nil, true, false] do
     Atom.to_string(atom)
   end
 
   # TODO: Remove this clause in v1.16 when we no longer quote operator :..//
-  defp atom_to_algebra(:"..//") do
+  defp atom_to_algebra(:"..//", _) do
     string(":\"..//\"")
   end
 
-  defp atom_to_algebra(atom) do
+  defp atom_to_algebra(:\\, meta) do
+    # Since we parse strings without unescaping, the atoms
+    # :\\ and :"\\" have the same representation, so we need
+    # to check the delimiter and handle them accordingly.
+    string =
+      case Keyword.get(meta, :delimiter) do
+        "\"" -> ":\"\\\\\""
+        _ -> ":\\\\"
+      end
+
+    string(string)
+  end
+
+  defp atom_to_algebra(atom, _) do
     string = Atom.to_string(atom)
 
     iodata =
-      case Code.Identifier.classify(atom) do
-        type when type in [:callable_local, :callable_operator, :not_callable] ->
-          [?:, string]
-
-        _ ->
-          [?:, ?", String.replace(string, "\"", "\\\""), ?"]
+      if Macro.classify_atom(atom) in [:unquoted, :identifier] do
+        [?:, string]
+      else
+        [?:, ?", String.replace(string, "\"", "\\\""), ?"]
       end
 
     iodata |> IO.iodata_to_binary() |> string()
@@ -1548,11 +1600,13 @@ defmodule Code.Formatter do
     end
   end
 
-  defp escape_heredoc(string) do
+  defp escape_heredoc(string, escape) do
+    string = String.replace(string, escape, "\\" <> escape)
     heredoc_to_algebra(["" | String.split(string, "\n")])
   end
 
-  defp escape_string(string, :heredoc) do
+  defp escape_string(string, <<_, _, _>> = escape) do
+    string = String.replace(string, escape, "\\" <> escape)
     heredoc_to_algebra(String.split(string, "\n"))
   end
 
@@ -1645,12 +1699,15 @@ defmodule Code.Formatter do
        ) do
     min_line = line(meta)
     {body_doc, state} = block_to_algebra(body, min_line, max_line, state)
+    break_or_line = clause_break_or_line(clauses, state)
 
     doc =
       "fn ->"
-      |> glue(body_doc)
+      |> concat(break_or_line)
+      |> concat(body_doc)
       |> nest(2)
-      |> glue("end")
+      |> concat(break_or_line)
+      |> concat("end")
       |> maybe_force_clauses(clauses, state)
       |> group()
 
@@ -1679,12 +1736,16 @@ defmodule Code.Formatter do
       |> nest(:cursor)
       |> group()
 
+    break_or_line = clause_break_or_line(clauses, state)
+
     doc =
       "fn "
       |> concat(head)
-      |> glue(body_doc)
+      |> concat(break_or_line)
+      |> concat(body_doc)
       |> nest(2)
-      |> glue("end")
+      |> concat(break_or_line)
+      |> concat("end")
       |> maybe_force_clauses(clauses, state)
       |> group()
 
@@ -1726,13 +1787,14 @@ defmodule Code.Formatter do
     min_line = line(meta)
     {args_doc, state} = clause_args_to_algebra(args, min_line, state)
     {body_doc, state} = block_to_algebra(body, min_line, max_line, state)
+    break_or_line = clause_break_or_line(clauses, state)
 
     doc =
       args_doc
       |> ungroup_if_group()
       |> concat(" ->")
       |> group()
-      |> concat(break() |> concat(body_doc) |> nest(2))
+      |> concat(break_or_line |> concat(body_doc) |> nest(2))
       |> wrap_in_parens()
       |> maybe_force_clauses(clauses, state)
       |> group()
@@ -1753,12 +1815,21 @@ defmodule Code.Formatter do
 
   ## Clauses
 
+  defp multi_line_clauses?(clauses, state) do
+    Enum.any?(clauses, fn {:->, meta, [_, block]} ->
+      eol?(meta, state) or multi_line_block?(block)
+    end)
+  end
+
+  defp multi_line_block?({:__block__, _, [_, _ | _]}), do: true
+  defp multi_line_block?(_), do: false
+
+  defp clause_break_or_line(clauses, state) do
+    if multi_line_clauses?(clauses, state), do: line(), else: break()
+  end
+
   defp maybe_force_clauses(doc, clauses, state) do
-    if Enum.any?(clauses, fn {:->, meta, _} -> eol?(meta, state) end) do
-      force_unfit(doc)
-    else
-      doc
-    end
+    if multi_line_clauses?(clauses, state), do: force_unfit(doc), else: doc
   end
 
   defp clauses_to_algebra([{:->, _, _} | _] = clauses, min_line, max_line, state) do
@@ -1873,19 +1944,25 @@ defmodule Code.Formatter do
   end
 
   defp each_quoted_to_algebra_with_comments([arg | args], acc, max_line, state, comments?, fun) do
-    {doc_start, doc_end} = traverse_line(arg, {@max_line, @min_line})
+    case traverse_line(arg, {@max_line, @min_line}) do
+      {@max_line, @min_line} ->
+        {doc_triplet, state} = fun.(arg, args, state)
+        acc = [doc_triplet | acc]
+        each_quoted_to_algebra_with_comments(args, acc, max_line, state, comments?, fun)
 
-    {acc, comments, comments?} =
-      extract_comments_before(doc_start, acc, state.comments, comments?)
+      {doc_start, doc_end} ->
+        {acc, comments, comments?} =
+          extract_comments_before(doc_start, acc, state.comments, comments?)
 
-    {doc_triplet, state} = fun.(arg, args, %{state | comments: comments})
+        {doc_triplet, state} = fun.(arg, args, %{state | comments: comments})
 
-    {acc, comments, comments?} =
-      extract_comments_trailing(doc_start, doc_end, acc, state.comments, comments?)
+        {acc, comments, comments?} =
+          extract_comments_trailing(doc_start, doc_end, acc, state.comments, comments?)
 
-    acc = [adjust_trailing_newlines(doc_triplet, doc_end, comments) | acc]
-    state = %{state | comments: comments}
-    each_quoted_to_algebra_with_comments(args, acc, max_line, state, comments?, fun)
+        acc = [adjust_trailing_newlines(doc_triplet, doc_end, comments) | acc]
+        state = %{state | comments: comments}
+        each_quoted_to_algebra_with_comments(args, acc, max_line, state, comments?, fun)
+    end
   end
 
   defp extract_comments_before(max, acc, [%{line: line} = comment | rest], _) when line < max do
@@ -2034,7 +2111,7 @@ defmodule Code.Formatter do
 
   defp module_attribute_read?({:@, _, [{var, _, var_context}]})
        when is_atom(var) and is_atom(var_context) do
-    Code.Identifier.classify(var) == :callable_local
+    Macro.classify_atom(var) == :identifier
   end
 
   defp module_attribute_read?(_), do: false

lib/elixir/lib/code/fragment.ex

@@ -42,12 +42,19 @@ defmodule Code.Fragment do
     * `{:alias, charlist}` - the context is an alias, potentially
       a nested one, such as `Hello.Wor` or `HelloWor`
 
+    * `{:alias, inside_alias, charlist}` - the context is an alias, potentially
+      a nested one, where `inside_alias` is an expression `{:module_attribute, charlist}`
+      or `{:local_or_var, charlist}` and `charlist` is a static part
+      Examples are `__MODULE__.Submodule` or `@hello.Submodule`
+
     * `{:dot, inside_dot, charlist}` - the context is a dot
       where `inside_dot` is either a `{:var, charlist}`, `{:alias, charlist}`,
       `{:module_attribute, charlist}`, `{:unquoted_atom, charlist}` or a `dot`
       itself. If a var is given, this may either be a remote call or a map
       field access. Examples are `Hello.wor`, `:hello.wor`, `hello.wor`,
-      `Hello.nested.wor`, `hello.nested.wor`, and `@hello.world`
+      `Hello.nested.wor`, `hello.nested.wor`, and `@hello.world`. If `charlist`
+      is empty and `inside_dot` is an alias, then the autocompletion may either
+      be an alias or a remote call.
 
     * `{:dot_arity, inside_dot, charlist}` - the context is a dot arity
       where `inside_dot` is either a `{:var, charlist}`, `{:alias, charlist}`,
@@ -95,7 +102,10 @@ defmodule Code.Fragment do
       of a sigil, such as `~` or `~s`, or an operator starting with `~`, such as
       `~>` and `~>>`
 
-    * `{:struct, charlist}` - the context is a struct, such as `%`, `%UR` or `%URI`
+    * `{:struct, inside_struct}` - the context is a struct, such as `%`, `%UR` or `%URI`.
+      `inside_struct` can either be a `charlist` in case of a static alias or an
+      expression `{:alias, inside_alias, charlist}`, `{:module_attribute, charlist}`,
+      `{:local_or_var, charlist}`, `{:dot, inside_dot, charlist}`
 
     * `{:unquoted_atom, charlist}` - the context is an unquoted atom. This
       can be any atom or an atom representing a module
@@ -109,6 +119,7 @@ defmodule Code.Fragment do
   @doc since: "1.13.0"
   @spec cursor_context(List.Chars.t(), keyword()) ::
           {:alias, charlist}
+          | {:alias, inside_alias, charlist}
           | {:dot, inside_dot, charlist}
           | {:dot_arity, inside_dot, charlist}
           | {:dot_call, inside_dot, charlist}
@@ -122,42 +133,30 @@ defmodule Code.Fragment do
           | {:operator_call, charlist}
           | :none
           | {:sigil, charlist}
-          | {:struct, charlist}
+          | {:struct, inside_struct}
           | {:unquoted_atom, charlist}
         when inside_dot:
                {:alias, charlist}
+               | {:alias, inside_alias, charlist}
                | {:dot, inside_dot, charlist}
                | {:module_attribute, charlist}
                | {:unquoted_atom, charlist}
-               | {:var, charlist}
+               | {:var, charlist},
+             inside_alias:
+               {:local_or_var, charlist}
+               | {:module_attribute, charlist},
+             inside_struct:
+               charlist
+               | {:alias, inside_alias, charlist}
+               | {:local_or_var, charlist}
+               | {:module_attribute, charlist}
+               | {:dot, inside_dot, charlist}
   def cursor_context(fragment, opts \\ [])
 
-  def cursor_context(binary, opts) when is_binary(binary) and is_list(opts) do
-    binary =
-      case :binary.matches(binary, "\n") do
-        [] ->
-          binary
-
-        matches ->
-          {position, _} = List.last(matches)
-          binary_part(binary, position + 1, byte_size(binary) - position - 1)
-      end
-
-    binary
-    |> String.to_charlist()
-    |> :lists.reverse()
-    |> codepoint_cursor_context(opts)
-    |> elem(0)
-  end
-
-  def cursor_context(charlist, opts) when is_list(charlist) and is_list(opts) do
-    charlist =
-      case charlist |> Enum.chunk_by(&(&1 == ?\n)) |> List.last([]) do
-        [?\n | _] -> []
-        rest -> rest
-      end
-
-    charlist
+  def cursor_context(fragment, opts)
+      when (is_binary(fragment) or is_list(fragment)) and is_list(opts) do
+    fragment
+    |> last_line()
     |> :lists.reverse()
     |> codepoint_cursor_context(opts)
     |> elem(0)
@@ -178,7 +177,7 @@ defmodule Code.Fragment do
                     @operators ++ @starter_punctuation ++ @non_starter_punctuation ++ @space
 
   @textual_operators ~w(when not and or in)c
-  @incomplete_operators ~w(^^ ~~ ~)c
+  @keywords ~w(do end after else catch rescue fn true false nil)c
 
   defp codepoint_cursor_context(reverse, _opts) do
     {stripped, spaces} = strip_spaces(reverse, 0)
@@ -250,6 +249,9 @@ defmodule Code.Fragment do
       :operator ->
         operator(reverse, count, [], call_op?)
 
+      {:struct, {:module_attribute, acc}, count} ->
+        {{:struct, {:module_attribute, acc}}, count + 1}
+
       {:module_attribute, acc, count} ->
         {{:module_attribute, acc}, count}
 
@@ -274,6 +276,12 @@ defmodule Code.Fragment do
       {:identifier, _, acc, count} when call_op? and acc in @textual_operators ->
         {{:operator, acc}, count}
 
+      {:identifier, [?%], acc, count} ->
+        case identifier_to_cursor_context(acc |> Enum.reverse(), count, true) do
+          {{:local_or_var, _} = idenifier, _} -> {{:struct, idenifier}, count + 1}
+          _ -> {:none, 0}
+        end
+
       {:identifier, rest, acc, count} ->
         case strip_spaces(rest, count) do
           {'.' ++ rest, count} when rest == [] or hd(rest) != ?. ->
@@ -300,6 +308,7 @@ defmodule Code.Fragment do
 
   defp rest_identifier(rest, count, [?@ | acc]) do
     case tokenize_identifier(rest, count, acc) do
+      {:identifier, [?% | _rest], acc, count} -> {:struct, {:module_attribute, acc}, count}
       {:identifier, _rest, acc, count} -> {:module_attribute, acc, count}
       :none when acc == [] -> {:module_attribute, '', count}
       _ -> :none
@@ -338,7 +347,7 @@ defmodule Code.Fragment do
         :none
 
       {kind, _, [], _, _, extra} ->
-        if ?@ in extra do
+        if :at in extra do
           :none
         else
           {kind, rest, acc, count}
@@ -353,9 +362,29 @@ defmodule Code.Fragment do
     {rest, count} = strip_spaces(rest, count)
 
     case identifier_to_cursor_context(rest, count, true) do
-      {{:struct, prev}, count} -> {{:struct, prev ++ '.' ++ acc}, count}
-      {{:alias, prev}, count} -> {{:alias, prev ++ '.' ++ acc}, count}
-      _ -> {:none, 0}
+      {{:struct, prev}, count} when is_list(prev) ->
+        {{:struct, prev ++ '.' ++ acc}, count}
+
+      {{:struct, {:alias, parent, prev}}, count} ->
+        {{:struct, {:alias, parent, prev ++ '.' ++ acc}}, count}
+
+      {{:struct, prev}, count} ->
+        {{:struct, {:alias, prev, acc}}, count}
+
+      {{:alias, prev}, count} ->
+        {{:alias, prev ++ '.' ++ acc}, count}
+
+      {{:alias, parent, prev}, count} ->
+        {{:alias, parent, prev ++ '.' ++ acc}, count}
+
+      {{:local_or_var, prev}, count} ->
+        {{:alias, {:local_or_var, prev}, acc}, count}
+
+      {{:module_attribute, prev}, count} ->
+        {{:alias, {:module_attribute, prev}, acc}, count}
+
+      _ ->
+        {:none, 0}
     end
   end
 
@@ -363,13 +392,32 @@ defmodule Code.Fragment do
     {rest, count} = strip_spaces(rest, count)
 
     case identifier_to_cursor_context(rest, count, true) do
-      {{:local_or_var, var}, count} -> {{:dot, {:var, var}, acc}, count}
-      {{:unquoted_atom, _} = prev, count} -> {{:dot, prev, acc}, count}
-      {{:alias, _} = prev, count} -> {{:dot, prev, acc}, count}
-      {{:dot, _, _} = prev, count} -> {{:dot, prev, acc}, count}
-      {{:module_attribute, _} = prev, count} -> {{:dot, prev, acc}, count}
-      {{:struct, acc}, count} -> {{:struct, acc ++ '.'}, count}
-      {_, _} -> {:none, 0}
+      {{:local_or_var, var}, count} ->
+        {{:dot, {:var, var}, acc}, count}
+
+      {{:unquoted_atom, _} = prev, count} ->
+        {{:dot, prev, acc}, count}
+
+      {{:alias, _} = prev, count} ->
+        {{:dot, prev, acc}, count}
+
+      {{:alias, _, _} = prev, count} ->
+        {{:dot, prev, acc}, count}
+
+      {{:struct, inner}, count} when is_list(inner) ->
+        {{:struct, {:dot, {:alias, inner}, acc}}, count}
+
+      {{:struct, inner}, count} ->
+        {{:struct, {:dot, inner, acc}}, count}
+
+      {{:dot, _, _} = prev, count} ->
+        {{:dot, prev, acc}, count}
+
+      {{:module_attribute, _} = prev, count} ->
+        {{:dot, prev, acc}, count}
+
+      {_, _} ->
+        {:none, 0}
     end
   end
 
@@ -377,24 +425,6 @@ defmodule Code.Fragment do
     operator(rest, count + 1, [h | acc], call_op?)
   end
 
-  defp operator(rest, count, acc, call_op?) when acc in @incomplete_operators do
-    {rest, dot_count} = strip_spaces(rest, count)
-
-    cond do
-      call_op? ->
-        {:none, 0}
-
-      match?([?. | rest] when rest == [] or hd(rest) != ?., rest) ->
-        dot(tl(rest), dot_count + 1, acc)
-
-      acc == '~' ->
-        {{:sigil, ''}, count}
-
-      true ->
-        {{:operator, acc}, count}
-    end
-  end
-
   # If we are opening a sigil, ignore the operator.
   defp operator([letter, ?~ | rest], _count, [op], _call_op?)
        when op in '<|/' and (letter in ?A..?Z or letter in ?a..?z) and
@@ -402,6 +432,16 @@ defmodule Code.Fragment do
     {:none, 0}
   end
 
+  defp operator(rest, count, '~', call_op?) do
+    {rest, _} = strip_spaces(rest, count)
+
+    if call_op? or match?([?. | rest] when rest == [] or hd(rest) != ?., rest) do
+      {:none, 0}
+    else
+      {{:sigil, ''}, count}
+    end
+  end
+
   defp operator(rest, count, acc, _call_op?) do
     case :elixir_tokenizer.tokenize(acc, 1, 1, []) do
       {:ok, _, _, _, [{:atom, _, _}]} ->
@@ -489,43 +529,63 @@ defmodule Code.Fragment do
 
     * This function never returns empty sigils `{:sigil, ''}` or empty structs
       `{:struct, ''}` as context
+
+    * This function returns keywords as `{:keyword, 'do'}`
+
+    * This function never returns `:expr`
+
   """
   @doc since: "1.13.0"
   @spec surround_context(List.Chars.t(), position(), keyword()) ::
           %{begin: position, end: position, context: context} | :none
         when context:
                {:alias, charlist}
+               | {:alias, inside_alias, charlist}
                | {:dot, inside_dot, charlist}
                | {:local_or_var, charlist}
                | {:local_arity, charlist}
                | {:local_call, charlist}
                | {:module_attribute, charlist}
                | {:operator, charlist}
-               | {:unquoted_atom, charlist},
+               | {:sigil, charlist}
+               | {:struct, inside_struct}
+               | {:unquoted_atom, charlist}
+               | {:keyword, charlist},
              inside_dot:
                {:alias, charlist}
+               | {:alias, inside_alias, charlist}
                | {:dot, inside_dot, charlist}
                | {:module_attribute, charlist}
                | {:unquoted_atom, charlist}
-               | {:var, charlist}
+               | {:var, charlist},
+             inside_alias:
+               {:local_or_var, charlist}
+               | {:module_attribute, charlist},
+             inside_struct:
+               charlist
+               | {:alias, inside_alias, charlist}
+               | {:local_or_var, charlist}
+               | {:module_attribute, charlist}
+               | {:dot, inside_dot, charlist}
   def surround_context(fragment, position, options \\ [])
 
-  def surround_context(binary, {line, column}, opts) when is_binary(binary) do
-    binary
-    |> String.split("\n")
-    |> Enum.at(line - 1, '')
-    |> String.to_charlist()
-    |> position_surround_context(line, column, opts)
-  end
+  def surround_context(string, {line, column}, opts)
+      when (is_binary(string) or is_list(string)) and is_list(opts) do
+    {charlist, lines_before_lengths, lines_current_and_after_lengths} =
+      surround_line(string, line, column)
+
+    prepended_columns = Enum.sum(lines_before_lengths)
 
-  def surround_context(charlist, {line, column}, opts) when is_list(charlist) do
     charlist
-    |> :string.split('\n', :all)
-    |> Enum.at(line - 1, '')
-    |> position_surround_context(line, column, opts)
+    |> position_surround_context(line, column + prepended_columns, opts)
+    |> to_multiline_range(
+      prepended_columns,
+      lines_before_lengths,
+      lines_current_and_after_lengths
+    )
   end
 
-  def surround_context(other, position, opts) do
+  def surround_context(other, {_, _} = position, opts) do
     surround_context(to_charlist(other), position, opts)
   end
 
@@ -549,6 +609,9 @@ defmodule Code.Fragment do
           {{:alias, acc}, offset} ->
             build_surround({:alias, acc}, reversed, line, offset)
 
+          {{:alias, parent, acc}, offset} ->
+            build_surround({:alias, parent, acc}, reversed, line, offset)
+
           {{:dot, _, [_ | _]} = dot, offset} ->
             build_surround(dot, reversed, line, offset)
 
@@ -561,7 +624,10 @@ defmodule Code.Fragment do
           {{:local_or_var, acc}, offset} when acc in @textual_operators ->
             build_surround({:operator, acc}, reversed, line, offset)
 
-          {{:local_or_var, acc}, offset} when acc not in ~w(do end after else catch rescue)c ->
+          {{:local_or_var, acc}, offset} when acc in @keywords ->
+            build_surround({:keyword, acc}, reversed, line, offset)
+
+          {{:local_or_var, acc}, offset} ->
             build_surround({:local_or_var, acc}, reversed, line, offset)
 
           {{:module_attribute, ''}, offset} ->
@@ -605,7 +671,7 @@ defmodule Code.Fragment do
         reversed = reversed_post ++ reversed_pre
 
         case codepoint_cursor_context(reversed, opts) do
-          {{:operator, acc}, offset} when acc not in @incomplete_operators ->
+          {{:operator, acc}, offset} ->
             build_surround({:operator, acc}, reversed, line, offset)
 
           {{:sigil, ''}, offset} when hd(rest) in ?A..?Z or hd(rest) in ?a..?z ->
@@ -720,10 +786,156 @@ defmodule Code.Fragment do
   defp enum_reverse_at([h | t], n, acc) when n > 0, do: enum_reverse_at(t, n - 1, [h | acc])
   defp enum_reverse_at(rest, _, acc), do: {acc, rest}
 
+  defp last_line(binary) when is_binary(binary) do
+    [last_line | lines_reverse] =
+      binary
+      |> String.split(["\r\n", "\n"])
+      |> Enum.reverse()
+
+    prepend_cursor_lines(lines_reverse, String.to_charlist(last_line))
+  end
+
+  defp last_line(charlist) when is_list(charlist) do
+    [last_line | lines_reverse] =
+      charlist
+      |> :string.replace('\r\n', '\n', :all)
+      |> :string.join('')
+      |> :string.split('\n', :all)
+      |> Enum.reverse()
+
+    prepend_cursor_lines(lines_reverse, last_line)
+  end
+
+  defp prepend_cursor_lines(lines, last_line) do
+    with [line | lines] <- lines,
+         {trimmed_line, incomplete?} = ends_as_incomplete(to_charlist(line), [], true),
+         true <- incomplete? or starts_with_dot?(last_line) do
+      prepend_cursor_lines(lines, Enum.reverse(trimmed_line, last_line))
+    else
+      _ -> last_line
+    end
+  end
+
+  defp starts_with_dot?([?. | _]), do: true
+  defp starts_with_dot?([h | t]) when h in @space, do: starts_with_dot?(t)
+  defp starts_with_dot?(_), do: false
+
+  defp ends_as_incomplete([?# | _], acc, incomplete?),
+    do: {acc, incomplete?}
+
+  defp ends_as_incomplete([h | t], acc, _incomplete?) when h in [?(, ?.],
+    do: ends_as_incomplete(t, [h | acc], true)
+
+  defp ends_as_incomplete([h | t], acc, incomplete?) when h in @space,
+    do: ends_as_incomplete(t, [h | acc], incomplete?)
+
+  defp ends_as_incomplete([h | t], acc, _incomplete?),
+    do: ends_as_incomplete(t, [h | acc], false)
+
+  defp ends_as_incomplete([], acc, incomplete?),
+    do: {acc, incomplete?}
+
+  defp surround_line(binary, line, column) when is_binary(binary) do
+    binary
+    |> String.split(["\r\n", "\n"])
+    |> Enum.map(&String.to_charlist/1)
+    |> surround_lines(line, column)
+  end
+
+  defp surround_line(charlist, line, column) when is_list(charlist) do
+    charlist
+    |> :string.replace('\r\n', '\n', :all)
+    |> :string.join('')
+    |> :string.split('\n', :all)
+    |> surround_lines(line, column)
+  end
+
+  defp surround_lines(lines, line, column) do
+    {lines_before_reverse, cursor_line, lines_after} = split_at(lines, line, [])
+    {trimmed_cursor_line, incomplete?} = ends_as_incomplete(to_charlist(cursor_line), [], true)
+
+    reversed_cursor_line =
+      if column - 1 > length(trimmed_cursor_line) do
+        # Don't strip comments if cursor is inside a comment
+        Enum.reverse(cursor_line)
+      else
+        trimmed_cursor_line
+      end
+
+    {cursor_line, after_lengths} =
+      append_surround_lines(lines_after, [], [reversed_cursor_line], incomplete?)
+
+    {cursor_line, before_lengths} = prepend_surround_lines(lines_before_reverse, [], cursor_line)
+    {cursor_line, before_lengths, [length(reversed_cursor_line) | after_lengths]}
+  end
+
+  defp split_at([line], _, acc), do: {acc, line, []}
+  defp split_at([line | lines], 1, acc), do: {acc, line, lines}
+  defp split_at([line | lines], count, acc), do: split_at(lines, count - 1, [line | acc])
+
+  defp prepend_surround_lines(lines, lengths, last_line) do
+    with [line | lines] <- lines,
+         {trimmed_line, incomplete?} = ends_as_incomplete(to_charlist(line), [], true),
+         true <- incomplete? or starts_with_dot?(last_line) do
+      lengths = [length(trimmed_line) | lengths]
+      prepend_surround_lines(lines, lengths, Enum.reverse(trimmed_line, last_line))
+    else
+      _ -> {last_line, Enum.reverse(lengths)}
+    end
+  end
+
+  defp append_surround_lines(lines, lengths, acc_lines, incomplete?) do
+    with [line | lines] <- lines,
+         line = to_charlist(line),
+         true <- incomplete? or starts_with_dot?(line) do
+      {trimmed_line, incomplete?} = ends_as_incomplete(line, [], true)
+      lengths = [length(trimmed_line) | lengths]
+      append_surround_lines(lines, lengths, [trimmed_line | acc_lines], incomplete?)
+    else
+      _ -> {Enum.reduce(acc_lines, [], &Enum.reverse/2), Enum.reverse(lengths)}
+    end
+  end
+
+  defp to_multiline_range(:none, _, _, _), do: :none
+
+  defp to_multiline_range(
+         %{begin: {begin_line, begin_column}, end: {end_line, end_column}} = context,
+         prepended,
+         lines_before_lengths,
+         lines_current_and_after_lengths
+       ) do
+    {begin_line, begin_column} =
+      Enum.reduce_while(lines_before_lengths, {begin_line, begin_column - prepended}, fn
+        line_length, {acc_line, acc_column} ->
+          if acc_column < 1 do
+            {:cont, {acc_line - 1, acc_column + line_length}}
+          else
+            {:halt, {acc_line, acc_column}}
+          end
+      end)
+
+    {end_line, end_column} =
+      Enum.reduce_while(lines_current_and_after_lengths, {end_line, end_column - prepended}, fn
+        line_length, {acc_line, acc_column} ->
+          if acc_column > line_length + 1 do
+            {:cont, {acc_line + 1, acc_column - line_length}}
+          else
+            {:halt, {acc_line, acc_column}}
+          end
+      end)
+
+    %{context | begin: {begin_line, begin_column}, end: {end_line, end_column}}
+  end
+
   @doc """
-  Receives a code fragment and returns a quoted expression
+  Receives a string and returns a quoted expression
   with a cursor at the nearest argument position.
 
+  This function receives a string with an Elixir code fragment,
+  representing a cursor position, and converts such string to
+  AST with the inclusion of special `__cursor__()` node based
+  on the position of the cursor with a container.
+
   A container is any Elixir expression starting with `(`,
   `{`, and `[`. This includes function calls, tuples, lists,
   maps, and so on. For example, take this code, which would
@@ -765,7 +977,7 @@ defmodule Code.Fragment do
       max(some_value, 1 + another_val
       max(some_value, 1 |> some_fun() |> another_fun
 
-  On the other hand, tuples, lists, maps, etc all retain the
+  On the other hand, tuples, lists, maps, and binaries all retain the
   cursor position:
 
       max(some_value, [1, 2,
@@ -789,9 +1001,21 @@ defmodule Code.Fragment do
 
   ## Examples
 
+  Function call:
+
       iex> Code.Fragment.container_cursor_to_quoted("max(some_value, ")
       {:ok, {:max, [line: 1], [{:some_value, [line: 1], nil}, {:__cursor__, [line: 1], []}]}}
 
+  Containers (for example, a list):
+
+      iex> Code.Fragment.container_cursor_to_quoted("[some, value")
+      {:ok, [{:some, [line: 1], nil}, {:__cursor__, [line: 1], []}]}
+
+  For binaries, the `::` is exclusively kept as an operator:
+
+      iex> Code.Fragment.container_cursor_to_quoted("<<some::integer")
+      {:ok, {:<<>>, [line: 1], [{:"::", [line: 1], [{:some, [line: 1], nil}, {:__cursor__, [line: 1], []}]}]}}
+
   ## Options
 
     * `:file` - the filename to be reported in case of parsing errors.
@@ -811,31 +1035,17 @@ defmodule Code.Fragment do
       tokens, for closing tokens, end of expressions, as well as delimiters
       for sigils. See `t:Macro.metadata/0`. Defaults to `false`.
 
+    * `:literal_encoder` - a function to encode literals in the AST.
+      See the documentation for `Code.string_to_quoted/2` for more information.
+
   """
   @doc since: "1.13.0"
   @spec container_cursor_to_quoted(List.Chars.t(), keyword()) ::
           {:ok, Macro.t()} | {:error, {location :: keyword, binary | {binary, binary}, binary}}
   def container_cursor_to_quoted(fragment, opts \\ []) do
-    file = Keyword.get(opts, :file, "nofile")
-    line = Keyword.get(opts, :line, 1)
-    column = Keyword.get(opts, :column, 1)
-    columns = Keyword.get(opts, :columns, false)
-    token_metadata = Keyword.get(opts, :token_metadata, false)
+    opts =
+      Keyword.take(opts, [:file, :line, :column, :columns, :token_metadata, :literal_encoder])
 
-    fragment = to_charlist(fragment)
-    tokenizer_opts = [file: file, cursor_completion: true, columns: columns]
-
-    case :elixir_tokenizer.tokenize(fragment, line, column, tokenizer_opts) do
-      {:ok, _, _, _warnings, tokens} ->
-        :elixir.tokens_to_quoted(tokens, file, columns: columns, token_metadata: token_metadata)
-
-      {:error, {line, column, {prefix, suffix}, token}, _rest, _warnings, _so_far} ->
-        location = [line: line, column: column]
-        {:error, {location, {to_string(prefix), to_string(suffix)}, to_string(token)}}
-
-      {:error, {line, column, error, token}, _rest, _warnings, _so_far} ->
-        location = [line: line, column: column]
-        {:error, {location, to_string(error), to_string(token)}}
-    end
+    Code.string_to_quoted(fragment, [cursor_completion: true, emit_warnings: false] ++ opts)
   end
 end

lib/elixir/lib/code/identifier.ex

@@ -14,7 +14,7 @@ defmodule Code.Identifier do
   def unary_op(op) do
     cond do
       op in [:&] -> {:non_associative, 90}
-      op in [:!, :^, :not, :+, :-, :~~~] -> {:non_associative, 300}
+      op in [:!, :^, :not, :+, :-, :"~~~"] -> {:non_associative, 300}
       op in [:@] -> {:non_associative, 320}
       true -> :error
     end
@@ -41,9 +41,9 @@ defmodule Code.Identifier do
       op in [:&&, :&&&, :and] -> {:left, 130}
       op in [:==, :!=, :=~, :===, :!==] -> {:left, 140}
       op in [:<, :<=, :>=, :>] -> {:left, 150}
-      op in [:|>, :<<<, :>>>, :<~, :~>, :<<~, :~>>, :<~>, :<|>] -> {:left, 160}
+      op in [:|>, :<<<, :>>>, :<~, :~>, :<<~, :~>>, :<~>, :"<|>"] -> {:left, 160}
       op in [:in] -> {:left, 170}
-      op in [:^^^] -> {:left, 180}
+      op in [:"^^^"] -> {:left, 180}
       op in [:"//"] -> {:right, 190}
       op in [:++, :--, :.., :<>, :+++, :---] -> {:right, 200}
       op in [:+, :-] -> {:left, 210}
@@ -54,149 +54,6 @@ defmodule Code.Identifier do
     end
   end
 
-  @doc """
-  Classifies the given atom into one of the following categories:
-
-    * `:alias` - a valid Elixir alias, like `Foo`, `Foo.Bar` and so on
-
-    * `:callable_local` - an atom that can be used as a local call;
-      this category includes identifiers like `:foo`
-
-    * `:callable_operator` - all callable operators, such as `:<>`. Note
-      operators such as `:..` are not callable because of ambiguity
-
-    * `:not_atomable` - callable operators that must be wrapped in quotes when
-      defined as an atom. For example, `::` must be written as `:"::"` to avoid
-      the ambiguity between the atom and the keyword identifier
-
-    * `:not_callable` - an atom that cannot be used as a function call after the
-      `.` operator. Those are typically AST nodes that are special forms (such as
-      `:%{}` and `:<<>>>`) as well as nodes that are ambiguous in calls (such as
-      `:..` and `:...`). This category also includes atoms like `:Foo`, since
-      they are valid identifiers but they need quotes to be used in function
-      calls (`Foo."Bar"`)
-
-    * `:other` - any other atom (these are usually escaped when inspected, like
-      `:"foo and bar"`)
-
-  """
-  def classify(atom) when is_atom(atom) do
-    charlist = Atom.to_charlist(atom)
-
-    cond do
-      atom in [:%, :%{}, :{}, :<<>>, :..., :.., :., :"..//", :->] ->
-        :not_callable
-
-      atom in [:"::", :"//"] ->
-        :not_atomable
-
-      unary_op(atom) != :error or binary_op(atom) != :error ->
-        :callable_operator
-
-      valid_alias?(charlist) ->
-        :alias
-
-      true ->
-        case :elixir_config.identifier_tokenizer().tokenize(charlist) do
-          {kind, _acc, [], _, _, special} ->
-            if kind == :identifier and not :lists.member(?@, special) do
-              :callable_local
-            else
-              :not_callable
-            end
-
-          _ ->
-            :other
-        end
-    end
-  end
-
-  defp valid_alias?('Elixir' ++ rest), do: valid_alias_piece?(rest)
-  defp valid_alias?(_other), do: false
-
-  defp valid_alias_piece?([?., char | rest]) when char >= ?A and char <= ?Z,
-    do: valid_alias_piece?(trim_leading_while_valid_identifier(rest))
-
-  defp valid_alias_piece?([]), do: true
-  defp valid_alias_piece?(_other), do: false
-
-  defp trim_leading_while_valid_identifier([char | rest])
-       when char >= ?a and char <= ?z
-       when char >= ?A and char <= ?Z
-       when char >= ?0 and char <= ?9
-       when char == ?_ do
-    trim_leading_while_valid_identifier(rest)
-  end
-
-  defp trim_leading_while_valid_identifier(other) do
-    other
-  end
-
-  @doc """
-  Inspects the identifier as an atom.
-  """
-  def inspect_as_atom(atom) when is_nil(atom) or is_boolean(atom) do
-    Atom.to_string(atom)
-  end
-
-  def inspect_as_atom(atom) when is_atom(atom) do
-    binary = Atom.to_string(atom)
-
-    case classify(atom) do
-      :alias ->
-        case binary do
-          binary when binary in ["Elixir", "Elixir.Elixir"] -> binary
-          "Elixir.Elixir." <> _rest -> binary
-          "Elixir." <> rest -> rest
-        end
-
-      type when type in [:callable_local, :callable_operator, :not_callable] ->
-        ":" <> binary
-
-      _ ->
-        {escaped, _} = escape(binary, ?")
-        IO.iodata_to_binary([?:, ?", escaped, ?"])
-    end
-  end
-
-  @doc """
-  Inspects the given identifier as a key.
-  """
-  def inspect_as_key(atom) when is_atom(atom) do
-    binary = Atom.to_string(atom)
-
-    case classify(atom) do
-      type when type in [:callable_local, :callable_operator, :not_callable] ->
-        IO.iodata_to_binary([binary, ?:])
-
-      _ ->
-        {escaped, _} = escape(binary, ?")
-        IO.iodata_to_binary([?", escaped, ?", ?:])
-    end
-  end
-
-  @doc """
-  Inspects the given identifier as a function name.
-  """
-  def inspect_as_function(atom) when is_atom(atom) do
-    binary = Atom.to_string(atom)
-
-    case classify(atom) do
-      type when type in [:callable_local, :callable_operator, :not_atomable] ->
-        binary
-
-      type ->
-        escaped =
-          if type in [:not_callable, :alias] do
-            binary
-          else
-            elem(escape(binary, ?"), 0)
-          end
-
-        IO.iodata_to_binary([?", escaped, ?"])
-    end
-  end
-
   @doc """
   Extracts the name and arity of the parent from the anonymous function identifier.
   """
@@ -214,8 +71,12 @@ defmodule Code.Identifier do
   @doc """
   Escapes the given identifier.
   """
-  def escape(other, char, count \\ :infinity, fun \\ &escape_map/1) do
-    escape(other, char, count, [], fun)
+  @spec escape(binary(), char() | nil, :infinity | non_neg_integer, (char() -> iolist() | false)) ::
+          {escaped :: iolist(), remaining :: binary()}
+  def escape(binary, char, limit \\ :infinity, fun \\ &escape_map/1)
+      when ((char in 0..0x10FFFF or is_nil(char)) and limit == :infinity) or
+             (is_integer(limit) and limit >= 0) do
+    escape(binary, char, limit, [], fun)
   end
 
   defp escape(<<_, _::binary>> = binary, _char, 0, acc, _fun) do

lib/elixir/lib/code/normalizer.ex

@@ -63,15 +63,17 @@ defmodule Code.Normalizer do
   end
 
   # Bit containers
-  defp do_normalize({:<<>>, _, _} = quoted, state) do
+  defp do_normalize({:<<>>, _, args} = quoted, state) when is_list(args) do
     normalize_bitstring(quoted, state)
   end
 
   # Atoms with interpolations
   defp do_normalize(
-         {{:., dot_meta, [:erlang, :binary_to_atom]}, call_meta, [{:<<>>, _, _} = string, :utf8]},
+         {{:., dot_meta, [:erlang, :binary_to_atom]}, call_meta,
+          [{:<<>>, _, args} = string, :utf8]},
          state
-       ) do
+       )
+       when is_list(args) do
     dot_meta = patch_meta_line(dot_meta, state.parent_meta)
     call_meta = patch_meta_line(call_meta, dot_meta)
 
@@ -166,8 +168,8 @@ defmodule Code.Normalizer do
   end
 
   # Sigils
-  defp do_normalize({sigil, meta, [{:<<>>, _, _} = string, modifiers]} = quoted, state)
-       when is_atom(sigil) do
+  defp do_normalize({sigil, meta, [{:<<>>, _, args} = string, modifiers]} = quoted, state)
+       when is_list(args) and is_atom(sigil) do
     case Atom.to_string(sigil) do
       <<"sigil_", _name>> ->
         meta =
@@ -183,19 +185,40 @@ defmodule Code.Normalizer do
   end
 
   # Tuples
-  defp do_normalize({:{}, meta, args} = quoted, state) do
+  defp do_normalize({:{}, meta, args} = quoted, state) when is_list(args) do
     {last_arg, args} = List.pop_at(args, -1)
 
-    with [{{:__block__, key_meta, _}, _} | _] <- last_arg, :keyword <- key_meta[:format] do
-      args = normalize_kw_args(args, state)
-      kw_list = normalize_kw_args(last_arg, state)
+    if args != [] and match?([_ | _], last_arg) and keyword?(last_arg) do
+      args = normalize_args(args, state)
+      kw_list = normalize_kw_args(last_arg, state, true)
       {:{}, meta, args ++ kw_list}
     else
-      _ ->
-        normalize_call(quoted, state)
+      normalize_call(quoted, state)
     end
   end
 
+  # Module attributes
+  defp do_normalize({:@, meta, [{name, name_meta, [value]}]}, state) do
+    value =
+      cond do
+        keyword?(value) ->
+          normalize_kw_args(value, state, true)
+
+        is_list(value) ->
+          normalize_literal(value, meta, state)
+
+        true ->
+          do_normalize(value, state)
+      end
+
+    {:@, meta, [{name, name_meta, [value]}]}
+  end
+
+  # Regular blocks
+  defp do_normalize({:__block__, meta, args}, state) when is_list(args) do
+    {:__block__, meta, normalize_args(args, state)}
+  end
+
   # Calls
   defp do_normalize({_, _, args} = quoted, state) when is_list(args) do
     normalize_call(quoted, state)
@@ -226,14 +249,18 @@ defmodule Code.Normalizer do
     meta = patch_meta_line(meta, state.parent_meta)
     literal = maybe_escape_literal(literal, state)
 
-    if is_atom(literal) and Code.Identifier.classify(literal) == :alias and
+    if is_atom(literal) and Macro.classify_atom(literal) == :alias and
          is_nil(meta[:delimiter]) do
-      "Elixir." <> segments = Atom.to_string(literal)
-
       segments =
-        segments
-        |> String.split(".")
-        |> Enum.map(&String.to_atom/1)
+        case Atom.to_string(literal) do
+          "Elixir" ->
+            [:"Elixir"]
+
+          "Elixir." <> segments ->
+            segments
+            |> String.split(".")
+            |> Enum.map(&String.to_atom/1)
+        end
 
       {:__aliases__, meta, segments}
     else
@@ -246,11 +273,10 @@ defmodule Code.Normalizer do
     meta = patch_meta_line(meta, state.parent_meta)
     state = %{state | parent_meta: meta}
 
-    with [{{:__block__, key_meta, _}, _} | _] <- right, :keyword <- key_meta[:format] do
-      {:__block__, meta, [{do_normalize(left, state), normalize_kw_args(right, state)}]}
+    if match?([_ | _], right) and keyword?(right) do
+      {:__block__, meta, [{do_normalize(left, state), normalize_kw_args(right, state, true)}]}
     else
-      _ ->
-        {:__block__, meta, [{do_normalize(left, state), do_normalize(right, state)}]}
+      {:__block__, meta, [{do_normalize(left, state), do_normalize(right, state)}]}
     end
   end
 
@@ -260,7 +286,7 @@ defmodule Code.Normalizer do
       # It's a charlist
       list =
         if state.escape do
-          {string, _} = Code.Identifier.escape(IO.chardata_to_string(list), -1)
+          {string, _} = Code.Identifier.escape(IO.chardata_to_string(list), nil)
           IO.iodata_to_binary(string) |> to_charlist()
         else
           list
@@ -282,7 +308,7 @@ defmodule Code.Normalizer do
           meta
         end
 
-      {:__block__, meta, [normalize_kw_args(list, state)]}
+      {:__block__, meta, [normalize_kw_args(list, state, false)]}
     end
   end
 
@@ -402,7 +428,7 @@ defmodule Code.Normalizer do
   end
 
   defp normalize_map_args(args, state) do
-    Enum.map(normalize_kw_args(args, state), fn
+    Enum.map(normalize_kw_args(args, state, false), fn
       {:__block__, _, [{_, _} = pair]} -> pair
       pair -> pair
     end)
@@ -435,7 +461,7 @@ defmodule Code.Normalizer do
     {form, meta, leading_args ++ [kw_blocks]}
   end
 
-  defp normalize_kw_args(elems, state, keyword? \\ false)
+  defp normalize_kw_args(elems, state, keyword?)
 
   defp normalize_kw_args(
          [{{:__block__, key_meta, [key]}, value} = first | rest] = current,
@@ -494,7 +520,7 @@ defmodule Code.Normalizer do
   end
 
   defp maybe_escape_literal(string, %{escape: true}) when is_binary(string) do
-    {string, _} = Code.Identifier.escape(string, -1)
+    {string, _} = Code.Identifier.escape(string, nil)
     IO.iodata_to_binary(string)
   end
 

lib/elixir/lib/code/typespec.ex

@@ -174,9 +174,11 @@ defmodule Code.Typespec do
   end
 
   defp get_module_and_beam(module) when is_atom(module) do
-    case :code.get_object_code(module) do
-      {^module, beam, _filename} -> {module, beam}
-      :error -> :error
+    with {^module, beam, _filename} <- :code.get_object_code(module),
+         {:ok, ^module} <- beam |> :beam_lib.info() |> Keyword.fetch(:module) do
+      {module, beam}
+    else
+      _ -> :error
     end
   end
 

lib/elixir/lib/collectable.ex

@@ -35,7 +35,7 @@ defprotocol Collectable do
       ...>   collector_fun.(acc, {:cont, elem})
       ...> end)
       iex> collector_fun.(updated_acc, :done)
-      #MapSet<[1, 2, 3]>
+      MapSet.new([1, 2, 3])
 
   To show how the protocol can be implemented, we can again look at the
   simplified implementation for `MapSet`. In this implementation "collecting" elements
@@ -63,7 +63,7 @@ defprotocol Collectable do
   So now we can call `Enum.into/2`:
 
       iex> Enum.into([1, 2, 3], MapSet.new())
-      #MapSet<[1, 2, 3]>
+      MapSet.new([1, 2, 3])
 
   """
 

lib/elixir/lib/config.ex

@@ -34,12 +34,12 @@ defmodule Config do
   `Config` also provides a low-level API for evaluating and reading
   configuration, under the `Config.Reader` module.
 
-  **Important:** if you are writing a library to be used by other developers,
-  it is generally recommended to avoid the application environment, as the
-  application environment is effectively a global storage. Also note that
-  the `config/config.exs` of a library is not evaluated when the library is
-  used as a dependency, as configuration is always meant to configure the
-  current project. For more information, read our [library guidelines](library-guidelines.md).
+  > **Important:** if you are writing a library to be used by other developers,
+  > it is generally recommended to avoid the application environment, as the
+  > application environment is effectively a global storage. Also note that
+  > the `config/config.exs` of a library is not evaluated when the library is
+  > used as a dependency, as configuration is always meant to configure the
+  > current project. For more information, read our [library guidelines](library-guidelines.md).
 
   ## Migrating from `use Mix.Config`
 
@@ -62,7 +62,27 @@ defmodule Config do
         import_config config
       end
 
-  The last step is to replace all `Mix.env()` calls by `config_env()`.
+  The last step is to replace all `Mix.env()` calls in the config files with `config_env()`.
+
+  Keep in mind you must also avoid using `Mix.env()` inside your project files.
+  To check the environment at _runtime_, you may add a configuration key:
+
+      # config.exs
+      ...
+      config :my_app, env: config_env()
+
+  Then, in other scripts and modules, you may get the environment with
+  `Application.fetch_env!/2`:
+
+      # router.exs
+      ...
+      if Application.fetch_env!(:my_app, :env) == :prod do
+        ...
+      end
+
+  The only files where you may access functions from the `Mix` module are
+  the `mix.exs` file and inside custom Mix tasks, which always within the
+  `Mix.Tasks` namespace.
 
   ## config/runtime.exs
 
@@ -145,16 +165,24 @@ defmodule Config do
 
       config :ecto, Repo,
         log_level: :warn,
-        adapter: Ecto.Adapters.Postgres
+        adapter: Ecto.Adapters.Postgres,
+        metadata: [read_only: true]
 
       config :ecto, Repo,
         log_level: :info,
-        pool_size: 10
+        pool_size: 10,
+        metadata: [replica: true]
 
   will have a final value of the configuration for the `Repo`
   key in the `:ecto` application of:
 
-      [log_level: :info, pool_size: 10, adapter: Ecto.Adapters.Postgres]
+      Application.get_env(:ecto, Repo)
+      #=> [
+      #=>   log_level: :info,
+      #=>   pool_size: 10,
+      #=>   adapter: Ecto.Adapters.Postgres,
+      #=>   metadata: [read_only: true, replica: true]
+      #=> ]
 
   """
   @doc since: "1.9.0"
@@ -293,8 +321,6 @@ defmodule Config do
         :ok
     end
 
-    # TODO: Emit a warning if Mix.env() is found in said files in Elixir v1.15.
-    # Note this won't be a deprecation warning as it will always be emitted.
     Code.eval_string(contents, [], file: file)
   end
 

lib/elixir/lib/config/provider.ex

@@ -341,8 +341,7 @@ defmodule Config.Provider do
   defp restart_and_sleep() do
     mode = Application.get_env(:elixir, @reboot_mode_key)
 
-    # TODO: Remove otp_release check once we require Erlang/OTP 23+
-    if :erlang.system_info(:otp_release) >= '23' and mode in [:embedded, :interactive] do
+    if mode in [:embedded, :interactive] do
       :init.restart(mode: mode)
     else
       :init.restart()
@@ -410,7 +409,7 @@ defmodule Config.Provider do
   end
 
   defp abort(msg) do
-    IO.puts(:stderr, "ERROR! " <> msg)
+    IO.puts("ERROR! " <> msg)
     :erlang.raise(:error, "aborting boot", [{Config.Provider, :boot, 2, []}])
   end
 end

lib/elixir/lib/config/reader.ex

@@ -37,7 +37,7 @@ defmodule Config.Reader do
       ]
 
   Remember Mix already loads `config/runtime.exs` by default.
-  For more examples and scenarios, see the `Config.Providers` module.
+  For more examples and scenarios, see the `Config.Provider` module.
   """
 
   @behaviour Config.Provider

lib/elixir/lib/dict.ex

@@ -23,7 +23,7 @@ defmodule Dict do
     import Kernel, except: [size: 1]
 
     if __CALLER__.module != HashDict do
-      IO.warn("use Dict is deprecated. " <> unquote(message), Macro.Env.stacktrace(__CALLER__))
+      IO.warn("use Dict is deprecated. " <> unquote(message), __CALLER__)
     end
 
     quote do

lib/elixir/lib/dynamic_supervisor.ex

@@ -1,21 +1,21 @@
 defmodule DynamicSupervisor do
   @moduledoc ~S"""
-  A supervisor that starts children dynamically.
+  A supervisor optimized to only start children dynamically.
 
   The `Supervisor` module was designed to handle mostly static children
   that are started in the given order when the supervisor starts. A
   `DynamicSupervisor` starts with no children. Instead, children are
-  started on demand via `start_child/2`. When a dynamic supervisor
-  terminates, all children are shut down at the same time, with no guarantee
-  of ordering.
+  started on demand via `start_child/2` and there is no ordering between
+  children. This allows the `DynamicSupervisor` to hold millions of
+  children by using efficient data structures and to execute certain
+  operations, such as shutting down, concurrently.
 
   ## Examples
 
-  A dynamic supervisor is started with no children, a supervision strategy
-  (the only strategy currently supported is `:one_for_one`), and a name:
+  A dynamic supervisor is started with no children and often a name:
 
       children = [
-        {DynamicSupervisor, strategy: :one_for_one, name: MyApp.DynamicSupervisor}
+        {DynamicSupervisor, name: MyApp.DynamicSupervisor}
       ]
 
       Supervisor.start_link(children, strategy: :one_for_one)
@@ -37,6 +37,46 @@ defmodule DynamicSupervisor do
       DynamicSupervisor.count_children(MyApp.DynamicSupervisor)
       #=> %{active: 2, specs: 2, supervisors: 0, workers: 2}
 
+  ## Scalability and partitioning
+
+  The `DynamicSupervisor` is a single process responsible for starting
+  other processes. In some applications, the `DynamicSupervisor` may
+  become a bottleneck. To address this, you can start multiple instances
+  of the `DynamicSupervisor` and then pick a "random" instance to start
+  the child on.
+
+  Instead of:
+
+      children = [
+        {DynamicSupervisor, name: MyApp.DynamicSupervisor}
+      ]
+
+  and:
+
+      DynamicSupervisor.start_child(MyApp.DynamicSupervisor, {Agent, fn -> %{} end})
+
+  You can do this:
+
+      children = [
+        {PartitionSupervisor,
+         child_spec: DynamicSupervisor,
+         name: MyApp.DynamicSupervisors}
+      ]
+
+  and then:
+
+      DynamicSupervisor.start_child(
+        {:via, PartitionSupervisor, {MyApp.DynamicSupervisors, self()}},
+        {Agent, fn -> %{} end}
+      )
+
+  In the code above, we start a partition supervisor that will by default
+  start a dynamic supervisor for each core in your machine. Then, instead
+  of calling the `DynamicSupervisor` by name, you call it through the
+  partition supervisor, using `self()` as the routing key. This means each
+  process will be assigned one of the existing dynamic supervisors.
+  Read the `PartitionSupervisor` docs for more information.
+
   ## Module-based supervisors
 
   Similar to `Supervisor`, dynamic supervisors also support module-based
@@ -232,12 +272,74 @@ defmodule DynamicSupervisor do
   @doc """
   Starts a supervisor with the given options.
 
-  The `:strategy` is a required option and the currently supported
-  value is `:one_for_one`. The remaining options can be found in the
-  `init/1` docs.
+  This function is typically not invoked directly, instead it is invoked
+  when using a `DynamicSupervisor` as a child of another supervisor:
 
-  The `:name` option can also be used to register a supervisor name.
-  The supported values are described under the "Name registration"
+      children = [
+        {DynamicSupervisor, name: MySupervisor}
+      ]
+
+  If the supervisor is successfully spawned, this function returns
+  `{:ok, pid}`, where `pid` is the PID of the supervisor. If the supervisor
+  is given a name and a process with the specified name already exists,
+  the function returns `{:error, {:already_started, pid}}`, where `pid`
+  is the PID of that process.
+
+  Note that a supervisor started with this function is linked to the parent
+  process and exits not only on crashes but also if the parent process exits
+  with `:normal` reason.
+
+  ## Options
+
+    * `:name` - registers the supervisor under the given name.
+      The supported values are described under the "Name registration"
+      section in the `GenServer` module docs.
+
+    * `:strategy` - the restart strategy option. The only supported
+      value is `:one_for_one` which means that no other child is
+      terminated if a child process terminates. You can learn more
+      about strategies in the `Supervisor` module docs.
+
+    * `:max_restarts` - the maximum number of restarts allowed in
+      a time frame. Defaults to `3`.
+
+    * `:max_seconds` - the time frame in which `:max_restarts` applies.
+      Defaults to `5`.
+
+    * `:max_children` - the maximum amount of children to be running
+      under this supervisor at the same time. When `:max_children` is
+      exceeded, `start_child/2` returns `{:error, :max_children}`. Defaults
+      to `:infinity`.
+
+    * `:extra_arguments` - arguments that are prepended to the arguments
+      specified in the child spec given to `start_child/2`. Defaults to
+      an empty list.
+
+  """
+  @doc since: "1.6.0"
+  @spec start_link([option | init_option]) :: Supervisor.on_start()
+  def start_link(options) when is_list(options) do
+    keys = [:extra_arguments, :max_children, :max_seconds, :max_restarts, :strategy]
+    {sup_opts, start_opts} = Keyword.split(options, keys)
+    start_link(Supervisor.Default, init(sup_opts), start_opts)
+  end
+
+  @doc """
+  Starts a module-based supervisor process with the given `module` and `init_arg`.
+
+  To start the supervisor, the `c:init/1` callback will be invoked in the given
+  `module`, with `init_arg` as its argument. The `c:init/1` callback must return a
+  supervisor specification which can be created with the help of the `init/1`
+  function.
+
+  If the `c:init/1` callback returns `:ignore`, this function returns
+  `:ignore` as well and the supervisor terminates with reason `:normal`.
+  If it fails or returns an incorrect value, this function returns
+  `{:error, term}` where `term` is a term with information about the
+  error, and the supervisor terminates with reason `term`.
+
+  The `:name` option can also be given in order to register a supervisor
+  name, the supported values are described in the "Name registration"
   section in the `GenServer` module docs.
 
   If the supervisor is successfully spawned, this function returns
@@ -251,35 +353,9 @@ defmodule DynamicSupervisor do
   with `:normal` reason.
   """
   @doc since: "1.6.0"
-  @spec start_link([option | init_option]) :: Supervisor.on_start()
-  def start_link(options) when is_list(options) do
-    keys = [:extra_arguments, :max_children, :max_seconds, :max_restarts, :strategy]
-    {sup_opts, start_opts} = Keyword.split(options, keys)
-    start_link(Supervisor.Default, init(sup_opts), start_opts)
-  end
-
-  @doc """
-  Starts a module-based supervisor process with the given `module` and `arg`.
-
-  To start the supervisor, the `c:init/1` callback will be invoked in the given
-  `module`, with `arg` as its argument. The `c:init/1` callback must return a
-  supervisor specification which can be created with the help of the `init/1`
-  function.
-
-  If the `c:init/1` callback returns `:ignore`, this function returns
-  `:ignore` as well and the supervisor terminates with reason `:normal`.
-  If it fails or returns an incorrect value, this function returns
-  `{:error, term}` where `term` is a term with information about the
-  error, and the supervisor terminates with reason `term`.
-
-  The `:name` option can also be given in order to register a supervisor
-  name, the supported values are described in the "Name registration"
-  section in the `GenServer` module docs.
-  """
-  @doc since: "1.6.0"
   @spec start_link(module, term, [option]) :: Supervisor.on_start()
-  def start_link(mod, init_arg, opts \\ []) do
-    GenServer.start_link(__MODULE__, {mod, init_arg, opts[:name]}, opts)
+  def start_link(module, init_arg, opts \\ []) do
+    GenServer.start_link(__MODULE__, {module, init_arg, opts[:name]}, opts)
   end
 
   @doc """
@@ -287,7 +363,9 @@ defmodule DynamicSupervisor do
 
   `child_spec` should be a valid child specification as detailed in the
   "Child specification" section of the documentation for `Supervisor`. The child
-  process will be started as defined in the child specification.
+  process will be started as defined in the child specification. Note that while
+  the `:id` field is still required in the spec, the value is ignored and
+  therefore does not need to be unique.
 
   If the child process start function returns `{:ok, child}` or `{:ok, child,
   info}`, then child specification and PID are added to the supervisor and
@@ -476,46 +554,20 @@ defmodule DynamicSupervisor do
   module-based supervisors. See the "Module-based supervisors" section
   in the module documentation for more information.
 
-  The `options` received by this function are also supported by `start_link/1`.
-
-  This function returns a tuple containing the supervisor options.
+  It accepts the same `options` as `start_link/1` (except for `:name`)
+  and it returns a tuple containing the supervisor options.
 
   ## Examples
 
       def init(_arg) do
-        DynamicSupervisor.init(max_children: 1000, strategy: :one_for_one)
+        DynamicSupervisor.init(max_children: 1000)
       end
 
-  ## Options
-
-    * `:strategy` - the restart strategy option. The only supported
-      value is `:one_for_one` which means that no other child is
-      terminated if a child process terminates. You can learn more
-      about strategies in the `Supervisor` module docs.
-
-    * `:max_restarts` - the maximum number of restarts allowed in
-      a time frame. Defaults to `3`.
-
-    * `:max_seconds` - the time frame in which `:max_restarts` applies.
-      Defaults to `5`.
-
-    * `:max_children` - the maximum amount of children to be running
-      under this supervisor at the same time. When `:max_children` is
-      exceeded, `start_child/2` returns `{:error, :max_children}`. Defaults
-      to `:infinity`.
-
-    * `:extra_arguments` - arguments that are prepended to the arguments
-      specified in the child spec given to `start_child/2`. Defaults to
-      an empty list.
-
   """
   @doc since: "1.6.0"
   @spec init([init_option]) :: {:ok, sup_flags()}
   def init(options) when is_list(options) do
-    unless strategy = options[:strategy] do
-      raise ArgumentError, "expected :strategy option to be given"
-    end
-
+    strategy = Keyword.get(options, :strategy, :one_for_one)
     intensity = Keyword.get(options, :max_restarts, 3)
     period = Keyword.get(options, :max_seconds, 5)
     max_children = Keyword.get(options, :max_children, :infinity)

lib/elixir/lib/enum.ex

@@ -37,6 +37,23 @@ defprotocol Enumerable do
   than linear time.
   """
 
+  @typedoc """
+  An enumerable of elements of type `element`.
+
+  This type is equivalent to `t:t/0` but is especially useful for documentation.
+
+  For example, imagine you define a function that expects an enumerable of
+  integers and returns an enumerable of strings:
+
+      @spec integers_to_strings(Enumerable.t(integer())) :: Enumerable.t(String.t())
+      def integers_to_strings(integers) do
+        Stream.map(integers, &Integer.to_string/1)
+      end
+
+  """
+  @typedoc since: "1.14.0"
+  @type t(_element) :: t()
+
   @typedoc """
   The accumulator value for each step.
 
@@ -105,18 +122,24 @@ defprotocol Enumerable do
   @type continuation :: (acc -> result)
 
   @typedoc """
-  A slicing function that receives the initial position and the
-  number of elements in the slice.
+  A slicing function that receives the initial position,
+  the number of elements in the slice, and the step.
 
   The `start` position is a number `>= 0` and guaranteed to
-  exist in the `enumerable`. The length is a number `>= 1` in a way
-  that `start + length <= count`, where `count` is the maximum
-  amount of elements in the enumerable.
+  exist in the `enumerable`. The length is a number `>= 1`
+  in a way that `start + length * step <= count`, where
+  `count` is the maximum amount of elements in the enumerable.
 
   The function should return a non empty list where
   the amount of elements is equal to `length`.
   """
-  @type slicing_fun :: (start :: non_neg_integer, length :: pos_integer -> [term()])
+  @type slicing_fun ::
+          (start :: non_neg_integer, length :: pos_integer, step :: pos_integer -> [term()])
+
+  @typedoc """
+  Receives an enumerable and returns a list.
+  """
+  @type to_list_fun :: (t -> [term()])
 
   @doc """
   Reduces the `enumerable` into an element.
@@ -146,7 +169,7 @@ defprotocol Enumerable do
   Retrieves the number of elements in the `enumerable`.
 
   It should return `{:ok, count}` if you can count the number of elements
-  in `enumerable` without traversing it.
+  in `enumerable` in a faster way than fully traversing it.
 
   Otherwise it should return `{:error, __MODULE__}` and a default algorithm
   built on top of `reduce/3` that runs in linear time will be used.
@@ -173,28 +196,36 @@ defprotocol Enumerable do
   @doc """
   Returns a function that slices the data structure contiguously.
 
-  It should return `{:ok, size, slicing_fun}` if the `enumerable` has
-  a known bound and can access a position in the `enumerable` without
-  traversing all previous elements.
+  It should return either:
 
-  Otherwise it should return `{:error, __MODULE__}` and a default
-  algorithm built on top of `reduce/3` that runs in linear time will be
-  used.
+    * `{:ok, size, slicing_fun}` - if the `enumerable` has a known
+      bound and can access a position in the `enumerable` without
+      traversing all previous elements. The `slicing_fun` will receive
+      a `start` position, the `amount` of elements to fetch, and a
+      `step`.
+
+    * `{:ok, size, to_list_fun}` - if the `enumerable` has a known bound
+      and can access a position in the `enumerable` by first converting
+      it to a list via `to_list_fun`.
+
+    * `{:error, __MODULE__}` - the enumerable cannot be sliced efficiently
+      and a default algorithm built on top of `reduce/3` that runs in
+      linear time will be used.
 
   ## Differences to `count/1`
 
   The `size` value returned by this function is used for boundary checks,
   therefore it is extremely important that this function only returns `:ok`
-  if retrieving the `size` of the `enumerable` is cheap, fast and takes constant
-  time. Otherwise the simplest of operations, such as `Enum.at(enumerable, 0)`,
-  will become too expensive.
+  if retrieving the `size` of the `enumerable` is cheap, fast, and takes
+  constant time. Otherwise the simplest of operations, such as
+  `Enum.at(enumerable, 0)`, will become too expensive.
 
   On the other hand, the `count/1` function in this protocol should be
-  implemented whenever you can count the number of elements in the collection without
-  traversing it.
+  implemented whenever you can count the number of elements in the collection
+  without traversing it.
   """
   @spec slice(t) ::
-          {:ok, size :: non_neg_integer(), slicing_fun()}
+          {:ok, size :: non_neg_integer(), slicing_fun() | to_list_fun()}
           | {:error, module()}
   def slice(enumerable)
 end
@@ -203,7 +234,7 @@ defmodule Enum do
   import Kernel, except: [max: 2, min: 2]
 
   @moduledoc """
-  Provides a set of algorithms to work with enumerables.
+  Functions for working with collections (known as enumerables).
 
   In Elixir, an enumerable is any data type that implements the
   `Enumerable` protocol. `List`s (`[1, 2, 3]`), `Map`s (`%{foo: 1, bar: 2}`)
@@ -434,7 +465,7 @@ defmodule Enum do
   """
   @spec at(t, index, default) :: element | default
   def at(enumerable, index, default \\ nil) when is_integer(index) do
-    case slice_any(enumerable, index, 1) do
+    case slice_forward(enumerable, index, 1, 1) do
       [value] -> value
       [] -> default
     end
@@ -498,6 +529,9 @@ defmodule Enum do
       iex> Enum.chunk_every([1, 2, 3, 4, 5], 2, 3, [])
       [[1, 2], [4, 5]]
 
+      iex> Enum.chunk_every([1, 2, 3, 4], 3, 3, Stream.cycle([0]))
+      [[1, 2, 3], [4, 0, 0]]
+
   """
   @doc since: "1.5.0"
   @spec chunk_every(t, pos_integer, pos_integer, t | :discard) :: [list]
@@ -617,7 +651,7 @@ defmodule Enum do
   Concatenates the enumerable on the `right` with the enumerable on the
   `left`.
 
-  This function produces the same result as the `Kernel.++/2` operator
+  This function produces the same result as the `++/2` operator
   for lists.
 
   ## Examples
@@ -850,17 +884,21 @@ defmodule Enum do
     drop_list(enumerable, amount)
   end
 
-  def drop(enumerable, amount) when is_integer(amount) and amount >= 0 do
+  def drop(enumerable, 0) do
+    to_list(enumerable)
+  end
+
+  def drop(enumerable, amount) when is_integer(amount) and amount > 0 do
     {result, _} = reduce(enumerable, {[], amount}, R.drop())
     if is_list(result), do: :lists.reverse(result), else: []
   end
 
   def drop(enumerable, amount) when is_integer(amount) and amount < 0 do
-    {count, fun} = slice_count_and_fun(enumerable)
+    {count, fun} = slice_count_and_fun(enumerable, 1)
     amount = Kernel.min(amount + count, count)
 
     if amount > 0 do
-      fun.(0, amount)
+      fun.(0, amount, 1)
     else
       []
     end
@@ -1003,7 +1041,7 @@ defmodule Enum do
   """
   @spec fetch(t, index) :: {:ok, element} | :error
   def fetch(enumerable, index) when is_integer(index) do
-    case slice_any(enumerable, index, 1) do
+    case slice_forward(enumerable, index, 1, 1) do
       [value] -> {:ok, value}
       [] -> :error
     end
@@ -1029,7 +1067,7 @@ defmodule Enum do
   """
   @spec fetch!(t, index) :: element
   def fetch!(enumerable, index) when is_integer(index) do
-    case slice_any(enumerable, index, 1) do
+    case slice_forward(enumerable, index, 1, 1) do
       [value] -> value
       [] -> raise Enum.OutOfBoundsError
     end
@@ -1460,9 +1498,27 @@ defmodule Enum do
   defp into_protocol(enumerable, collectable) do
     {initial, fun} = Collectable.into(collectable)
 
-    into_protocol(enumerable, initial, fun, fn entry, acc ->
-      fun.(acc, {:cont, entry})
+    try do
+      reduce_into_protocol(enumerable, initial, fun)
+    catch
+      kind, reason ->
+        fun.(initial, :halt)
+        :erlang.raise(kind, reason, __STACKTRACE__)
+    else
+      acc -> fun.(acc, :done)
+    end
+  end
+
+  defp reduce_into_protocol(enumerable, initial, fun) when is_list(enumerable) do
+    :lists.foldl(fn x, acc -> fun.(acc, {:cont, x}) end, initial, enumerable)
+  end
+
+  defp reduce_into_protocol(enumerable, initial, fun) do
+    enumerable
+    |> Enumerable.reduce({:cont, initial}, fn x, acc ->
+      {:cont, fun.(acc, {:cont, x})}
     end)
+    |> elem(1)
   end
 
   @doc """
@@ -1509,14 +1565,8 @@ defmodule Enum do
   defp into_protocol(enumerable, collectable, transform) do
     {initial, fun} = Collectable.into(collectable)
 
-    into_protocol(enumerable, initial, fun, fn entry, acc ->
-      fun.(acc, {:cont, transform.(entry)})
-    end)
-  end
-
-  defp into_protocol(enumerable, initial, fun, callback) do
     try do
-      reduce(enumerable, initial, callback)
+      reduce_into_protocol(enumerable, initial, transform, fun)
     catch
       kind, reason ->
         fun.(initial, :halt)
@@ -1526,6 +1576,18 @@ defmodule Enum do
     end
   end
 
+  defp reduce_into_protocol(enumerable, initial, transform, fun) when is_list(enumerable) do
+    :lists.foldl(fn x, acc -> fun.(acc, {:cont, transform.(x)}) end, initial, enumerable)
+  end
+
+  defp reduce_into_protocol(enumerable, initial, transform, fun) do
+    enumerable
+    |> Enumerable.reduce({:cont, initial}, fn x, acc ->
+      {:cont, fun.(acc, {:cont, transform.(x)})}
+    end)
+    |> elem(1)
+  end
+
   @doc """
   Joins the given `enumerable` into a string using `joiner` as a
   separator.
@@ -1543,6 +1605,9 @@ defmodule Enum do
       iex> Enum.join([1, 2, 3], " = ")
       "1 = 2 = 3"
 
+      iex> Enum.join([["a", "b"], ["c", "d", "e", ["f", "g"]], "h", "i"], " ")
+      "ab cdefg h i"
+
   """
   @spec join(t, String.t()) :: String.t()
   def join(enumerable, joiner \\ "")
@@ -2292,9 +2357,16 @@ defmodule Enum do
         {:ok, 0, _} ->
           []
 
-        {:ok, count, fun} when is_function(fun) ->
+        {:ok, count, fun} when is_function(fun, 1) ->
+          slice_list(fun.(enumerable), random_integer(0, count - 1), 1, 1)
+
+        # TODO: Deprecate me in Elixir v1.18.
+        {:ok, count, fun} when is_function(fun, 2) ->
           fun.(random_integer(0, count - 1), 1)
 
+        {:ok, count, fun} when is_function(fun, 3) ->
+          fun.(random_integer(0, count - 1), 1, 1)
+
         {:error, _} ->
           take_random(enumerable, 1)
       end
@@ -2573,7 +2645,13 @@ defmodule Enum do
       iex> Enum.slide([:a, :b, :c, :d, :e, :f, :g], -4..-2, 1)
       [:a, :d, :e, :f, :b, :c, :g]
 
+      # Insert at negative indices (counting from the end)
+      iex> Enum.slide([:a, :b, :c, :d, :e, :f, :g], 3, -1)
+      [:a, :b, :c, :e, :f, :g, :d]
+
   """
+  @doc since: "1.13.0"
+  @spec slide(t, Range.t() | index, index) :: list
   def slide(enumerable, range_or_single_index, insertion_index)
 
   def slide(enumerable, single_index, insertion_index) when is_integer(single_index) do
@@ -2587,14 +2665,18 @@ defmodule Enum do
   end
 
   # Normalize negative input ranges like Enum.slice/2
-  def slide(enumerable, first..last, insertion_index) when first < 0 or last < 0 do
+  def slide(enumerable, first..last, insertion_index)
+      when first < 0 or last < 0 or insertion_index < 0 do
     count = Enum.count(enumerable)
-    normalized_first = if first >= 0, do: first, else: first + count
+    normalized_first = if first >= 0, do: first, else: Kernel.max(first + count, 0)
     normalized_last = if last >= 0, do: last, else: last + count
 
-    if normalized_first >= 0 and normalized_first < count and normalized_first != insertion_index do
+    normalized_insertion_index =
+      if insertion_index >= 0, do: insertion_index, else: insertion_index + count
+
+    if normalized_first < count and normalized_first != normalized_insertion_index do
       normalized_range = normalized_first..normalized_last//1
-      slide(enumerable, normalized_range, insertion_index)
+      slide(enumerable, normalized_range, normalized_insertion_index)
     else
       Enum.to_list(enumerable)
     end
@@ -2605,11 +2687,16 @@ defmodule Enum do
   end
 
   def slide(_, first..last, insertion_index)
-      when insertion_index > first and insertion_index < last do
-    raise "Insertion index for slide must be outside the range being moved " <>
+      when insertion_index > first and insertion_index <= last do
+    raise ArgumentError,
+          "insertion index for slide must be outside the range being moved " <>
             "(tried to insert #{first}..#{last} at #{insertion_index})"
   end
 
+  def slide(enumerable, first..last, _insertion_index) when first > last do
+    Enum.to_list(enumerable)
+  end
+
   # Guarantees at this point: step size == 1 and first <= last and (insertion_index < first or insertion_index > last)
   def slide(enumerable, first..last, insertion_index) do
     impl = if is_list(enumerable), do: &slide_list_start/4, else: &slide_any/4
@@ -2658,6 +2745,7 @@ defmodule Enum do
   end
 
   defp slide_list_start(list, 0, middle, last), do: slide_list_middle(list, middle, last, [])
+  defp slide_list_start([], _start, _middle, _last), do: []
 
   defp slide_list_middle([h | t], middle, last, acc) when middle > 0 do
     slide_list_middle(t, middle - 1, last - 1, [h | acc])
@@ -2780,31 +2868,49 @@ defmodule Enum do
   `enumerable`, or this one is greater than the normalized `index_range.last`,
   then `[]` is returned.
 
+  If a step `n` (other than `1`) is used in `index_range`, then it takes
+  every `n`th element from `index_range.first` to `index_range.last`
+  (according to the same rules described above).
+
   ## Examples
 
-      iex> Enum.slice(1..100, 5..10)
-      [6, 7, 8, 9, 10, 11]
+      iex> Enum.slice([1, 2, 3, 4, 5], 1..3)
+      [2, 3, 4]
 
-      iex> Enum.slice(1..10, 5..20)
-      [6, 7, 8, 9, 10]
+      iex> Enum.slice([1, 2, 3, 4, 5], 3..10)
+      [4, 5]
 
-      # last five elements (negative indexes)
-      iex> Enum.slice(1..30, -5..-1)
-      [26, 27, 28, 29, 30]
+      # Last three elements (negative indexes)
+      iex> Enum.slice([1, 2, 3, 4, 5], -3..-1)
+      [3, 4, 5]
 
   For ranges where `start > stop`, you need to explicit
   mark them as increasing:
 
-      iex> Enum.slice(1..30, 25..-1//1)
-      [26, 27, 28, 29, 30]
+      iex> Enum.slice([1, 2, 3, 4, 5], 1..-2//1)
+      [2, 3, 4]
 
-  If values are out of bounds, it returns an empty list:
+  The step can be any positive number. For example, to
+  get every 2 elements of the collection:
 
-      iex> Enum.slice(1..10, 11..20)
+      iex> Enum.slice([1, 2, 3, 4, 5], 0..-1//2)
+      [1, 3, 5]
+
+  To get every third element of the first ten elements:
+
+      iex> integers = Enum.to_list(1..20)
+      iex> Enum.slice(integers, 0..9//3)
+      [1, 4, 7, 10]
+
+  If the first position is after the end of the enumerable
+  or after the last position of the range, it returns an
+  empty list:
+
+      iex> Enum.slice([1, 2, 3, 4, 5], 6..10)
       []
 
       # first is greater than last
-      iex> Enum.slice(1..10, 6..5)
+      iex> Enum.slice([1, 2, 3, 4, 5], 6..5)
       []
 
   """
@@ -2812,16 +2918,17 @@ defmodule Enum do
   @spec slice(t, Range.t()) :: list
   def slice(enumerable, first..last//step = index_range) do
     # TODO: Deprecate negative steps on Elixir v1.16
-    # TODO: There are two features we can add to slicing ranges:
-    # 1. We can allow the step to be any positive number
-    # 2. We can allow slice and reverse at the same time. However, we can't
-    #    implement so right now. First we will have to raise if a decreasing
-    #    range is given on Elixir v2.0.
-    if step == 1 or (step == -1 and first > last) do
-      slice_range(enumerable, first, last)
-    else
-      raise ArgumentError,
-            "Enum.slice/2 does not accept ranges with custom steps, got: #{inspect(index_range)}"
+    # TODO: Support negative steps as a reverse on Elixir v2.0.
+    cond do
+      step > 0 ->
+        slice_range(enumerable, first, last, step)
+
+      step == -1 and first > last ->
+        slice_range(enumerable, first, last, 1)
+
+      true ->
+        raise ArgumentError,
+              "Enum.slice/2 does not accept ranges with negative steps, got: #{inspect(index_range)}"
     end
   end
 
@@ -2831,18 +2938,29 @@ defmodule Enum do
     slice(enumerable, Map.put(index_range, :step, step))
   end
 
-  defp slice_range(enumerable, first, last) when last >= first and last >= 0 and first >= 0 do
-    slice_any(enumerable, first, last - first + 1)
+  defp slice_range(enumerable, first, -1, step) when first >= 0 do
+    if step == 1 do
+      drop(enumerable, first)
+    else
+      enumerable |> drop(first) |> take_every_list(step - 1)
+    end
   end
 
-  defp slice_range(enumerable, first, last) do
-    {count, fun} = slice_count_and_fun(enumerable)
-    first = if first >= 0, do: first, else: first + count
+  defp slice_range(enumerable, first, last, step)
+       when last >= first and last >= 0 and first >= 0 do
+    slice_forward(enumerable, first, last - first + 1, step)
+  end
+
+  defp slice_range(enumerable, first, last, step) do
+    {count, fun} = slice_count_and_fun(enumerable, step)
+    first = if first >= 0, do: first, else: Kernel.max(first + count, 0)
     last = if last >= 0, do: last, else: last + count
     amount = last - first + 1
 
-    if first >= 0 and first < count and amount > 0 do
-      fun.(first, Kernel.min(amount, count - first))
+    if first < count and amount > 0 do
+      amount = Kernel.min(amount, count - first)
+      amount = if step == 1, do: amount, else: div(amount - 1, step) + 1
+      fun.(first, amount, step)
     else
       []
     end
@@ -2877,22 +2995,33 @@ defmodule Enum do
       # using a negative start index
       iex> Enum.slice(1..10, -6, 3)
       [5, 6, 7]
-
-      # out of bound start index (positive)
-      iex> Enum.slice(1..10, 10, 5)
-      []
-
-      # out of bound start index (negative)
       iex> Enum.slice(1..10, -11, 5)
+      [1, 2, 3, 4, 5]
+
+      # out of bound start index
+      iex> Enum.slice(1..10, 10, 5)
       []
 
   """
   @spec slice(t, index, non_neg_integer) :: list
   def slice(_enumerable, start_index, 0) when is_integer(start_index), do: []
 
+  def slice(enumerable, start_index, amount)
+      when is_integer(start_index) and start_index < 0 and is_integer(amount) and amount >= 0 do
+    {count, fun} = slice_count_and_fun(enumerable, 1)
+    start_index = Kernel.max(count + start_index, 0)
+    amount = Kernel.min(amount, count - start_index)
+
+    if amount > 0 do
+      fun.(start_index, amount, 1)
+    else
+      []
+    end
+  end
+
   def slice(enumerable, start_index, amount)
       when is_integer(start_index) and is_integer(amount) and amount >= 0 do
-    slice_any(enumerable, start_index, amount)
+    slice_forward(enumerable, start_index, amount, 1)
   end
 
   @doc """
@@ -2941,10 +3070,10 @@ defmodule Enum do
       iex> Enum.sort(["some", "kind", "of", "monster"], &(byte_size(&1) < byte_size(&2)))
       ["of", "kind", "some", "monster"]
 
-  ## Ascending and descending
+  ## Ascending and descending (since v1.10.0)
 
-  `sort/2` allows a developer to pass `:asc` or `:desc` as the sorting
-  function, which is a convenience for `<=/2` and `>=/2` respectively.
+  `sort/2` allows a developer to pass `:asc` or `:desc` as the sorter, which is a convenience for
+  [`&<=/2`](`<=/2`) and [`&>=/2`](`>=/2`) respectively.
 
       iex> Enum.sort([2, 3, 1], :asc)
       [1, 2, 3]
@@ -2992,12 +3121,12 @@ defmodule Enum do
           t,
           (element, element -> boolean) | :asc | :desc | module() | {:asc | :desc, module()}
         ) :: list
-  def sort(enumerable, fun) when is_list(enumerable) do
-    :lists.sort(to_sort_fun(fun), enumerable)
+  def sort(enumerable, sorter) when is_list(enumerable) do
+    :lists.sort(to_sort_fun(sorter), enumerable)
   end
 
-  def sort(enumerable, fun) do
-    fun = to_sort_fun(fun)
+  def sort(enumerable, sorter) do
+    fun = to_sort_fun(sorter)
 
     reduce(enumerable, [], &sort_reducer(&1, &2, fun))
     |> sort_terminator(fun)
@@ -3016,17 +3145,27 @@ defmodule Enum do
 
   This function maps each element of the `enumerable` using the
   provided `mapper` function. The enumerable is then sorted by
-  the mapped elements using the `sorter` function, which defaults
-  to `Kernel.<=/2`.
+  the mapped elements using the `sorter`, which defaults to `:asc`
+  and sorts the elements ascendingly.
 
   `sort_by/3` differs from `sort/2` in that it only calculates the
   comparison value for each element in the enumerable once instead of
   once for each element in each comparison. If the same function is
   being called on both elements, it's more efficient to use `sort_by/3`.
 
+  ## Ascending and descending (since v1.10.0)
+
+  `sort_by/3` allows a developer to pass `:asc` or `:desc` as the sorter,
+  which is a convenience for [`&<=/2`](`<=/2`) and [`&>=/2`](`>=/2`) respectively:
+      iex> Enum.sort_by([2, 3, 1], &(&1), :asc)
+      [1, 2, 3]
+
+      iex> Enum.sort_by([2, 3, 1], &(&1), :desc)
+      [3, 2, 1]
+
   ## Examples
 
-  Using the default `sorter` of `<=/2`:
+  Using the default `sorter` of `:asc` :
 
       iex> Enum.sort_by(["some", "kind", "of", "monster"], &byte_size/1)
       ["of", "some", "kind", "monster"]
@@ -3039,19 +3178,15 @@ defmodule Enum do
 
   Similar to `sort/2`, you can pass a custom sorter:
 
-      iex> Enum.sort_by(["some", "kind", "of", "monster"], &byte_size/1, &>=/2)
-      ["monster", "some", "kind", "of"]
-
-  Or use `:asc` and `:desc`:
-
       iex> Enum.sort_by(["some", "kind", "of", "monster"], &byte_size/1, :desc)
       ["monster", "some", "kind", "of"]
 
-  As in `sort/2`, avoid using the default sorting function to sort structs, as by default
-  it performs structural comparison instead of a semantic one. In such cases,
-  you shall pass a sorting function as third element or any module that implements
-  a `compare/2` function. For example, to sort users by their birthday in both
-  ascending and descending order respectively:
+  As in `sort/2`, avoid using the default sorting function to sort
+  structs, as by default it performs structural comparison instead of
+  a semantic one. In such cases, you shall pass a sorting function as
+  third element or any module that implements a `compare/2` function.
+  For example, to sort users by their birthday in both ascending and
+  descending order respectively:
 
       iex> users = [
       ...>   %{name: "Ellis", birthday: ~D[1943-05-11]},
@@ -3071,6 +3206,42 @@ defmodule Enum do
         %{name: "Lovelace", birthday: ~D[1815-12-10]}
       ]
 
+  ## Performance characteristics
+
+  As detailed in the initial section, `sort_by/3` calculates the comparison
+  value for each element in the enumerable once instead of once for each
+  element in each comparison. This implies `sort_by/3` must do an initial
+  pass on the data to compute those values.
+
+  However, if those values are cheap to compute, for example, you have
+  already extracted the field you want to sort by into a tuple, then those
+  extra passes become overhead. In such cases, consider using `List.keysort/3`
+  instead.
+
+  Let's see an example. Imagine you have a list of products and you have a
+  list of IDs. You want to keep all products that are in the given IDs and
+  return their names sorted by their price. You could write it like this:
+
+      for(
+        product <- products,
+        product.id in ids,
+        do: product
+      )
+      |> Enum.sort_by(& &1.price)
+      |> Enum.map(& &1.name)
+
+  However, you could also write it like this:
+
+      for(
+        product <- products,
+        product.id in ids,
+        do: {product.name, product.price}
+      )
+      |> List.keysort(1)
+      |> Enum.map(&elem(&1, 0))
+
+  Using `List.keysort/3` will be a better choice for performance sensitive
+  code as it avoids additional traversals.
   """
   @spec sort_by(
           t,
@@ -3079,30 +3250,21 @@ defmodule Enum do
         ) ::
           list
         when mapped_element: element
-  def sort_by(enumerable, mapper, sorter \\ &<=/2) do
+  def sort_by(enumerable, mapper, sorter \\ :asc)
+
+  def sort_by(enumerable, mapper, :desc) when is_function(mapper, 1) do
     enumerable
-    |> map(&{&1, mapper.(&1)})
-    |> sort(to_sort_by_fun(sorter))
-    |> map(&elem(&1, 0))
+    |> Enum.reduce([], &[{&1, mapper.(&1)} | &2])
+    |> List.keysort(1, :asc)
+    |> List.foldl([], &[elem(&1, 0) | &2])
   end
 
-  defp to_sort_by_fun(sorter) when is_function(sorter, 2),
-    do: &sorter.(elem(&1, 1), elem(&2, 1))
-
-  defp to_sort_by_fun(:asc),
-    do: &(elem(&1, 1) <= elem(&2, 1))
-
-  defp to_sort_by_fun(:desc),
-    do: &(elem(&1, 1) >= elem(&2, 1))
-
-  defp to_sort_by_fun(module) when is_atom(module),
-    do: &(module.compare(elem(&1, 1), elem(&2, 1)) != :gt)
-
-  defp to_sort_by_fun({:asc, module}) when is_atom(module),
-    do: &(module.compare(elem(&1, 1), elem(&2, 1)) != :gt)
-
-  defp to_sort_by_fun({:desc, module}) when is_atom(module),
-    do: &(module.compare(elem(&1, 1), elem(&2, 1)) != :lt)
+  def sort_by(enumerable, mapper, sorter) when is_function(mapper, 1) do
+    enumerable
+    |> map(&{&1, mapper.(&1)})
+    |> List.keysort(1, sorter)
+    |> map(&elem(&1, 0))
+  end
 
   @doc """
   Splits the `enumerable` into two enumerables, leaving `count`
@@ -3294,9 +3456,9 @@ defmodule Enum do
   end
 
   def take(enumerable, amount) when is_integer(amount) and amount < 0 do
-    {count, fun} = slice_count_and_fun(enumerable)
+    {count, fun} = slice_count_and_fun(enumerable, 1)
     first = Kernel.max(amount + count, 0)
-    fun.(first, count - first)
+    fun.(first, count - first, 1)
   end
 
   @doc """
@@ -3323,9 +3485,12 @@ defmodule Enum do
   @spec take_every(t, non_neg_integer) :: list
   def take_every(enumerable, nth)
 
-  def take_every(enumerable, 1), do: to_list(enumerable)
   def take_every(_enumerable, 0), do: []
-  def take_every([], nth) when is_integer(nth) and nth > 1, do: []
+  def take_every(enumerable, 1), do: to_list(enumerable)
+
+  def take_every(list, nth) when is_list(list) and is_integer(nth) and nth > 1 do
+    take_every_list(list, nth - 1)
+  end
 
   def take_every(enumerable, nth) when is_integer(nth) and nth > 1 do
     {res, _} = reduce(enumerable, {[], :first}, R.take_every(nth))
@@ -3605,6 +3770,14 @@ defmodule Enum do
   @spec with_index(t, (element, index -> value)) :: [value] when value: any
   def with_index(enumerable, fun_or_offset \\ 0)
 
+  def with_index(enumerable, offset) when is_list(enumerable) and is_integer(offset) do
+    with_index_list(enumerable, offset)
+  end
+
+  def with_index(enumerable, fun) when is_list(enumerable) and is_function(fun, 2) do
+    with_index_list(enumerable, 0, fun)
+  end
+
   def with_index(enumerable, offset) when is_integer(offset) do
     enumerable
     |> map_reduce(offset, fn x, i -> {{x, i}, i + 1} end)
@@ -3669,7 +3842,7 @@ defmodule Enum do
   Zips corresponding elements from two enumerables into a list, transforming them with
   the `zip_fun` function as it goes.
 
-  The corresponding elements from each collection are passed to the provided 2-arity `zip_fun`
+  The corresponding elements from each collection are passed to the provided two-arity `zip_fun`
   function in turn. Returns a list that contains the result of calling `zip_fun` for each pair of
   elements.
 
@@ -3720,7 +3893,7 @@ defmodule Enum do
   into list, transforming them with the `zip_fun` function as it goes.
 
   The first element from each of the enums in `enumerables` will be put
-  into a list which is then passed to the 1-arity `zip_fun` function.
+  into a list which is then passed to the one-arity `zip_fun` function.
   Then, the second elements from each of the enums are put into a list
   and passed to `zip_fun`, and so on until any one of the enums in
   `enumerables` runs out of elements.
@@ -4184,35 +4357,63 @@ defmodule Enum do
 
   ## slice
 
-  defp slice_any(enumerable, start, amount) when start < 0 do
-    {count, fun} = slice_count_and_fun(enumerable)
+  defp slice_forward(enumerable, start, amount, step) when start < 0 do
+    {count, fun} = slice_count_and_fun(enumerable, step)
     start = count + start
 
     if start >= 0 do
-      fun.(start, Kernel.min(amount, count - start))
+      amount = Kernel.min(amount, count - start)
+      amount = if step == 1, do: amount, else: div(amount - 1, step) + 1
+      fun.(start, amount, step)
     else
       []
     end
   end
 
-  defp slice_any(list, start, amount) when is_list(list) do
-    list |> drop_list(start) |> take_list(amount)
+  defp slice_forward(list, start, amount, step) when is_list(list) do
+    amount = if step == 1, do: amount, else: div(amount - 1, step) + 1
+    slice_list(list, start, amount, step)
   end
 
-  defp slice_any(enumerable, start, amount) do
+  defp slice_forward(enumerable, start, amount, step) do
     case Enumerable.slice(enumerable) do
       {:ok, count, _} when start >= count ->
         []
 
-      {:ok, count, fun} when is_function(fun) ->
-        fun.(start, Kernel.min(amount, count - start))
+      {:ok, count, fun} when is_function(fun, 1) ->
+        amount = Kernel.min(amount, count - start)
+        enumerable |> fun.() |> slice_exact(start, amount, step, count)
+
+      # TODO: Deprecate me in Elixir v1.18.
+      {:ok, count, fun} when is_function(fun, 2) ->
+        amount = Kernel.min(amount, count - start)
+
+        if step == 1 do
+          fun.(start, amount)
+        else
+          fun.(start, Kernel.min(amount * step, count - start))
+          |> take_every_list(amount, step - 1)
+        end
+
+      {:ok, count, fun} when is_function(fun, 3) ->
+        amount = Kernel.min(amount, count - start)
+        amount = if step == 1, do: amount, else: div(amount - 1, step) + 1
+        fun.(start, amount, step)
 
       {:error, module} ->
-        slice_enum(enumerable, module, start, amount)
+        slice_enum(enumerable, module, start, amount, step)
     end
   end
 
-  defp slice_enum(enumerable, module, start, amount) do
+  defp slice_list(list, start, amount, step) do
+    if step == 1 do
+      list |> drop_list(start) |> take_list(amount)
+    else
+      list |> drop_list(start) |> take_every_list(amount, step - 1)
+    end
+  end
+
+  defp slice_enum(enumerable, module, start, amount, 1) do
     {_, {_, _, slice}} =
       module.reduce(enumerable, {:cont, {start, amount, []}}, fn
         _entry, {start, amount, _list} when start > 0 ->
@@ -4228,26 +4429,86 @@ defmodule Enum do
     :lists.reverse(slice)
   end
 
-  defp slice_count_and_fun(enumerable) when is_list(enumerable) do
-    length = length(enumerable)
-    {length, &Enumerable.List.slice(enumerable, &1, &2, length)}
+  defp slice_enum(enumerable, module, start, amount, step) do
+    {_, {_, _, _, slice}} =
+      module.reduce(enumerable, {:cont, {start, amount, 1, []}}, fn
+        _entry, {start, amount, to_drop, _list} when start > 0 ->
+          {:cont, {start - 1, amount, to_drop, []}}
+
+        entry, {start, amount, to_drop, list} when amount > 1 ->
+          case to_drop do
+            1 -> {:cont, {start, amount - 1, step, [entry | list]}}
+            _ -> {:cont, {start, amount - 1, to_drop - 1, list}}
+          end
+
+        entry, {start, amount, to_drop, list} ->
+          case to_drop do
+            1 -> {:halt, {start, amount, to_drop, [entry | list]}}
+            _ -> {:halt, {start, amount, to_drop, list}}
+          end
+      end)
+
+    :lists.reverse(slice)
   end
 
-  defp slice_count_and_fun(enumerable) do
+  defp slice_count_and_fun(list, _step) when is_list(list) do
+    length = length(list)
+    {length, &slice_exact(list, &1, &2, &3, length)}
+  end
+
+  defp slice_count_and_fun(enumerable, step) do
     case Enumerable.slice(enumerable) do
-      {:ok, count, fun} when is_function(fun, 2) ->
+      {:ok, count, fun} when is_function(fun, 3) ->
         {count, fun}
 
+      # TODO: Deprecate me in Elixir v1.18.
+      {:ok, count, fun} when is_function(fun, 2) ->
+        if step == 1 do
+          {count, fn start, amount, 1 -> fun.(start, amount) end}
+        else
+          {count,
+           fn start, amount, step ->
+             fun.(start, Kernel.min(amount * step, count - start))
+             |> take_every_list(amount, step - 1)
+           end}
+        end
+
+      {:ok, count, fun} when is_function(fun, 1) ->
+        {count, &slice_exact(fun.(enumerable), &1, &2, &3, count)}
+
       {:error, module} ->
-        {_, {list, count}} =
-          module.reduce(enumerable, {:cont, {[], 0}}, fn elem, {acc, count} ->
+        {list, count} =
+          enumerable
+          |> module.reduce({:cont, {[], 0}}, fn elem, {acc, count} ->
             {:cont, {[elem | acc], count + 1}}
           end)
+          |> elem(1)
 
-        {count, &Enumerable.List.slice(:lists.reverse(list), &1, &2, count)}
+        {count,
+         fn start, amount, step ->
+           list |> :lists.reverse() |> slice_exact(start, amount, step, count)
+         end}
     end
   end
 
+  # Slice a list when we know the bounds
+  defp slice_exact(_list, _start, 0, _step, _), do: []
+
+  defp slice_exact(list, start, amount, 1, size) when start + amount == size,
+    do: list |> drop_exact(start)
+
+  defp slice_exact(list, start, amount, 1, _),
+    do: list |> drop_exact(start) |> take_exact(amount)
+
+  defp slice_exact(list, start, amount, step, _),
+    do: list |> drop_exact(start) |> take_every_list(amount, step - 1)
+
+  defp drop_exact(list, 0), do: list
+  defp drop_exact([_ | tail], amount), do: drop_exact(tail, amount - 1)
+
+  defp take_exact(_list, 0), do: []
+  defp take_exact([head | tail], amount), do: [head | take_exact(tail, amount - 1)]
+
   ## sort
 
   defp sort_reducer(entry, {:split, y, x, r, rs, bool}, fun) do
@@ -4392,10 +4653,22 @@ defmodule Enum do
 
   ## take
 
-  defp take_list([head | _], 1), do: [head]
+  defp take_list(_list, 0), do: []
   defp take_list([head | tail], counter), do: [head | take_list(tail, counter - 1)]
   defp take_list([], _counter), do: []
 
+  defp take_every_list([head | tail], to_drop),
+    do: [head | tail |> drop_list(to_drop) |> take_every_list(to_drop)]
+
+  defp take_every_list([], _to_drop), do: []
+
+  defp take_every_list(_list, 0, _to_drop), do: []
+
+  defp take_every_list([head | tail], counter, to_drop),
+    do: [head | tail |> drop_list(to_drop) |> take_every_list(counter - 1, to_drop)]
+
+  defp take_every_list([], _counter, _to_drop), do: []
+
   ## take_while
 
   defp take_while_list([head | tail], fun) do
@@ -4425,6 +4698,20 @@ defmodule Enum do
     []
   end
 
+  ## with_index
+
+  defp with_index_list([head | tail], offset) do
+    [{head, offset} | with_index_list(tail, offset + 1)]
+  end
+
+  defp with_index_list([], _offset), do: []
+
+  defp with_index_list([head | tail], offset, fun) do
+    [fun.(head, offset) | with_index_list(tail, offset + 1, fun)]
+  end
+
+  defp with_index_list([], _offset, _fun), do: []
+
   ## zip
 
   defp zip_list([head1 | next1], [head2 | next2], acc) do
@@ -4450,30 +4737,18 @@ defmodule Enum do
 end
 
 defimpl Enumerable, for: List do
-  def count([]), do: {:ok, 0}
-  def count(_list), do: {:error, __MODULE__}
+  def count(list), do: {:ok, length(list)}
 
   def member?([], _value), do: {:ok, false}
   def member?(_list, _value), do: {:error, __MODULE__}
 
-  def slice([]), do: {:ok, 0, fn _, _ -> [] end}
+  def slice([]), do: {:ok, 0, fn _, _, _ -> [] end}
   def slice(_list), do: {:error, __MODULE__}
 
   def reduce(_list, {:halt, acc}, _fun), do: {:halted, acc}
   def reduce(list, {:suspend, acc}, fun), do: {:suspended, acc, &reduce(list, &1, fun)}
   def reduce([], {:cont, acc}, _fun), do: {:done, acc}
   def reduce([head | tail], {:cont, acc}, fun), do: reduce(tail, fun.(head, acc), fun)
-
-  @doc false
-  def slice(_list, _start, 0, _size), do: []
-  def slice(list, start, count, size) when start + count == size, do: list |> drop(start)
-  def slice(list, start, count, _size), do: list |> drop(start) |> take(count)
-
-  defp drop(list, 0), do: list
-  defp drop([_ | tail], count), do: drop(tail, count - 1)
-
-  defp take(_list, 0), do: []
-  defp take([head | tail], count), do: [head | take(tail, count - 1)]
 end
 
 defimpl Enumerable, for: Map do
@@ -4491,7 +4766,7 @@ defimpl Enumerable, for: Map do
 
   def slice(map) do
     size = map_size(map)
-    {:ok, size, &Enumerable.List.slice(:maps.to_list(map), &1, &2, size)}
+    {:ok, size, &:maps.to_list/1}
   end
 
   def reduce(map, acc, fun) do

lib/elixir/lib/exception.ex

@@ -227,7 +227,11 @@ defmodule Exception do
             |> Enum.zip()
             |> Enum.map_reduce([], &blame_arg/2)
 
-          guards = Enum.map(guards, &blame_guard(&1, ann, scope, binding))
+          guards =
+            guards
+            |> Enum.map(&blame_guard(&1, ann, scope, binding))
+            |> Enum.map(&Macro.prewalk(&1, fn guard -> translate_guard(guard) end))
+
           {args, guards}
         end
 
@@ -237,6 +241,71 @@ defmodule Exception do
     end
   end
 
+  defp is_map_node?({:is_map, _, [_]}), do: true
+  defp is_map_node?(_), do: false
+  defp is_map_key_node?({:is_map_key, _, [_, _]}), do: true
+  defp is_map_key_node?(_), do: false
+
+  defp struct_validation_node?(
+         {:is_atom, _, [{{:., [], [:erlang, :map_get]}, _, [:__struct__, _]}]}
+       ),
+       do: true
+
+  defp struct_validation_node?(
+         {:==, _, [{{:., [], [:erlang, :map_get]}, _, [:__struct__, _]}, _module]}
+       ),
+       do: true
+
+  defp struct_validation_node?(_), do: false
+
+  defp is_struct_macro?(
+         {:and, _,
+          [
+            {:and, _, [%{node: node_1 = {_, _, [arg]}}, %{node: node_2 = {_, _, [arg, _]}}]},
+            %{node: node_3 = {_, _, [{_, _, [_, arg]}]}}
+          ]}
+       ),
+       do: is_map_node?(node_1) and is_map_key_node?(node_2) and struct_validation_node?(node_3)
+
+  defp is_struct_macro?(
+         {:and, _,
+          [
+            {:and, _,
+             [
+               {:and, _,
+                [
+                  %{node: node_1 = {_, _, [arg]}},
+                  {:or, _, [%{node: {:is_atom, _, [_]}}, %{node: :fail}]}
+                ]},
+               %{node: node_2 = {_, _, [arg, _]}}
+             ]},
+            %{node: node_3 = {_, _, [{_, _, [_, arg]}, _]}}
+          ]}
+       ),
+       do: is_map_node?(node_1) and is_map_key_node?(node_2) and struct_validation_node?(node_3)
+
+  defp is_struct_macro?(_), do: false
+
+  defp translate_guard(guard) do
+    if is_struct_macro?(guard) do
+      undo_is_struct_guard(guard)
+    else
+      guard
+    end
+  end
+
+  defp undo_is_struct_guard(
+         {:and, meta, [_, %{node: {_, _, [{_, _, [_, {struct, _, _}]} | optional]}}]}
+       ) do
+    args =
+      case optional do
+        [] -> [{struct, meta, nil}]
+        [module] -> [{struct, meta, nil}, module]
+      end
+
+    %{match?: meta[:value], node: {:is_struct, meta, args}}
+  end
+
   defp blame_arg({call_arg, ex_arg, erl_arg}, binding) do
     {match?, binding} = blame_arg(erl_arg, call_arg, binding)
     {blame_wrap(match?, rewrite_arg(ex_arg)), binding}
@@ -280,23 +349,38 @@ defmodule Exception do
         :andalso -> :and
       end
 
-    {kernel_op, meta, guards}
+    evaluate_guard(kernel_op, meta, guards)
   end
 
   defp blame_guard(ex_guard, ann, scope, binding) do
-    {erl_guard, _} = :elixir_erl_pass.translate(ex_guard, ann, scope)
+    ex_guard
+    |> blame_guard?(binding, ann, scope)
+    |> blame_wrap(rewrite_guard(ex_guard))
+  end
 
-    match? =
-      try do
-        {:value, true, _} = :erl_eval.expr(erl_guard, binding, :none)
-        true
-      rescue
-        _ -> false
+  defp blame_guard?(ex_guard, binding, ann, scope) do
+    {erl_guard, _} = :elixir_erl_pass.translate(ex_guard, ann, scope)
+    {:value, true, _} = :erl_eval.expr(erl_guard, binding, :none)
+    true
+  rescue
+    _ -> false
+  end
+
+  defp evaluate_guard(kernel_op, meta, guards = [_, _]) do
+    [x, y] = Enum.map(guards, &evaluate_guard/1)
+
+    logic_value =
+      case kernel_op do
+        :or -> x or y
+        :and -> x and y
       end
 
-    blame_wrap(match?, rewrite_guard(ex_guard))
+    {kernel_op, Keyword.put(meta, :value, logic_value), guards}
   end
 
+  defp evaluate_guard(%{match?: value}), do: value
+  defp evaluate_guard({_, meta, _}) when is_list(meta), do: meta[:value]
+
   defp rewrite_guard(guard) do
     Macro.prewalk(guard, fn
       {{:., _, [mod, fun]}, meta, args} -> erl_to_ex(mod, fun, args, meta)
@@ -622,12 +706,12 @@ defmodule Exception do
     case Code.Identifier.extract_anonymous_fun_parent(fun) do
       {outer_name, outer_arity} ->
         "anonymous fn#{format_arity(arity)} in " <>
-          "#{Code.Identifier.inspect_as_atom(module)}." <>
-          "#{Code.Identifier.inspect_as_function(outer_name)}/#{outer_arity}"
+          "#{Macro.inspect_atom(:literal, module)}." <>
+          "#{Macro.inspect_atom(:remote_call, outer_name)}/#{outer_arity}"
 
       :error ->
-        "#{Code.Identifier.inspect_as_atom(module)}." <>
-          "#{Code.Identifier.inspect_as_function(fun)}#{format_arity(arity)}"
+        "#{Macro.inspect_atom(:literal, module)}." <>
+          "#{Macro.inspect_atom(:remote_call, fun)}#{format_arity(arity)}"
     end
   end
 
@@ -732,12 +816,16 @@ defmodule ArgumentError do
       ) do
     message =
       cond do
+        not proper_list?(args) ->
+          "you attempted to apply a function named #{inspect(function)} on module #{inspect(module)} " <>
+            "with arguments #{inspect(args)}. Arguments (the third argument of apply) must always be a proper list"
+
         # Note that args may be an empty list even if they were supplied
         not is_atom(module) and is_atom(function) and args == [] ->
           "you attempted to apply a function named #{inspect(function)} on #{inspect(module)}. " <>
             "If you are using Kernel.apply/3, make sure the module is an atom. " <>
-            "If you are using the dot syntax, such as map.field or module.function(), " <>
-            "make sure the left side of the dot is an atom or a map"
+            "If you are using the dot syntax, such as module.function(), " <>
+            "make sure the left-hand side of the dot is a module atom"
 
         not is_atom(module) ->
           "you attempted to apply a function on #{inspect(module)}. " <>
@@ -747,10 +835,6 @@ defmodule ArgumentError do
           "you attempted to apply a function named #{inspect(function)} on module #{inspect(module)}. " <>
             "However #{inspect(function)} is not a valid function name. Function names (the second argument " <>
             "of apply) must always be an atom"
-
-        not is_list(args) ->
-          "you attempted to apply a function named #{inspect(function)} on module #{inspect(module)} " <>
-            "with arguments #{inspect(args)}. Arguments (the third argument of apply) must always be a list"
       end
 
     {%{exception | message: message}, stacktrace}
@@ -759,6 +843,9 @@ defmodule ArgumentError do
   def blame(exception, stacktrace) do
     {exception, stacktrace}
   end
+
+  defp proper_list?(list) when length(list) >= 0, do: true
+  defp proper_list?(_), do: false
 end
 
 defmodule ArithmeticError do
@@ -1027,8 +1114,8 @@ defmodule UndefinedFunctionError do
   end
 
   defp hint(nil, _function, 0, _loaded?) do
-    ". If you are using the dot syntax, such as map.field or module.function(), " <>
-      "make sure the left side of the dot is an atom or a map"
+    ". If you are using the dot syntax, such as module.function(), " <>
+      "make sure the left-hand side of the dot is a module atom"
   end
 
   defp hint(module, function, arity, true) do
@@ -1093,7 +1180,7 @@ defmodule UndefinedFunctionError do
   end
 
   defp format_fa({_dist, fun, arity}) do
-    ["      * ", Code.Identifier.inspect_as_function(fun), ?/, Integer.to_string(arity), ?\n]
+    ["      * ", Macro.inspect_atom(:remote_call, fun), ?/, Integer.to_string(arity), ?\n]
   end
 
   defp behaviour_hint(module, function, arity) do
@@ -1251,11 +1338,13 @@ defmodule FunctionClauseError do
 end
 
 defmodule Code.LoadError do
-  defexception [:file, :message]
+  defexception [:file, :message, :reason]
 
   def exception(opts) do
     file = Keyword.fetch!(opts, :file)
-    %Code.LoadError{message: "could not load #{file}", file: file}
+    reason = Keyword.fetch!(opts, :reason)
+    message = "could not load #{file}. Reason: #{reason}"
+    %Code.LoadError{message: message, file: file, reason: reason}
   end
 end
 
@@ -1470,22 +1559,24 @@ defmodule File.LinkError do
 end
 
 defmodule ErlangError do
-  defexception [:original]
+  defexception [:original, :reason]
 
   @impl true
-  def message(exception) do
-    "Erlang error: #{inspect(exception.original)}"
+  def message(exception)
+
+  def message(%__MODULE__{original: original, reason: nil}) do
+    "Erlang error: #{inspect(original)}"
+  end
+
+  def message(%__MODULE__{original: original, reason: reason}) do
+    IO.iodata_to_binary(["Erlang error: ", inspect(original), reason])
   end
 
   @doc false
   def normalize(:badarg, stacktrace) do
-    case error_info(:badarg, stacktrace) do
-      {:ok, args} ->
-        message = "errors were found at the given arguments:\n\n#{args}"
-        %ArgumentError{message: message}
-
-      :error ->
-        %ArgumentError{}
+    case error_info(:badarg, stacktrace, "errors were found at the given arguments") do
+      {:ok, reason, details} -> %ArgumentError{message: reason <> details}
+      :error -> %ArgumentError{}
     end
   end
 
@@ -1494,15 +1585,11 @@ defmodule ErlangError do
   end
 
   def normalize(:system_limit, stacktrace) do
-    case error_info(:system_limit, stacktrace) do
-      {:ok, args} ->
-        message =
-          "a system limit has been reached due to errors at the given arguments:\n\n#{args}"
+    default_reason = "a system limit has been reached due to errors at the given arguments"
 
-        %SystemLimitError{message: message}
-
-      :error ->
-        %SystemLimitError{}
+    case error_info(:system_limit, stacktrace, default_reason) do
+      {:ok, reason, details} -> %SystemLimitError{message: reason <> details}
+      :error -> %SystemLimitError{}
     end
   end
 
@@ -1548,10 +1635,19 @@ defmodule ErlangError do
     %KeyError{key: key, term: term}
   end
 
-  def normalize({:badkey, key, map}, _stacktrace) do
+  def normalize({:badkey, key, map}, _stacktrace) when is_map(map) do
     %KeyError{key: key, term: map}
   end
 
+  def normalize({:badkey, key, term}, _stacktrace) do
+    message =
+      "key #{inspect(key)} not found in: #{inspect(term)}. " <>
+        "If you are using the dot syntax, such as map.field, " <>
+        "make sure the left-hand side of the dot is a map"
+
+    %KeyError{key: key, term: term, message: message}
+  end
+
   def normalize({:case_clause, term}, _stacktrace) do
     %CaseClauseError{term: term}
   end
@@ -1578,8 +1674,11 @@ defmodule ErlangError do
     %ArgumentError{message: "argument error: #{inspect(payload)}"}
   end
 
-  def normalize(other, _stacktrace) do
-    %ErlangError{original: other}
+  def normalize(other, stacktrace) do
+    case error_info(other, stacktrace, "") do
+      {:ok, _reason, details} -> %ErlangError{original: other, reason: details}
+      :error -> %ErlangError{original: other}
+    end
   end
 
   defp from_stacktrace([{module, function, args, _} | _]) when is_list(args) do
@@ -1594,30 +1693,35 @@ defmodule ErlangError do
     {nil, nil, nil}
   end
 
-  defp error_info(:badarg, [{:erlang, fun, _, _} | _]) when fun in [:byte_size, :bit_size] do
-    {:ok,
-     """
-       * 1st argument: not a bitstring
-
-     This typically happens when calling Kernel.#{fun}/1 with an invalid argument \
-     or when performing binary construction or binary concatenation with <> and \
-     one of the arguments is not a binary\
-     """}
-  end
-
-  defp error_info(erl_exception, stacktrace) do
-    with [{module, _, args_or_arity, opts} | _] <- stacktrace,
+  defp error_info(erl_exception, stacktrace, default_reason) do
+    with [{module, fun, args_or_arity, opts} | tail] <- stacktrace,
          %{} = error_info <- opts[:error_info] do
-      module = Map.get(error_info, :module, module)
-      function = Map.get(error_info, :function, :format_error)
-      arity = if is_integer(args_or_arity), do: args_or_arity, else: length(args_or_arity)
-      extra = apply(module, function, [erl_exception, stacktrace])
-      args_errors = Map.take(extra, Enum.to_list(1..arity//1))
+      error_module = Map.get(error_info, :module, module)
+      error_fun = Map.get(error_info, :function, :format_error)
 
-      if map_size(args_errors) > 0 do
-        {:ok, IO.iodata_to_binary(Enum.map(args_errors, &arg_error/1))}
-      else
-        :error
+      error_info = Map.put(error_info, :pretty_printer, &inspect/1)
+      head = {module, fun, args_or_arity, Keyword.put(opts, :error_info, error_info)}
+
+      extra =
+        try do
+          apply(error_module, error_fun, [erl_exception, [head | tail]])
+        rescue
+          _ -> %{}
+        end
+
+      arity = if is_integer(args_or_arity), do: args_or_arity, else: length(args_or_arity)
+      args_errors = Map.take(extra, Enum.to_list(1..arity//1))
+      reason = Map.get(extra, :reason, default_reason)
+
+      cond do
+        map_size(args_errors) > 0 ->
+          {:ok, reason, IO.iodata_to_binary([":\n\n" | Enum.map(args_errors, &arg_error/1)])}
+
+        general = extra[:general] ->
+          {:ok, reason, ": " <> general}
+
+        true ->
+          :error
       end
     else
       _ -> :error
@@ -1631,3 +1735,61 @@ defmodule ErlangError do
   defp nth(3), do: "3rd"
   defp nth(n), do: "#{n}th"
 end
+
+defmodule Inspect.Error do
+  @moduledoc """
+  Raised when a struct cannot be inspected.
+  """
+  @enforce_keys [:exception_module, :exception_message, :stacktrace, :inspected_struct]
+  defexception @enforce_keys
+
+  @impl true
+  def exception(arguments) when is_list(arguments) do
+    exception = Keyword.fetch!(arguments, :exception)
+    exception_module = exception.__struct__
+    exception_message = Exception.message(exception) |> String.trim_trailing("\n")
+    stacktrace = Keyword.fetch!(arguments, :stacktrace)
+    inspected_struct = Keyword.fetch!(arguments, :inspected_struct)
+
+    %Inspect.Error{
+      exception_module: exception_module,
+      exception_message: exception_message,
+      stacktrace: stacktrace,
+      inspected_struct: inspected_struct
+    }
+  end
+
+  @impl true
+  def message(%__MODULE__{
+        exception_module: exception_module,
+        exception_message: exception_message,
+        inspected_struct: inspected_struct
+      }) do
+    ~s'''
+    got #{inspect(exception_module)} with message:
+
+        """
+    #{pad(exception_message, 4)}
+        """
+
+    while inspecting:
+
+    #{pad(inspected_struct, 4)}
+    '''
+  end
+
+  @doc false
+  def pad(message, padding_length)
+      when is_binary(message) and is_integer(padding_length) and padding_length >= 0 do
+    padding = String.duplicate(" ", padding_length)
+
+    message
+    |> String.split("\n")
+    |> Enum.map(fn
+      "" -> "\n"
+      line -> [padding, line, ?\n]
+    end)
+    |> IO.iodata_to_binary()
+    |> String.trim_trailing("\n")
+  end
+end

lib/elixir/lib/file.ex

@@ -112,6 +112,7 @@ defmodule File do
           encoding_mode()
           | :append
           | :compressed
+          | :delayed_write
           | :trim_bom
           | {:read_ahead, pos_integer | false}
           | {:delayed_write, non_neg_integer, non_neg_integer}
@@ -122,6 +123,8 @@ defmodule File do
 
   @type posix_time :: integer()
 
+  @type on_conflict_callback :: (Path.t(), Path.t() -> boolean)
+
   @doc """
   Returns `true` if the path is a regular file.
 
@@ -693,7 +696,10 @@ defmodule File do
   @spec copy(Path.t() | io_device, Path.t() | io_device, pos_integer | :infinity) ::
           {:ok, non_neg_integer} | {:error, posix}
   def copy(source, destination, bytes_count \\ :infinity) do
-    :file.copy(maybe_to_string(source), maybe_to_string(destination), bytes_count)
+    source = normalize_path_or_io_device(source)
+    destination = normalize_path_or_io_device(destination)
+
+    :file.copy(source, destination, bytes_count)
   end
 
   @doc """
@@ -711,8 +717,8 @@ defmodule File do
         raise File.CopyError,
           reason: reason,
           action: "copy",
-          source: maybe_to_string(source),
-          destination: maybe_to_string(destination)
+          source: normalize_path_or_io_device(source),
+          destination: normalize_path_or_io_device(destination)
     end
   end
 
@@ -740,6 +746,8 @@ defmodule File do
   @doc since: "1.1.0"
   @spec rename(Path.t(), Path.t()) :: :ok | {:error, posix}
   def rename(source, destination) do
+    source = IO.chardata_to_string(source)
+    destination = IO.chardata_to_string(destination)
     :file.rename(source, destination)
   end
 
@@ -770,11 +778,6 @@ defmodule File do
   be a path to a non-existent file. If either is a directory, `{:error, :eisdir}`
   will be returned.
 
-  The `callback` function is invoked if the `destination_file` already exists.
-  The function receives arguments for `source_file` and `destination_file`;
-  it should return `true` if the existing file should be overwritten, `false` if
-  otherwise. The default callback returns `true`.
-
   The function returns `:ok` in case of success. Otherwise, it returns
   `{:error, reason}`.
 
@@ -786,13 +789,30 @@ defmodule File do
   whether the destination is an existing directory or not. We have chosen to
   explicitly disallow copying to a destination which is a directory,
   and an error will be returned if tried.
+
+  ## Options
+
+    * `:on_conflict` - (since v1.14.0) Invoked when a file already exists in the destination.
+      The function receives arguments for `source_file` and `destination_file`. It should
+      return `true` if the existing file should be overwritten, `false` if otherwise.
+      The default callback returns `true`. On earlier versions, this callback could be
+      given as third argument, but such behaviour is now deprecated.
+
   """
-  @spec cp(Path.t(), Path.t(), (Path.t(), Path.t() -> boolean)) :: :ok | {:error, posix}
-  def cp(source_file, destination_file, callback \\ fn _, _ -> true end) do
+  @spec cp(Path.t(), Path.t(), on_conflict: on_conflict_callback) :: :ok | {:error, posix}
+  def cp(source_file, destination_file, options \\ [])
+
+  # TODO: Deprecate me on Elixir v1.19
+  def cp(source_file, destination_file, callback) when is_function(callback, 2) do
+    cp(source_file, destination_file, on_conflict: callback)
+  end
+
+  def cp(source_file, destination_file, options) when is_list(options) do
+    on_conflict = Keyword.get(options, :on_conflict, fn _, _ -> true end)
     source_file = IO.chardata_to_string(source_file)
     destination_file = IO.chardata_to_string(destination_file)
 
-    case do_cp_file(source_file, destination_file, callback, []) do
+    case do_cp_file(source_file, destination_file, on_conflict, []) do
       {:error, reason, _} -> {:error, reason}
       _ -> :ok
     end
@@ -808,9 +828,9 @@ defmodule File do
   The same as `cp/3`, but raises a `File.CopyError` exception if it fails.
   Returns `:ok` otherwise.
   """
-  @spec cp!(Path.t(), Path.t(), (Path.t(), Path.t() -> boolean)) :: :ok
-  def cp!(source_file, destination_file, callback \\ fn _, _ -> true end) do
-    case cp(source_file, destination_file, callback) do
+  @spec cp!(Path.t(), Path.t(), on_conflict: on_conflict_callback) :: :ok
+  def cp!(source_file, destination_file, options \\ []) do
+    case cp(source_file, destination_file, options) do
       :ok ->
         :ok
 
@@ -833,18 +853,15 @@ defmodule File do
   If `source` is a directory, or a symbolic link to it, then `destination` must
   be an existent `directory` or a symbolic link to one, or a path to a non-existent directory.
 
-  If the source is a file, it copies `source` to
-  `destination`. If the `source` is a directory, it copies
-  the contents inside source into the `destination` directory.
+  If the source is a file, it copies `source` to `destination`. If the `source`
+  is a directory, it copies the contents inside source into the `destination` directory.
 
-  If a file already exists in the destination, it invokes `callback`.
-  `callback` must be a function that takes two arguments: `source` and `destination`.
-  The callback should return `true` if the existing file should be overwritten and `false` otherwise.
+  If a file already exists in the destination, it invokes the optional `on_conflict`
+  callback given as an option. See "Options" for more information.
 
-  This function may fail while copying files,
-  in such cases, it will leave the destination
-  directory in a dirty state, where file which have already been copied
-  won't be removed.
+  This function may fail while copying files, in such cases, it will leave the
+  destination directory in a dirty state, where file which have already been
+  copied won't be removed.
 
   The function returns `{:ok, files_and_directories}` in case of
   success, `files_and_directories` lists all files and directories copied in no
@@ -855,6 +872,19 @@ defmodule File do
   explicitly disallow this behaviour. If `source` is a `file` and `destination`
   is a directory, `{:error, :eisdir}` will be returned.
 
+  ## Options
+
+    * `:on_conflict` - (since v1.14.0) Invoked when a file already exists in the destination.
+      The function receives arguments for `source` and `destination`. It should return
+      `true` if the existing file should be overwritten, `false` if otherwise. The default
+      callback returns `true`. On earlier versions, this callback could be given as third
+      argument, but such behaviour is now deprecated.
+
+    * `:dereference_symlinks` - (since v1.14.0) By default, this function will copy symlinks
+      by creating symlinks that point to the same location. This option forces symlinks to be
+      dereferenced and have their contents copied instead when set to `true`. If the dereferenced
+      files do not exist, than the operation fails. The default is `false`.
+
   ## Examples
 
       # Copies file "a.txt" to "b.txt"
@@ -864,14 +894,28 @@ defmodule File do
       File.cp_r("samples", "tmp")
 
       # Same as before, but asks the user how to proceed in case of conflicts
-      File.cp_r("samples", "tmp", fn source, destination ->
+      File.cp_r("samples", "tmp", on_conflict: fn source, destination ->
         IO.gets("Overwriting #{destination} by #{source}. Type y to confirm. ") == "y\n"
       end)
 
   """
-  @spec cp_r(Path.t(), Path.t(), (Path.t(), Path.t() -> boolean)) ::
+  @spec cp_r(Path.t(), Path.t(),
+          on_conflict: on_conflict_callback,
+          dereference_symlinks: boolean()
+        ) ::
           {:ok, [binary]} | {:error, posix, binary}
-  def cp_r(source, destination, callback \\ fn _, _ -> true end) when is_function(callback, 2) do
+
+  def cp_r(source, destination, options \\ [])
+
+  # TODO: Deprecate me on Elixir v1.19
+  def cp_r(source, destination, callback) when is_function(callback, 2) do
+    cp_r(source, destination, on_conflict: callback)
+  end
+
+  def cp_r(source, destination, options) when is_list(options) do
+    on_conflict = Keyword.get(options, :on_conflict, fn _, _ -> true end)
+    dereference? = Keyword.get(options, :dereference_symlinks, false)
+
     source =
       source
       |> IO.chardata_to_string()
@@ -882,7 +926,7 @@ defmodule File do
       |> IO.chardata_to_string()
       |> assert_no_null_byte!("File.cp_r/3")
 
-    case do_cp_r(source, destination, callback, []) do
+    case do_cp_r(source, destination, on_conflict, dereference?, []) do
       {:error, _, _} = error -> error
       res -> {:ok, res}
     end
@@ -892,9 +936,12 @@ defmodule File do
   The same as `cp_r/3`, but raises a `File.CopyError` exception if it fails.
   Returns the list of copied files otherwise.
   """
-  @spec cp_r!(Path.t(), Path.t(), (Path.t(), Path.t() -> boolean)) :: [binary]
-  def cp_r!(source, destination, callback \\ fn _, _ -> true end) do
-    case cp_r(source, destination, callback) do
+  @spec cp_r!(Path.t(), Path.t(),
+          on_conflict: on_conflict_callback,
+          dereference_symlinks: boolean()
+        ) :: [binary]
+  def cp_r!(source, destination, options \\ []) do
+    case cp_r(source, destination, options) do
       {:ok, files} ->
         files
 
@@ -908,15 +955,21 @@ defmodule File do
     end
   end
 
-  defp do_cp_r(src, dest, callback, acc) when is_list(acc) do
+  defp do_cp_r(src, dest, on_conflict, dereference?, acc) when is_list(acc) do
     case :elixir_utils.read_link_type(src) do
       {:ok, :regular} ->
-        do_cp_file(src, dest, callback, acc)
+        do_cp_file(src, dest, on_conflict, acc)
 
       {:ok, :symlink} ->
         case :file.read_link(src) do
-          {:ok, link} -> do_cp_link(link, src, dest, callback, acc)
-          {:error, reason} -> {:error, reason, src}
+          {:ok, link} when dereference? ->
+            do_cp_r(Path.expand(link, Path.dirname(src)), dest, on_conflict, dereference?, acc)
+
+          {:ok, link} ->
+            do_cp_link(link, src, dest, on_conflict, acc)
+
+          {:error, reason} ->
+            {:error, reason, src}
         end
 
       {:ok, :directory} ->
@@ -925,7 +978,7 @@ defmodule File do
             case mkdir(dest) do
               success when success in [:ok, {:error, :eexist}] ->
                 Enum.reduce(files, [dest | acc], fn x, acc ->
-                  do_cp_r(Path.join(src, x), Path.join(dest, x), callback, acc)
+                  do_cp_r(Path.join(src, x), Path.join(dest, x), on_conflict, dereference?, acc)
                 end)
 
               {:error, reason} ->
@@ -944,9 +997,8 @@ defmodule File do
     end
   end
 
-  # If we reach this clause, there was an error while
-  # processing a file.
-  defp do_cp_r(_, _, _, acc) do
+  # If we reach this clause, there was an error while processing a file.
+  defp do_cp_r(_, _, _, _, acc) do
     acc
   end
 
@@ -955,14 +1007,14 @@ defmodule File do
   end
 
   # Both src and dest are files.
-  defp do_cp_file(src, dest, callback, acc) do
+  defp do_cp_file(src, dest, on_conflict, acc) do
     case :file.copy(src, {dest, [:exclusive]}) do
       {:ok, _} ->
         copy_file_mode!(src, dest)
         [dest | acc]
 
       {:error, :eexist} ->
-        if path_differs?(src, dest) and callback.(src, dest) do
+        if path_differs?(src, dest) and on_conflict.(src, dest) do
           case copy(src, dest) do
             {:ok, _} ->
               copy_file_mode!(src, dest)
@@ -981,13 +1033,13 @@ defmodule File do
   end
 
   # Both src and dest are files.
-  defp do_cp_link(link, src, dest, callback, acc) do
+  defp do_cp_link(link, src, dest, on_conflict, acc) do
     case :file.make_symlink(link, dest) do
       :ok ->
         [dest | acc]
 
       {:error, :eexist} ->
-        if path_differs?(src, dest) and callback.(src, dest) do
+        if path_differs?(src, dest) and on_conflict.(src, dest) do
           # If rm/1 fails, :file.make_symlink/2 will fail
           _ = rm(dest)
 
@@ -1044,9 +1096,7 @@ defmodule File do
   """
   @spec write!(Path.t(), iodata, [mode]) :: :ok
   def write!(path, content, modes \\ []) do
-    modes = normalize_modes(modes, false)
-
-    case :file.write_file(path, content, modes) do
+    case write(path, content, modes) do
       :ok ->
         :ok
 
@@ -1194,82 +1244,79 @@ defmodule File do
   """
   @spec rm_rf(Path.t()) :: {:ok, [binary]} | {:error, posix, binary}
   def rm_rf(path) do
+    {major, _} = :os.type()
+
     path
     |> IO.chardata_to_string()
     |> assert_no_null_byte!("File.rm_rf/1")
-    |> do_rm_rf({:ok, []})
+    |> do_rm_rf([], major)
   end
 
-  defp do_rm_rf(path, {:ok, _} = entry) do
-    case safe_list_dir(path) do
+  defp do_rm_rf(path, acc, major) do
+    case safe_list_dir(path, major) do
       {:ok, files} when is_list(files) ->
-        res =
-          Enum.reduce(files, entry, fn file, tuple ->
-            do_rm_rf(Path.join(path, file), tuple)
+        acc =
+          Enum.reduce(files, acc, fn file, acc ->
+            # In case we can't delete, continue anyway, we might succeed
+            # to delete it on Windows due to how they handle symlinks.
+            case do_rm_rf(Path.join(path, file), acc, major) do
+              {:ok, acc} -> acc
+              {:error, _, _} -> acc
+            end
           end)
 
-        case res do
-          {:ok, acc} ->
-            case rmdir(path) do
-              :ok -> {:ok, [path | acc]}
-              {:error, :enoent} -> res
-              {:error, reason} -> {:error, reason, path}
-            end
-
-          reason ->
-            reason
+        case rmdir(path) do
+          :ok -> {:ok, [path | acc]}
+          {:error, :enoent} -> {:ok, acc}
+          {:error, reason} -> {:error, reason, path}
         end
 
       {:ok, :directory} ->
-        do_rm_directory(path, entry)
+        do_rm_directory(path, acc)
 
       {:ok, :regular} ->
-        do_rm_regular(path, entry)
+        do_rm_regular(path, acc)
 
       {:error, reason} when reason in [:enoent, :enotdir] ->
-        entry
+        {:ok, acc}
 
       {:error, reason} ->
         {:error, reason, path}
     end
   end
 
-  defp do_rm_rf(_, reason) do
-    reason
-  end
-
-  defp do_rm_regular(path, {:ok, acc} = entry) do
+  defp do_rm_regular(path, acc) do
     case rm(path) do
       :ok -> {:ok, [path | acc]}
-      {:error, :enoent} -> entry
+      {:error, :enoent} -> {:ok, acc}
       {:error, reason} -> {:error, reason, path}
     end
   end
 
   # On Windows, symlinks are treated as directory and must be removed
-  # with rmdir/1. But on Unix-like systems, we remove them via rm/1. So we first try
-  # to remove it as a directory and, if we get :enotdir, we fall back to
-  # a file removal.
-  defp do_rm_directory(path, {:ok, acc} = entry) do
+  # with rmdir/1. But on Unix-like systems, we remove them via rm/1.
+  # So we first try to remove it as a directory and, if we get :enotdir,
+  # we fall back to a file removal.
+  defp do_rm_directory(path, acc) do
     case rmdir(path) do
       :ok -> {:ok, [path | acc]}
-      {:error, :enotdir} -> do_rm_regular(path, entry)
-      {:error, :enoent} -> entry
+      {:error, :enotdir} -> do_rm_regular(path, acc)
+      {:error, :enoent} -> {:ok, acc}
       {:error, reason} -> {:error, reason, path}
     end
   end
 
-  defp safe_list_dir(path) do
+  defp safe_list_dir(path, major) do
     case :elixir_utils.read_link_type(path) do
-      {:ok, :symlink} ->
+      {:ok, :directory} ->
+        :file.list_dir_all(path)
+
+      {:ok, :symlink} when major == :win32 ->
         case :elixir_utils.read_file_type(path) do
           {:ok, :directory} -> {:ok, :directory}
           _ -> {:ok, :regular}
         end
 
-      {:ok, :directory} ->
-        :file.list_dir(path)
-
       {:ok, _} ->
         {:ok, :regular}
 
@@ -1607,7 +1654,7 @@ defmodule File do
     :file.close(io_device)
   end
 
-  @doc """
+  @doc ~S"""
   Returns a `File.Stream` for the given `path` with the given `modes`.
 
   The stream implements both `Enumerable` and `Collectable` protocols,
@@ -1805,7 +1852,8 @@ defmodule File do
   defp normalize_modes([], true), do: [:binary]
   defp normalize_modes([], false), do: []
 
-  defp maybe_to_string(path) when is_list(path), do: IO.chardata_to_string(path)
-  defp maybe_to_string(path) when is_binary(path), do: path
-  defp maybe_to_string(path), do: path
+  defp normalize_path_or_io_device(path) when is_list(path), do: IO.chardata_to_string(path)
+  defp normalize_path_or_io_device(path) when is_binary(path), do: path
+  defp normalize_path_or_io_device(io_device) when is_pid(io_device), do: io_device
+  defp normalize_path_or_io_device(io_device = {:file_descriptor, _, _}), do: io_device
 end

lib/elixir/lib/float.ex

@@ -15,7 +15,7 @@ defmodule Float do
   ## Known issues
 
   There are some very well known problems with floating-point numbers
-  and arithmetics due to the fact most decimal fractions cannot be
+  and arithmetic due to the fact most decimal fractions cannot be
   represented by a floating-point binary and most operations are not exact,
   but operate on approximations. Those issues are not specific
   to Elixir, they are a property of floating point representation itself.
@@ -46,6 +46,31 @@ defmodule Float do
   @precision_range 0..15
   @type precision_range :: 0..15
 
+  @min_finite then(<<0xFFEFFFFFFFFFFFFF::64>>, fn <<num::float>> -> num end)
+  @max_finite then(<<0x7FEFFFFFFFFFFFFF::64>>, fn <<num::float>> -> num end)
+
+  @doc """
+  Returns the maximum finite value for a float.
+
+  ## Examples
+
+      iex> Float.max_finite()
+      1.7976931348623157e308
+
+  """
+  def max_finite, do: @max_finite
+
+  @doc """
+  Returns the minimum finite value for a float.
+
+  ## Examples
+
+      iex> Float.min_finite()
+      -1.7976931348623157e308
+
+  """
+  def min_finite, do: @min_finite
+
   @doc """
   Computes `base` raised to power of `exponent`.
 
@@ -509,13 +534,20 @@ defmodule Float do
   defp sign(1, num), do: -num
 
   @doc """
-  Returns a charlist which corresponds to the text representation
+  Returns a charlist which corresponds to the shortest text representation
   of the given float.
 
-  It uses the shortest representation according to algorithm described
-  in "Printing Floating-Point Numbers Quickly and Accurately" in
-  Proceedings of the SIGPLAN '96 Conference on Programming Language
-  Design and Implementation.
+  The underlying algorithm changes depending on the Erlang/OTP version:
+
+    * For OTP >= 24, it uses the algorithm presented in "Ryū: fast
+      float-to-string conversion" in Proceedings of the SIGPLAN '2018
+      Conference on Programming Language Design and Implementation.
+
+    * For OTP < 24, it uses the algorithm presented in "Printing Floating-Point
+      Numbers Quickly and Accurately" in Proceedings of the SIGPLAN '1996
+      Conference on Programming Language Design and Implementation.
+
+  For a configurable representation, use `:erlang.float_to_list/2`.
 
   ## Examples
 
@@ -529,13 +561,20 @@ defmodule Float do
   end
 
   @doc """
-  Returns a binary which corresponds to the text representation
+  Returns a binary which corresponds to the shortest text representation
   of the given float.
 
-  It uses the shortest representation according to algorithm described
-  in "Printing Floating-Point Numbers Quickly and Accurately" in
-  Proceedings of the SIGPLAN '96 Conference on Programming Language
-  Design and Implementation.
+  The underlying algorithm changes depending on the Erlang/OTP version:
+
+    * For OTP >= 24, it uses the algorithm presented in "Ryū: fast
+      float-to-string conversion" in Proceedings of the SIGPLAN '2018
+      Conference on Programming Language Design and Implementation.
+
+    * For OTP < 24, it uses the algorithm presented in "Printing Floating-Point
+      Numbers Quickly and Accurately" in Proceedings of the SIGPLAN '1996
+      Conference on Programming Language Design and Implementation.
+
+  For a configurable representation, use `:erlang.float_to_binary/2`.
 
   ## Examples
 

lib/elixir/lib/function.ex

@@ -22,7 +22,7 @@ defmodule Function do
 
   It is also possible to capture public module functions and pass them
   around as if they were anonymous functions by using the capture
-  operator `Kernel.SpecialForms.&/1`:
+  operator `&/1`:
 
       iex> add = &Kernel.+/2
       iex> add.(1, 2)

lib/elixir/lib/gen_event.ex

@@ -2,7 +2,7 @@ defmodule GenEvent do
   # Functions from this module are deprecated in elixir_dispatch.
 
   @moduledoc """
-  A event manager with event handlers behaviour.
+  An event manager with event handlers behaviour.
 
   If you are interested in implementing an event manager, please read the
   "Alternatives" section below. If you have to implement an event handler to
@@ -91,7 +91,7 @@ defmodule GenEvent do
     deprecation_message =
       "the GenEvent module is deprecated, see its documentation for alternatives"
 
-    IO.warn(deprecation_message, Macro.Env.stacktrace(__CALLER__))
+    IO.warn(deprecation_message, __CALLER__)
 
     quote location: :keep do
       @behaviour :gen_event

lib/elixir/lib/gen_server.ex

@@ -153,6 +153,11 @@ defmodule GenServer do
   detailed information. The `@doc` annotation immediately preceding
   `use GenServer` will be attached to the generated `child_spec/1` function.
 
+  When stopping the GenServer, for example by returning a `{:stop, reason, new_state}`
+  tuple from a callback, the exit reason is used by the supervisor to determine
+  whether the GenServer needs to be restarted. See the "Exit reasons and restarts"
+  section in the `Supervisor` module.
+
   ## Name registration
 
   Both `start_link/3` and `start/3` support the `GenServer` to register
@@ -207,7 +212,7 @@ defmodule GenServer do
   the GenServer callbacks as doing so will cause the GenServer to misbehave.
 
   Besides the synchronous and asynchronous communication provided by `call/3`
-  and `cast/2`, "regular" messages sent by functions such as `Kernel.send/2`,
+  and `cast/2`, "regular" messages sent by functions such as `send/2`,
   `Process.send_after/4` and similar, can be handled inside the `c:handle_info/2`
   callback.
 
@@ -317,7 +322,7 @@ defmodule GenServer do
 
   ## Debugging with the :sys module
 
-  GenServers, as [special processes](https://erlang.org/doc/design_principles/spec_proc.html),
+  GenServers, as [special processes](https://www.erlang.org/doc/design_principles/spec_proc.html),
   can be debugged using the [`:sys` module](`:sys`).
   Through various hooks, this module allows developers to introspect the state of
   the process and trace system events that happen during its execution, such as
@@ -407,7 +412,7 @@ defmodule GenServer do
 
     * [GenServer - Elixir's Getting Started Guide](https://elixir-lang.org/getting-started/mix-otp/genserver.html)
     * [`:gen_server` module documentation](`:gen_server`)
-    * [gen_server Behaviour - OTP Design Principles](https://erlang.org/doc/design_principles/gen_server_concepts.html)
+    * [gen_server Behaviour - OTP Design Principles](https://www.erlang.org/doc/design_principles/gen_server_concepts.html)
     * [Clients and Servers - Learn You Some Erlang for Great Good!](http://learnyousomeerlang.com/clients-and-servers)
 
   """
@@ -429,10 +434,10 @@ defmodule GenServer do
   except the process is hibernated before entering the loop. See
   `c:handle_call/3` for more information on hibernation.
 
-  Returning `{:ok, state, {:continue, continue}}` is similar to
+  Returning `{:ok, state, {:continue, continue_arg}}` is similar to
   `{:ok, state}` except that immediately after entering the loop,
-  the `c:handle_continue/2` callback will be invoked with the value
-  `continue` as first argument.
+  the `c:handle_continue/2` callback will be invoked with `continue_arg`
+  as the first argument and `state` as the second one.
 
   Returning `:ignore` will cause `start_link/3` to return `:ignore` and
   the process will exit normally without entering the loop or calling
@@ -455,7 +460,7 @@ defmodule GenServer do
   """
   @callback init(init_arg :: term) ::
               {:ok, state}
-              | {:ok, state, timeout | :hibernate | {:continue, term}}
+              | {:ok, state, timeout | :hibernate | {:continue, continue_arg :: term}}
               | :ignore
               | {:stop, reason :: any}
             when state: any
@@ -482,9 +487,10 @@ defmodule GenServer do
   `GenServer` causes garbage collection and leaves a continuous heap that
   minimises the memory used by the process.
 
-  Returning `{:reply, reply, new_state, {:continue, continue}}` is similar to
-  `{:reply, reply, new_state}` except `c:handle_continue/2` will be invoked
-  immediately after with the value `continue` as first argument.
+  Returning `{:reply, reply, new_state, {:continue, continue_arg}}` is similar to
+  `{:reply, reply, new_state}` except that `c:handle_continue/2` will be invoked
+  immediately after with `continue_arg` as the first argument and
+  `state` as the second one.
 
   Hibernating should not be used aggressively as too much time could be spent
   garbage collecting. Normally it should only be used when a message is not
@@ -507,7 +513,7 @@ defmodule GenServer do
   process exits without replying as the caller will be blocking awaiting a
   reply.
 
-  Returning `{:noreply, new_state, timeout | :hibernate | {:continue, continue}}`
+  Returning `{:noreply, new_state, timeout | :hibernate | {:continue, continue_arg}}`
   is similar to `{:noreply, new_state}` except a timeout, hibernation or continue
   occurs as with a `:reply` tuple.
 
@@ -523,9 +529,10 @@ defmodule GenServer do
   """
   @callback handle_call(request :: term, from, state :: term) ::
               {:reply, reply, new_state}
-              | {:reply, reply, new_state, timeout | :hibernate | {:continue, term}}
+              | {:reply, reply, new_state,
+                 timeout | :hibernate | {:continue, continue_arg :: term}}
               | {:noreply, new_state}
-              | {:noreply, new_state, timeout | :hibernate | {:continue, term}}
+              | {:noreply, new_state, timeout | :hibernate | {:continue, continue_arg :: term}}
               | {:stop, reason, reply, new_state}
               | {:stop, reason, new_state}
             when reply: term, new_state: term, reason: term
@@ -546,9 +553,10 @@ defmodule GenServer do
   `{:noreply, new_state}` except the process is hibernated before continuing the
   loop. See `c:handle_call/3` for more information.
 
-  Returning `{:noreply, new_state, {:continue, continue}}` is similar to
+  Returning `{:noreply, new_state, {:continue, continue_arg}}` is similar to
   `{:noreply, new_state}` except `c:handle_continue/2` will be invoked
-  immediately after with the value `continue` as first argument.
+  immediately after with `continue_arg` as the first argument and
+  `state` as the second one.
 
   Returning `{:stop, reason, new_state}` stops the loop and `c:terminate/2` is
   called with the reason `reason` and state `new_state`. The process exits with
@@ -559,7 +567,7 @@ defmodule GenServer do
   """
   @callback handle_cast(request :: term, state :: term) ::
               {:noreply, new_state}
-              | {:noreply, new_state, timeout | :hibernate | {:continue, term}}
+              | {:noreply, new_state, timeout | :hibernate | {:continue, continue_arg :: term}}
               | {:stop, reason :: term, new_state}
             when new_state: term
 
@@ -576,12 +584,12 @@ defmodule GenServer do
   """
   @callback handle_info(msg :: :timeout | term, state :: term) ::
               {:noreply, new_state}
-              | {:noreply, new_state, timeout | :hibernate | {:continue, term}}
+              | {:noreply, new_state, timeout | :hibernate | {:continue, continue_arg :: term}}
               | {:stop, reason :: term, new_state}
             when new_state: term
 
   @doc """
-  Invoked to handle `continue` instructions.
+  Invoked to handle continue instructions.
 
   It is useful for performing work after initialization or for splitting the work
   in a callback in multiple steps, updating the process state along the way.
@@ -591,11 +599,11 @@ defmodule GenServer do
   This callback is optional. If one is not implemented, the server will fail
   if a continue instruction is used.
   """
-  @callback handle_continue(continue :: term, state :: term) ::
+  @callback handle_continue(continue_arg, state :: term) ::
               {:noreply, new_state}
-              | {:noreply, new_state, timeout | :hibernate | {:continue, term}}
+              | {:noreply, new_state, timeout | :hibernate | {:continue, continue_arg}}
               | {:stop, reason :: term, new_state}
-            when new_state: term
+            when new_state: term, continue_arg: term
 
   @doc """
   Invoked when the server is about to exit. It should do any cleanup required.
@@ -608,7 +616,7 @@ defmodule GenServer do
   does one of the following:
 
     * returns a `:stop` tuple
-    * raises (via `Kernel.raise/2`) or exits (via `Kernel.exit/1`)
+    * raises (via `raise/2`) or exits (via `exit/1`)
     * returns an invalid value
 
   If part of a supervision tree, a `GenServer` will receive an exit
@@ -675,11 +683,7 @@ defmodule GenServer do
             when old_vsn: term | {:down, term}
 
   @doc """
-  Invoked in some cases to retrieve a formatted version of the `GenServer` status.
-
-  This callback can be useful to control the *appearance* of the status of the
-  `GenServer`. For example, it can be used to return a compact representation of
-  the `GenServer`'s state to avoid having large state terms printed.
+  Invoked in some cases to retrieve a formatted version of the `GenServer` status:
 
     * one of `:sys.get_status/1` or `:sys.get_status/2` is invoked to get the
       status of the `GenServer`; in such cases, `reason` is `:normal`
@@ -687,6 +691,10 @@ defmodule GenServer do
     * the `GenServer` terminates abnormally and logs an error; in such cases,
       `reason` is `:terminate`
 
+  This callback can be useful to control the *appearance* of the status of the
+  `GenServer`. For example, it can be used to return a compact representation of
+  the `GenServer`'s state to avoid having large state terms printed.
+
   `pdict_and_state` is a two-elements list `[pdict, state]` where `pdict` is a
   list of `{key, value}` tuples representing the current process dictionary of
   the `GenServer` and `state` is the current state of the `GenServer`.
@@ -858,7 +866,7 @@ defmodule GenServer do
       the arguments given to GenServer.start_link/3 to the server state.
       """
 
-      IO.warn(message, Macro.Env.stacktrace(env))
+      IO.warn(message, env)
 
       quote do
         @doc false
@@ -1166,11 +1174,8 @@ defmodule GenServer do
 
   """
   @spec reply(from, term) :: :ok
-  def reply(client, reply)
-
-  def reply({to, tag}, reply) when is_pid(to) do
-    send(to, {tag, reply})
-    :ok
+  def reply(client, reply) do
+    :gen.reply(client, reply)
   end
 
   @doc """

lib/elixir/lib/inspect.ex

@@ -8,16 +8,85 @@ defprotocol Inspect do
   The `Inspect` protocol converts an Elixir data structure into an
   algebra document.
 
+  This is typically done when you want to customize how your own
+  structs are inspected in logs and the terminal.
+
   This documentation refers to implementing the `Inspect` protocol
   for your own data structures. To learn more about using inspect,
   see `Kernel.inspect/2` and `IO.inspect/2`.
 
-  The `inspect/2` function receives the entity to be inspected
-  followed by the inspecting options, represented by the struct
-  `Inspect.Opts`. Building of the algebra document is done with
-  `Inspect.Algebra`.
+  ## Inspect representation
 
-  ## Examples
+  There are typically three choices of inspect representation. In order
+  to understand them, let's imagine we have the following `User` struct:
+
+      defmodule User do
+        defstruct [:id, :name, :address]
+      end
+
+  Our choices are:
+
+    1. Print the struct using Elixir's struct syntax, for example:
+       `%User{address: "Earth", id: 13, name: "Jane"}`. This is the
+       default representation and best choice if all struct fields
+       are public.
+
+    2. Print using the `#User<...>` notation, for example: `#User<id: 13, name: "Jane", ...>`.
+       This notation does not emit valid Elixir code and is typically
+       used when the struct has private fields (for example, you may want
+       to hide the field `:address` to redact person identifiable information).
+
+    3. Print the struct using the expression syntax, for example:
+       `User.new(13, "Jane", "Earth")`. This assumes there is a `User.new/3`
+       function. This option is mostly used as an alternative to option 2
+       for representing custom data structures, such as `MapSet`, `Date.Range`,
+       and others.
+
+  You can implement the Inspect protocol for your own structs while
+  adhering to the conventions above. Option 1 is the default representation
+  and you can quickly achieve option 2 by deriving the `Inspect` protocol.
+  For option 3, you need your custom implementation.
+
+  ## Deriving
+
+  The `Inspect` protocol can be derived to customize the order of fields
+  (the default is alphabetical) and hide certain fields from structs,
+  so they don't show up in logs, inspects and similar. The latter is
+  especially useful for fields containing private information.
+
+  The supported options are:
+
+    * `:only` - only include the given fields when inspecting.
+
+    * `:except` - remove the given fields when inspecting.
+
+    * `:optional` - (since v1.14.0) do not include a field if it
+      matches its default value. This can be used to simplify the
+      struct representation at the cost of hiding information.
+
+  Whenever `:only` or `:except` are used to restrict fields,
+  the struct will be printed using the `#User<...>` notation,
+  as the struct can no longer be copy and pasted as valid Elixir
+  code. Let's see an example:
+
+      defmodule User do
+        @derive {Inspect, only: [:id, :name]}
+        defstruct [:id, :name, :address]
+      end
+
+      inspect(%User{id: 1, name: "Jane", address: "Earth"})
+      #=> #User<id: 1, name: "Jane", ...>
+
+  If you use only the `:optional` option, the struct will still be
+  printed as `%User{...}`.
+
+  ## Custom implementation
+
+  You can also define your custom protocol implementation by
+  defining the `inspect/2` function. The function receives the
+  entity to be inspected followed by the inspecting options,
+  represented by the struct `Inspect.Opts`. Building of the
+  algebra document is done with `Inspect.Algebra`.
 
   Many times, inspecting a structure can be implemented in function
   of existing entities. For example, here is `MapSet`'s `inspect/2`
@@ -27,23 +96,24 @@ defprotocol Inspect do
         import Inspect.Algebra
 
         def inspect(map_set, opts) do
-          concat(["#MapSet<", to_doc(MapSet.to_list(map_set), opts), ">"])
+          concat(["MapSet.new(", Inspect.List.inspect(MapSet.to_list(map_set), opts), ")"])
         end
       end
 
   The [`concat/1`](`Inspect.Algebra.concat/1`) function comes from
   `Inspect.Algebra` and it concatenates algebra documents together.
-  In the example above it is concatenating the string `"#MapSet<"`,
+  In the example above it is concatenating the string `"MapSet.new("`,
   the document returned by `Inspect.Algebra.to_doc/2`, and the final
-  string `">"`. We prefix the module name `#` to denote the inspect
-  presentation is not actually valid Elixir syntax.
+  string `")"`. Therefore, the MapSet with the numbers 1, 2, and 3
+  will be printed as:
 
-  Finally, note strings themselves are valid algebra documents that
-  keep their formatting when pretty printed. This means your `Inspect`
-  implementation may simply return a string, although that will devoid
-  it of any pretty-printing.
+      iex> MapSet.new([1, 2, 3], fn x -> x * 2 end)
+      MapSet.new([2, 4, 6])
 
-  ## Error handling
+  In other words, `MapSet`'s inspect representation returns an expression
+  that, when evaluated, builds the `MapSet` itself.
+
+  ### Error handling
 
   In case there is an error while your structure is being inspected,
   Elixir will raise an `ArgumentError` error and will automatically fall back
@@ -55,24 +125,6 @@ defprotocol Inspect do
 
       Inspect.MapSet.inspect(MapSet.new(), %Inspect.Opts{})
 
-  ## Deriving
-
-  The `Inspect` protocol can be derived to hide certain fields from
-  structs, so they don't show up in logs, inspects and similar. This
-  is especially useful for fields containing private information.
-
-  The options `:only` and `:except` can be used with `@derive` to
-  specify which fields should and should not appear in the
-  algebra document:
-
-      defmodule User do
-        @derive {Inspect, only: [:id, :name]}
-        defstruct [:id, :name, :address]
-      end
-
-      inspect(%User{id: 1, name: "Homer", address: "742 Evergreen Terrace"})
-      #=> #User<id: 1, name: "Homer", ...>
-
   """
 
   # Handle structs in Any
@@ -94,7 +146,7 @@ defimpl Inspect, for: Atom do
   require Macro
 
   def inspect(atom, opts) do
-    color(Identifier.inspect_as_atom(atom), color_key(atom), opts)
+    color(Macro.inspect_atom(:literal, atom), color_key(atom), opts)
   end
 
   defp color_key(atom) when is_boolean(atom), do: :boolean
@@ -210,7 +262,7 @@ defimpl Inspect, for: List do
             {escaped, _} -> [?', escaped, ?', " ++ ..."]
           end
 
-        IO.iodata_to_binary(inspected)
+        color(IO.iodata_to_binary(inspected), :charlist, opts)
 
       keyword?(term) ->
         container_doc(open, term, close, opts, &keyword/2, separator: sep, break: :strict)
@@ -222,7 +274,7 @@ defimpl Inspect, for: List do
 
   @doc false
   def keyword({key, value}, opts) do
-    key = color(Identifier.inspect_as_key(key), :atom, opts)
+    key = color(Macro.inspect_atom(:key, key), :atom, opts)
     concat(key, concat(" ", to_doc(value, opts)))
   end
 
@@ -250,28 +302,33 @@ end
 
 defimpl Inspect, for: Map do
   def inspect(map, opts) do
-    inspect(map, "", opts)
+    list = Map.to_list(map)
+
+    fun =
+      if Inspect.List.keyword?(list) do
+        &Inspect.List.keyword/2
+      else
+        sep = color(" => ", :map, opts)
+        &to_assoc(&1, &2, sep)
+      end
+
+    map_container_doc(list, "", opts, fun)
   end
 
-  def inspect(map, name, opts) do
-    map = Map.to_list(map)
+  def inspect(map, name, infos, opts) do
+    fun = fn %{field: field}, opts -> Inspect.List.keyword({field, Map.get(map, field)}, opts) end
+    map_container_doc(infos, name, opts, fun)
+  end
+
+  defp to_assoc({key, value}, opts, sep) do
+    concat(concat(to_doc(key, opts), sep), to_doc(value, opts))
+  end
+
+  defp map_container_doc(list, name, opts, fun) do
     open = color("%" <> name <> "{", :map, opts)
     sep = color(",", :map, opts)
     close = color("}", :map, opts)
-    container_doc(open, map, close, opts, traverse_fun(map, opts), separator: sep, break: :strict)
-  end
-
-  defp traverse_fun(list, opts) do
-    if Inspect.List.keyword?(list) do
-      &Inspect.List.keyword/2
-    else
-      sep = color(" => ", :map, opts)
-      &to_map(&1, &2, sep)
-    end
-  end
-
-  defp to_map({key, value}, opts, sep) do
-    concat(concat(to_doc(key, opts), sep), to_doc(value, opts))
+    container_doc(open, list, close, opts, fun, separator: sep, break: :strict)
   end
 end
 
@@ -309,13 +366,31 @@ defimpl Inspect, for: Integer do
 end
 
 defimpl Inspect, for: Float do
-  def inspect(term, opts) do
-    inspected = IO.iodata_to_binary(:io_lib_format.fwrite_g(term))
-    color(inspected, :number, opts)
+  def inspect(float, opts) do
+    abs = abs(float)
+
+    formatted =
+      if abs >= 1.0 and abs < 1.0e16 and trunc(float) == float do
+        [Integer.to_string(trunc(float)), ?., ?0]
+      else
+        :io_lib_format.fwrite_g(float)
+      end
+
+    color(IO.iodata_to_binary(formatted), :number, opts)
   end
 end
 
 defimpl Inspect, for: Regex do
+  def inspect(regex = %{opts: regex_opts}, opts) when is_list(regex_opts) do
+    concat([
+      "Regex.compile!(",
+      Inspect.BitString.inspect(regex.source, opts),
+      ", ",
+      Inspect.List.inspect(regex_opts, opts),
+      ")"
+    ])
+  end
+
   def inspect(regex, opts) do
     {escaped, _} =
       regex.source
@@ -347,9 +422,12 @@ defimpl Inspect, for: Function do
     name = fun_info[:name]
 
     cond do
+      not is_atom(mod) ->
+        "#Function<#{uniq(fun_info)}/#{fun_info[:arity]}>"
+
       fun_info[:type] == :external and fun_info[:env] == [] ->
-        inspected_as_atom = Identifier.inspect_as_atom(mod)
-        inspected_as_function = Identifier.inspect_as_function(name)
+        inspected_as_atom = Macro.inspect_atom(:literal, mod)
+        inspected_as_function = Macro.inspect_atom(:remote_call, name)
         "&#{inspected_as_atom}.#{inspected_as_function}/#{fun_info[:arity]}"
 
       match?('elixir_compiler_' ++ _, Atom.to_charlist(mod)) ->
@@ -365,7 +443,7 @@ defimpl Inspect, for: Function do
   end
 
   defp default_inspect(mod, fun_info) do
-    inspected_as_atom = Identifier.inspect_as_atom(mod)
+    inspected_as_atom = Macro.inspect_atom(:literal, mod)
     extracted_name = extract_name(fun_info[:name])
     "#Function<#{uniq(fun_info)}/#{fun_info[:arity]} in #{inspected_as_atom}#{extracted_name}>"
   end
@@ -377,10 +455,10 @@ defimpl Inspect, for: Function do
   defp extract_name(name) do
     case Identifier.extract_anonymous_fun_parent(name) do
       {name, arity} ->
-        "." <> Identifier.inspect_as_function(name) <> "/" <> arity
+        "." <> Macro.inspect_atom(:remote_call, name) <> "/" <> arity
 
       :error ->
-        "." <> Identifier.inspect_as_function(name)
+        "." <> Macro.inspect_atom(:remote_call, name)
     end
   end
 
@@ -389,6 +467,36 @@ defimpl Inspect, for: Function do
   end
 end
 
+defimpl Inspect, for: Inspect.Error do
+  @impl true
+  def inspect(%{stacktrace: stacktrace} = inspect_error, _opts) do
+    message = Exception.message(inspect_error)
+    format_output(message, stacktrace)
+  end
+
+  defp format_output(message, [_ | _] = stacktrace) do
+    stacktrace = Exception.format_stacktrace(stacktrace)
+
+    """
+    #Inspect.Error<
+    #{Inspect.Error.pad(message, 2)}
+
+      Stacktrace:
+
+    #{stacktrace}
+    >\
+    """
+  end
+
+  defp format_output(message, []) do
+    """
+    #Inspect.Error<
+      #{Inspect.Error.pad(message, 2)}
+    >\
+    """
+  end
+end
+
 defimpl Inspect, for: PID do
   def inspect(pid, _opts) do
     "#PID" <> IO.iodata_to_binary(:erlang.pid_to_list(pid))
@@ -413,11 +521,11 @@ defimpl Inspect, for: Any do
     fields = Map.keys(struct) -- [:__exception__, :__struct__]
     only = Keyword.get(options, :only, fields)
     except = Keyword.get(options, :except, [])
+    optional = Keyword.get(options, :optional, [])
 
-    filtered_fields =
-      fields
-      |> Enum.reject(&(&1 in except))
-      |> Enum.filter(&(&1 in only))
+    :ok = validate_option(:only, only, fields, module)
+    :ok = validate_option(:except, except, fields, module)
+    :ok = validate_option(:optional, optional, fields, module)
 
     inspect_module =
       if fields == only and except == [] do
@@ -426,45 +534,86 @@ defimpl Inspect, for: Any do
         Inspect.Any
       end
 
+    filtered_fields =
+      fields
+      |> Enum.reject(&(&1 in except))
+      |> Enum.filter(&(&1 in only))
+
+    optional? =
+      if optional == [] do
+        false
+      else
+        optional_map = for field <- optional, into: %{}, do: {field, Map.fetch!(struct, field)}
+
+        quote do
+          case unquote(Macro.escape(optional_map)) do
+            %{^var!(field) => var!(default)} ->
+              var!(default) == Map.get(var!(struct), var!(field))
+
+            %{} ->
+              false
+          end
+        end
+      end
+
     quote do
       defimpl Inspect, for: unquote(module) do
         def inspect(var!(struct), var!(opts)) do
-          var!(map) = Map.take(var!(struct), unquote(filtered_fields))
-          var!(name) = Identifier.inspect_as_atom(unquote(module))
-          unquote(inspect_module).inspect(var!(map), var!(name), var!(opts))
+          var!(infos) =
+            for %{field: var!(field)} = var!(info) <- unquote(module).__info__(:struct),
+                var!(field) in unquote(filtered_fields) and not unquote(optional?),
+                do: var!(info)
+
+          var!(name) = Macro.inspect_atom(:literal, unquote(module))
+          unquote(inspect_module).inspect(var!(struct), var!(name), var!(infos), var!(opts))
         end
       end
     end
   end
 
+  defp validate_option(option, option_list, fields, module) do
+    case option_list -- fields do
+      [] ->
+        :ok
+
+      unknown_fields ->
+        raise ArgumentError,
+              "unknown fields #{Kernel.inspect(unknown_fields)} in #{Kernel.inspect(option)} " <>
+                "when deriving the Inspect protocol for #{Kernel.inspect(module)}"
+    end
+  end
+
   def inspect(%module{} = struct, opts) do
     try do
-      module.__struct__()
+      {module.__struct__(), module.__info__(:struct)}
     rescue
       _ -> Inspect.Map.inspect(struct, opts)
     else
-      dunder ->
+      {dunder, fields} ->
         if Map.keys(dunder) == Map.keys(struct) do
-          pruned = Map.drop(struct, [:__struct__, :__exception__])
-          Inspect.Map.inspect(pruned, Identifier.inspect_as_atom(module), opts)
+          infos =
+            for %{field: field} = info <- fields,
+                field not in [:__struct__, :__exception__],
+                do: info
+
+          Inspect.Map.inspect(struct, Macro.inspect_atom(:literal, module), infos, opts)
         else
           Inspect.Map.inspect(struct, opts)
         end
     end
   end
 
-  def inspect(map, name, opts) do
-    map = Map.to_list(map) ++ [:...]
+  def inspect(map, name, infos, opts) do
     open = color("#" <> name <> "<", :map, opts)
     sep = color(",", :map, opts)
     close = color(">", :map, opts)
 
     fun = fn
-      {key, value}, opts -> Inspect.List.keyword({key, value}, opts)
+      %{field: field}, opts -> Inspect.List.keyword({field, Map.get(map, field)}, opts)
       :..., _opts -> "..."
     end
 
-    container_doc(open, map, close, opts, fun, separator: sep, break: :strict)
+    container_doc(open, infos ++ [:...], close, opts, fun, separator: sep, break: :strict)
   end
 end
 

lib/elixir/lib/inspect/algebra.ex

@@ -53,7 +53,7 @@ defmodule Inspect.Opts do
     * `:safe` - when `false`, failures while inspecting structs will be raised
       as errors instead of being wrapped in the `Inspect.Error` exception. This
       is useful when debugging failures and crashes for custom inspect
-      implementations.
+      implementations. Defaults to `true`.
 
     * `:structs` - when `false`, structs are not formatted by the inspect
       protocol, they are instead printed as maps. Defaults to `true`.
@@ -64,6 +64,7 @@ defmodule Inspect.Opts do
       `:atom`, `:binary`, `:boolean`, `:list`, `:map`, `:number`, `:regex`,
       `:string`, and `:tuple`. Custom data types may provide their own options.
       Colors can be any `t:IO.ANSI.ansidata/0` as accepted by `IO.ANSI.format/1`.
+      A default list of colors can be retrieved from `IO.ANSI.syntax_colors/0`.
 
     * `:width` - number of characters per line used when pretty is `true` or when
       printing to IO devices. Set to `0` to force each item to be printed on its
@@ -89,11 +90,9 @@ defmodule Inspect.Opts do
 
   @type color_key :: atom
 
-  # TODO: Remove :char_lists key and :as_char_lists value on v2.0
   @type t :: %__MODULE__{
           base: :decimal | :binary | :hex | :octal,
           binaries: :infer | :as_binaries | :as_strings,
-          char_lists: :infer | :as_lists | :as_char_lists,
           charlists: :infer | :as_lists | :as_charlists,
           custom_options: keyword,
           inspect_fun: (any, t -> Inspect.Algebra.t()),
@@ -163,13 +162,6 @@ defmodule Inspect.Opts do
   end
 end
 
-defmodule Inspect.Error do
-  @moduledoc """
-  Raised when a struct cannot be inspected.
-  """
-  defexception [:message]
-end
-
 defmodule Inspect.Algebra do
   @moduledoc ~S"""
   A set of functions for creating and manipulating algebra
@@ -262,12 +254,18 @@ defmodule Inspect.Algebra do
           | doc_group
           | doc_nest
           | doc_string
+          | doc_limit
 
   @typep doc_string :: {:doc_string, t, non_neg_integer}
   defmacrop doc_string(string, length) do
     quote do: {:doc_string, unquote(string), unquote(length)}
   end
 
+  @typep doc_limit :: {:doc_limit, t, pos_integer | :infinity}
+  defmacrop doc_limit(doc, limit) do
+    quote do: {:doc_limit, unquote(doc), unquote(limit)}
+  end
+
   @typep doc_cons :: {:doc_cons, t, t}
   defmacrop doc_cons(left, right) do
     quote do: {:doc_cons, unquote(left), unquote(right)}
@@ -317,7 +315,8 @@ defmodule Inspect.Algebra do
     :doc_force,
     :doc_group,
     :doc_nest,
-    :doc_string
+    :doc_string,
+    :doc_limit
   ]
 
   defguard is_doc(doc)
@@ -354,28 +353,28 @@ defmodule Inspect.Algebra do
             try do
               Process.put(:inspect_trap, true)
 
-              res =
-                Inspect.Map.inspect(struct, %{
+              inspected_struct =
+                struct
+                |> Inspect.Map.inspect(%{
                   opts
                   | syntax_colors: [],
                     inspect_fun: Inspect.Opts.default_inspect_fun()
                 })
+                |> format(opts.width)
+                |> IO.iodata_to_binary()
 
-              res = IO.iodata_to_binary(format(res, :infinity))
-
-              message =
-                "got #{inspect(caught_exception.__struct__)} with message " <>
-                  "#{inspect(Exception.message(caught_exception))} while inspecting #{res}"
-
-              exception = Inspect.Error.exception(message: message)
+              inspect_error =
+                Inspect.Error.exception(
+                  exception: caught_exception,
+                  stacktrace: __STACKTRACE__,
+                  inspected_struct: inspected_struct
+                )
 
               if opts.safe do
-                Inspect.inspect(exception, %{
-                  opts
-                  | inspect_fun: Inspect.Opts.default_inspect_fun()
-                })
+                opts = %{opts | inspect_fun: Inspect.Opts.default_inspect_fun()}
+                Inspect.inspect(inspect_error, opts)
               else
-                reraise(exception, __STACKTRACE__)
+                reraise(inspect_error, __STACKTRACE__)
               end
             after
               Process.delete(:inspect_trap)
@@ -469,8 +468,9 @@ defmodule Inspect.Algebra do
 
   defp container_each([term | terms], limit, opts, fun, acc, simple?)
        when is_list(terms) and is_limit(limit) do
-    limit = decrement(limit)
-    doc = fun.(term, %{opts | limit: limit})
+    new_limit = decrement(limit)
+    doc = fun.(term, %{opts | limit: new_limit})
+    limit = if doc == :doc_nil, do: limit, else: new_limit
     container_each(terms, limit, opts, fun, [doc | acc], simple? and simple?(doc))
   end
 
@@ -582,6 +582,10 @@ defmodule Inspect.Algebra do
     doc_cons(doc1, doc2)
   end
 
+  def no_limit(doc) do
+    doc_limit(doc, :infinity)
+  end
+
   @doc ~S"""
   Concatenates a list of documents returning a new document.
 
@@ -631,7 +635,7 @@ defmodule Inspect.Algebra do
       ["hello", "\n     ", "world"]
 
   """
-  @spec nest(t, non_neg_integer | :cursor | :reset, :always | :break) :: doc_nest
+  @spec nest(t, non_neg_integer | :cursor | :reset, :always | :break) :: doc_nest | t
   def nest(doc, level, mode \\ :always)
 
   def nest(doc, :cursor, mode) when is_doc(doc) and mode in [:always, :break] do
@@ -972,7 +976,7 @@ defmodule Inspect.Algebra do
   @typep mode :: :flat | :flat_no_break | :break | :break_no_flat
 
   @spec fits?(
-          width :: non_neg_integer(),
+          width :: non_neg_integer() | :infinity,
           column :: non_neg_integer(),
           break? :: boolean(),
           entries
@@ -1037,9 +1041,17 @@ defmodule Inspect.Algebra do
   defp fits?(w, k, b?, [{i, m, doc_group(x, _)} | t]),
     do: fits?(w, k, b?, [{i, m, x} | {:tail, b?, t}])
 
-  @spec format(width :: non_neg_integer() | :infinity, column :: non_neg_integer(), [
-          {integer, mode, t}
-        ]) :: [binary]
+  defp fits?(w, k, b?, [{i, m, doc_limit(x, :infinity)} | t]) when w != :infinity,
+    do: fits?(:infinity, k, b?, [{i, :flat, x}, {i, m, doc_limit(empty(), w)} | t])
+
+  defp fits?(_w, k, b?, [{i, m, doc_limit(x, w)} | t]),
+    do: fits?(w, k, b?, [{i, m, x} | t])
+
+  @spec format(
+          width :: non_neg_integer() | :infinity,
+          column :: non_neg_integer(),
+          [{integer, mode, t}]
+        ) :: [binary]
   defp format(_, _, []), do: []
   defp format(w, k, [{_, _, :doc_nil} | t]), do: format(w, k, t)
   defp format(w, _, [{i, _, :doc_line} | t]), do: [indent(i) | format(w, i, t)]
@@ -1093,6 +1105,15 @@ defmodule Inspect.Algebra do
     end
   end
 
+  # Limit is set to infinity and then reverts
+  defp format(w, k, [{i, m, doc_limit(x, :infinity)} | t]) when w != :infinity do
+    format(:infinity, k, [{i, :flat, x}, {i, m, doc_limit(empty(), w)} | t])
+  end
+
+  defp format(_w, k, [{i, m, doc_limit(x, w)} | t]) do
+    format(w, k, [{i, m, x} | t])
+  end
+
   defp collapse(["\n" <> _ | t], max, count, i) do
     collapse(t, max, count + 1, i)
   end

lib/elixir/lib/integer.ex

@@ -4,11 +4,11 @@ defmodule Integer do
 
   Some functions that work on integers are found in `Kernel`:
 
-    * `abs/1`
-    * `div/2`
-    * `max/2`
-    * `min/2`
-    * `rem/2`
+    * `Kernel.abs/1`
+    * `Kernel.div/2`
+    * `Kernel.max/2`
+    * `Kernel.min/2`
+    * `Kernel.rem/2`
 
   """
 

lib/elixir/lib/io.ex

@@ -172,8 +172,17 @@ defmodule IO do
   @doc """
   Reads from the IO `device`. The operation is Unicode unsafe.
 
-  The `device` is iterated by the given number of bytes, line by line if
-  `:line` is given, or until `:eof`.
+  The `device` is iterated as specified by the `line_or_chars` argument:
+
+    * if `line_or_chars` is an integer, it represents a number of bytes. The device is
+      iterated by that number of bytes.
+
+    * if `line_or_chars` is `:line`, the device is iterated line by line.
+
+    * if `line_or_chars` is `:eof`, the device is iterated until `:eof`. `line_or_chars`
+      can only be `:eof` since Elixir 1.13.0. `:eof` replaces the deprecated `:all`,
+      with the difference that `:all` returns `""` on end of file, while `:eof` returns
+      `:eof` itself.
 
   It returns:
 
@@ -286,14 +295,24 @@ defmodule IO do
   end
 
   @doc """
-  Writes a `message` to stderr, along with the given `stacktrace`.
+  Writes a `message` to stderr, along with the given `stacktrace_info`.
+
+  The `stacktrace_info` must be one of:
+
+    * a `__STACKTRACE__`, where all entries in the stacktrace will be
+      included in the error message
+
+    * a `Macro.Env` structure (since v1.14.0), where a single stacktrace
+      entry from the compilation environment will be used
+
+    * a keyword list with at least the `:file` option representing
+      a single stacktrace entry (since v1.14.0). The `:line`, `:module`,
+      `:function` options are also supported
 
   This function also notifies the compiler a warning was printed
   (in case --warnings-as-errors was enabled). It returns `:ok`
   if it succeeds.
 
-  An empty list can be passed to avoid stacktrace printing.
-
   ## Examples
 
       stacktrace = [{MyApp, :main, 1, [file: 'my_app.ex', line: 4]}]
@@ -302,12 +321,36 @@ defmodule IO do
       #=>   my_app.ex:4: MyApp.main/1
 
   """
-  @spec warn(chardata | String.Chars.t(), Exception.stacktrace()) :: :ok
+  @spec warn(chardata | String.Chars.t(), Exception.stacktrace() | keyword() | Macro.Env.t()) ::
+          :ok
+  def warn(message, stacktrace_info)
+
   def warn(message, []) do
     message = [to_chardata(message), ?\n]
     :elixir_errors.log_and_print_warning(0, nil, message, message)
   end
 
+  def warn(message, %Macro.Env{} = env) do
+    warn(message, Macro.Env.stacktrace(env))
+  end
+
+  def warn(message, [{_, _} | _] = keyword) do
+    if file = keyword[:file] do
+      warn(
+        message,
+        %{
+          __ENV__
+          | module: keyword[:module],
+            function: keyword[:function],
+            line: keyword[:line],
+            file: file
+        }
+      )
+    else
+      warn(message, [])
+    end
+  end
+
   def warn(message, [{_, _, _, opts} | _] = stacktrace) do
     message = to_chardata(message)
     formatted_trace = Enum.map_join(stacktrace, "\n  ", &Exception.format_stacktrace_entry(&1))
@@ -545,7 +588,7 @@ defmodule IO do
   Note that an IO stream has side effects and every time
   you go over the stream you may get different results.
 
-  `stream/1` has been introduced in Elixir v1.12.0,
+  `stream/0` has been introduced in Elixir v1.12.0,
   while `stream/2` has been available since v1.0.0.
 
   ## Examples
@@ -590,7 +633,7 @@ defmodule IO do
   Finally, do not use this function on IO devices in Unicode
   mode as it will return the wrong result.
 
-  `binstream/1` has been introduced in Elixir v1.12.0,
+  `binstream/0` has been introduced in Elixir v1.12.0,
   while `binstream/2` has been available since v1.0.0.
   """
   @spec binstream(device, :line | pos_integer) :: Enumerable.t()

lib/elixir/lib/io/ansi.ex

@@ -3,6 +3,7 @@ defmodule IO.ANSI.Sequence do
 
   defmacro defsequence(name, code, terminator \\ "m") do
     quote bind_quoted: [name: name, code: code, terminator: terminator] do
+      @spec unquote(name)() :: String.t()
       def unquote(name)() do
         "\e[#{unquote(code)}#{unquote(terminator)}"
       end
@@ -68,6 +69,34 @@ defmodule IO.ANSI do
     Application.get_env(:elixir, :ansi_enabled, false)
   end
 
+  @doc """
+  Syntax colors to be used by `Inspect`.
+
+  Those colors are used throughout Elixir's standard library,
+  such as `dbg/2` and `IEx`.
+
+  The colors can be changed by setting the `:ansi_syntax_colors`
+  in the `:elixir` application configuration. Configuration for
+  most built-in data types are supported: `:atom`, `:binary`,
+  `:boolean`, `:charlist`, `:list`, `:map`, `:nil`, `:number`,
+  `:string`, and `:tuple`. The default is:
+
+      [
+        atom: :cyan
+        boolean: :magenta,
+        charlist: :yellow,
+        nil: :magenta,
+        number: :yellow,
+        string: :green
+      ]
+
+  """
+  @doc since: "1.14.0"
+  @spec syntax_colors :: Keyword.t(ansidata)
+  def syntax_colors do
+    Application.fetch_env!(:elixir, :ansi_syntax_colors)
+  end
+
   @doc "Sets foreground color."
   @spec color(0..255) :: String.t()
   def color(code) when code in 0..255, do: "\e[38;5;#{code}m"
@@ -251,8 +280,9 @@ defmodule IO.ANSI do
       [[[[[[], "Hello, "] | "\e[31m"] | "\e[1m"], "world!"] | "\e[0m"]
 
   """
-  def format(chardata, emit? \\ enabled?()) when is_boolean(emit?) do
-    do_format(chardata, [], [], emit?, :maybe)
+  @spec format(ansidata, boolean) :: IO.chardata()
+  def format(ansidata, emit? \\ enabled?()) when is_boolean(emit?) do
+    do_format(ansidata, [], [], emit?, :maybe)
   end
 
   @doc ~S"""
@@ -271,8 +301,9 @@ defmodule IO.ANSI do
       [[[[[[] | "\e[1m"], 87], 111], 114], 100]
 
   """
-  def format_fragment(chardata, emit? \\ enabled?()) when is_boolean(emit?) do
-    do_format(chardata, [], [], emit?, false)
+  @spec format_fragment(ansidata, boolean) :: IO.chardata()
+  def format_fragment(ansidata, emit? \\ enabled?()) when is_boolean(emit?) do
+    do_format(ansidata, [], [], emit?, false)
   end
 
   defp do_format([term | rest], rem, acc, emit?, append_reset) do

lib/elixir/lib/io/stream.ex

@@ -26,7 +26,11 @@ defmodule IO.Stream do
 
   defstruct device: nil, raw: true, line_or_bytes: :line
 
-  @type t :: %__MODULE__{}
+  @type t :: %__MODULE__{
+          device: IO.device(),
+          raw: boolean(),
+          line_or_bytes: :line | non_neg_integer()
+        }
 
   @doc false
   def __build__(device, raw, line_or_bytes) do

lib/elixir/lib/kernel/cli.ex

@@ -13,7 +13,8 @@ defmodule Kernel.CLI do
     pa: [],
     pz: [],
     verbose_compile: false,
-    profile: nil
+    profile: nil,
+    pry: false
   }
 
   @standalone_opts ["-h", "--help", "--short-version"]
@@ -28,6 +29,10 @@ defmodule Kernel.CLI do
     System.argv(argv)
     System.no_halt(config.no_halt)
 
+    if config.pry do
+      Application.put_env(:elixir, :dbg_callback, {IEx.Pry, :dbg, []})
+    end
+
     fun = fn _ ->
       errors = process_commands(config)
 
@@ -218,12 +223,16 @@ defmodule Kernel.CLI do
 
   # Parse shared options
 
-  defp parse_shared([opt | _], _config) when opt in @standalone_opts do
+  defp halt_standalone(opt) do
     IO.puts(:stderr, "#{opt} : Standalone options can't be combined with other options")
     System.halt(1)
   end
 
-  defp parse_shared([opt | t], config) when opt in ["-v", "--version"] do
+  defp parse_shared([opt | _], _config) when opt in @standalone_opts do
+    halt_standalone(opt)
+  end
+
+  defp parse_shared([opt | t], _config) when opt in ["-v", "--version"] do
     if function_exported?(IEx, :started?, 0) and IEx.started?() do
       IO.puts("IEx " <> System.build_info()[:build])
     else
@@ -231,7 +240,11 @@ defmodule Kernel.CLI do
       IO.puts("Elixir " <> System.build_info()[:build])
     end
 
-    parse_shared(t, config)
+    if t != [] do
+      halt_standalone(opt)
+    else
+      System.halt(0)
+    end
   end
 
   defp parse_shared(["-pa", h | t], config) do
@@ -267,6 +280,11 @@ defmodule Kernel.CLI do
     parse_shared(t, %{config | commands: [{:rpc_eval, node, h} | config.commands]})
   end
 
+  defp parse_shared(["--rpc-eval" | _], config) do
+    new_config = %{config | errors: ["--rpc-eval : wrong number of arguments" | config.errors]}
+    {[], new_config}
+  end
+
   defp parse_shared(["-r", h | t], config) do
     parse_shared(t, %{config | commands: [{:require, h} | config.commands]})
   end
@@ -306,7 +324,7 @@ defmodule Kernel.CLI do
   end
 
   defp parse_argv(["+iex" | t], config) do
-    parse_iex(t, config)
+    parse_iex(t, %{config | pry: true})
   end
 
   defp parse_argv(["-S", h | t], config) do
@@ -391,20 +409,16 @@ defmodule Kernel.CLI do
     {config, t}
   end
 
-  # This clause is here so that Kernel.CLI does not
-  # error out with "unknown option"
-  defp parse_iex(["--dot-iex", _ | t], config) do
-    parse_iex(t, config)
-  end
-
-  defp parse_iex([opt, _ | t], config) when opt in ["--remsh"] do
-    parse_iex(t, config)
-  end
-
   defp parse_iex(["-S", h | t], config) do
     {%{config | commands: [{:script, h} | config.commands]}, t}
   end
 
+  # These clauses are here so that Kernel.CLI does not error out with "unknown option"
+  defp parse_iex(["--dot-iex", _ | t], config), do: parse_iex(t, config)
+  defp parse_iex(["--remsh", _ | t], config), do: parse_iex(t, config)
+
+  defp parse_iex(["--no-pry" | t], config), do: parse_iex(t, %{config | pry: false})
+
   defp parse_iex([h | t] = list, config) do
     case h do
       "-" <> _ -> shared_option?(list, config, &parse_iex(&1, &2))

lib/elixir/lib/kernel/lexical_tracker.ex

@@ -30,8 +30,8 @@ defmodule Kernel.LexicalTracker do
   end
 
   @doc false
-  def add_require(pid, module) when is_atom(module) do
-    :gen_server.cast(pid, {:add_require, module})
+  def add_export(pid, module) when is_atom(module) do
+    :gen_server.cast(pid, {:add_export, module})
   end
 
   @doc false
@@ -59,6 +59,11 @@ defmodule Kernel.LexicalTracker do
     :gen_server.cast(pid, {:alias_dispatch, module})
   end
 
+  @doc false
+  def import_quoted(pid, module, function, arities) when is_atom(module) do
+    :gen_server.cast(pid, {:import_quoted, module, function, arities})
+  end
+
   @doc false
   def add_compile_env(pid, app, path, return) do
     :gen_server.cast(pid, {:compile_env, app, path, return})
@@ -88,23 +93,24 @@ defmodule Kernel.LexicalTracker do
 
   @doc false
   def collect_unused_imports(pid) do
-    unused(pid, :import)
+    unused(pid, :unused_imports)
   end
 
   @doc false
   def collect_unused_aliases(pid) do
-    unused(pid, :alias)
+    unused(pid, :unused_aliases)
   end
 
   defp unused(pid, tag) do
-    :gen_server.call(pid, {:unused, tag}, @timeout)
+    :gen_server.call(pid, tag, @timeout)
   end
 
   # Callbacks
 
   def init(:ok) do
     state = %{
-      directives: %{},
+      aliases: %{},
+      imports: %{},
       references: %{},
       exports: %{},
       cache: %{},
@@ -116,13 +122,12 @@ defmodule Kernel.LexicalTracker do
   end
 
   @doc false
-  def handle_call({:unused, tag}, _from, state) do
-    directives =
-      for {{^tag, module_or_mfa}, marker} <- state.directives, is_integer(marker) do
-        {module_or_mfa, marker}
-      end
+  def handle_call(:unused_aliases, _from, state) do
+    {:reply, Enum.sort(state.aliases), state}
+  end
 
-    {:reply, Enum.sort(directives), state}
+  def handle_call(:unused_imports, _from, state) do
+    {:reply, Enum.sort(state.imports), state}
   end
 
   def handle_call(:references, _from, state) do
@@ -148,12 +153,44 @@ defmodule Kernel.LexicalTracker do
   end
 
   def handle_cast({:import_dispatch, module, {function, arity}, mode}, state) do
-    state = add_import_dispatch(state, module, function, arity, mode)
-    {:noreply, state}
+    %{imports: imports, references: references} = state
+
+    imports =
+      case imports do
+        %{^module => modules_and_fas} ->
+          modules_and_fas
+          |> Map.delete(module)
+          |> Map.delete({function, arity})
+          |> then(&Map.put(imports, module, &1))
+
+        %{} ->
+          imports
+      end
+
+    references = add_reference(references, module, mode)
+    {:noreply, %{state | imports: imports, references: references}}
   end
 
-  def handle_cast({:alias_dispatch, module}, state) do
-    {:noreply, %{state | directives: add_dispatch(state.directives, module, :alias)}}
+  def handle_cast({:alias_dispatch, module}, %{aliases: aliases} = state) do
+    {:noreply, %{state | aliases: Map.delete(aliases, module)}}
+  end
+
+  def handle_cast({:import_quoted, module, function, arities}, state) do
+    %{imports: imports} = state
+
+    imports =
+      case imports do
+        %{^module => modules_and_fas} ->
+          arities
+          |> Enum.reduce(modules_and_fas, &Map.delete(&2, {function, &1}))
+          |> Map.delete(module)
+          |> then(&Map.put(imports, module, &1))
+
+        %{} ->
+          imports
+      end
+
+    {:noreply, %{state | imports: imports}}
   end
 
   def handle_cast({:set_file, file}, state) do
@@ -168,28 +205,25 @@ defmodule Kernel.LexicalTracker do
     {:noreply, update_in(state.compile_env, &:ordsets.add_element({app, path, return}, &1))}
   end
 
-  def handle_cast({:add_require, module}, state) do
+  def handle_cast({:add_export, module}, state) do
     {:noreply, put_in(state.exports[module], true)}
   end
 
   def handle_cast({:add_import, module, fas, line, warn}, state) do
-    to_remove = for {{:import, {^module, _, _}} = key, _} <- state.directives, do: key
-
-    directives =
-      state.directives
-      |> Map.drop(to_remove)
-      |> add_directive(module, line, warn, :import)
-
-    directives =
-      Enum.reduce(fas, directives, fn {function, arity}, directives ->
-        add_directive(directives, {module, function, arity}, line, warn, :import)
-      end)
-
-    {:noreply, %{state | directives: directives}}
+    if warn do
+      imports = for module_or_fa <- [module | fas], do: {module_or_fa, line}, into: %{}
+      {:noreply, put_in(state.imports[module], imports)}
+    else
+      {:noreply, state}
+    end
   end
 
   def handle_cast({:add_alias, module, line, warn}, state) do
-    {:noreply, %{state | directives: add_directive(state.directives, module, line, warn, :alias)}}
+    if warn do
+      {:noreply, put_in(state.aliases[module], line)}
+    else
+      {:noreply, state}
+    end
   end
 
   @doc false
@@ -221,31 +255,9 @@ defmodule Kernel.LexicalTracker do
     do: Map.put(references, module, :compile)
 
   defp add_reference(references, module, :runtime) when is_atom(module) do
-    case Map.fetch(references, module) do
-      {:ok, _} -> references
-      :error -> Map.put(references, module, :runtime)
+    case references do
+      %{^module => _} -> references
+      %{} -> Map.put(references, module, :runtime)
     end
   end
-
-  defp add_import_dispatch(state, module, function, arity, mode) do
-    directives =
-      state.directives
-      |> add_dispatch(module, :import)
-      |> add_dispatch({module, function, arity}, :import)
-
-    references = add_reference(state.references, module, mode)
-    %{state | directives: directives, references: references}
-  end
-
-  # In the map we keep imports and aliases.
-  # If the value is a line, it was imported/aliased and has a pending warning
-  # If the value is true, it was imported/aliased and used
-  defp add_directive(directives, module_or_mfa, line, warn, tag) do
-    marker = if warn, do: line, else: true
-    Map.put(directives, {tag, module_or_mfa}, marker)
-  end
-
-  defp add_dispatch(directives, module_or_mfa, tag) do
-    Map.put(directives, {tag, module_or_mfa}, true)
-  end
 end

lib/elixir/lib/kernel/parallel_compiler.ex

@@ -5,9 +5,9 @@ defmodule Kernel.ParallelCompiler do
 
   @typedoc "The line. 0 indicates no line."
   @type line() :: non_neg_integer()
-  @type location() :: line() | {line(), column :: non_neg_integer}
+  @type location() :: line() | {pos_integer(), column :: non_neg_integer}
   @type warning() :: {file :: Path.t(), location(), message :: String.t()}
-  @type error() :: {file :: Path.t(), line(), message :: String.t()}
+  @type error() :: {file :: Path.t(), location(), message :: String.t()}
 
   @doc """
   Starts a task for parallel compilation.
@@ -28,7 +28,7 @@ defmodule Kernel.ParallelCompiler do
         dest = :erlang.get(:elixir_compiler_dest)
 
         {:error_handler, error_handler} = :erlang.process_info(self(), :error_handler)
-        checker = Module.ParallelChecker.get()
+        {_parent, checker} = Module.ParallelChecker.get()
 
         Task.async(fn ->
           send(compiler, {:async, self()})
@@ -241,7 +241,7 @@ defmodule Kernel.ParallelCompiler do
 
   defp write_module_binaries(result, {:compile, path}, timestamp) do
     Enum.flat_map(result, fn
-      {{:module, module}, {binary, _map}} ->
+      {{:module, module}, binary} ->
         full_path = Path.join(path, Atom.to_string(module) <> ".beam")
         File.write!(full_path, binary)
         if timestamp, do: File.touch!(full_path, timestamp)
@@ -268,8 +268,8 @@ defmodule Kernel.ParallelCompiler do
     %{profile: profile, checker: checker} = state
 
     compiled_modules =
-      for {{:module, _module}, {_binary, info}} <- result,
-          do: info
+      for {{:module, module}, _} <- result,
+          do: module
 
     runtime_modules =
       for module <- runtime_modules,
@@ -278,7 +278,7 @@ defmodule Kernel.ParallelCompiler do
           do: {module, path}
 
     profile_checker(profile, compiled_modules, runtime_modules, fn ->
-      Module.ParallelChecker.verify(checker, compiled_modules, runtime_modules)
+      Module.ParallelChecker.verify(checker, runtime_modules)
     end)
   end
 
@@ -479,16 +479,24 @@ defmodule Kernel.ParallelCompiler do
     Enum.count(result, &match?({{:module, _}, _}, &1))
   end
 
-  # TODO: Deprecate other returns on v1.14
   defp each_cycle_return({kind, modules, warnings}), do: {kind, modules, warnings}
-  defp each_cycle_return({kind, modules}), do: {kind, modules, []}
-  defp each_cycle_return(modules) when is_list(modules), do: {:compile, modules, []}
+
+  defp each_cycle_return(other) do
+    IO.warn(
+      "the :each_cycle callback must return a tuple of format {:compile | :runtime, modules, warnings}"
+    )
+
+    case other do
+      {kind, modules} -> {kind, modules, []}
+      modules when is_list(modules) -> {:compile, modules, []}
+    end
+  end
 
   # The goal of this function is to find leaves in the dependency graph,
   # i.e. to find code that depends on code that we know is not being defined.
   # Note that not all files have been compiled yet, so they may not be in waiting.
   defp without_definition(waiting, files) do
-    nillify_empty(
+    nilify_empty(
       for %{pid: pid} <- files,
           {_, _, ref, ^pid, on, _, _} <- waiting,
           not defining?(on, waiting),
@@ -497,7 +505,7 @@ defmodule Kernel.ParallelCompiler do
   end
 
   defp deadlocked(waiting, type, defining?) do
-    nillify_empty(
+    nilify_empty(
       for {_, _, ref, _, on, _, ^type} <- waiting,
           defining?(on, waiting) == defining?,
           do: {ref, :deadlock}
@@ -508,8 +516,8 @@ defmodule Kernel.ParallelCompiler do
     Enum.any?(waiting, fn {_, _, _, _, _, defining, _} -> on in defining end)
   end
 
-  defp nillify_empty([]), do: nil
-  defp nillify_empty([_ | _] = list), do: list
+  defp nilify_empty([]), do: nil
+  defp nilify_empty([_ | _] = list), do: list
 
   # Wait for messages from child processes
   defp wait_for_messages(queue, spawned, waiting, files, result, warnings, state) do
@@ -528,7 +536,7 @@ defmodule Kernel.ParallelCompiler do
         result = Map.put(result, {kind, module}, true)
         spawn_workers(available ++ queue, spawned, waiting, files, result, warnings, state)
 
-      {:module_available, child, ref, file, module, binary, checker_info} ->
+      {:module_available, child, ref, file, module, binary} ->
         state.each_module.(file, module, binary)
 
         # Release the module loader which is waiting for an ack
@@ -538,7 +546,7 @@ defmodule Kernel.ParallelCompiler do
           for {:module, _, ref, _, ^module, _defining, _deadlock} <- waiting,
               do: {ref, :found}
 
-        result = Map.put(result, {:module, module}, {binary, checker_info})
+        result = Map.put(result, {:module, module}, binary)
         spawn_workers(available ++ queue, spawned, waiting, files, result, warnings, state)
 
       # If we are simply requiring files, we do not add to waiting.
@@ -752,6 +760,11 @@ defmodule Kernel.ParallelCompiler do
     {file, line || 0, message}
   end
 
+  defp get_line(_file, %{line: line, column: column}, _stack)
+       when is_integer(line) and line > 0 and is_integer(column) and column >= 0 do
+    {line, column}
+  end
+
   defp get_line(_file, %{line: line}, _stack) when is_integer(line) and line > 0 do
     line
   end
@@ -762,7 +775,8 @@ defmodule Kernel.ParallelCompiler do
     end
   end
 
-  defp get_line(file, _reason, [{_, _, _, [file: 'expanding macro']}, {_, _, _, info} | _]) do
+  defp get_line(file, _reason, [{_, _, _, [file: expanding]}, {_, _, _, info} | _])
+       when expanding in ['expanding macro', 'expanding struct'] do
     if Keyword.get(info, :file) == to_charlist(Path.relative_to_cwd(file)) do
       Keyword.get(info, :line)
     end

lib/elixir/lib/kernel/special_forms.ex

@@ -182,7 +182,7 @@ defmodule Kernel.SpecialForms do
       <<1, 2, 3>>
 
   Elixir also accepts by default the segment to be a literal
-  string or a literal charlist, which are by default expanded to integers:
+  string which expands to integers:
 
       iex> <<0, "foo">>
       <<0, 102, 111, 111>>
@@ -246,20 +246,20 @@ defmodule Kernel.SpecialForms do
       iex> {name, species}
       {"Frank", "Walrus"}
 
-  The size can be a variable:
+  The size can be a variable or any valid guard expression:
 
       iex> name_size = 5
       iex> <<name::binary-size(name_size), " the ", species::binary>> = <<"Frank the Walrus">>
       iex> {name, species}
       {"Frank", "Walrus"}
 
-  And the variable can be defined in the match itself (prior to its use):
+  The size can access prior variables defined in the binary itself:
 
       iex> <<name_size::size(8), name::binary-size(name_size), " the ", species::binary>> = <<5, "Frank the Walrus">>
       iex> {name, species}
       {"Frank", "Walrus"}
 
-  However, the size cannot be defined in the match outside the binary/bitstring match:
+  However, it cannot access variables defined in the match outside of the binary/bitstring:
 
       {name_size, <<name::binary-size(name_size), _rest::binary>>} = {5, <<"Frank the Walrus">>}
       ** (CompileError): undefined variable "name_size" in bitstring segment
@@ -366,7 +366,7 @@ defmodule Kernel.SpecialForms do
 
   To learn more about specific optimizations and performance considerations,
   check out the
-  ["Constructing and matching binaries" chapter of the Erlang's Efficiency Guide](https://erlang.org/doc/efficiency_guide/binaryhandling.html).
+  ["Constructing and matching binaries" chapter of the Erlang's Efficiency Guide](https://www.erlang.org/doc/efficiency_guide/binaryhandling.html).
   """
   defmacro unquote(:<<>>)(args), do: error!([args])
 
@@ -604,11 +604,12 @@ defmodule Kernel.SpecialForms do
 
       import List
 
-  A developer can filter to import only macros or functions via
-  the only option:
+  A developer can filter to import only functions, macros, or sigils
+  (which can be functions or macros) via the `:only` option:
 
       import List, only: :functions
       import List, only: :macros
+      import Kernel, only: :sigils
 
   Alternatively, Elixir allows a developer to pass pairs of
   name/arities to `:only` or `:except` as a fine grained control
@@ -778,7 +779,7 @@ defmodule Kernel.SpecialForms do
 
       <<int::integer-little, rest::bits>> = bits
 
-  Read the documentation on the `Typespec` page and
+  Read the documentation on the [Typespecs page](typespecs.md) and
   `<<>>/1` for more information on typespecs and
   bitstrings respectively.
   """
@@ -1315,11 +1316,13 @@ defmodule Kernel.SpecialForms do
         sum(1, value, 3)
       end
 
-  Which would then return:
+
+  Which the argument for the `:sum` function call is not the
+  expected result:
 
       {:sum, [], [1, {:value, [], Elixir}, 3]}
 
-  Which is not the expected result. For this, we use `unquote`:
+  For this, we use `unquote`:
 
       iex> value =
       ...>   quote do
@@ -1386,6 +1389,10 @@ defmodule Kernel.SpecialForms do
       iex> for n <- [1, 2, 3, 4, 5, 6], rem(n, 2) == 0, do: n
       [2, 4, 6]
 
+  Filters must evaluate to truthy values (everything but `nil`
+  and `false`). If a filter is falsy, then the current value is
+  discarded.
+
   Generators can also be used to filter as it removes any value
   that doesn't match the pattern on the left side of `<-`:
 
@@ -1406,6 +1413,35 @@ defmodule Kernel.SpecialForms do
   filters or inside the block, are not reflected outside of the
   comprehension.
 
+  Variable assignments inside filters must still return a truthy value,
+  otherwise values are discarded. Let's see an example. Imagine you have
+  a keyword list where the key is a programming language and the value
+  is its direct parent. Then let's try to compute the grandparent of each
+  language. You could try this:
+
+      iex> languages = [elixir: :erlang, erlang: :prolog, prolog: nil]
+      iex> for {language, parent} <- languages, grandparent = languages[parent], do: {language, grandparent}
+      [elixir: :prolog]
+
+  Given the grandparents of Erlang and Prolog were nil, those values were
+  filtered out. If you don't want this behaviour, a simple option is to
+  move the filter inside the do-block:
+
+      iex> languages = [elixir: :erlang, erlang: :prolog, prolog: nil]
+      iex> for {language, parent} <- languages do
+      ...>   grandparent = languages[parent]
+      ...>   {language, grandparent}
+      ...> end
+      [elixir: :prolog, erlang: nil, prolog: nil]
+
+  However, such option is not always available, as you may have further
+  filters. An alternative is to convert the filter into a generator by
+  wrapping the right side of `=` in a list:
+
+      iex> languages = [elixir: :erlang, erlang: :prolog, prolog: nil]
+      iex> for {language, parent} <- languages, grandparent <- [languages[parent]], do: {language, grandparent}
+      [elixir: :prolog, erlang: nil, prolog: nil]
+
   ## The `:into` and `:uniq` options
 
   In the examples above, the result returned by the comprehension was
@@ -1602,7 +1638,7 @@ defmodule Kernel.SpecialForms do
         {:ok, backup_path}
       end
 
-      defp validate_extname(path) do
+      defp validate_extension(path) do
         if Path.extname(path) == ".ex", do: :ok, else: {:error, :invalid_extension}
       end
 
@@ -1611,7 +1647,7 @@ defmodule Kernel.SpecialForms do
       end
 
   Note how the code above is better organized and clearer once we
-  make sure each clause in `with` returns a normalize format.
+  make sure each clause in `with` returns a normalized format.
   """
   defmacro with(args), do: error!([args])
 
@@ -2057,6 +2093,25 @@ defmodule Kernel.SpecialForms do
         File.rm("tmp/story.txt")
       end
 
+  Although `after` clauses are invoked whether or not there was an error, they do not
+  modify the return value. All of the following examples return `:return_me`:
+
+      try do
+        :return_me
+      after
+        IO.puts("I will be printed")
+        :not_returned
+      end
+
+      try do
+        raise "boom"
+      rescue
+        _ -> :return_me
+      after
+        IO.puts("I will be printed")
+        :not_returned
+      end
+
   ## `else` clauses
 
   `else` clauses allow the result of the body passed to `try/1` to be pattern

lib/elixir/lib/kernel/typespec.ex

@@ -104,7 +104,7 @@ defmodule Kernel.Typespec do
   @doc """
   Defines a typespec.
 
-  Invoked by `Kernel.@/1` expansion.
+  Invoked by `@/1` expansion.
   """
   def deftypespec(:spec, expr, _line, _file, module, pos) do
     {_set, bag} = :elixir_module.data_tables(module)
@@ -194,14 +194,14 @@ defmodule Kernel.Typespec do
 
   defp get_doc_info(set, attr, line) do
     case :ets.take(set, attr) do
-      [{^attr, {line, doc}, _}] -> {line, doc}
+      [{^attr, {line, doc}, _, _}] -> {line, doc}
       [] -> {line, nil}
     end
   end
 
   defp get_doc_meta(spec_meta, doc_kind, set) do
     case :ets.take(set, {doc_kind, :meta}) do
-      [{{^doc_kind, :meta}, metadata, _}] -> Map.merge(metadata, spec_meta)
+      [{{^doc_kind, :meta}, metadata}] -> Map.merge(metadata, spec_meta)
       [] -> spec_meta
     end
   end
@@ -567,7 +567,10 @@ defmodule Kernel.Typespec do
 
     types =
       :lists.map(
-        fn {field, _} -> {field, Keyword.get(fields, field, quote(do: term()))} end,
+        fn
+          {:__exception__ = field, true} -> {field, Keyword.get(fields, field, true)}
+          {field, _} -> {field, Keyword.get(fields, field, quote(do: term()))}
+        end,
         :lists.sort(struct)
       )
 
@@ -678,10 +681,20 @@ defmodule Kernel.Typespec do
     end
   end
 
-  defp typespec({:"::", meta, [left, right]} = expr, vars, caller, state) do
+  defp typespec({:"::", meta, [left, right]}, vars, caller, state) do
     message =
-      "invalid type annotation. When using the | operator to represent the union of types, " <>
-        "make sure to wrap type annotations in parentheses: #{Macro.to_string(expr)}"
+      "invalid type annotation. The left side of :: must be a variable, got: #{Macro.to_string(left)}"
+
+    message =
+      case left do
+        {:|, _, _} ->
+          message <>
+            ". Note \"left | right :: ann\" is the same as \"(left | right) :: ann\". " <>
+            "To solve this, use parentheses around the union operands: \"left | (right :: ann)\""
+
+        _ ->
+          message
+      end
 
     # TODO: Make this an error on v2.0, and remove the code below and
     # the :undefined_type_error_enabled? key from the state

lib/elixir/lib/kernel/utils.ex

@@ -22,9 +22,38 @@ defmodule Kernel.Utils do
   defp destructure_nil(count), do: [nil | destructure_nil(count - 1)]
 
   @doc """
-  Callback for defdelegate.
+  Callback for defdelegate entry point.
   """
-  def defdelegate(fun, opts) when is_list(opts) do
+  def defdelegate_all(funs, opts, env) do
+    to = Keyword.get(opts, :to) || raise ArgumentError, "expected to: to be given as argument"
+    as = Keyword.get(opts, :as)
+
+    if to == env.module and is_nil(as) do
+      raise ArgumentError,
+            "defdelegate function is calling itself, which will lead to an infinite loop. You should either change the value of the :to option or specify the :as option"
+    end
+
+    if is_list(funs) do
+      IO.warn(
+        "passing a list to Kernel.defdelegate/2 is deprecated, please define each delegate separately",
+        Macro.Env.stacktrace(env)
+      )
+    end
+
+    if Keyword.has_key?(opts, :append_first) do
+      IO.warn(
+        "Kernel.defdelegate/2 :append_first option is deprecated",
+        Macro.Env.stacktrace(env)
+      )
+    end
+
+    to
+  end
+
+  @doc """
+  Callback for each function in defdelegate.
+  """
+  def defdelegate_each(fun, opts) when is_list(opts) do
     # TODO: Remove on v2.0
     append_first? = Keyword.get(opts, :append_first, false)
 
@@ -71,7 +100,15 @@ defmodule Kernel.Utils do
   @doc """
   Callback for defstruct.
   """
-  def defstruct(module, fields) do
+  def defstruct(module, fields, bootstrapped?) do
+    {set, bag} = :elixir_module.data_tables(module)
+
+    if :ets.member(set, :__struct__) do
+      raise ArgumentError,
+            "defstruct has already been called for " <>
+              "#{Kernel.inspect(module)}, defstruct can only be called once per module"
+    end
+
     case fields do
       fs when is_list(fs) ->
         :ok
@@ -83,7 +120,7 @@ defmodule Kernel.Utils do
     mapper = fn
       {key, val} when is_atom(key) ->
         try do
-          Macro.escape(val)
+          :elixir_quote.escape(val, false, :none)
         rescue
           e in [ArgumentError] ->
             raise ArgumentError, "invalid value for struct field #{key}, " <> Exception.message(e)
@@ -99,7 +136,13 @@ defmodule Kernel.Utils do
     end
 
     fields = :lists.map(mapper, fields)
-    enforce_keys = List.wrap(Module.get_attribute(module, :enforce_keys))
+
+    enforce_keys =
+      case :ets.take(set, :enforce_keys) do
+        [{_, enforce_keys, _, _}] when is_list(enforce_keys) -> enforce_keys
+        [{_, enforce_key, _, _}] -> [enforce_key]
+        [] -> []
+      end
 
     # TODO: Make it raise on v2.0
     warn_on_duplicate_struct_key(:lists.keysort(1, fields))
@@ -113,12 +156,62 @@ defmodule Kernel.Utils do
     end
 
     :lists.foreach(foreach, enforce_keys)
-
     struct = :maps.put(:__struct__, module, :maps.from_list(fields))
 
+    body =
+      case bootstrapped? do
+        true ->
+          case enforce_keys do
+            [] ->
+              quote do
+                Enum.reduce(kv, @__struct__, fn {key, val}, map ->
+                  %{map | key => val}
+                end)
+              end
+
+            _ ->
+              quote do
+                {map, keys} =
+                  Enum.reduce(kv, {@__struct__, unquote(enforce_keys)}, fn
+                    {key, val}, {map, keys} ->
+                      {%{map | key => val}, List.delete(keys, key)}
+                  end)
+
+                case keys do
+                  [] ->
+                    map
+
+                  _ ->
+                    raise ArgumentError,
+                          "the following keys must also be given when building " <>
+                            "struct #{inspect(__MODULE__)}: #{inspect(keys)}"
+                end
+              end
+          end
+
+        false ->
+          quote do
+            :lists.foldl(
+              fn {key, val}, acc -> %{acc | key => val} end,
+              @__struct__,
+              kv
+            )
+          end
+      end
+
     case enforce_keys -- :maps.keys(struct) do
       [] ->
-        {struct, enforce_keys, Module.get_attribute(module, :derive)}
+        # The __struct__ field is used for expansion and for loading remote structs
+        :ets.insert(set, {:__struct__, struct, nil, []})
+
+        # Store all field metadata to go into __info__(:struct)
+        mapper = fn {key, val} ->
+          %{field: key, default: val, required: :lists.member(key, enforce_keys)}
+        end
+
+        :ets.insert(set, {{:elixir, :struct}, :lists.map(mapper, fields)})
+        derive = :lists.map(fn {_, value} -> value end, :ets.take(bag, {:accumulate, :derive}))
+        {struct, :lists.reverse(derive), quote(do: kv), body}
 
       error_keys ->
         raise ArgumentError,

lib/elixir/lib/keyword.ex

@@ -92,6 +92,7 @@ defmodule Keyword do
 
       iex> %{1 => 2, foo: :bar}
       %{1 => 2, :foo => :bar}
+
   """
 
   @compile :inline_list_funcs
@@ -102,6 +103,21 @@ defmodule Keyword do
   @type t :: [{key, value}]
   @type t(value) :: [{key, value}]
 
+  @doc """
+  Builds a keyword from the given `keys` and the fixed `value`.
+
+  ## Examples
+
+      iex> Keyword.from_keys([:foo, :bar, :baz], :atom)
+      [foo: :atom, bar: :atom, baz: :atom]
+
+  """
+  @doc since: "1.14.0"
+  @spec from_keys([key], value) :: t(value)
+  def from_keys(keys, value) when is_list(keys) do
+    :lists.map(&{&1, value}, keys)
+  end
+
   @doc """
   Returns `true` if `term` is a keyword list, otherwise `false`.
 
@@ -158,7 +174,7 @@ defmodule Keyword do
       [a: 3]
 
   """
-  @spec new(Enum.t()) :: t
+  @spec new(Enumerable.t()) :: t
   def new(pairs) do
     new(pairs, fn pair -> pair end)
   end
@@ -176,7 +192,7 @@ defmodule Keyword do
       [a: :a, b: :b]
 
   """
-  @spec new(Enum.t(), (term -> {key, value})) :: t
+  @spec new(Enumerable.t(), (term -> {key, value})) :: t
   def new(pairs, transform) when is_function(transform, 1) do
     fun = fn el, acc ->
       {k, v} = transform.(el)
@@ -187,8 +203,7 @@ defmodule Keyword do
   end
 
   @doc """
-  Ensures the first argument is a `keyword` with the given
-  keys and default values.
+  Ensures the given `keyword` has only the keys given in `values`.
 
   The second argument must be a list of atoms, specifying
   a given key, or tuples specifying a key and a default value.
@@ -224,6 +239,12 @@ defmodule Keyword do
 
       iex> Keyword.validate([three: 3, four: 4], [one: 1, two: 2])
       {:error, [:four, :three]}
+
+  Passing the same key multiple times also errors:
+
+      iex> Keyword.validate([one: 1, two: 2, one: 1], [:one, :two])
+      {:error, [:one]}
+
   """
   @doc since: "1.13.0"
   @spec validate(keyword(), values :: [atom() | {atom(), term()}]) ::
@@ -302,6 +323,12 @@ defmodule Keyword do
 
       iex> Keyword.validate!([three: 3], [one: 1, two: 2])
       ** (ArgumentError) unknown keys [:three] in [three: 3], the allowed keys are: [:one, :two]
+
+  Passing the same key multiple times also errors:
+
+      iex> Keyword.validate!([one: 1, two: 2, one: 1], [:one, :two])
+      ** (ArgumentError) duplicate keys [:one] in [one: 1, two: 2, one: 1]
+
   """
   @doc since: "1.13.0"
   @spec validate!(keyword(), values :: [atom() | {atom(), term()}]) :: keyword()
@@ -315,8 +342,17 @@ defmodule Keyword do
           for value <- values,
               do: if(is_atom(value), do: value, else: elem(value, 0))
 
-        raise ArgumentError,
-              "unknown keys #{inspect(invalid_keys)} in #{inspect(keyword)}, the allowed keys are: #{inspect(keys)}"
+        message =
+          case Enum.split_with(invalid_keys, &(&1 in keys)) do
+            {_, [_ | _] = unknown} ->
+              "unknown keys #{inspect(unknown)} in #{inspect(keyword)}, " <>
+                "the allowed keys are: #{inspect(keys)}"
+
+            {[_ | _] = known, _} ->
+              "duplicate keys #{inspect(known)} in #{inspect(keyword)}"
+          end
+
+        raise ArgumentError, message
     end
   end
 
@@ -853,6 +889,43 @@ defmodule Keyword do
     raise KeyError, key: key, term: original
   end
 
+  @doc """
+  Replaces the value under `key` using the given function only if
+  `key` already exists in `keywords`.
+
+  In comparison to `replace/3`, this can be useful when it's expensive to calculate the value.
+
+  If `key` does not exist, the original keyword list is returned unchanged.
+
+  ## Examples
+
+      iex> Keyword.replace_lazy([a: 1, b: 2], :a, fn v -> v * 4 end)
+      [a: 4, b: 2]
+
+      iex> Keyword.replace_lazy([a: 2, b: 2, a: 1], :a, fn v -> v * 4 end)
+      [a: 8, b: 2]
+
+      iex> Keyword.replace_lazy([a: 1, b: 2], :c, fn v -> v * 4 end)
+      [a: 1, b: 2]
+
+  """
+  @doc since: "1.14.0"
+  @spec replace_lazy(t, key, (existing_value :: value -> new_value :: value)) :: t
+  def replace_lazy(keywords, key, fun)
+      when is_list(keywords) and is_atom(key) and is_function(fun, 1) do
+    do_replace_lazy(keywords, key, fun)
+  end
+
+  defp do_replace_lazy([{key, value} | keywords], key, fun) do
+    [{key, fun.(value)} | delete(keywords, key)]
+  end
+
+  defp do_replace_lazy([{_, _} = e | keywords], key, fun) do
+    [e | do_replace_lazy(keywords, key, fun)]
+  end
+
+  defp do_replace_lazy([], _key, _value), do: []
+
   @doc """
   Checks if two keywords are equal.
 
@@ -1128,7 +1201,7 @@ defmodule Keyword do
   """
   @spec take(t, [key]) :: t
   def take(keywords, keys) when is_list(keywords) and is_list(keys) do
-    :lists.filter(fn {k, _} -> k in keys end, keywords)
+    :lists.filter(fn {k, _} -> :lists.member(k, keys) end, keywords)
   end
 
   @doc """
@@ -1374,27 +1447,9 @@ defmodule Keyword do
     end
   end
 
-  @doc """
-  Maps the function `fun` over all key-value pairs in `keywords`,
-  returning a keyword list with all the values replaced with
-  the result of the function.
-
-  ## Examples
-
-      iex> Keyword.map([one: 1, two: 2, three: 3], fn {_key, val} -> to_string(val) end)
-      [one: "1", two: "2", three: "3"]
-
-  """
-  @doc since: "1.13.0"
-  @spec map(t, ({key, value} -> value)) :: t
-  def map(keywords, fun) when is_list(keywords) and is_function(fun, 1) do
-    do_map(keywords, fun)
-  end
-
-  defp do_map([], _fun), do: []
-
-  defp do_map([{key, value} | rest], fun) do
-    new_value = fun.({key, value})
-    [{key, new_value} | do_map(rest, fun)]
+  @doc false
+  @deprecated "Use Keyword.new/2 instead"
+  def map(keywords, fun) when is_list(keywords) do
+    Enum.map(keywords, fn {k, v} -> {k, fun.({k, v})} end)
   end
 end

lib/elixir/lib/list.ex

@@ -8,7 +8,7 @@ defmodule List do
       [1, "two", 3, :four]
 
   Two lists can be concatenated and subtracted using the
-  `Kernel.++/2` and `Kernel.--/2` operators:
+  `++/2` and `--/2` operators:
 
       iex> [1, 2, 3] ++ [4, 5, 6]
       [1, 2, 3, 4, 5, 6]
@@ -239,7 +239,7 @@ defmodule List do
 
       iex> List.foldl([1, 2, 3, 4], 0, fn x, acc -> x - acc end)
       2
-      
+
       iex> List.foldl([1, 2, 3], {0, 0}, fn x, {a1, a2} -> {a1 + x, a2 - x} end)
       {6, -6}
 
@@ -257,7 +257,7 @@ defmodule List do
 
       iex> List.foldr([1, 2, 3, 4], 0, fn x, acc -> x - acc end)
       -2
-      
+
       iex> List.foldr([1, 2, 3, 4], %{sum: 0, product: 1}, fn x, %{sum: a1, product: a2} -> %{sum: a1 + x, product: a2 * x} end)
       %{product: 24, sum: 10}
 
@@ -339,6 +339,11 @@ defmodule List do
       iex> List.keyfind([a: 1, b: 2], :c, 0)
       nil
 
+  This function works for any list of tuples:
+
+      iex> List.keyfind([{22, "SSH"}, {80, "HTTP"}], 22, 0)
+      {22, "SSH"}
+
   """
   @spec keyfind([tuple], any, non_neg_integer, any) :: any
   def keyfind(list, key, position, default \\ nil) when is_integer(position) do
@@ -363,6 +368,11 @@ defmodule List do
       iex> List.keyfind!([a: 1, b: 2], :c, 0)
       ** (KeyError) key :c at position 0 not found in: [a: 1, b: 2]
 
+  This function works for any list of tuples:
+
+      iex> List.keyfind!([{22, "SSH"}, {80, "HTTP"}], 22, 0)
+      {22, "SSH"}
+
   """
   @doc since: "1.13.0"
   @spec keyfind!([tuple], any, non_neg_integer) :: any
@@ -391,6 +401,11 @@ defmodule List do
       iex> List.keymember?([a: 1, b: 2], :c, 0)
       false
 
+  This function works for any list of tuples:
+
+      iex> List.keymember?([{22, "SSH"}, {80, "HTTP"}], 22, 0)
+      true
+
   """
   @spec keymember?([tuple], any, non_neg_integer) :: boolean
   def keymember?(list, key, position) when is_integer(position) do
@@ -409,6 +424,11 @@ defmodule List do
       iex> List.keyreplace([a: 1, b: 2], :a, 1, {:a, 3})
       [a: 1, b: 2]
 
+  This function works for any list of tuples:
+
+      iex> List.keyreplace([{22, "SSH"}, {80, "HTTP"}], 22, 0, {22, "Secure Shell"})
+      [{22, "Secure Shell"}, {80, "HTTP"}]
+
   """
   @spec keyreplace([tuple], any, non_neg_integer, tuple) :: [tuple]
   def keyreplace(list, key, position, new_tuple) when is_integer(position) do
@@ -417,7 +437,13 @@ defmodule List do
 
   @doc """
   Receives a list of tuples and sorts the elements
-  at `position` of the tuples. The sort is stable.
+  at `position` of the tuples.
+
+  The sort is stable.
+
+  A `sorter` argument is available since Elixir v1.14.0. Similar to
+  `Enum.sort/2`, the sorter can be an anonymous function, the atoms
+  `:asc` or `:desc`, or module that implements a compare function.
 
   ## Examples
 
@@ -427,12 +453,69 @@ defmodule List do
       iex> List.keysort([a: 5, c: 1, b: 3], 0)
       [a: 5, b: 3, c: 1]
 
+  To sort in descending order:
+
+      iex> List.keysort([a: 5, c: 1, b: 3], 0, :desc)
+      [c: 1, b: 3, a: 5]
+
+  As in `Enum.sort/2`, avoid using the default sorting function to sort
+  structs, as by default it performs structural comparison instead of a
+  semantic one. In such cases, you shall pass a sorting function as third
+  element or any module that implements a `compare/2` function. For example,
+  if you have tuples with user names and their birthday, and you want to
+  sort on their birthday, in both ascending and descending order, you should
+  do:
+
+      iex> users = [
+      ...>   {"Ellis", ~D[1943-05-11]},
+      ...>   {"Lovelace", ~D[1815-12-10]},
+      ...>   {"Turing", ~D[1912-06-23]}
+      ...> ]
+      iex> List.keysort(users, 1, Date)
+      [
+        {"Lovelace", ~D[1815-12-10]},
+        {"Turing", ~D[1912-06-23]},
+        {"Ellis", ~D[1943-05-11]}
+      ]
+      iex> List.keysort(users, 1, {:desc, Date})
+      [
+        {"Ellis", ~D[1943-05-11]},
+        {"Turing", ~D[1912-06-23]},
+        {"Lovelace", ~D[1815-12-10]}
+      ]
+
   """
-  @spec keysort([tuple], non_neg_integer) :: [tuple]
-  def keysort(list, position) when is_integer(position) do
+  @doc since: "1.14.0"
+  @spec keysort(
+          [tuple],
+          non_neg_integer,
+          (any, any -> boolean) | :asc | :desc | module() | {:asc | :desc, module()}
+        ) :: [tuple]
+  def keysort(list, position, sorter \\ :asc)
+
+  def keysort(list, position, :asc) when is_list(list) and is_integer(position) do
     :lists.keysort(position + 1, list)
   end
 
+  def keysort(list, position, sorter) when is_list(list) and is_integer(position) do
+    :lists.sort(keysort_fun(sorter, position + 1), list)
+  end
+
+  defp keysort_fun(sorter, position) when is_function(sorter, 2),
+    do: &sorter.(:erlang.element(position, &1), :erlang.element(position, &2))
+
+  defp keysort_fun(:desc, position),
+    do: &(:erlang.element(position, &1) >= :erlang.element(position, &2))
+
+  defp keysort_fun(module, position) when is_atom(module),
+    do: &(module.compare(:erlang.element(position, &1), :erlang.element(position, &2)) != :gt)
+
+  defp keysort_fun({:asc, module}, position) when is_atom(module),
+    do: &(module.compare(:erlang.element(position, &1), :erlang.element(position, &2)) != :gt)
+
+  defp keysort_fun({:desc, module}, position) when is_atom(module),
+    do: &(module.compare(:erlang.element(position, &1), :erlang.element(position, &2)) != :lt)
+
   @doc """
   Receives a `list` of tuples and replaces the element
   identified by `key` at `position` with `new_tuple`.
@@ -447,6 +530,11 @@ defmodule List do
       iex> List.keystore([a: 1, b: 2], :c, 0, {:c, 3})
       [a: 1, b: 2, c: 3]
 
+  This function works for any list of tuples:
+
+      iex> List.keystore([{22, "SSH"}], 80, 0, {80, "HTTP"})
+      [{22, "SSH"}, {80, "HTTP"}]
+
   """
   @spec keystore([tuple], any, non_neg_integer, tuple) :: [tuple, ...]
   def keystore(list, key, position, new_tuple) when is_integer(position) do
@@ -469,6 +557,11 @@ defmodule List do
       iex> List.keydelete([a: 1, b: 2], :c, 0)
       [a: 1, b: 2]
 
+  This function works for any list of tuples:
+
+      iex> List.keydelete([{22, "SSH"}, {80, "HTTP"}], 80, 0)
+      [{22, "SSH"}]
+
   """
   @spec keydelete([tuple], any, non_neg_integer) :: [tuple]
   def keydelete(list, key, position) when is_integer(position) do
@@ -493,6 +586,11 @@ defmodule List do
       iex> List.keytake([a: 1, b: 2], :c, 0)
       nil
 
+  This function works for any list of tuples:
+
+      iex> List.keytake([{22, "SSH"}, {80, "HTTP"}], 80, 0)
+      {{80, "HTTP"}, [{22, "SSH"}]}
+
   """
   @spec keytake([tuple], any, non_neg_integer) :: {tuple, [tuple]} | nil
   def keytake(list, key, position) when is_integer(position) do
@@ -849,14 +947,22 @@ defmodule List do
   end
 
   @doc """
-  Converts a charlist to an existing atom. Raises an `ArgumentError`
-  if the atom does not exist.
+  Converts a charlist to an existing atom.
 
   Elixir supports conversions from charlists which contains any Unicode
-  code point.
+  code point. Raises an `ArgumentError` if the atom does not exist.
 
   Inlined by the compiler.
 
+  > #### Atoms and modules {: .info}
+  >
+  > Since Elixir is a compiled language, the atoms defined in a module
+  > will only exist after said module is loaded, which typically happens
+  > whenever a function in the module is executed. Therefore, it is
+  > generally recommended to call `List.to_existing_atom/1` only to
+  > convert atoms defined within the module making the function call
+  > to `to_existing_atom/1`.
+
   ## Examples
 
       iex> _ = :my_atom

lib/elixir/lib/macro/env.ex

@@ -24,7 +24,7 @@ defmodule Macro.Env do
     * `context` - the context of the environment; it can be `nil`
       (default context), `:guard` (inside a guard) or `:match` (inside a match)
     * `context_modules` - a list of modules defined in the current context
-    * `file` - the current file name as a binary
+    * `file` - the current absolute file name as a binary
     * `function` - a tuple as `{atom, integer}`, where the first
       element is the function name and the second its arity; returns
       `nil` if not inside a function
@@ -79,31 +79,39 @@ defmodule Macro.Env do
           versioned_vars: versioned_vars
         }
 
-  # Define the __struct__ callbacks by hand for bootstrap reasons.
-  @doc false
-  def __struct__ do
-    %{
-      __struct__: __MODULE__,
-      aliases: [],
-      context: nil,
-      context_modules: [],
-      file: "nofile",
-      function: nil,
-      functions: [],
-      lexical_tracker: nil,
-      line: 0,
-      macro_aliases: [],
-      macros: [],
-      module: nil,
-      requires: [],
-      tracers: [],
-      versioned_vars: %{}
-    }
-  end
+  fields = [
+    aliases: [],
+    context: nil,
+    context_modules: [],
+    file: "nofile",
+    function: nil,
+    functions: [],
+    lexical_tracker: nil,
+    line: 0,
+    macro_aliases: [],
+    macros: [],
+    module: nil,
+    requires: [],
+    tracers: [],
+    versioned_vars: %{}
+  ]
 
-  @doc false
-  def __struct__(kv) do
-    Enum.reduce(kv, __struct__(), fn {k, v}, acc -> :maps.update(k, v, acc) end)
+  # Define the __struct__ callbacks by hand for bootstrap reasons.
+  {struct, [], kv, body} = Kernel.Utils.defstruct(__MODULE__, fields, false)
+  def __struct__(), do: unquote(:elixir_quote.escape(struct, false, :none))
+  def __struct__(unquote(kv)), do: unquote(body)
+
+  @doc """
+  Prunes compile information from the environment.
+
+  This happens when the environment is captured at compilation
+  time, for example, in the module body, and then used to
+  evaluate code after the module has been defined.
+  """
+  @doc since: "1.14.0"
+  @spec prune_compile_info(t) :: t
+  def prune_compile_info(env) do
+    %{env | lexical_tracker: nil, tracers: []}
   end
 
   @doc """
@@ -158,7 +166,7 @@ defmodule Macro.Env do
   @doc """
   Fetches the alias for the given atom.
 
-  Returns `{:ok, alias}` if the alias exists, `:error` 
+  Returns `{:ok, alias}` if the alias exists, `:error`
   otherwise.
 
   ## Examples

lib/elixir/lib/map.ex

@@ -88,12 +88,18 @@ defmodule Map do
       %{1 => :one, 2 => :two, 3 => :three}
 
   Maps also support a specific update syntax to update the value stored under
-  *existing* atom keys:
+  *existing* keys. You can update using the atom keys syntax:
 
       iex> map = %{one: 1, two: 2}
       iex> %{map | one: "one"}
       %{one: "one", two: 2}
 
+  Or any other key:
+
+      iex> other_map = %{"three" => 3, "four" => 4}
+      iex> %{other_map | "three" => "three"}
+      %{"four" => 4, "three" => "three"}
+
   When a key that does not exist in the map is updated a `KeyError` exception will be raised:
 
       %{map | three: 3}
@@ -117,6 +123,27 @@ defmodule Map do
   @type value :: any
   @compile {:inline, fetch: 2, fetch!: 2, get: 2, put: 3, delete: 2, has_key?: 2, replace!: 3}
 
+  # TODO: Remove conditional on Erlang/OTP 24+
+  @compile {:no_warn_undefined, {:maps, :from_keys, 2}}
+  @doc """
+  Builds a map from the given `keys` and the fixed `value`.
+
+  ## Examples
+
+      iex> Map.from_keys([1, 2, 3], :number)
+      %{1 => :number, 2 => :number, 3 => :number}
+
+  """
+  @doc since: "1.14.0"
+  @spec from_keys([key], value) :: map
+  def from_keys(keys, value) do
+    if function_exported?(:maps, :from_keys, 2) do
+      :maps.from_keys(keys, value)
+    else
+      :maps.from_list(:lists.map(&{&1, value}, keys))
+    end
+  end
+
   @doc """
   Returns all keys from `map`.
 
@@ -214,7 +241,24 @@ defmodule Map do
 
   """
   @spec new(Enumerable.t(), (term -> {key, value})) :: map
-  def new(enumerable, transform) when is_function(transform, 1) do
+  def new(enumerable, transform)
+  def new(%_{} = enumerable, transform), do: new_from_enum(enumerable, transform)
+  def new(%{} = map, transform), do: new_from_map(map, transform)
+  def new(enumerable, transform), do: new_from_enum(enumerable, transform)
+
+  defp new_from_map(map, transform) when is_function(transform, 1) do
+    iter = :maps.iterator(map)
+    next = :maps.next(iter)
+    :maps.from_list(do_map(next, transform))
+  end
+
+  defp do_map(:none, _fun), do: []
+
+  defp do_map({key, value, iter}, transform) do
+    [transform.({key, value}) | do_map(:maps.next(iter), transform)]
+  end
+
+  defp new_from_enum(enumerable, transform) when is_function(transform, 1) do
     enumerable
     |> Enum.map(transform)
     |> :maps.from_list()
@@ -350,6 +394,32 @@ defmodule Map do
     :maps.update(key, value, map)
   end
 
+  @doc """
+  Replaces the value under `key` using the given function only if
+  `key` already exists in `map`.
+
+  In comparison to `replace/3`, this can be useful when it's expensive to calculate the value.
+
+  If `key` does not exist, the original map is returned unchanged.
+
+  ## Examples
+
+      iex> Map.replace_lazy(%{a: 1, b: 2}, :a, fn v -> v * 4 end)
+      %{a: 4, b: 2}
+
+      iex> Map.replace_lazy(%{a: 1, b: 2}, :c, fn v -> v * 4 end)
+      %{a: 1, b: 2}
+
+  """
+  @doc since: "1.14.0"
+  @spec replace_lazy(map, key, (existing_value :: value -> new_value :: value)) :: map
+  def replace_lazy(map, key, fun) when is_map(map) and is_function(fun, 1) do
+    case map do
+      %{^key => val} -> %{map | key => fun.(val)}
+      %{} -> map
+    end
+  end
+
   @doc """
   Evaluates `fun` and puts the result under `key`
   in `map` unless `key` is already present.
@@ -546,7 +616,7 @@ defmodule Map do
   If you have a struct and you would like to merge a set of keys into the
   struct, do not use this function, as it would merge all keys on the right
   side into the struct, even if the key is not part of the struct. Instead,
-  use `Kernel.struct/2`.
+  use `struct/2`.
 
   Inlined by the compiler.
 
@@ -979,12 +1049,14 @@ defmodule Map do
   `fun` receives the key and value of each of the
   elements in the map as a key-value pair.
 
-  `Map.filter/2` is faster than using `map |> Enum.filter(fun) |> Enum.into(%{})`,
-  as no intermediate list is being built.
-
   See also `reject/2` which discards all elements where the
   function returns a truthy value.
 
+  > Note: if you find yourself doing multiple calls to `Map.filter/2`
+  > and `Map.reject/2` in a pipeline, it is likely more efficient
+  > to use `Enum.map/2` and `Enum.filter/2` instead and convert to
+  > a map at the end using `Map.new/1`.
+
   ## Examples
 
       iex> Map.filter(%{one: 1, two: 2, three: 3}, fn {_key, val} -> rem(val, 2) == 1 end)
@@ -1010,9 +1082,8 @@ defmodule Map do
   end
 
   @doc """
-  Returns map excluding the pairs from `map` for which `fun` returns a truthy value.
-  `Map.reject/2` is faster than using `map |> Enum.reject(fun) |> Enum.into(%{})`,
-  as no intermediate list is being built.
+  Returns map excluding the pairs from `map` for which `fun` returns
+  a truthy value.
 
   See also `filter/2`.
 
@@ -1040,28 +1111,9 @@ defmodule Map do
     end
   end
 
-  @doc """
-  Maps the function `fun` over all key-value pairs in `map`, returning a map
-  with all the values replaced with the result of the function.
-
-  ## Examples
-
-      iex> Map.map(%{1 => "joe", 2 => "mike", 3 => "robert"}, fn {_key, val} -> String.capitalize(val) end)
-      %{1 => "Joe", 2 => "Mike", 3 => "Robert"}
-
-  """
-  @doc since: "1.13.0"
-  @spec map(map, ({key, value} -> value)) :: map
-  def map(map, fun) when is_map(map) and is_function(fun, 1) do
-    iter = :maps.iterator(map)
-    next = :maps.next(iter)
-    :maps.from_list(do_map(next, fun))
-  end
-
-  defp do_map(:none, _fun), do: []
-
-  defp do_map({key, value, iter}, fun) do
-    new_value = fun.({key, value})
-    [{key, new_value} | do_map(:maps.next(iter), fun)]
+  @doc false
+  @deprecated "Use Map.new/2 instead (invoke Map.from_struct/1 before if you have a struct)"
+  def map(map, fun) when is_map(map) do
+    :maps.map(fn k, v -> fun.({k, v}) end, map)
   end
 end

lib/elixir/lib/map_set.ex

@@ -8,18 +8,18 @@ defmodule MapSet do
   A set can be constructed using `MapSet.new/0`:
 
       iex> MapSet.new()
-      #MapSet<[]>
+      MapSet.new([])
 
   Elements in a set don't have to be of the same type and they can be
   populated from an [enumerable](`t:Enumerable.t/0`) using `MapSet.new/1`:
 
       iex> MapSet.new([1, :two, {"three"}])
-      #MapSet<[1, :two, {"three"}]>
+      MapSet.new([1, :two, {"three"}])
 
   Elements can be inserted using `MapSet.put/2`:
 
       iex> MapSet.new([2]) |> MapSet.put(4) |> MapSet.put(0)
-      #MapSet<[0, 2, 4]>
+      MapSet.new([0, 2, 4])
 
   By definition, sets can't contain duplicate elements: when
   inserting an element in a set where it's already present, the insertion is
@@ -27,9 +27,9 @@ defmodule MapSet do
 
       iex> map_set = MapSet.new()
       iex> MapSet.put(map_set, "foo")
-      #MapSet<["foo"]>
+      MapSet.new(["foo"])
       iex> map_set |> MapSet.put("foo") |> MapSet.put("foo")
-      #MapSet<["foo"]>
+      MapSet.new(["foo"])
 
   A `MapSet` is represented internally using the `%MapSet{}` struct. This struct
   can be used whenever there's a need to pattern match on something being a `MapSet`:
@@ -54,10 +54,12 @@ defmodule MapSet do
 
   @type value :: term
 
-  @opaque t(value) :: %__MODULE__{map: %{optional(value) => []}}
+  @opaque internal(value) :: %{optional(value) => []}
+  @type t(value) :: %__MODULE__{map: internal(value)}
   @type t :: t(term)
 
-  # TODO: Remove version key on Elixir v2.0
+  # TODO: Remove version key when we require Erlang/OTP 24
+  # TODO: Implement the functions in this module using Erlang/OTP 24 new sets
   defstruct map: %{}, version: 2
 
   @doc """
@@ -66,7 +68,7 @@ defmodule MapSet do
   ## Examples
 
       iex> MapSet.new()
-      #MapSet<[]>
+      MapSet.new([])
 
   """
   @spec new :: t
@@ -78,23 +80,19 @@ defmodule MapSet do
   ## Examples
 
       iex> MapSet.new([:b, :a, 3])
-      #MapSet<[3, :a, :b]>
+      MapSet.new([3, :a, :b])
       iex> MapSet.new([3, 3, 3, 2, 2, 1])
-      #MapSet<[1, 2, 3]>
+      MapSet.new([1, 2, 3])
 
   """
-  @spec new(Enum.t()) :: t
+  @spec new(Enumerable.t()) :: t
   def new(enumerable)
 
   def new(%__MODULE__{} = map_set), do: map_set
 
   def new(enumerable) do
-    map =
-      enumerable
-      |> Enum.to_list()
-      |> new_from_list([])
-
-    %MapSet{map: map}
+    keys = Enum.to_list(enumerable)
+    %MapSet{map: Map.from_keys(keys, @dummy_value)}
   end
 
   @doc """
@@ -103,33 +101,13 @@ defmodule MapSet do
   ## Examples
 
       iex> MapSet.new([1, 2, 1], fn x -> 2 * x end)
-      #MapSet<[2, 4]>
+      MapSet.new([2, 4])
 
   """
-  @spec new(Enum.t(), (term -> val)) :: t(val) when val: value
+  @spec new(Enumerable.t(), (term -> val)) :: t(val) when val: value
   def new(enumerable, transform) when is_function(transform, 1) do
-    map =
-      enumerable
-      |> Enum.to_list()
-      |> new_from_list_transform(transform, [])
-
-    %MapSet{map: map}
-  end
-
-  defp new_from_list([], acc) do
-    Map.new(acc)
-  end
-
-  defp new_from_list([element | rest], acc) do
-    new_from_list(rest, [{element, @dummy_value} | acc])
-  end
-
-  defp new_from_list_transform([], _fun, acc) do
-    Map.new(acc)
-  end
-
-  defp new_from_list_transform([element | rest], fun, acc) do
-    new_from_list_transform(rest, fun, [{fun.(element), @dummy_value} | acc])
+    keys = Enum.map(enumerable, transform)
+    %MapSet{map: Map.from_keys(keys, @dummy_value)}
   end
 
   @doc """
@@ -141,9 +119,9 @@ defmodule MapSet do
 
       iex> map_set = MapSet.new([1, 2, 3])
       iex> MapSet.delete(map_set, 4)
-      #MapSet<[1, 2, 3]>
+      MapSet.new([1, 2, 3])
       iex> MapSet.delete(map_set, 2)
-      #MapSet<[1, 3]>
+      MapSet.new([1, 3])
 
   """
   @spec delete(t(val1), val2) :: t(val1) when val1: value, val2: value
@@ -157,7 +135,7 @@ defmodule MapSet do
   ## Examples
 
       iex> MapSet.difference(MapSet.new([1, 2]), MapSet.new([2, 3, 4]))
-      #MapSet<[1]>
+      MapSet.new([1])
 
   """
   @spec difference(t(val1), t(val2)) :: t(val1) when val1: value, val2: value
@@ -183,13 +161,51 @@ defmodule MapSet do
     %{map_set | map: Map.drop(map1, Map.keys(map2))}
   end
 
-  defp filter_not_in(:none, _map2, acc), do: Map.new(acc)
+  defp filter_not_in(:none, _map2, acc), do: Map.from_keys(acc, @dummy_value)
 
   defp filter_not_in({key, _val, iter}, map2, acc) do
-    if :erlang.is_map_key(key, map2) do
+    if is_map_key(map2, key) do
       filter_not_in(:maps.next(iter), map2, acc)
     else
-      filter_not_in(:maps.next(iter), map2, [{key, @dummy_value} | acc])
+      filter_not_in(:maps.next(iter), map2, [key | acc])
+    end
+  end
+
+  @doc """
+  Returns a set with elements that are present in only one but not both sets.
+
+  ## Examples
+
+      iex> MapSet.symmetric_difference(MapSet.new([1, 2, 3]), MapSet.new([2, 3, 4]))
+      MapSet.new([1, 4])
+  """
+  @doc since: "1.14.0"
+  @spec symmetric_difference(t(val1), t(val2)) :: t(val1 | val2) when val1: value, val2: value
+  def symmetric_difference(%MapSet{map: map1}, %MapSet{map: map2}) do
+    {small, large} = order_by_size(map1, map2)
+
+    map =
+      large
+      |> :maps.iterator()
+      |> :maps.next()
+      |> disjointer(small, [])
+
+    %MapSet{map: map}
+  end
+
+  defp disjointer(:none, small, list) do
+    list |> Map.from_keys(@dummy_value) |> Map.merge(small)
+  end
+
+  defp disjointer({key, _val, iter}, small, list) do
+    if is_map_key(small, key) do
+      iter
+      |> :maps.next()
+      |> disjointer(Map.delete(small, key), list)
+    else
+      iter
+      |> :maps.next()
+      |> disjointer(small, [key | list])
     end
   end
 
@@ -217,7 +233,7 @@ defmodule MapSet do
   defp none_in?(:none, _), do: true
 
   defp none_in?({key, _val, iter}, map2) do
-    not :erlang.is_map_key(key, map2) and none_in?(:maps.next(iter), map2)
+    not is_map_key(map2, key) and none_in?(:maps.next(iter), map2)
   end
 
   @doc """
@@ -254,10 +270,10 @@ defmodule MapSet do
   ## Examples
 
       iex> MapSet.intersection(MapSet.new([1, 2]), MapSet.new([2, 3, 4]))
-      #MapSet<[2]>
+      MapSet.new([2])
 
       iex> MapSet.intersection(MapSet.new([1, 2]), MapSet.new([3, 4]))
-      #MapSet<[]>
+      MapSet.new([])
 
   """
   @spec intersection(t(val), t(val)) :: t(val) when val: value
@@ -279,7 +295,7 @@ defmodule MapSet do
   """
   @spec member?(t, value) :: boolean
   def member?(%MapSet{map: map}, value) do
-    :erlang.is_map_key(value, map)
+    is_map_key(map, value)
   end
 
   @doc """
@@ -288,9 +304,9 @@ defmodule MapSet do
   ## Examples
 
       iex> MapSet.put(MapSet.new([1, 2, 3]), 3)
-      #MapSet<[1, 2, 3]>
+      MapSet.new([1, 2, 3])
       iex> MapSet.put(MapSet.new([1, 2, 3]), 4)
-      #MapSet<[1, 2, 3, 4]>
+      MapSet.new([1, 2, 3, 4])
 
   """
   @spec put(t(val), new_val) :: t(val | new_val) when val: value, new_val: value
@@ -363,7 +379,7 @@ defmodule MapSet do
   ## Examples
 
       iex> MapSet.union(MapSet.new([1, 2]), MapSet.new([2, 3, 4]))
-      #MapSet<[1, 2, 3, 4]>
+      MapSet.new([1, 2, 3, 4])
 
   """
   @spec union(t(val1), t(val2)) :: t(val1 | val2) when val1: value, val2: value
@@ -374,14 +390,88 @@ defmodule MapSet do
   end
 
   def union(%MapSet{map: map1}, %MapSet{map: map2}) do
-    map = new_from_list(Map.keys(map1) ++ Map.keys(map2), [])
-    %MapSet{map: map}
+    keys = Map.keys(map1) ++ Map.keys(map2)
+    %MapSet{map: Map.from_keys(keys, @dummy_value)}
   end
 
   @compile {:inline, [order_by_size: 2]}
   defp order_by_size(map1, map2) when map_size(map1) > map_size(map2), do: {map2, map1}
   defp order_by_size(map1, map2), do: {map1, map2}
 
+  @doc """
+  Filters the set by returning only the elements from `set` for which invoking
+  `fun` returns a truthy value.
+
+  Also see `reject/2` which discards all elements where the function returns
+  a truthy value.
+
+  > Note: if you find yourself doing multiple calls to `MapSet.filter/2`
+  > and `MapSet.reject/2` in a pipeline, it is likely more efficient
+  > to use `Enum.map/2` and `Enum.filter/2` instead and convert to
+  > a map at the end using `Map.new/1`.
+
+  ## Examples
+
+      iex> MapSet.filter(MapSet.new(1..5), fn x -> x > 3 end)
+      MapSet.new([4, 5])
+
+      iex> MapSet.filter(MapSet.new(["a", :b, "c"]), &is_atom/1)
+      MapSet.new([:b])
+
+  """
+  @doc since: "1.14.0"
+  @spec filter(t(a), (a -> as_boolean(term))) :: t(a) when a: value
+  def filter(%MapSet{map: map}, fun) when is_map(map) and is_function(fun) do
+    iter = :maps.iterator(map)
+    next = :maps.next(iter)
+    keys = filter_keys(next, fun)
+    %MapSet{map: Map.from_keys(keys, @dummy_value)}
+  end
+
+  defp filter_keys(:none, _fun), do: []
+
+  defp filter_keys({key, _value, iter}, fun) do
+    if fun.(key) do
+      [key | filter_keys(:maps.next(iter), fun)]
+    else
+      filter_keys(:maps.next(iter), fun)
+    end
+  end
+
+  @doc """
+  Returns a set by excluding the elements from `set` for which invoking `fun`
+  returns a truthy value.
+
+  See also `filter/2`.
+
+  ## Examples
+
+      iex> MapSet.reject(MapSet.new(1..5), fn x -> rem(x, 2) != 0 end)
+      MapSet.new([2, 4])
+
+      iex> MapSet.reject(MapSet.new(["a", :b, "c"]), &is_atom/1)
+      MapSet.new(["a", "c"])
+
+  """
+  @doc since: "1.14.0"
+  @spec reject(t(a), (a -> as_boolean(term))) :: t(a) when a: value
+  def reject(%MapSet{map: map}, fun) when is_map(map) and is_function(fun) do
+    iter = :maps.iterator(map)
+    next = :maps.next(iter)
+    keys = reject_keys(next, fun)
+    %MapSet{map: Map.from_keys(keys, @dummy_value)}
+  end
+
+  defp reject_keys(:none, _fun), do: []
+
+  defp reject_keys({key, _value, iter}, fun) do
+    if fun.(key) do
+      reject_keys(:maps.next(iter), fun)
+    else
+      [key | reject_keys(:maps.next(iter), fun)]
+    end
+  end
+
   defimpl Enumerable do
     def count(map_set) do
       {:ok, MapSet.size(map_set)}
@@ -393,7 +483,7 @@ defmodule MapSet do
 
     def slice(map_set) do
       size = MapSet.size(map_set)
-      {:ok, size, &Enumerable.List.slice(MapSet.to_list(map_set), &1, &2, size)}
+      {:ok, size, &MapSet.to_list/1}
     end
 
     def reduce(map_set, acc, fun) do
@@ -402,11 +492,10 @@ defmodule MapSet do
   end
 
   defimpl Collectable do
-    # TODO: Optimize into an empty mapset by using :maps.from_keys/2 on Erlang/OTP 24+
     def into(map_set) do
       fun = fn
-        list, {:cont, x} -> [{x, []} | list]
-        list, :done -> %{map_set | map: Map.merge(map_set.map, Map.new(list))}
+        list, {:cont, x} -> [x | list]
+        list, :done -> %{map_set | map: Map.merge(map_set.map, Map.from_keys(list, []))}
         _, :halt -> :ok
       end
 
@@ -419,7 +508,7 @@ defmodule MapSet do
 
     def inspect(map_set, opts) do
       opts = %Inspect.Opts{opts | charlists: :as_lists}
-      concat(["#MapSet<", Inspect.List.inspect(MapSet.to_list(map_set), opts), ">"])
+      concat(["MapSet.new(", Inspect.List.inspect(MapSet.to_list(map_set), opts), ")"])
     end
   end
 end

lib/elixir/lib/module.ex

@@ -22,6 +22,12 @@ defmodule Module do
   Accepts a module or a `{module, function_name}`. See the "Compile callbacks"
   section below.
 
+  ### `@after_verify` (since v1.14.0)
+
+  A hook that will be invoked right after the current module is verified for
+  undefined functions, deprecations, etc. Accepts a module or a `{module, function_name}`.
+  See the "Compile callbacks" section below.
+
   ### `@before_compile`
 
   A hook that will be invoked before the module is compiled.
@@ -128,7 +134,7 @@ defmodule Module do
   Multiple uses of `@compile` will accumulate instead of overriding
   previous ones. See the "Compile options" section below.
 
-  ### `@deprecated`
+  ### `@deprecated` (since v1.6.0)
 
   Provides the deprecation reason for a function. For example:
 
@@ -176,9 +182,14 @@ defmodule Module do
   `@doc` is to be used with a function, macro, callback, or
   macrocallback, while `@typedoc` with a type (public or opaque).
 
-  Accepts a string (often a heredoc) or `false` where `@doc false` will
-  make the entity invisible to documentation extraction tools like
-  [`ExDoc`](https://hexdocs.pm/ex_doc/). For example:
+  Accepts one of these:
+
+    * a string (often a heredoc)
+    * `false`, which will make the entity invisible to documentation-extraction
+      tools like [`ExDoc`](https://hexdocs.pm/ex_doc/)
+    * a keyword list, since Elixir 1.7.0
+
+  For example:
 
       defmodule MyModule do
         @typedoc "This type"
@@ -199,11 +210,11 @@ defmodule Module do
         end
       end
 
-  As can be seen in the example above, `@doc` and `@typedoc` also accept
-  a keyword list that serves as a way to provide arbitrary metadata
+  As can be seen in the example above, since Elixir 1.7.0 `@doc` and `@typedoc`
+  also accept a keyword list that serves as a way to provide arbitrary metadata
   about the entity. Tools like [`ExDoc`](https://hexdocs.pm/ex_doc/) and
   `IEx` may use this information to display annotations. A common use
-  case is `since` that may be used to annotate in which version the
+  case is the `:since` key, which may be used to annotate in which version the
   function was introduced.
 
   As illustrated in the example, it is possible to use these attributes
@@ -221,8 +232,7 @@ defmodule Module do
 
   ### `@dialyzer`
 
-  Defines warnings to request or suppress when using a version of
-  `:dialyzer` that supports module attributes.
+  Defines warnings to request or suppress when using `:dialyzer`.
 
   Accepts an atom, a tuple, or a list of atoms and tuples. For example:
 
@@ -234,8 +244,7 @@ defmodule Module do
         end
       end
 
-  For the list of supported warnings, see
-  [`:dialyzer` module](`:dialyzer`).
+  For the list of supported warnings, see [`:dialyzer` module](`:dialyzer`).
 
   Multiple uses of `@dialyzer` will accumulate instead of overriding
   previous ones.
@@ -296,156 +305,6 @@ defmodule Module do
   A hook that will be invoked when each function or macro in the current
   module is defined. Useful when annotating functions.
 
-  Accepts a module or a `{module, function_name}` tuple. See the
-  "Compile callbacks" section below.
-
-  ### `@on_load`
-
-  A hook that will be invoked whenever the module is loaded.
-
-  Accepts the function name (as an atom) of a function in the current module or
-  `{function_name, 0}` tuple where `function_name` is the name of a function in
-  the current module. The function must have an arity of 0 (no arguments). If
-  the function does not return `:ok`, the loading of the module will be aborted.
-  For example:
-
-      defmodule MyModule do
-        @on_load :load_check
-
-        def load_check do
-          if some_condition() do
-            :ok
-          else
-            :abort
-          end
-        end
-
-        def some_condition do
-          false
-        end
-      end
-
-  Modules compiled with HiPE would not call this hook.
-
-  ### `@vsn`
-
-  Specify the module version. Accepts any valid Elixir value, for example:
-
-      defmodule MyModule do
-        @vsn "1.0"
-      end
-
-  ### Struct attributes
-
-    * `@derive` - derives an implementation for the given protocol for the
-      struct defined in the current module
-
-    * `@enforce_keys` - ensures the given keys are always set when building
-      the struct defined in the current module
-
-  See `Kernel.defstruct/1` for more information on building and using structs.
-
-  ### Typespec attributes
-
-  The following attributes are part of typespecs and are also built-in in
-  Elixir:
-
-    * `@type` - defines a type to be used in `@spec`
-    * `@typep` - defines a private type to be used in `@spec`
-    * `@opaque` - defines an opaque type to be used in `@spec`
-    * `@spec` - provides a specification for a function
-    * `@callback` - provides a specification for a behaviour callback
-    * `@macrocallback` - provides a specification for a macro behaviour callback
-    * `@optional_callbacks` - specifies which behaviour callbacks and macro
-      behaviour callbacks are optional
-    * `@impl` - declares an implementation of a callback function or macro
-
-  For detailed documentation, see the [typespec documentation](typespecs.md).
-
-  ### Custom attributes
-
-  In addition to the built-in attributes outlined above, custom attributes may
-  also be added. Custom attributes are expressed using the `@/1` operator followed
-  by a valid variable name. The value given to the custom attribute must be a valid
-  Elixir value:
-
-      defmodule MyModule do
-        @custom_attr [some: "stuff"]
-      end
-
-  For more advanced options available when defining custom attributes, see
-  `register_attribute/3`.
-
-  ## Compile callbacks
-
-  There are three callbacks that are invoked when functions are defined,
-  as well as before and immediately after the module bytecode is generated.
-
-  ### `@after_compile`
-
-  A hook that will be invoked right after the current module is compiled.
-
-  Accepts a module or a `{module, function_name}` tuple. The function
-  must take two arguments: the module environment and its bytecode.
-  When just a module is provided, the function is assumed to be
-  `__after_compile__/2`.
-
-  Callbacks will run in the order they are registered.
-
-  #### Example
-
-      defmodule MyModule do
-        @after_compile __MODULE__
-
-        def __after_compile__(env, _bytecode) do
-          IO.inspect(env)
-        end
-      end
-
-  ### `@before_compile`
-
-  A hook that will be invoked before the module is compiled.
-
-  Accepts a module or a `{module, function_or_macro_name}` tuple. The
-  function/macro must take one argument: the module environment. If
-  it's a macro, its returned value will be injected at the end of the
-  module definition before the compilation starts.
-
-  When just a module is provided, the function/macro is assumed to be
-  `__before_compile__/1`.
-
-  Callbacks will run in the order they are registered. Any overridable
-  definition will be made concrete before the first callback runs.
-  A definition may be made overridable again in another before compile
-  callback and it will be made concrete one last time after all callbacks
-  run.
-
-  *Note*: unlike `@after_compile`, the callback function/macro must
-  be placed in a separate module (because when the callback is invoked,
-  the current module does not yet exist).
-
-  #### Example
-
-      defmodule A do
-        defmacro __before_compile__(_env) do
-          quote do
-            def hello, do: "world"
-          end
-        end
-      end
-
-      defmodule B do
-        @before_compile A
-      end
-
-      B.hello()
-      #=> "world"
-
-  ### `@on_definition`
-
-  A hook that will be invoked when each function or macro in the current
-  module is defined. Useful when annotating functions.
-
   Accepts a module or a `{module, function_name}` tuple. The function
   must take 6 arguments:
 
@@ -492,6 +351,177 @@ defmodule Module do
         end
       end
 
+  ### `@on_load`
+
+  A hook that will be invoked whenever the module is loaded.
+
+  Accepts the function name (as an atom) of a function in the current module.
+  The function must have an arity of 0 (no arguments). If the function does
+  not return `:ok`, the loading of the module will be aborted.
+  For example:
+
+      defmodule MyModule do
+        @on_load :load_check
+
+        def load_check do
+          if some_condition() do
+            :ok
+          else
+            :abort
+          end
+        end
+
+        def some_condition do
+          false
+        end
+      end
+
+  ### `@vsn`
+
+  Specify the module version. Accepts any valid Elixir value, for example:
+
+      defmodule MyModule do
+        @vsn "1.0"
+      end
+
+  ### Struct attributes
+
+    * `@derive` - derives an implementation for the given protocol for the
+      struct defined in the current module
+
+    * `@enforce_keys` - ensures the given keys are always set when building
+      the struct defined in the current module
+
+  See `defstruct/1` for more information on building and using structs.
+
+  ### Typespec attributes
+
+  The following attributes are part of typespecs and are also built-in in
+  Elixir:
+
+    * `@type` - defines a type to be used in `@spec`
+    * `@typep` - defines a private type to be used in `@spec`
+    * `@opaque` - defines an opaque type to be used in `@spec`
+    * `@spec` - provides a specification for a function
+    * `@callback` - provides a specification for a behaviour callback
+    * `@macrocallback` - provides a specification for a macro behaviour callback
+    * `@optional_callbacks` - specifies which behaviour callbacks and macro
+      behaviour callbacks are optional
+    * `@impl` - declares an implementation of a callback function or macro
+
+  For detailed documentation, see the [typespec documentation](typespecs.md).
+
+  ### Custom attributes
+
+  In addition to the built-in attributes outlined above, custom attributes may
+  also be added. Custom attributes are expressed using the `@/1` operator followed
+  by a valid variable name. The value given to the custom attribute must be a valid
+  Elixir value:
+
+      defmodule MyModule do
+        @custom_attr [some: "stuff"]
+      end
+
+  For more advanced options available when defining custom attributes, see
+  `register_attribute/3`.
+
+  ## Compile callbacks
+
+  There are three compilation callbacks, invoked in this order:
+  `@before_compile`, `@after_compile`, and `@after_verify`.
+  They are described next.
+
+  ### `@before_compile`
+
+  A hook that will be invoked before the module is compiled. This is
+  often used to change how the current module is being compiled.
+
+  Accepts a module or a `{module, function_or_macro_name}` tuple. The
+  function/macro must take one argument: the module environment. If
+  it's a macro, its returned value will be injected at the end of the
+  module definition before the compilation starts.
+
+  When just a module is provided, the function/macro is assumed to be
+  `__before_compile__/1`.
+
+  Callbacks will run in the order they are registered. Any overridable
+  definition will be made concrete before the first callback runs.
+  A definition may be made overridable again in another before compile
+  callback and it will be made concrete one last time after all callbacks
+  run.
+
+  *Note*: the callback function/macro must be placed in a separate module
+  (because when the callback is invoked, the current module does not yet exist).
+
+  #### Example
+
+      defmodule A do
+        defmacro __before_compile__(_env) do
+          quote do
+            def hello, do: "world"
+          end
+        end
+      end
+
+      defmodule B do
+        @before_compile A
+      end
+
+      B.hello()
+      #=> "world"
+
+  ### `@after_compile`
+
+  A hook that will be invoked right after the current module is compiled.
+
+  Accepts a module or a `{module, function_name}` tuple. The function
+  must take two arguments: the module environment and its bytecode.
+  When just a module is provided, the function is assumed to be
+  `__after_compile__/2`.
+
+  Callbacks will run in the order they are registered.
+
+  `Module` functions expecting not yet compiled modules (such as `definitions_in/1`)
+  are still available at the time `@after_compile` is invoked.
+
+  #### Example
+
+      defmodule MyModule do
+        @after_compile __MODULE__
+
+        def __after_compile__(env, _bytecode) do
+          IO.inspect(env)
+        end
+      end
+
+  ### `@after_verify`
+
+  A hook that will be invoked right after the current module is verified for
+  undefined functions, deprecations, etc. A module is always verified after
+  it is compiled. In Mix projects, a module is also verified when any of its
+  runtime dependencies change. Therefore this is useful to perform verification
+  of the current module while avoiding compile-time dependencies.
+
+  Accepts a module or a `{module, function_name}` tuple. The function
+  must take one argument: the module name. When just a module is provided,
+  the function is assumed to be `__after_verify__/2`.
+
+  Callbacks will run in the order they are registered.
+
+  `Module` functions expecting not yet compiled modules are no longer available
+  at the time `@after_verify` is invoked.
+
+  #### Example
+
+      defmodule MyModule do
+        @after_verify __MODULE__
+
+        def __after_verify__(module) do
+          IO.inspect(module)
+          :ok
+        end
+      end
+
   ## Compile options
 
   The `@compile` attribute accepts different options that are used by both
@@ -518,8 +548,8 @@ defmodule Module do
 
   '''
 
-  @typep definition :: {atom, arity}
-  @typep def_kind :: :def | :defp | :defmacro | :defmacrop
+  @type definition :: {atom, arity}
+  @type def_kind :: :def | :defp | :defmacro | :defmacrop
 
   @extra_error_msg_defines? "Use Kernel.function_exported?/3 and Kernel.macro_exported?/3 " <>
                               "to check for public functions and macros instead"
@@ -545,6 +575,8 @@ defmodule Module do
 
     * `:module` - the module atom name
 
+    * `:struct` - if the module defines a struct and if so each field in order
+
   """
   @callback __info__(:attributes) :: keyword()
   @callback __info__(:compile) :: [term()]
@@ -552,6 +584,7 @@ defmodule Module do
   @callback __info__(:macros) :: keyword()
   @callback __info__(:md5) :: binary()
   @callback __info__(:module) :: module()
+  @callback __info__(:struct) :: list(%{field: atom(), required: boolean()}) | nil
 
   @doc """
   Returns information about module attributes used by Elixir.
@@ -574,6 +607,9 @@ defmodule Module do
       after_compile: %{
         doc: "A hook that will be invoked right after the current module is compiled."
       },
+      after_verify: %{
+        doc: "A hook that will be invoked right after the current module is verified."
+      },
       before_compile: %{
         doc: "A hook that will be invoked before the module is compiled."
       },
@@ -642,10 +678,6 @@ defmodule Module do
       derive: %{
         doc:
           "Derives an implementation for the given protocol for the struct defined in the current module."
-      },
-      enforce_keys: %{
-        doc:
-          "Ensures the given keys are always set when building the struct defined in the current module."
       }
     }
   end
@@ -762,7 +794,7 @@ defmodule Module do
 
   `Module.create/3` works similarly to `Kernel.defmodule/2`
   and return the same results. While one could also use
-  `defmodule` to define modules dynamically, this function
+  `Kernel.defmodule/2` to define modules dynamically, this function
   is preferred when the module body is given by a quoted
   expression.
 
@@ -784,8 +816,8 @@ defmodule Module do
     end
 
     next = :elixir_module.next_counter(nil)
-    line = Keyword.get(opts, :line, 0)
-    quoted = :elixir_quote.linify_with_context_counter(line, {module, next}, quoted)
+    meta = Keyword.take(opts, [:line, :generated])
+    quoted = :elixir_quote.linify_with_context_counter(meta, {module, next}, quoted)
     :elixir_module.compile(module, quoted, [], :elixir.env_for_eval(opts))
   end
 
@@ -927,6 +959,10 @@ defmodule Module do
     simplify_arg(Macro.expand_once(attr, env), counters, env)
   end
 
+  defp simplify_arg({:var!, _, [{var, _, atom} | _]}, counters, _env) when is_atom(atom) do
+    {simplify_var(var, Elixir), counters}
+  end
+
   defp simplify_arg(other, counters, _env) when is_integer(other),
     do: autogenerated_key(counters, :int)
 
@@ -1100,7 +1136,7 @@ defmodule Module do
   """
   @doc since: "1.7.0"
   @spec defines_type?(module, definition) :: boolean
-  def defines_type?(module, definition) do
+  def defines_type?(module, definition) when is_atom(module) do
     Kernel.Typespec.defines_type?(module, definition)
   end
 
@@ -1141,7 +1177,7 @@ defmodule Module do
   def attributes_in(module) when is_atom(module) do
     assert_not_compiled!(__ENV__.function, module)
     {set, _} = data_tables_for(module)
-    :ets.select(set, [{{:"$1", :_, :_}, [{:is_atom, :"$1"}], [:"$1"]}])
+    :ets.select(set, [{{:"$1", :_, :_, :_}, [{:is_atom, :"$1"}], [:"$1"]}])
   end
 
   @doc """
@@ -1158,10 +1194,10 @@ defmodule Module do
         def foo, do: 1
         def bar, do: 2
 
-        defoverridable foo: 1, bar: 1
+        defoverridable foo: 0, bar: 0
         def foo, do: 3
 
-        [:bar, :foo] = Module.overridables_in(__MODULE__) |> Enum.sort()
+        [bar: 0, foo: 0] = Module.overridables_in(__MODULE__) |> Enum.sort()
       end
 
   """
@@ -1241,14 +1277,15 @@ defmodule Module do
 
   ## Options
 
-    * `:nillify_clauses` (since v1.13.0) - returns `nil` instead
+    * `:skip_clauses` (since v1.14.0) - returns `[]` instead
       of returning the clauses. This is useful when there is
-      only an interest in fetching the kind and metadata
+      only an interest in fetching the kind and the metadata
 
   """
   @spec get_definition(module, definition, keyword) ::
           {:v1, def_kind, meta :: keyword,
-           [{meta :: keyword, arguments :: [Macro.t()], guards :: [Macro.t()], Macro.t()}] | nil}
+           [{meta :: keyword, arguments :: [Macro.t()], guards :: [Macro.t()], Macro.t()}]}
+          | nil
   @doc since: "1.12.0"
   def get_definition(module, {name, arity}, options \\ [])
       when is_atom(module) and is_atom(name) and is_integer(arity) and is_list(options) do
@@ -1258,8 +1295,8 @@ defmodule Module do
     case :ets.lookup(set, {:def, {name, arity}}) do
       [{_key, kind, meta, _, _, _}] ->
         clauses =
-          if options[:nillify_clauses],
-            do: nil,
+          if options[:skip_clauses],
+            do: [],
             else: bag_lookup_element(bag, {:clauses, {name, arity}}, 2)
 
         {:v1, kind, meta, clauses}
@@ -1423,7 +1460,7 @@ defmodule Module do
   """
   @spec put_attribute(module, atom, term) :: :ok
   def put_attribute(module, key, value) when is_atom(module) and is_atom(key) do
-    __put_attribute__(module, key, value, nil)
+    __put_attribute__(module, key, value, nil, [])
   end
 
   @doc """
@@ -1465,7 +1502,7 @@ defmodule Module do
   """
   @spec get_attribute(module, atom, term) :: term
   def get_attribute(module, key, default \\ nil) when is_atom(module) and is_atom(key) do
-    case __get_attribute__(module, key, nil) do
+    case __get_attribute__(module, key, nil, true) do
       nil -> default
       value -> value
     end
@@ -1508,9 +1545,14 @@ defmodule Module do
   end
 
   @doc """
-  Deletes the module attribute that matches the given key.
+  Deletes the entry (or entries) for the given module attribute.
 
-  It returns the deleted attribute value (or `nil` if nothing was set).
+  It returns the deleted attribute value. If the attribute has not
+  been set nor configured to accumulate, it returns `nil`.
+
+  If the attribute is set to accumulate, then this function always
+  returns a list. Deleting the attribute removes existing entries
+  but the attribute will still accumulate.
 
   ## Examples
 
@@ -1526,10 +1568,12 @@ defmodule Module do
     {set, bag} = data_tables_for(module)
 
     case :ets.lookup(set, key) do
-      [{_, _, :accumulate}] ->
+      [{_, _, :accumulate, traces}] ->
+        trace_attribute(true, module, traces, set, key, [])
         reverse_values(:ets.take(bag, {:accumulate, key}), [])
 
-      [{_, value, _}] ->
+      [{_, value, _, traces}] ->
+        trace_attribute(module, traces)
         :ets.delete(set, key)
         value
 
@@ -1558,7 +1602,8 @@ defmodule Module do
     * `:persist` - the attribute will be persisted in the Erlang
       Abstract Format. Useful when interfacing with Erlang libraries.
 
-  By default, both options are `false`.
+  By default, both options are `false`. Once an attribute has been
+  set to accumulate or persist, the behaviour cannot be reverted.
 
   ## Examples
 
@@ -1582,11 +1627,11 @@ defmodule Module do
     end
 
     if Keyword.get(options, :accumulate) do
-      :ets.insert_new(set, {attribute, [], :accumulate}) ||
+      :ets.insert_new(set, {attribute, [], :accumulate, []}) ||
         :ets.update_element(set, attribute, {3, :accumulate})
     else
       :ets.insert_new(bag, {:warn_attributes, attribute})
-      :ets.insert_new(set, {attribute, nil, :unset})
+      :ets.insert_new(set, {attribute, nil, :unset, []})
     end
 
     :ok
@@ -1667,7 +1712,7 @@ defmodule Module do
         "#{kind} #{name}/#{arity} is private, " <>
           "@doc attribute is always discarded for private functions/macros/types"
 
-      IO.warn(message, Macro.Env.stacktrace(%{env | line: line}))
+      IO.warn(message, %{env | line: line})
     end
   end
 
@@ -1695,7 +1740,7 @@ defmodule Module do
               def #{name}(...)
           '''
 
-          IO.warn(message, Macro.Env.stacktrace(%{env | line: line}))
+          IO.warn(message, %{env | line: line})
         end
 
         signature = merge_signatures(current_sign, signature, 1)
@@ -1717,14 +1762,14 @@ defmodule Module do
 
   defp get_doc_meta(existing_meta, set) do
     case :ets.take(set, {:doc, :meta}) do
-      [{{:doc, :meta}, metadata, _}] -> Map.merge(existing_meta, metadata)
+      [{{:doc, :meta}, metadata}] -> Map.merge(existing_meta, metadata)
       [] -> existing_meta
     end
   end
 
   defp compile_deprecated(doc_meta, set, bag, name, arity, defaults) do
     case :ets.take(set, :deprecated) do
-      [{:deprecated, reason, _}] when is_binary(reason) ->
+      [{:deprecated, reason, _, _}] when is_binary(reason) ->
         :ets.insert(bag, deprecated_reasons(defaults, name, arity, reason))
         Map.put(doc_meta, :deprecated, reason)
 
@@ -1754,7 +1799,7 @@ defmodule Module do
     %{line: line, file: file} = env
 
     case :ets.take(set, :impl) do
-      [{:impl, value, _}] ->
+      [{:impl, value, _, _}] ->
         impl = {{name, arity}, context, defaults, kind, line, file, value}
         :ets.insert(bag, {:impls, impl})
         value
@@ -1775,7 +1820,8 @@ defmodule Module do
   defp args_count([], total, defaults), do: {total, defaults}
 
   @doc false
-  def check_behaviours_and_impls(env, _set, bag, all_definitions) do
+  def check_derive_behaviours_and_impls(env, set, bag, all_definitions) do
+    check_derive(env, set, bag)
     behaviours = bag_lookup_element(bag, {:accumulate, :behaviour}, 2)
     impls = bag_lookup_element(bag, :impls, 2)
     callbacks = check_behaviours(env, behaviours)
@@ -1793,6 +1839,25 @@ defmodule Module do
     :ok
   end
 
+  defp check_derive(env, set, bag) do
+    case bag_lookup_element(bag, {:accumulate, :derive}, 2) do
+      [] ->
+        :ok
+
+      _ ->
+        message =
+          case :ets.lookup(set, :__struct__) do
+            [] ->
+              "warning: module attribute @derive was set but never used (it must come before defstruct)"
+
+            _ ->
+              "warning: module attribute @derive was set after defstruct, all @derive calls must come before defstruct"
+          end
+
+        IO.warn(message, env)
+    end
+  end
+
   defp check_behaviours(env, behaviours) do
     Enum.reduce(behaviours, %{}, fn behaviour, acc ->
       cond do
@@ -1800,18 +1865,18 @@ defmodule Module do
           message =
             "@behaviour #{inspect(behaviour)} does not exist (in module #{inspect(env.module)})"
 
-          IO.warn(message, Macro.Env.stacktrace(env))
+          IO.warn(message, env)
           acc
 
         not function_exported?(behaviour, :behaviour_info, 1) ->
           message =
             "module #{inspect(behaviour)} is not a behaviour (in module #{inspect(env.module)})"
 
-          IO.warn(message, Macro.Env.stacktrace(env))
+          IO.warn(message, env)
           acc
 
         true ->
-          :elixir_env.trace({:require, [], behaviour, []}, env)
+          :elixir_env.trace({:require, [from_macro: true], behaviour, []}, env)
           optional_callbacks = behaviour_info(behaviour, :optional_callbacks)
           callbacks = behaviour_info(behaviour, :callbacks)
           Enum.reduce(callbacks, acc, &add_callback(&1, behaviour, env, optional_callbacks, &2))
@@ -1833,7 +1898,7 @@ defmodule Module do
               "#{inspect(conflict)} and #{inspect(behaviour)} (in module #{inspect(env.module)})"
           end
 
-        IO.warn(message, Macro.Env.stacktrace(env))
+        IO.warn(message, env)
 
       %{} ->
         :ok
@@ -1850,7 +1915,7 @@ defmodule Module do
             format_callback(callback, kind, behaviour) <>
               " is not implemented (in module #{inspect(env.module)})"
 
-          IO.warn(message, Macro.Env.stacktrace(env))
+          IO.warn(message, env)
 
         {_, wrong_kind, _, _} when kind != wrong_kind ->
           message =
@@ -1858,7 +1923,7 @@ defmodule Module do
               " was implemented as \"#{wrong_kind}\" but should have been \"#{kind}\" " <>
               "(in module #{inspect(env.module)})"
 
-          IO.warn(message, Macro.Env.stacktrace(env))
+          IO.warn(message, env)
 
         _ ->
           :ok
@@ -1894,7 +1959,7 @@ defmodule Module do
 
         {:error, message} ->
           formatted = format_impl_warning(fa, kind, message)
-          IO.warn(formatted, Macro.Env.stacktrace(%{env | line: line, file: file}))
+          IO.warn(formatted, %{env | line: line, file: file})
           acc
       end
     end)
@@ -2010,7 +2075,7 @@ defmodule Module do
             "This either means you forgot to add the \"@impl true\" annotation before the " <>
             "definition or that you are accidentally overriding this callback"
 
-        IO.warn(message, Macro.Env.stacktrace(%{env | line: :elixir_utils.get_line(meta)}))
+        IO.warn(message, %{env | line: :elixir_utils.get_line(meta)})
       end
     end
 
@@ -2050,7 +2115,7 @@ defmodule Module do
   @doc false
   # Used internally by Kernel's @.
   # This function is private and must be used only internally.
-  def __get_attribute__(module, key, line) when is_atom(key) do
+  def __get_attribute__(module, key, caller_line, trace?) when is_atom(key) do
     assert_not_compiled!(
       {:get_attribute, 2},
       module,
@@ -2060,23 +2125,25 @@ defmodule Module do
     {set, bag} = data_tables_for(module)
 
     case :ets.lookup(set, key) do
-      [{_, _, :accumulate}] ->
+      [{_, _, :accumulate, traces}] ->
+        trace_attribute(trace?, module, traces, set, key, [])
         :lists.reverse(bag_lookup_element(bag, {:accumulate, key}, 2))
 
-      [{_, val, line}] when is_integer(line) ->
-        :ets.update_element(set, key, {3, :used})
-        val
+      [{_, value, warn_line, traces}] when is_integer(warn_line) ->
+        trace_attribute(trace?, module, traces, set, key, [{3, :used}])
+        value
 
-      [{_, val, _}] ->
-        val
+      [{_, value, _, traces}] ->
+        trace_attribute(trace?, module, traces, set, key, [])
+        value
 
-      [] when is_integer(line) ->
+      [] when is_integer(caller_line) ->
         # TODO: Consider raising instead of warning on v2.0 as it usually cascades
         error_message =
           "undefined module attribute @#{key}, " <>
             "please remove access to @#{key} or explicitly set it before access"
 
-        IO.warn(error_message, attribute_stack(module, line))
+        IO.warn(error_message, attribute_stack(module, caller_line))
         nil
 
       [] ->
@@ -2084,25 +2151,90 @@ defmodule Module do
     end
   end
 
+  defp trace_attribute(module, traces) do
+    :lists.foreach(
+      fn {line, lexical_tracker, tracers, aliases} ->
+        env = %{
+          Macro.Env.__struct__()
+          | line: line,
+            lexical_tracker: lexical_tracker,
+            module: module,
+            tracers: tracers
+        }
+
+        :lists.foreach(
+          fn alias ->
+            :elixir_env.trace({:alias_reference, [line: line], alias}, env)
+          end,
+          aliases
+        )
+      end,
+      traces
+    )
+  end
+
+  defp trace_attribute(trace?, module, traces, set, key, updates) do
+    updates =
+      if trace? and traces != [] do
+        trace_attribute(module, traces)
+        updates ++ [{4, []}]
+      else
+        updates
+      end
+
+    case updates do
+      [] -> :ok
+      _ -> :ets.update_element(set, key, updates)
+    end
+
+    :ok
+  end
+
   @doc false
   # Used internally by Kernel's @.
   # This function is private and must be used only internally.
-  def __put_attribute__(module, key, value, line) when is_atom(key) do
-    assert_not_readonly!(__ENV__.function, module)
+  def __put_attribute__(module, key, value, warn_line, traces) when is_atom(key) do
+    assert_not_readonly!({:put_attribute, 3}, module)
     {set, bag} = data_tables_for(module)
-    value = preprocess_attribute(key, value)
-    put_attribute(module, key, value, line, set, bag)
+    put_attribute(module, key, value, warn_line, traces, set, bag)
     :ok
   end
 
+  defp put_attribute(_module, :on_load, value, warn_line, traces, set, bag) do
+    value =
+      case value do
+        _ when is_atom(value) ->
+          {value, 0}
+
+        {atom, 0} = tuple when is_atom(atom) ->
+          tuple
+
+        _ ->
+          raise ArgumentError,
+                "@on_load is a built-in module attribute that annotates a function to be invoked " <>
+                  "when the module is loaded. It should be an atom or an {atom, 0} tuple, " <>
+                  "got: #{inspect(value)}"
+      end
+
+    try do
+      :ets.lookup_element(set, :on_load, 3)
+    catch
+      :error, :badarg ->
+        :ets.insert(set, {:on_load, value, warn_line, traces})
+        :ets.insert(bag, {:warn_attributes, :on_load})
+    else
+      _ -> raise ArgumentError, "the @on_load attribute can only be set once per module"
+    end
+  end
+
   # If any of the doc attributes are called with a keyword list that
   # will become documentation metadata. Multiple calls will be merged
   # into the same map overriding duplicate keys.
-  defp put_attribute(module, key, {_, metadata}, line, set, _bag)
+  defp put_attribute(module, key, {_, metadata}, warn_line, _traces, set, _bag)
        when key in [:doc, :typedoc, :moduledoc] and is_list(metadata) do
-    metadata_map = preprocess_doc_meta(metadata, module, line, %{})
+    metadata_map = preprocess_doc_meta(metadata, module, warn_line, %{})
 
-    case :ets.insert_new(set, {{key, :meta}, metadata_map, line}) do
+    case :ets.insert_new(set, {{key, :meta}, metadata_map}) do
       true ->
         :ok
 
@@ -2114,46 +2246,45 @@ defmodule Module do
 
   # Optimize some attributes by avoiding writing to the attributes key
   # in the bag table since we handle them internally.
-  defp put_attribute(module, key, value, line, set, _bag)
+  defp put_attribute(module, key, value, warn_line, traces, set, _bag)
        when key in [:doc, :typedoc, :moduledoc, :impl, :deprecated] do
+    value = preprocess_attribute(key, value)
+
     try do
       :ets.lookup_element(set, key, 3)
     catch
       :error, :badarg -> :ok
     else
-      unread_line when is_integer(line) and is_integer(unread_line) ->
+      unread_line when is_integer(warn_line) and is_integer(unread_line) ->
         message = "redefining @#{key} attribute previously set at line #{unread_line}"
-        IO.warn(message, attribute_stack(module, line))
+        IO.warn(message, attribute_stack(module, warn_line))
 
       _ ->
         :ok
     end
 
-    :ets.insert(set, {key, value, line})
+    :ets.insert(set, {key, value, warn_line, traces})
   end
 
-  defp put_attribute(_module, :on_load, value, line, set, bag) do
-    try do
-      :ets.lookup_element(set, :on_load, 3)
-    catch
-      :error, :badarg ->
-        :ets.insert(set, {:on_load, value, line})
-        :ets.insert(bag, {:warn_attributes, :on_load})
-    else
-      _ -> raise ArgumentError, "the @on_load attribute can only be set once per module"
-    end
-  end
+  defp put_attribute(_module, key, value, warn_line, traces, set, bag) do
+    value = preprocess_attribute(key, value)
 
-  defp put_attribute(_module, key, value, line, set, bag) do
     try do
       :ets.lookup_element(set, key, 3)
     catch
       :error, :badarg ->
-        :ets.insert(set, {key, value, line})
+        :ets.insert(set, {key, value, warn_line, traces})
         :ets.insert(bag, {:warn_attributes, key})
     else
-      :accumulate -> :ets.insert(bag, {{:accumulate, key}, value})
-      _ -> :ets.insert(set, {key, value, line})
+      :accumulate ->
+        if traces != [] do
+          :ets.update_element(set, key, {4, traces ++ :ets.lookup_element(set, key, 4)})
+        end
+
+        :ets.insert(bag, {{:accumulate, key}, value})
+
+      _ ->
+        :ets.insert(set, {key, value, warn_line, traces})
     end
   end
 
@@ -2169,9 +2300,6 @@ defmodule Module do
       {line, doc} when is_integer(line) and (is_binary(doc) or doc == false or is_nil(doc)) ->
         value
 
-      {line, [{key, _} | _]} when is_integer(line) and is_atom(key) ->
-        value
-
       {line, doc} when is_integer(line) ->
         raise ArgumentError,
               "@#{key} is a built-in module attribute for documentation. It should be either " <>
@@ -2194,22 +2322,6 @@ defmodule Module do
     end
   end
 
-  defp preprocess_attribute(:on_load, value) do
-    case value do
-      _ when is_atom(value) ->
-        {value, 0}
-
-      {atom, 0} = tuple when is_atom(atom) ->
-        tuple
-
-      _ ->
-        raise ArgumentError,
-              "@on_load is a built-in module attribute that annotates a function to be invoked " <>
-                "when the module is loaded. It should be an atom or a {atom, 0} tuple, " <>
-                "got: #{inspect(value)}"
-    end
-  end
-
   defp preprocess_attribute(:impl, value) do
     if is_boolean(value) or (is_atom(value) and value != nil) do
       value
@@ -2227,6 +2339,9 @@ defmodule Module do
   defp preprocess_attribute(:after_compile, atom) when is_atom(atom),
     do: {atom, :__after_compile__}
 
+  defp preprocess_attribute(:after_verify, atom) when is_atom(atom),
+    do: {atom, :__after_verify__}
+
   defp preprocess_attribute(:on_definition, atom) when is_atom(atom),
     do: {atom, :__on_definition__}
 
@@ -2347,7 +2462,7 @@ defmodule Module do
 
   defp get_doc_info(table, env) do
     case :ets.take(table, :doc) do
-      [{:doc, {_, _} = pair, _}] ->
+      [{:doc, {_, _} = pair, _, _}] ->
         pair
 
       [] ->

lib/elixir/lib/module/parallel_checker.ex

@@ -27,14 +27,21 @@ defmodule Module.ParallelChecker do
   Gets the parallel checker data from pdict.
   """
   def get do
-    {_, checker} = :erlang.get(:elixir_checker_info)
-    checker
+    case :erlang.get(:elixir_checker_info) do
+      {parent, nil} ->
+        {:ok, checker} = start_link()
+        put(parent, checker)
+        {parent, checker}
+
+      {parent, checker} ->
+        {parent, checker}
+    end
   end
 
   @doc """
   Stores the parallel checker information.
   """
-  def put(pid, checker) do
+  def put(pid, checker) when is_pid(pid) and is_pid(checker) do
     :erlang.put(:elixir_checker_info, {pid, checker})
   end
 
@@ -51,21 +58,21 @@ defmodule Module.ParallelChecker do
 
         receive do
           {^ref, :cache, ets} ->
-            loaded_info =
+            module_map =
               if is_map(info) do
-                cache_from_module_map(ets, info)
                 info
               else
-                info = File.read!(info)
-                cache_from_chunk(ets, module, info)
-                info
+                info |> File.read!() |> fetch_module_map!(module)
               end
 
+            cache_from_module_map(ets, module_map)
             send(checker, {ref, :cached})
 
             receive do
               {^ref, :check} ->
-                warnings = check_module(module, loaded_info, {checker, ets})
+                # Set the compiler info so we can collect warnings
+                :erlang.put(:elixir_compiler_info, {pid, self()})
+                warnings = check_module(module_map, {checker, ets})
                 send(pid, {__MODULE__, module, warnings})
                 send(checker, {__MODULE__, :done})
             end
@@ -75,7 +82,8 @@ defmodule Module.ParallelChecker do
         end
       end)
 
-    {spawned, ref}
+    register(checker, spawned, ref)
+    :ok
   end
 
   @doc """
@@ -86,28 +94,33 @@ defmodule Module.ParallelChecker do
   def verify(fun) do
     case :erlang.get(:elixir_compiler_info) do
       :undefined ->
-        previous = :erlang.get(:elixir_checker_info)
-        {:ok, checker} = start_link()
-        put(self(), checker)
+        previous = :erlang.put(:elixir_checker_info, {self(), nil})
 
         try do
-          {result, compile_info} = Enum.unzip(fun.())
-          _ = verify(checker, compile_info, [])
+          result = fun.()
+
+          case :erlang.get(:elixir_checker_info) do
+            {_, nil} -> :ok
+            {_, checker} -> verify(checker, [])
+          end
+
           result
         after
+          {_, checker} = :erlang.get(:elixir_checker_info)
+
           if previous != :undefined do
             :erlang.put(:elixir_checker_info, previous)
           else
             :erlang.erase(:elixir_checker_info)
           end
 
-          stop(checker)
+          checker && stop(checker)
         end
 
       _ ->
         # If we are during compilation, then they will be
         # reported to the compiler, which will validate them.
-        Enum.map(fun.(), &elem(&1, 0))
+        fun.()
     end
   end
 
@@ -116,15 +129,13 @@ defmodule Module.ParallelChecker do
   the modules and adds the ExCk chunk to the binaries. Returns the updated
   list of warnings from the verification.
   """
-  @spec verify(pid(), [{pid(), reference()}], [{module(), binary()}]) :: [warning()]
-  def verify(checker, compiled_info, runtime_files) do
-    runtime_info =
-      for {module, file} <- runtime_files do
-        spawn({self(), checker}, module, file)
-      end
+  @spec verify(pid(), [{module(), binary()}]) :: [warning()]
+  def verify(checker, runtime_files) do
+    for {module, file} <- runtime_files do
+      spawn({self(), checker}, module, file)
+    end
 
-    modules = compiled_info ++ runtime_info
-    :gen_server.cast(checker, {:start, modules})
+    modules = :gen_server.call(checker, :start)
     collect_results(modules, [])
   end
 
@@ -132,10 +143,16 @@ defmodule Module.ParallelChecker do
     warnings
   end
 
-  defp collect_results([_ | modules], warnings) do
+  defp collect_results(modules, warnings) do
     receive do
+      {:warning, file, location, message} ->
+        file = file && Path.absname(file)
+        message = :unicode.characters_to_binary(message)
+        warning = {file, location, message}
+        collect_results(modules, [warning | warnings])
+
       {__MODULE__, _module, new_warnings} ->
-        collect_results(modules, new_warnings ++ warnings)
+        collect_results(tl(modules), new_warnings ++ warnings)
     end
   end
 
@@ -195,35 +212,26 @@ defmodule Module.ParallelChecker do
 
   ## Module checking
 
-  defp check_module(module, info, cache) do
-    case extract_definitions(module, info) do
-      {:ok, module, file, definitions, no_warn_undefined} ->
-        Module.Types.warnings(module, file, definitions, no_warn_undefined, cache)
-        |> group_warnings()
-        |> emit_warnings()
+  defp check_module(module_map, cache) do
+    %{module: module, file: file, compile_opts: compile_opts, definitions: definitions} =
+      module_map
 
-      :error ->
-        []
-    end
-  end
-
-  defp extract_definitions(module, module_map) when is_map(module_map) do
     no_warn_undefined =
-      module_map.compile_opts
+      compile_opts
       |> extract_no_warn_undefined()
       |> merge_compiler_no_warn_undefined()
 
-    {:ok, module, module_map.file, module_map.definitions, no_warn_undefined}
-  end
+    warnings =
+      module
+      |> Module.Types.warnings(file, definitions, no_warn_undefined, cache)
+      |> group_warnings()
+      |> emit_warnings()
 
-  defp extract_definitions(module, binary) when is_binary(binary) do
-    with {:ok, {_, [debug_info: chunk]}} <- :beam_lib.chunks(binary, [:debug_info]),
-         {:debug_info_v1, backend, data} <- chunk,
-         {:ok, module_map} <- backend.debug_info(:elixir_v1, module, data, []) do
-      extract_definitions(module, module_map)
-    else
-      _ -> :error
-    end
+    module_map
+    |> Map.get(:after_verify, [])
+    |> Enum.each(fn {verify_mod, verify_fun} -> apply(verify_mod, verify_fun, [module]) end)
+
+    warnings
   end
 
   defp extract_no_warn_undefined(compile_opts) do
@@ -236,11 +244,8 @@ defmodule Module.ParallelChecker do
 
   defp merge_compiler_no_warn_undefined(no_warn_undefined) do
     case Code.get_compiler_option(:no_warn_undefined) do
-      :all ->
-        :all
-
-      list when is_list(list) ->
-        no_warn_undefined ++ list
+      :all -> :all
+      list when is_list(list) -> no_warn_undefined ++ list
     end
   end
 
@@ -311,14 +316,9 @@ defmodule Module.ParallelChecker do
   end
 
   defp cache_from_chunk(ets, module) do
-    case :code.get_object_code(module) do
-      {^module, binary, _filename} -> cache_from_chunk(ets, module, binary)
-      _other -> false
-    end
-  end
-
-  defp cache_from_chunk(ets, module, binary) do
-    with {:ok, {_, [{'ExCk', chunk}]}} <- :beam_lib.chunks(binary, ['ExCk']),
+    with {^module, binary, _filename} <- :code.get_object_code(module),
+         {:ok, ^module} <- binary |> :beam_lib.info() |> Keyword.fetch(:module),
+         {:ok, {_, [{'ExCk', chunk}]}} <- :beam_lib.chunks(binary, ['ExCk']),
          {:elixir_checker_v1, contents} <- :erlang.binary_to_term(chunk) do
       cache_chunk(ets, module, contents.exports)
       true
@@ -327,16 +327,6 @@ defmodule Module.ParallelChecker do
     end
   end
 
-  defp cache_from_module_map(ets, map) do
-    exports =
-      [{{:__info__, 1}, :def}] ++
-        behaviour_exports(map) ++
-        definitions_to_exports(map.definitions)
-
-    deprecated = Map.new(map.deprecated)
-    cache_info(ets, map.module, exports, deprecated, :elixir)
-  end
-
   defp cache_from_info(ets, module) do
     if Code.ensure_loaded?(module) do
       {mode, exports} = info_exports(module)
@@ -367,6 +357,23 @@ defmodule Module.ParallelChecker do
     _ -> %{}
   end
 
+  defp fetch_module_map!(binary, module) when is_binary(binary) do
+    {:ok, {_, [debug_info: chunk]}} = :beam_lib.chunks(binary, [:debug_info])
+    {:debug_info_v1, backend, data} = chunk
+    {:ok, module_map} = backend.debug_info(:elixir_v1, module, data, [])
+    module_map
+  end
+
+  defp cache_from_module_map(ets, map) do
+    exports =
+      [{{:__info__, 1}, :def}] ++
+        behaviour_exports(map) ++
+        definitions_to_exports(map.definitions)
+
+    deprecated = Map.new(map.deprecated)
+    cache_info(ets, map.module, exports, deprecated, :elixir)
+  end
+
   defp cache_info(ets, module, exports, deprecated, mode) do
     Enum.each(exports, fn {{fun, arity}, kind} ->
       reason = Map.get(deprecated, {fun, arity})
@@ -414,7 +421,11 @@ defmodule Module.ParallelChecker do
   end
 
   defp unlock(server, module) do
-    :gen_server.call(server, {:unlock, module})
+    :gen_server.call(server, {:unlock, module}, :infinity)
+  end
+
+  defp register(server, pid, ref) do
+    :gen_server.cast(server, {:register, pid, ref})
   end
 
   ## Server callbacks
@@ -433,6 +444,20 @@ defmodule Module.ParallelChecker do
     {:ok, state}
   end
 
+  def handle_call(:start, _from, %{ets: ets, modules: modules} = state) do
+    for {pid, ref} <- modules do
+      send(pid, {ref, :cache, ets})
+    end
+
+    for {_pid, ref} <- modules do
+      receive do
+        {^ref, :cached} -> :ok
+      end
+    end
+
+    {:reply, modules, run_checkers(state)}
+  end
+
   def handle_call(:ets, _from, state) do
     {:reply, state.ets, state}
   end
@@ -465,18 +490,8 @@ defmodule Module.ParallelChecker do
     {:stop, :normal, state}
   end
 
-  def handle_cast({:start, modules}, %{ets: ets} = state) do
-    for {pid, ref} <- modules do
-      send(pid, {ref, :cache, ets})
-    end
-
-    for {_pid, ref} <- modules do
-      receive do
-        {^ref, :cached} -> :ok
-      end
-    end
-
-    {:noreply, run_checkers(%{state | modules: modules})}
+  def handle_cast({:register, pid, ref}, %{modules: modules} = state) do
+    {:noreply, %{state | modules: [{pid, ref} | modules]}}
   end
 
   defp run_checkers(%{modules: []} = state) do

lib/elixir/lib/module/types.ex

@@ -354,7 +354,7 @@ defmodule Module.Types do
   end
 
   defp simplify_type?(type, other) do
-    map_type?(type) and not map_type?(other)
+    map_like_type?(type) and not map_like_type?(other)
   end
 
   ## EXPRESSION FORMATTING
@@ -505,6 +505,10 @@ defmodule Module.Types do
   defp map_type?({:map, _}), do: true
   defp map_type?(_other), do: false
 
+  defp map_like_type?({:map, _}), do: true
+  defp map_like_type?({:union, union}), do: Enum.any?(union, &map_like_type?/1)
+  defp map_like_type?(_other), do: false
+
   defp atom_type?(:atom), do: true
   defp atom_type?({:atom, _}), do: false
   defp atom_type?({:union, union}), do: Enum.all?(union, &atom_type?/1)

lib/elixir/lib/module/types/expr.ex

@@ -151,7 +151,7 @@ defmodule Module.Types.Expr do
          dynamic_value_pairs =
            Enum.map(arg_pairs, fn {:required, key, _value} -> {:required, key, :dynamic} end),
          args_type = {:map, dynamic_value_pairs ++ [{:optional, :dynamic, :dynamic}]},
-         {:ok, type, context} <- unify(args_type, map_type, stack, context) do
+         {:ok, type, context} <- unify(map_type, args_type, stack, context) do
       # Retrieve map type and overwrite with the new value types from the map update
       {:map, pairs} = resolve_var(type, context)
 
@@ -216,6 +216,30 @@ defmodule Module.Types.Expr do
     end
   end
 
+  # cond do pat -> expr end
+  def of_expr({:cond, _meta, [[{:do, clauses}]]} = expr, _expected, stack, context) do
+    stack = push_expr_stack(expr, stack)
+
+    {result, context} =
+      reduce_ok(clauses, context, fn {:->, meta, [head, body]}, context = acc ->
+        case of_expr(head, :dynamic, stack, context) do
+          {:ok, _, context} ->
+            with {:ok, _expr_type, context} <- of_expr(body, :dynamic, stack, context) do
+              {:ok, keep_warnings(acc, context)}
+            end
+
+          error ->
+            # Skip the clause if it the head has an error
+            if meta[:generated], do: {:ok, acc}, else: error
+        end
+      end)
+
+    case result do
+      :ok -> {:ok, :dynamic, context}
+      :error -> {:error, context}
+    end
+  end
+
   # case expr do pat -> expr end
   def of_expr({:case, _meta, [case_expr, [{:do, clauses}]]} = expr, _expected, stack, context) do
     stack = push_expr_stack(expr, stack)
@@ -301,7 +325,7 @@ defmodule Module.Types.Expr do
   end
 
   # for pat <- expr do expr end
-  def of_expr({:for, _meta, args} = expr, _expected, stack, context) do
+  def of_expr({:for, _meta, [_ | _] = args} = expr, _expected, stack, context) do
     stack = push_expr_stack(expr, stack)
     {clauses, [[{:do, block} | opts]]} = Enum.split(args, -1)
 
@@ -320,7 +344,7 @@ defmodule Module.Types.Expr do
   end
 
   # with pat <- expr do expr end
-  def of_expr({:with, _meta, clauses} = expr, _expected, stack, context) do
+  def of_expr({:with, _meta, [_ | _] = clauses} = expr, _expected, stack, context) do
     stack = push_expr_stack(expr, stack)
 
     case reduce_ok(clauses, context, &with_clause(&1, stack, &2)) do
@@ -469,12 +493,19 @@ defmodule Module.Types.Expr do
   end
 
   defp of_clauses(clauses, stack, context) do
-    reduce_ok(clauses, context, fn {:->, _meta, [head, body]}, context = acc ->
+    reduce_ok(clauses, context, fn {:->, meta, [head, body]}, context = acc ->
       {patterns, guards} = extract_head(head)
 
-      with {:ok, _, context} <- Pattern.of_head(patterns, guards, stack, context),
-           {:ok, _expr_type, context} <- of_expr(body, :dynamic, stack, context),
-           do: {:ok, keep_warnings(acc, context)}
+      case Pattern.of_head(patterns, guards, stack, context) do
+        {:ok, _, context} ->
+          with {:ok, _expr_type, context} <- of_expr(body, :dynamic, stack, context) do
+            {:ok, keep_warnings(acc, context)}
+          end
+
+        error ->
+          # Skip the clause if it the head has an error
+          if meta[:generated], do: {:ok, acc}, else: error
+      end
     end)
   end
 

lib/elixir/lib/module/types/of.ex

@@ -237,7 +237,7 @@ defmodule Module.Types.Of do
   def remote(module, fun, arity, meta, context) when is_atom(module) do
     # TODO: In the future we may want to warn for modules defined
     # in the local context
-    if Keyword.get(meta, :context_module, false) and context.module != module do
+    if Keyword.get(meta, :context_module, false) do
       context
     else
       ParallelChecker.preload_module(context.cache, module)

lib/elixir/lib/module/types/pattern.ex

@@ -403,10 +403,8 @@ defmodule Module.Types.Pattern do
     # bar, {:ok, baz}
     # bar, {:ok, bat}
 
-    expanded_args =
-      args
-      |> Enum.map(&flatten_union(&1, context))
-      |> cartesian_product()
+    flatten_args = Enum.map(args, &flatten_union(&1, context))
+    cartesian_args = cartesian_product(flatten_args)
 
     # Remove clauses that do not match the expected type
     # Ignore type variables in parameters by changing them to dynamic
@@ -425,11 +423,11 @@ defmodule Module.Types.Pattern do
     # the type contexts from unifying argument and parameter to
     # infer type variables in arguments
     result =
-      flat_map_ok(expanded_args, fn expanded_args ->
+      flat_map_ok(cartesian_args, fn cartesian_args ->
         result =
           Enum.flat_map(clauses, fn {params, return} ->
             result =
-              map_ok(Enum.zip(expanded_args, params), fn {arg, param} ->
+              map_ok(Enum.zip(cartesian_args, params), fn {arg, param} ->
                 case unify(arg, param, stack, context) do
                   {:ok, _type, context} -> {:ok, context}
                   {:error, reason} -> {:error, reason}
@@ -453,7 +451,13 @@ defmodule Module.Types.Pattern do
       {:ok, returns_contexts} ->
         {success_returns, contexts} = Enum.unzip(returns_contexts)
         contexts = Enum.concat(contexts)
-        indexes = Enum.uniq(Enum.flat_map(args, &collect_var_indexes_from_type/1))
+
+        indexes =
+          for types <- flatten_args,
+              type <- types,
+              index <- collect_var_indexes_from_type(type),
+              do: index,
+              uniq: true
 
         # Build unions from collected type contexts to unify with
         # type variables from arguments

lib/elixir/lib/module/types/unify.ex

@@ -43,14 +43,14 @@ defmodule Module.Types.Unify do
     {:ok, same, context}
   end
 
-  def unify(type, {:var, var}, stack, context) do
-    unify_var(var, type, stack, context, _var_source = false)
-  end
-
   def unify({:var, var}, type, stack, context) do
     unify_var(var, type, stack, context, _var_source = true)
   end
 
+  def unify(type, {:var, var}, stack, context) do
+    unify_var(var, type, stack, context, _var_source = false)
+  end
+
   def unify({:tuple, n, sources}, {:tuple, n, targets}, stack, context) do
     result =
       map_reduce_ok(Enum.zip(sources, targets), context, fn {source, target}, context ->
@@ -130,10 +130,15 @@ defmodule Module.Types.Unify do
 
       %{^var => {:var, new_var} = var_type} ->
         unify_result =
-          if var_source? do
-            unify(var_type, type, stack, context)
-          else
-            unify(type, var_type, stack, context)
+          cond do
+            recursive_type?(var_type, [], context) ->
+              {:ok, var_type, put_in(context.types[var], var_type)}
+
+            var_source? ->
+              unify(var_type, type, stack, context)
+
+            true ->
+              unify(type, var_type, stack, context)
           end
 
         case unify_result do

lib/elixir/lib/node.ex

@@ -257,6 +257,36 @@ defmodule Node do
     :erlang.spawn_link(node, module, fun, args)
   end
 
+  @doc """
+  Spawns the given function on a node, monitors it and returns its PID
+  and monitoring reference.
+
+  This functionality was added on Erlang/OTP 23. Using this function to
+  communicate with nodes running on earlier versions will fail.
+
+  Inlined by the compiler.
+  """
+  @doc since: "1.14.0"
+  @spec spawn_monitor(t, (() -> any)) :: {pid, reference}
+  def spawn_monitor(node, fun) do
+    :erlang.spawn_monitor(node, fun)
+  end
+
+  @doc """
+  Spawns the given module and function passing the given args on a node,
+  monitors it and returns its PID and monitoring reference.
+
+  This functionality was added on Erlang/OTP 23. Using this function
+  to communicate with nodes running on earlier versions will fail.
+
+  Inlined by the compiler.
+  """
+  @doc since: "1.14.0"
+  @spec spawn_monitor(t, module, atom, [any]) :: {pid, reference}
+  def spawn_monitor(node, module, fun, args) do
+    :erlang.spawn_monitor(node, module, fun, args)
+  end
+
   @doc """
   Sets the magic cookie of `node` to the atom `cookie`.
 

lib/elixir/lib/option_parser.ex

@@ -29,7 +29,12 @@ defmodule OptionParser do
   @type argv :: [String.t()]
   @type parsed :: keyword
   @type errors :: [{String.t(), String.t() | nil}]
-  @type options :: [switches: keyword, strict: keyword, aliases: keyword]
+  @type options :: [
+          switches: keyword,
+          strict: keyword,
+          aliases: keyword,
+          allow_nonexistent_atoms: boolean
+        ]
 
   defmodule ParseError do
     defexception [:message]
@@ -487,7 +492,7 @@ defmodule OptionParser do
   Keys must be atoms. Keys with `nil` value are discarded,
   boolean values are converted to `--key` or `--no-key`
   (if the value is `true` or `false`, respectively),
-  and all other values are converted using `Kernel.to_string/1`.
+  and all other values are converted using `to_string/1`.
 
   It is advised to pass to `to_argv/2` the same set of `options`
   given to `parse/2`. Some switches can only be reconstructed

lib/elixir/lib/partition_supervisor.ex

@@ -0,0 +1,386 @@
+defmodule PartitionSupervisor do
+  @moduledoc """
+  A supervisor that starts multiple partitions of the same child.
+
+  Certain processes may become bottlenecks in large systems.
+  If those processes can have their state trivially partitioned,
+  in a way there is no dependency between them, then they can use
+  the `PartitionSupervisor` to create multiple isolated and
+  independent partitions.
+
+  Once the `PartitionSupervisor` starts, you can dispatch to its
+  children using `{:via, PartitionSupervisor, {name, key}}`, where
+  `name` is the name of the `PartitionSupervisor` and key is used
+  for routing.
+
+  ## Example
+
+  The `DynamicSupervisor` is a single process responsible for starting
+  other processes. In some applications, the `DynamicSupervisor` may
+  become a bottleneck. To address this, you can start multiple instances
+  of the `DynamicSupervisor` through a `PartitionSupervisor`, and then
+  pick a "random" instance to start the child on.
+
+  Instead of starting a single `DynamicSupervisor`:
+
+      children = [
+        {DynamicSupervisor, name: MyApp.DynamicSupervisor}
+      ]
+
+      Supervisor.start_link(children, strategy: :one_for_one)
+
+  and starting children on that dynamic supervisor directly:
+
+      DynamicSupervisor.start_child(MyApp.DynamicSupervisor, {Agent, fn -> %{} end})
+
+  You can do start the dynamic supervisors under a `PartitionSupervisor`:
+
+      children = [
+        {PartitionSupervisor,
+         child_spec: DynamicSupervisor,
+         name: MyApp.DynamicSupervisors}
+      ]
+
+      Supervisor.start_link(children, strategy: :one_for_one)
+
+  and then:
+
+      DynamicSupervisor.start_child(
+        {:via, PartitionSupervisor, {MyApp.DynamicSupervisors, self()}},
+        {Agent, fn -> %{} end}
+      )
+
+  In the code above, we start a partition supervisor that will by default
+  start a dynamic supervisor for each core in your machine. Then, instead
+  of calling the `DynamicSupervisor` by name, you call it through the
+  partition supervisor using the `{:via, PartitionSupervisor, {name, key}}`
+  format. We picked `self()` as the routing key, which means each process
+  will be assigned one of the existing dynamic supervisors. See `start_link/1`
+  to see all options supported by the `PartitionSupervisor`.
+
+  ## Implementation notes
+
+  The `PartitionSupervisor` uses either an ETS table or a `Registry` to
+  manage all of the partitions. Under the hood, the `PartitionSupervisor`
+  generates a child spec for each partition and then acts as a regular
+  supervisor. The ID of each child spec is the partition number.
+
+  For routing, two strategies are used. If `key` is an integer, it is routed
+  using `rem(abs(key), partitions)` where `partitions` is the number of
+  partitions. Otherwise it uses `:erlang.phash2(key, partitions)`.
+  The particular routing may change in the future, and therefore must not
+  be relied on. If you want to retrieve a particular PID for a certain key,
+  you can use `GenServer.whereis({:via, PartitionSupervisor, {name, key}})`.
+  """
+
+  @behaviour Supervisor
+
+  @registry PartitionSupervisor.Registry
+
+  @typedoc """
+  The name of the `PartitionSupervisor`.
+  """
+  @type name :: atom() | {:via, module(), term()}
+
+  @doc false
+  def child_spec(opts) when is_list(opts) do
+    id =
+      case Keyword.get(opts, :name, DynamicSupervisor) do
+        name when is_atom(name) -> name
+        {:via, _module, name} -> name
+      end
+
+    %{
+      id: id,
+      start: {PartitionSupervisor, :start_link, [opts]},
+      type: :supervisor
+    }
+  end
+
+  @doc """
+  Starts a partition supervisor with the given options.
+
+  This function is typically not invoked directly, instead it is invoked
+  when using a `PartitionSupervisor` as a child of another supervisor:
+
+      children = [
+        {PartitionSupervisor, child_spec: SomeChild, name: MyPartitionSupervisor}
+      ]
+
+  If the supervisor is successfully spawned, this function returns
+  `{:ok, pid}`, where `pid` is the PID of the supervisor. If the given name
+  for the partition supervisor is already assigned to a process,
+  the function returns `{:error, {:already_started, pid}}`, where `pid`
+  is the PID of that process.
+
+  Note that a supervisor started with this function is linked to the parent
+  process and exits not only on crashes but also if the parent process exits
+  with `:normal` reason.
+
+  ## Options
+
+    * `:name` - an atom or via tuple representing the name of the partition
+      supervisor (see `t:name/0`).
+
+    * `:partitions` - a positive integer with the number of partitions.
+      Defaults to `System.schedulers_online()` (typically the number of cores).
+
+    * `:strategy` - the restart strategy option, defaults to `:one_for_one`.
+      You can learn more about strategies in the `Supervisor` module docs.
+
+    * `:max_restarts` - the maximum number of restarts allowed in
+      a time frame. Defaults to `3`.
+
+    * `:max_seconds` - the time frame in which `:max_restarts` applies.
+      Defaults to `5`.
+
+    * `:with_arguments` - a two-argument anonymous function that allows
+      the partition to be given to the child starting function. See the
+      `:with_arguments` section below.
+
+  ## `:with_arguments`
+
+  Sometimes you want each partition to know their partition assigned number.
+  This can be done with the `:with_arguments` option. This function receives
+  the list of arguments of the child specification and the partition. It
+  must return a new list of arguments that will be passed to the child specification
+  of children.
+
+  For example, most processes are started by calling `start_link(opts)`,
+  where `opts` is a keyword list. You could inject the partition into the
+  options given to the child:
+
+      with_arguments: fn [opts], partition ->
+        [Keyword.put(opts, :partition, partition)]
+      end
+
+  """
+  @doc since: "1.14.0"
+  @spec start_link(keyword) :: Supervisor.on_start()
+  def start_link(opts) when is_list(opts) do
+    name = opts[:name]
+
+    unless name do
+      raise ArgumentError, "the :name option must be given to PartitionSupervisor"
+    end
+
+    {child_spec, opts} = Keyword.pop(opts, :child_spec)
+
+    unless child_spec do
+      raise ArgumentError, "the :child_spec option must be given to PartitionSupervisor"
+    end
+
+    {partitions, opts} = Keyword.pop(opts, :partitions, System.schedulers_online())
+
+    unless is_integer(partitions) and partitions >= 1 do
+      raise ArgumentError,
+            "the :partitions option must be a positive integer, got: #{inspect(partitions)}"
+    end
+
+    {with_arguments, opts} = Keyword.pop(opts, :with_arguments, fn args, _partition -> args end)
+
+    unless is_function(with_arguments, 2) do
+      raise ArgumentError,
+            "the :with_arguments option must be a function that receives two arguments, " <>
+              "the current call arguments and the partition, got: #{inspect(with_arguments)}"
+    end
+
+    %{start: {mod, fun, args}} = map = Supervisor.child_spec(child_spec, [])
+    modules = map[:modules] || [mod]
+
+    children =
+      for partition <- 0..(partitions - 1) do
+        args = with_arguments.(args, partition)
+
+        unless is_list(args) do
+          raise "the call to the function in :with_arguments must return a list, got: #{inspect(args)}"
+        end
+
+        start = {__MODULE__, :start_child, [mod, fun, args, name, partition]}
+        Map.merge(map, %{id: partition, start: start, modules: modules})
+      end
+
+    {init_opts, start_opts} = Keyword.split(opts, [:strategy, :max_seconds, :max_restarts])
+    Supervisor.start_link(__MODULE__, {name, partitions, children, init_opts}, start_opts)
+  end
+
+  @doc false
+  def start_child(mod, fun, args, name, partition) do
+    case apply(mod, fun, args) do
+      {:ok, pid} ->
+        register_child(name, partition, pid)
+        {:ok, pid}
+
+      {:ok, pid, info} ->
+        register_child(name, partition, pid)
+        {:ok, pid, info}
+
+      other ->
+        other
+    end
+  end
+
+  defp register_child(name, partition, pid) when is_atom(name) do
+    :ets.insert(name, {partition, pid})
+  end
+
+  defp register_child({:via, _, _}, partition, pid) do
+    Registry.register(@registry, {self(), partition}, pid)
+  end
+
+  @impl true
+  def init({name, partitions, children, init_opts}) do
+    init_partitions(name, partitions)
+    Supervisor.init(children, Keyword.put_new(init_opts, :strategy, :one_for_one))
+  end
+
+  defp init_partitions(name, partitions) when is_atom(name) do
+    :ets.new(name, [:set, :named_table, :protected, read_concurrency: true])
+    :ets.insert(name, {:partitions, partitions})
+  end
+
+  defp init_partitions({:via, _, _}, partitions) do
+    child_spec = {Registry, keys: :unique, name: @registry}
+
+    unless Process.whereis(@registry) do
+      Supervisor.start_child(:elixir_sup, child_spec)
+    end
+
+    Registry.register(@registry, self(), partitions)
+  end
+
+  @doc """
+  Returns the number of partitions for the partition supervisor.
+  """
+  @doc since: "1.14.0"
+  @spec partitions(name()) :: pos_integer()
+  def partitions(name) do
+    {_name, partitions} = name_partitions(name)
+    partitions
+  end
+
+  # For whereis_name, we want to lookup on GenServer.whereis/1
+  # just once, so we lookup the name and partitions together.
+  defp name_partitions(name) when is_atom(name) do
+    try do
+      {name, :ets.lookup_element(name, :partitions, 2)}
+    rescue
+      _ -> exit({:noproc, {__MODULE__, :partitions, [name]}})
+    end
+  end
+
+  defp name_partitions(name) when is_tuple(name) do
+    with pid when is_pid(pid) <- GenServer.whereis(name),
+         [name_partitions] <- Registry.lookup(@registry, pid) do
+      name_partitions
+    else
+      _ -> exit({:noproc, {__MODULE__, :partitions, [name]}})
+    end
+  end
+
+  @doc """
+  Returns a list with information about all children.
+
+  This function returns a list of tuples containing:
+
+    * `id` - the partition number
+
+    * `child` - the PID of the corresponding child process or the
+      atom `:restarting` if the process is about to be restarted
+
+    * `type` - `:worker` or `:supervisor` as defined in the child
+      specification
+
+    * `modules` - as defined in the child specification
+
+  """
+  @doc since: "1.14.0"
+  @spec which_children(name()) :: [
+          # Inlining [module()] | :dynamic here because :supervisor.modules() is not exported
+          {:undefined, pid | :restarting, :worker | :supervisor, [module()] | :dynamic}
+        ]
+  def which_children(name) when is_atom(name) or elem(name, 0) == :via do
+    Supervisor.which_children(name)
+  end
+
+  @doc """
+  Returns a map containing count values for the supervisor.
+
+  The map contains the following keys:
+
+    * `:specs` - the number of partitions (children processes)
+
+    * `:active` - the count of all actively running child processes managed by
+      this supervisor
+
+    * `:supervisors` - the count of all supervisors whether or not the child
+      process is still alive
+
+    * `:workers` - the count of all workers, whether or not the child process
+      is still alive
+
+  """
+  @doc since: "1.14.0"
+  @spec count_children(name()) :: %{
+          specs: non_neg_integer,
+          active: non_neg_integer,
+          supervisors: non_neg_integer,
+          workers: non_neg_integer
+        }
+  def count_children(supervisor) when is_atom(supervisor) do
+    Supervisor.count_children(supervisor)
+  end
+
+  @doc """
+  Synchronously stops the given partition supervisor with the given `reason`.
+
+  It returns `:ok` if the supervisor terminates with the given
+  reason. If it terminates with another reason, the call exits.
+
+  This function keeps OTP semantics regarding error reporting.
+  If the reason is any other than `:normal`, `:shutdown` or
+  `{:shutdown, _}`, an error report is logged.
+  """
+  @doc since: "1.14.0"
+  @spec stop(name(), reason :: term, timeout) :: :ok
+  def stop(supervisor, reason \\ :normal, timeout \\ :infinity) when is_atom(supervisor) do
+    Supervisor.stop(supervisor, reason, timeout)
+  end
+
+  ## Via callbacks
+
+  @doc false
+  def whereis_name({name, key}) when is_atom(name) or is_tuple(name) do
+    {name, partitions} = name_partitions(name)
+
+    partition =
+      if is_integer(key), do: rem(abs(key), partitions), else: :erlang.phash2(key, partitions)
+
+    whereis_name(name, partition)
+  end
+
+  defp whereis_name(name, partition) when is_atom(name) do
+    :ets.lookup_element(name, partition, 2)
+  end
+
+  defp whereis_name(name, partition) when is_pid(name) do
+    @registry
+    |> Registry.values({name, partition}, name)
+    |> List.first(:undefined)
+  end
+
+  @doc false
+  def send(name_key, msg) do
+    Kernel.send(whereis_name(name_key), msg)
+  end
+
+  @doc false
+  def register_name(_, _) do
+    raise "{:via, PartitionSupervisor, _} cannot be given on registration"
+  end
+
+  @doc false
+  def unregister_name(_, _) do
+    raise "{:via, PartitionSupervisor, _} cannot be given on unregistration"
+  end
+end

lib/elixir/lib/path.ex

@@ -3,21 +3,25 @@ defmodule Path do
   This module provides conveniences for manipulating or
   retrieving file system paths.
 
-  The functions in this module may receive a chardata as
-  argument (i.e. a string or a list of characters / string)
-  and will always return a string (encoded in UTF-8). If a binary
-  is given, in whatever encoding, its encoding will be kept.
+  The functions in this module may receive chardata as
+  arguments and will always return a string encoded in UTF-8. Chardata
+  is a string or a list of characters and strings, see `t:IO.chardata/0`.
+  If a binary is given, in whatever encoding, its encoding will be kept.
 
   The majority of the functions in this module do not
   interact with the file system, except for a few functions
   that require it (like `wildcard/2` and `expand/1`).
   """
 
+  @typedoc """
+  A path.
+  """
   @type t :: IO.chardata()
 
   @doc """
-  Converts the given path to an absolute one. Unlike
-  `expand/1`, no attempt is made to resolve `..`, `.` or `~`.
+  Converts the given path to an absolute one.
+
+  Unlike `expand/1`, no attempt is made to resolve `..`, `.`, or `~`.
 
   ## Examples
 
@@ -148,8 +152,8 @@ defmodule Path do
   defp reverse_maybe_remove_dir_sep(name, _), do: :lists.reverse(name)
 
   @doc """
-  Converts the path to an absolute one and expands
-  any `.` and `..` characters and a leading `~`.
+  Converts the path to an absolute one, expanding
+  any `.` and `..` components and a leading `~`.
 
   ## Examples
 
@@ -367,6 +371,9 @@ defmodule Path do
       iex> Path.basename("foo/bar")
       "bar"
 
+      iex> Path.basename("lib/module/submodule.ex")
+      "submodule.ex"
+
       iex> Path.basename("/")
       ""
 
@@ -428,10 +435,10 @@ defmodule Path do
 
   The behaviour of this function changed in Erlang/OTP 24 for filenames
   starting with a dot and without an extension. For example, for a file
-  named ".gitignore", `extname/1` now returns an empty string, while it
-  would return ".gitignore" in previous Erlang/OTP versions. This was
+  named `.gitignore`, `extname/1` now returns an empty string, while it
+  would return `".gitignore"` in previous Erlang/OTP versions. This was
   done to match the behaviour of `rootname/1`, which would return
-  ".gitignore" as its name (and therefore it cannot also be an extension).
+  `".gitignore"` as its name (and therefore it cannot also be an extension).
 
   See `basename/1` and `rootname/1` for related functions to extract
   information from paths.
@@ -493,6 +500,8 @@ defmodule Path do
   This function should be used to convert a list of paths to a path.
   Note that any trailing slash is removed when joining.
 
+  Raises an error if the given list of paths is empty.
+
   ## Examples
 
       iex> Path.join(["~", "foo"])
@@ -532,6 +541,7 @@ defmodule Path do
       iex> Path.join(["foo", "bar"], "fiz")
       "foobar/fiz"
 
+  Use `join/1` if you need to join a list of paths instead.
   """
   @spec join(t, t) :: binary
   def join(left, right) do
@@ -565,7 +575,7 @@ defmodule Path do
 
   If an empty string is given, returns an empty list.
 
-  On Windows, path is split on both "\" and "/" separators
+  On Windows, path is split on both `"\"` and `"/"` separators
   and the driver letter, if there is one, is always returned
   in lowercase.
 
@@ -582,7 +592,6 @@ defmodule Path do
 
   """
   @spec split(t) :: [binary]
-
   def split(path) do
     :filename.split(IO.chardata_to_string(path))
   end
@@ -658,7 +667,7 @@ defmodule Path do
 
   """
   @spec wildcard(t, keyword) :: [binary]
-  def wildcard(glob, opts \\ []) do
+  def wildcard(glob, opts \\ []) when is_list(opts) do
     mod = if Keyword.get(opts, :match_dot), do: :file, else: Path.Wildcard
 
     glob
@@ -721,4 +730,74 @@ defmodule Path do
   defp major_os_type do
     :os.type() |> elem(0)
   end
+
+  @doc """
+  Returns a relative path that is protected from directory-traversal attacks.
+
+  The given relative path is sanitized by eliminating `..` and `.` components.
+
+  This function checks that, after expanding those components, the path is still "safe".
+  Paths are considered unsafe if either of these is true:
+
+    * The path is not relative, such as `"/foo/bar"`.
+
+    * A `..` component would make it so that the path would travers up above
+      the root of `relative_to`.
+
+    * A symbolic link in the path points to something above the root of `relative_to`.
+
+  ## Examples
+
+      iex> Path.safe_relative_to("deps/my_dep/app.beam", "deps")
+      {:ok, "deps/my_dep/app.beam"}
+
+      iex> Path.safe_relative_to("deps/my_dep/./build/../app.beam", "deps")
+      {:ok, "deps/my_dep/app.beam"}
+
+      iex> Path.safe_relative_to("my_dep/../..", "deps")
+      :error
+
+      iex> Path.safe_relative_to("/usr/local", ".")
+      :error
+
+  """
+  @doc since: "1.14.0"
+  @spec safe_relative_to(t, t) :: {:ok, binary} | :error
+  def safe_relative_to(path, relative_to) do
+    path = IO.chardata_to_string(path)
+
+    case :filelib.safe_relative_path(path, relative_to) do
+      :unsafe -> :error
+      relative_path -> {:ok, IO.chardata_to_string(relative_path)}
+    end
+  end
+
+  @doc """
+  Returns a path relative to the current working directory that is
+  protected from directory-traversal attacks.
+
+  Same as `safe_relative_to/2` with the current working directory as
+  the second argument. If there is an issue retrieving the current working
+  directory, this function raises an error.
+
+  ## Examples
+
+      iex> Path.safe_relative("foo")
+      {:ok, "foo"}
+
+      iex> Path.safe_relative("foo/../bar")
+      {:ok, "bar"}
+
+      iex> Path.safe_relative("foo/../..")
+      :error
+
+      iex> Path.safe_relative("/usr/local")
+      :error
+
+  """
+  @doc since: "1.14.0"
+  @spec safe_relative(t) :: {:ok, binary} | :error
+  def safe_relative(path) do
+    safe_relative_to(path, File.cwd!())
+  end
 end

lib/elixir/lib/port.ex

@@ -24,7 +24,7 @@ defmodule Port do
   receives data from multiple inputs and concatenates them in the output.
 
   After the port was created, we sent it two commands in the form of
-  messages using `Kernel.send/2`. The first command has the binary payload
+  messages using `send/2`. The first command has the binary payload
   of "hello" and the second has "world".
 
   After sending those two messages, we invoked the IEx helper `flush()`,
@@ -250,7 +250,7 @@ defmodule Port do
   """
   @spec info(port) :: keyword | nil
   def info(port) do
-    nillify(:erlang.port_info(port))
+    nilify(:erlang.port_info(port))
   end
 
   @doc """
@@ -270,7 +270,7 @@ defmodule Port do
   end
 
   def info(port, item) do
-    nillify(:erlang.port_info(port, item))
+    nilify(:erlang.port_info(port, item))
   end
 
   @doc """
@@ -323,7 +323,7 @@ defmodule Port do
     :erlang.ports()
   end
 
-  @compile {:inline, nillify: 1}
-  defp nillify(:undefined), do: nil
-  defp nillify(other), do: other
+  @compile {:inline, nilify: 1}
+  defp nilify(:undefined), do: nil
+  defp nilify(other), do: other
 end

lib/elixir/lib/process.ex

@@ -116,7 +116,7 @@ defmodule Process do
   """
   @spec put(term, term) :: term | nil
   def put(key, value) do
-    nillify(:erlang.put(key, value))
+    nilify(:erlang.put(key, value))
   end
 
   @doc """
@@ -136,7 +136,7 @@ defmodule Process do
   """
   @spec delete(term) :: term | nil
   def delete(key) do
-    nillify(:erlang.erase(key))
+    nilify(:erlang.erase(key))
   end
 
   @doc """
@@ -383,7 +383,7 @@ defmodule Process do
   @type spawn_opt ::
           :link
           | :monitor
-          | {:monitor, :erlang.monitor_option()}
+          | {:monitor, monitor_option()}
           | {:priority, :low | :normal | :high}
           | {:fullsweep_after, non_neg_integer}
           | {:min_heap_size, non_neg_integer}
@@ -392,6 +392,10 @@ defmodule Process do
           | {:message_queue_data, :off_heap | :on_heap}
   @type spawn_opts :: [spawn_opt]
 
+  # TODO: Use :erlang.monitor_option() on Erlang/OTP 24+
+  @typep monitor_option ::
+           [alias: :explicit_unalias | :demonitor | :reply_demonitor, tag: term()]
+
   @doc """
   Spawns the given function according to the given options.
 
@@ -646,7 +650,7 @@ defmodule Process do
   """
   @spec whereis(atom) :: pid | port | nil
   def whereis(name) do
-    nillify(:erlang.whereis(name))
+    nilify(:erlang.whereis(name))
   end
 
   @doc """
@@ -745,7 +749,7 @@ defmodule Process do
   """
   @spec info(pid) :: keyword | nil
   def info(pid) do
-    nillify(:erlang.process_info(pid))
+    nilify(:erlang.process_info(pid))
   end
 
   @doc """
@@ -766,7 +770,7 @@ defmodule Process do
   end
 
   def info(pid, spec) when is_atom(spec) or is_list(spec) do
-    nillify(:erlang.process_info(pid, spec))
+    nilify(:erlang.process_info(pid, spec))
   end
 
   @doc """
@@ -784,7 +788,7 @@ defmodule Process do
   @spec hibernate(module, atom, list) :: no_return
   defdelegate hibernate(mod, fun_name, args), to: :erlang
 
-  @compile {:inline, nillify: 1}
-  defp nillify(:undefined), do: nil
-  defp nillify(other), do: other
+  @compile {:inline, nilify: 1}
+  defp nilify(:undefined), do: nil
+  defp nilify(other), do: other
 end

lib/elixir/lib/protocol.ex

@@ -244,8 +244,16 @@ defmodule Protocol do
         ...
       end
 
-  Although doing so is not recommended as it may affect your test suite
-  performance.
+  If you are using `Mix.install/2`, you can do by passing the `consolidate_protocols`
+  option:
+
+      Mix.install(
+        deps,
+        consolidate_protocols: false
+      )
+
+  Although doing so is not recommended as it may affect the performance of
+  your code.
 
   Finally, note all protocols are compiled with `debug_info` set to `true`,
   regardless of the option set by the `elixirc` compiler. The debug info is
@@ -723,14 +731,14 @@ defmodule Protocol do
 
   defp callback_ast_to_fa({kind, {:"::", meta, [{name, _, args}, _return]}, _pos})
        when kind in [:callback, :macrocallback] do
-    [{{name, length(args)}, meta}]
+    [{{name, length(List.wrap(args))}, meta}]
   end
 
   defp callback_ast_to_fa(
          {kind, {:when, _, [{:"::", meta, [{name, _, args}, _return]}, _vars]}, _pos}
        )
        when kind in [:callback, :macrocallback] do
-    [{{name, length(args)}, meta}]
+    [{{name, length(List.wrap(args))}, meta}]
   end
 
   defp callback_ast_to_fa({kind, _, _pos}) when kind in [:callback, :macrocallback] do
@@ -747,7 +755,7 @@ defmodule Protocol do
     do: :maps.get(fa, metas, [])[:line]
 
   defp warn(message, env, nil) do
-    IO.warn(message, Macro.Env.stacktrace(env))
+    IO.warn(message, env)
   end
 
   defp warn(message, env, line) when is_integer(line) do
@@ -755,13 +763,20 @@ defmodule Protocol do
     IO.warn(message, stacktrace)
   end
 
-  # TODO: Convert the following warnings into errors future Elixir versions
   def __before_compile__(env) do
-    # Callbacks
     callback_metas = callback_metas(env.module, :callback)
     callbacks = :maps.keys(callback_metas)
     functions = Module.get_attribute(env.module, :__functions__)
 
+    if functions == [] do
+      warn(
+        "protocols must define at least one function, but none was defined",
+        env,
+        nil
+      )
+    end
+
+    # TODO: Convert the following warnings into errors in future Elixir versions
     :lists.map(
       fn {name, arity} = fa ->
         warn(
@@ -791,7 +806,7 @@ defmodule Protocol do
     # Optional Callbacks
     optional_callbacks = Module.get_attribute(env.module, :optional_callbacks)
 
-    if length(optional_callbacks) > 0 do
+    if optional_callbacks != [] do
       warn(
         "cannot define @optional_callbacks inside protocol, all of the protocol definitions are required",
         env,
@@ -907,26 +922,40 @@ defmodule Protocol do
     do: [:lists.foldl(&{:|, [], [&1, &2]}, head, tail), quote(do: ...)]
 
   @doc false
-  def __impl__(protocol, opts) do
-    do_defimpl(protocol, :lists.keysort(1, opts))
+  def __impl__(protocol, opts, do_block, env) do
+    opts = Keyword.merge(opts, do_block)
+
+    {for, opts} =
+      Keyword.pop_lazy(opts, :for, fn ->
+        env.module ||
+          raise ArgumentError, "defimpl/3 expects a :for option when declared outside a module"
+      end)
+
+    for = Macro.expand_literal(for, %{env | module: Kernel, function: {:defimpl, 3}})
+
+    case opts do
+      [] -> raise ArgumentError, "defimpl expects a do-end block"
+      [do: block] -> __impl__(protocol, for, block)
+      _ -> raise ArgumentError, "unknown options given to defimpl, got: #{Macro.to_string(opts)}"
+    end
   end
 
-  defp do_defimpl(protocol, do: block, for: for) when is_list(for) do
-    for f <- for, do: do_defimpl(protocol, do: block, for: f)
+  defp __impl__(protocol, for, block) when is_list(for) do
+    for f <- for, do: __impl__(protocol, f, block)
   end
 
-  defp do_defimpl(protocol, do: block, for: for) do
+  defp __impl__(protocol, for, block) do
     # Unquote the implementation just later
     # when all variables will already be injected
     # into the module body.
     impl =
       quote unquote: false do
         @doc false
-        @spec __impl__(:for) :: unquote(for)
         @spec __impl__(:target) :: __MODULE__
+        @spec __impl__(:for) :: unquote(for)
         @spec __impl__(:protocol) :: unquote(protocol)
-        def __impl__(:for), do: unquote(for)
         def __impl__(:target), do: __MODULE__
+        def __impl__(:for), do: unquote(for)
         def __impl__(:protocol), do: unquote(protocol)
       end
 
@@ -943,12 +972,12 @@ defmodule Protocol do
         @protocol protocol
         @for for
 
-        unquote(block)
-
+        res = unquote(block)
         Module.register_attribute(__MODULE__, :__impl__, persist: true)
         @__impl__ [protocol: @protocol, for: @for]
 
         unquote(impl)
+        res
       end
     end
   end
@@ -1006,14 +1035,15 @@ defmodule Protocol do
 
   @doc false
   def __ensure_defimpl__(protocol, for, env) do
-    if Protocol.consolidated?(protocol) do
+    if not Code.get_compiler_option(:ignore_already_consolidated) and
+         Protocol.consolidated?(protocol) do
       message =
         "the #{inspect(protocol)} protocol has already been consolidated, an " <>
           "implementation for #{inspect(for)} has no effect. If you want to " <>
           "implement protocols after compilation or during tests, check the " <>
           "\"Consolidation\" section in the Protocol module documentation"
 
-      IO.warn(message, Macro.Env.stacktrace(env))
+      IO.warn(message, env)
     end
 
     :ok

lib/elixir/lib/range.ex

@@ -3,17 +3,55 @@ defmodule Range do
   Ranges represent a sequence of zero, one or many, ascending
   or descending integers with a common difference called step.
 
-  Ranges are always inclusive and they may have custom steps.
   The most common form of creating and matching on ranges is
   via the [`first..last`](`../2`) and [`first..last//step`](`..///3`)
   notations, auto-imported from `Kernel`:
 
+      iex> 1 in 1..10
+      true
+      iex> 5 in 1..10
+      true
+      iex> 10 in 1..10
+      true
+
+  Ranges are always inclusive in Elixir. When a step is defined,
+  integers will only belong to the range if they match the step:
+
+      iex> 5 in 1..10//2
+      true
+      iex> 4 in 1..10//2
+      false
+
+  When defining a range without a step, the step will be
+  defined based on the first and last position of the
+  range, If `first >= last`, it will be an increasing range
+  with a step of 1. Otherwise, it is a decreasing range.
+  Note however implicit decreasing ranges are deprecated.
+  Therefore, if you need a decreasing range from `3` to `1`,
+  prefer to write `3..1//-1` instead.
+
+  `../0` can also be used as a shortcut to create the range `0..-1//1`,
+  also known as the full-slice range:
+
+      iex> ..
+      0..-1//1
+
+  ## Use cases
+
+  Ranges typically have two uses in Elixir: as a collection or
+  to represent a slice of another data structure.
+
+  ### Ranges as collections
+
+  Ranges in Elixir are enumerables and therefore can be used
+  with the `Enum` module:
+
       iex> Enum.to_list(1..3)
       [1, 2, 3]
-      iex> Enum.to_list(1..3//2)
-      [1, 3]
       iex> Enum.to_list(3..1//-1)
       [3, 2, 1]
+      iex> Enum.to_list(1..5//2)
+      [1, 3, 5]
 
   Ranges may also have a single element:
 
@@ -29,27 +67,54 @@ defmodule Range do
       iex> Enum.to_list(0..10//-1)
       []
 
-  When defining a range without a step, the step will be
-  defined based on the first and last position of the
-  range, If `first >= last`, it will be an increasing range
-  with a step of 1. Otherwise, it is a decreasing range.
-  Note however implicitly decreasing ranges are deprecated.
-  Therefore, if you need a decreasing range from `3` to `1`,
-  prefer to write `3..1//-1` instead.
+  The full-slice range, returned by `../0`, is an empty collection:
+
+      iex> Enum.to_list(..)
+      []
+
+  ### Ranges as slices
+
+  Ranges are also frequently used to slice collections.
+  You can slice strings or any enumerable:
+
+      iex> String.slice("elixir", 1..4)
+      "lixi"
+      iex> Enum.slice([0, 1, 2, 3, 4, 5], 1..4)
+      [1, 2, 3, 4]
+
+  In those cases, the first and last values of the range
+  are mapped to positions in the collections.
+
+  If a negative number is given, it maps to a position
+  from the back:
+
+      iex> String.slice("elixir", 1..-2//1)
+      "lixi"
+      iex> Enum.slice([0, 1, 2, 3, 4, 5], 1..-2//1)
+      [1, 2, 3, 4]
+
+  The range `0..-1//1`, returned by `../0`, returns the
+  collection as is, which is why it is called the full-slice
+  range:
+
+      iex> String.slice("elixir", ..)
+      "elixir"
+      iex> Enum.slice([0, 1, 2, 3, 4, 5], ..)
+      [0, 1, 2, 3, 4, 5]
 
   ## Definition
 
-  An increasing range `first..last//step` is a range from
-  `first` to `last` increasing by `step` where  `step` must be a positive
-  integer and all values `v` must be `first <= v and v <= last`. Therefore, a range
-  `10..0//1` is an empty range because there is no value `v`
-  that is `10 <= v and v <= 0`.
+  An increasing range `first..last//step` is a range from `first`
+  to `last` increasing by `step` where  `step` must be a positive
+  integer and all values `v` must be `first <= v and v <= last`.
+  Therefore, a range `10..0//1` is an empty range because there
+  is no value `v` that is `10 <= v and v <= 0`.
 
   Similarly, a decreasing range `first..last//step` is a range
-  from `first` to `last` decreasing by `step` where `step` must be a negative
-  integer and  values `v` must be `first >= v and v >= last`. Therefore, a range
-  `0..10//-1` is an empty range because there is no value `v`
-  that is `0 >= v and v >= 10`.
+  from `first` to `last` decreasing by `step` where `step` must
+  be a negative integer and  values `v` must be `first >= v and v >= last`.
+  Therefore, a range `0..10//-1` is an empty range because there
+  is no value `v` that is `0 >= v and v >= 10`.
 
   ## Representation
 
@@ -71,9 +136,8 @@ defmodule Range do
   directly but you should not modify nor create ranges by hand.
   Instead use the proper operators or `new/2` and `new/3`.
 
-  A range implements the `Enumerable` protocol, which means
-  functions in the `Enum` module can be used to work with
-  ranges:
+  Ranges implement the `Enumerable` protocol with memory
+  efficient versions of all `Enumerable` callbacks:
 
       iex> range = 1..10
       1..10
@@ -191,6 +255,26 @@ defmodule Range do
     size(Map.put(range, :step, step))
   end
 
+  @doc """
+  Shifts a range by the given number of steps.
+
+  ## Examples
+
+      iex> Range.shift(0..10, 1)
+      1..11
+      iex> Range.shift(0..10, 2)
+      2..12
+
+      iex> Range.shift(0..10//2, 2)
+      4..14//2
+  """
+  @doc since: "1.14.0"
+  def shift(first..last//step, steps_to_shift)
+      when is_integer(first) and is_integer(last) and is_integer(step) and
+             is_integer(steps_to_shift) do
+    new(first + steps_to_shift * step, last + steps_to_shift * step, step)
+  end
+
   @doc """
   Checks if two ranges are disjoint.
 
@@ -332,7 +416,7 @@ defimpl Enumerable, for: Range do
   end
 
   def slice(first.._//step = range) do
-    {:ok, Range.size(range), &slice(first + &1 * step, step, &2)}
+    {:ok, Range.size(range), &slice(first + &1 * step, step + &3 - 1, &2)}
   end
 
   # TODO: Remove me on v2.0
@@ -341,7 +425,7 @@ defimpl Enumerable, for: Range do
     slice(Map.put(range, :step, step))
   end
 
-  defp slice(current, _step, 1), do: [current]
+  defp slice(_current, _step, 0), do: []
   defp slice(current, step, remaining), do: [current | slice(current + step, step, remaining - 1)]
 end
 

lib/elixir/lib/record.ex

@@ -434,7 +434,7 @@ defmodule Record do
 
     if Keyword.has_key?(keyword, :_) do
       message = "updating a record with a default (:_) is equivalent to creating a new record"
-      IO.warn(message, Macro.Env.stacktrace(caller))
+      IO.warn(message, caller)
       create(tag, fields, keyword, caller)
     else
       updates =

lib/elixir/lib/regex.ex

@@ -7,7 +7,7 @@ defmodule Regex do
   in the [`:re` module documentation](`:re`).
 
   Regular expressions in Elixir can be created using the sigils
-  `~r` (see `Kernel.sigil_r/2`) or `~R` (see `Kernel.sigil_R/2`):
+  `~r` (see `sigil_r/2`) or `~R` (see `sigil_R/2`):
 
       # A simple regular expression that matches foo anywhere in the string
       ~r/foo/
@@ -38,35 +38,35 @@ defmodule Regex do
 
   The modifiers available when creating a Regex are:
 
-    * `unicode` (u) - enables Unicode specific patterns like `\p` and causes
-      character classes like `\w`, `\W`, `\s`, etc. to also match on Unicode
+    * `:unicode` (u) - enables Unicode specific patterns like `\p` and causes
+      character classes like `\w`, `\W`, `\s`, and the like to also match on Unicode
       (see examples below in "Character classes"). It expects valid Unicode
       strings to be given on match
 
-    * `caseless` (i) - adds case insensitivity
+    * `:caseless` (i) - adds case insensitivity
 
-    * `dotall` (s) - causes dot to match newlines and also set newline to
+    * `:dotall` (s) - causes dot to match newlines and also set newline to
       anycrlf; the new line setting can be overridden by setting `(*CR)` or
       `(*LF)` or `(*CRLF)` or `(*ANY)` according to `:re` documentation
 
-    * `multiline` (m) - causes `^` and `$` to mark the beginning and end of
+    * `:multiline` (m) - causes `^` and `$` to mark the beginning and end of
       each line; use `\A` and `\z` to match the end or beginning of the string
 
-    * `extended` (x) - whitespace characters are ignored except when escaped
+    * `:extended` (x) - whitespace characters are ignored except when escaped
       and allow `#` to delimit comments
 
-    * `firstline` (f) - forces the unanchored pattern to match before or at the
+    * `:firstline` (f) - forces the unanchored pattern to match before or at the
       first newline, though the matched text may continue over the newline
 
-    * `ungreedy` (U) - inverts the "greediness" of the regexp
+    * `:ungreedy` (U) - inverts the "greediness" of the regexp
       (the previous `r` option is deprecated in favor of `U`)
 
   The options not available are:
 
-    * `anchored` - not available, use `^` or `\A` instead
-    * `dollar_endonly` - not available, use `\z` instead
-    * `no_auto_capture` - not available, use `?:` instead
-    * `newline` - not available, use `(*CR)` or `(*LF)` or `(*CRLF)` or
+    * `:anchored` - not available, use `^` or `\A` instead
+    * `:dollar_endonly` - not available, use `\z` instead
+    * `:no_auto_capture` - not available, use `?:` instead
+    * `:newline` - not available, use `(*CR)` or `(*LF)` or `(*CRLF)` or
       `(*ANYCRLF)` or `(*ANY)` at the beginning of the regexp according to the
       `:re` documentation
 
@@ -155,7 +155,7 @@ defmodule Regex do
 
   defstruct re_pattern: nil, source: "", opts: "", re_version: ""
 
-  @type t :: %__MODULE__{re_pattern: term, source: binary, opts: binary}
+  @type t :: %__MODULE__{re_pattern: term, source: binary, opts: binary | [term]}
 
   defmodule CompileError do
     defexception message: "regex could not be compiled"
@@ -166,8 +166,8 @@ defmodule Regex do
 
   The given options can either be a binary with the characters
   representing the same regex options given to the
-  `~r` (see `Kernel.sigil_r/2`) sigil, or a list of options, as
-  expected by the Erlang's `:re` module.
+  `~r` (see `sigil_r/2`) sigil, or a list of options, as
+  expected by the Erlang's [`:re`](`:re`) module.
 
   It returns `{:ok, regex}` in case of success,
   `{:error, reason}` otherwise.
@@ -180,6 +180,12 @@ defmodule Regex do
       iex> Regex.compile("*foo")
       {:error, {'nothing to repeat', 0}}
 
+      iex> Regex.compile("foo", "i")
+      {:ok, ~r/foo/i}
+
+      iex> Regex.compile("foo", [:caseless])
+      {:ok, Regex.compile!("foo", [:caseless])}
+
   """
   @spec compile(binary, binary | [term]) :: {:ok, t} | {:error, any}
   def compile(source, options \\ "") when is_binary(source) do
@@ -203,6 +209,7 @@ defmodule Regex do
   defp compile(source, opts, doc_opts, version) do
     case :re.compile(source, opts) do
       {:ok, re_pattern} ->
+        doc_opts = format_doc_opts(doc_opts, opts)
         {:ok, %Regex{re_pattern: re_pattern, re_version: version, source: source, opts: doc_opts}}
 
       error ->
@@ -210,6 +217,10 @@ defmodule Regex do
     end
   end
 
+  defp format_doc_opts(_doc_opts = "", _opts = []), do: ""
+  defp format_doc_opts(_doc_opts = "", opts), do: opts
+  defp format_doc_opts(doc_opts, _opts), do: doc_opts
+
   @doc """
   Compiles the regular expression and raises `Regex.CompileError` in case of errors.
   """
@@ -274,7 +285,7 @@ defmodule Regex do
       iex> Regex.match?(~r/foo/, "bar")
       false
 
-  Elixir also provides `Kernel.=~/2` and `String.match?/2` as
+  Elixir also provides text-based match operator `=~/2` and function `String.match?/2` as
   an alternative to test strings against regular expressions and
   strings.
   """
@@ -384,15 +395,21 @@ defmodule Regex do
   end
 
   @doc """
-  Returns the regex options as a string.
+  Returns the regex options, as a string or list depending on how
+  it was compiled.
+
+  See the documentation of `Regex.compile/2` for more information.
 
   ## Examples
 
       iex> Regex.opts(~r/foo/m)
       "m"
 
+      iex> Regex.opts(Regex.compile!("foo", [:caseless]))
+      [:caseless]
+
   """
-  @spec opts(t) :: String.t()
+  @spec opts(t) :: String.t() | [term]
   def opts(%Regex{opts: opts}) do
     opts
   end

lib/elixir/lib/registry.ex

@@ -47,9 +47,9 @@ defmodule Registry do
 
       {:ok, _} = Registry.start_link(keys: :unique, name: Registry.ViaTest)
       name = {:via, Registry, {Registry.ViaTest, "agent", :hello}}
-      {:ok, _} = Agent.start_link(fn -> 0 end, name: name)
+      {:ok, agent_pid} = Agent.start_link(fn -> 0 end, name: name)
       Registry.lookup(Registry.ViaTest, "agent")
-      #=> [{self(), :hello}]
+      #=> [{agent_pid, :hello}]
 
   To this point, we have been starting `Registry` using `start_link/1`.
   Typically the registry is started as part of a supervision tree though:
@@ -165,7 +165,7 @@ defmodule Registry do
   the value from the registry and sending it a message. Many parts of the standard
   library are designed to cope with that, such as `Process.monitor/1` which will
   deliver the `:DOWN` message immediately if the monitored process is already dead
-  and `Kernel.send/2` which acts as a no-op for dead processes.
+  and `send/2` which acts as a no-op for dead processes.
 
   ## ETS
 
@@ -260,6 +260,10 @@ defmodule Registry do
     end
   end
 
+  def send({registry, key, _value}, msg) do
+    Registry.send({registry, key}, msg)
+  end
+
   @doc false
   def unregister_name({registry, key}), do: unregister(registry, key)
   def unregister_name({registry, key, _value}), do: unregister(registry, key)
@@ -1274,7 +1278,7 @@ defmodule Registry do
 
   ## Examples
 
-  This example shows how to get everything from the registry.
+  This example shows how to get everything from the registry:
 
       iex> Registry.start_link(keys: :unique, name: Registry.SelectAllTest)
       iex> {:ok, _} = Registry.register(Registry.SelectAllTest, "hello", :value)
@@ -1282,7 +1286,7 @@ defmodule Registry do
       iex> Registry.select(Registry.SelectAllTest, [{{:"$1", :"$2", :"$3"}, [], [{{:"$1", :"$2", :"$3"}}]}])
       [{"world", self(), :value}, {"hello", self(), :value}]
 
-  Get all keys in the registry.
+  Get all keys in the registry:
 
       iex> Registry.start_link(keys: :unique, name: Registry.SelectAllTest)
       iex> {:ok, _} = Registry.register(Registry.SelectAllTest, "hello", :value)
@@ -1295,17 +1299,7 @@ defmodule Registry do
   @spec select(registry, spec) :: [term]
   def select(registry, spec)
       when is_atom(registry) and is_list(spec) do
-    spec =
-      for part <- spec do
-        case part do
-          {{key, pid, value}, guards, select} ->
-            {{key, {pid, value}}, guards, select}
-
-          _ ->
-            raise ArgumentError,
-                  "invalid match specification in Registry.select/2: #{inspect(spec)}"
-        end
-      end
+    spec = group_match_headers(spec, __ENV__.function)
 
     case key_info!(registry) do
       {_kind, partitions, nil} ->
@@ -1318,6 +1312,51 @@ defmodule Registry do
     end
   end
 
+  @doc """
+  Works like `select/2`, but only returns the number of matching records.
+
+  ## Examples
+
+  In the example below we register the current process under different
+  keys in a unique registry but with the same value:
+
+      iex> Registry.start_link(keys: :unique, name: Registry.CountSelectTest)
+      iex> {:ok, _} = Registry.register(Registry.CountSelectTest, "hello", :value)
+      iex> {:ok, _} = Registry.register(Registry.CountSelectTest, "world", :value)
+      iex> Registry.count_select(Registry.CountSelectTest, [{{:_, :_, :value}, [], [true]}])
+      2
+  """
+  @doc since: "1.14.0"
+  @spec count_select(registry, spec) :: non_neg_integer()
+  def count_select(registry, spec)
+      when is_atom(registry) and is_list(spec) do
+    spec = group_match_headers(spec, __ENV__.function)
+
+    case key_info!(registry) do
+      {_kind, partitions, nil} ->
+        Enum.reduce(0..(partitions - 1), 0, fn partition_index, acc ->
+          count = :ets.select_count(key_ets!(registry, partition_index), spec)
+          acc + count
+        end)
+
+      {_kind, 1, key_ets} ->
+        :ets.select_count(key_ets, spec)
+    end
+  end
+
+  defp group_match_headers(spec, {fun, arity}) do
+    for part <- spec do
+      case part do
+        {{key, pid, value}, guards, select} ->
+          {{key, {pid, value}}, guards, select}
+
+        _ ->
+          raise ArgumentError,
+                "invalid match specification in Registry.#{fun}/#{arity}: #{inspect(spec)}"
+      end
+    end
+  end
+
   ## Helpers
 
   @compile {:inline, hash: 2}

lib/elixir/lib/stream.ex

@@ -186,6 +186,9 @@ defmodule Stream do
       iex> Stream.chunk_every([1, 2, 3, 4, 5, 6], 3, 3, []) |> Enum.to_list()
       [[1, 2, 3], [4, 5, 6]]
 
+      iex> Stream.chunk_every([1, 2, 3, 4], 3, 3, Stream.cycle([0])) |> Enum.to_list()
+      [[1, 2, 3], [4, 0, 0]]
+
   """
   @doc since: "1.5.0"
   @spec chunk_every(Enumerable.t(), pos_integer, pos_integer, Enumerable.t() | :discard) ::
@@ -417,10 +420,47 @@ defmodule Stream do
     lazy(enum, true, fn f1 -> R.drop_while(fun, f1) end)
   end
 
+  @doc """
+  Duplicates the given element `n` times in a stream.
+
+  `n` is an integer greater than or equal to `0`.
+
+  If `n` is `0`, an empty stream is returned.
+
+  ## Examples
+
+      iex> stream = Stream.duplicate("hello", 0)
+      iex> Enum.to_list(stream)
+      []
+
+      iex> stream = Stream.duplicate("hi", 1)
+      iex> Enum.to_list(stream)
+      ["hi"]
+
+      iex> stream = Stream.duplicate("bye", 2)
+      iex> Enum.to_list(stream)
+      ["bye", "bye"]
+
+      iex> stream = Stream.duplicate([1, 2], 3)
+      iex> Enum.to_list(stream)
+      [[1, 2], [1, 2], [1, 2]]
+  """
+  @doc since: "1.14.0"
+  @spec duplicate(any, non_neg_integer) :: Enumerable.t()
+  def duplicate(value, n) when is_integer(n) and n >= 0 do
+    unfold(n, fn
+      0 -> nil
+      remaining -> {value, remaining - 1}
+    end)
+  end
+
   @doc """
   Executes the given function for each element.
 
-  Useful for adding side effects (like printing) to a stream.
+  The values in the stream do not change, therefore this
+  function is useful for adding side effects (like printing)
+  to a stream. See `map/2` if producing a different stream
+  is desired.
 
   ## Examples
 
@@ -800,10 +840,10 @@ defmodule Stream do
   @doc """
   Transforms an existing stream.
 
-  It expects an accumulator and a function that receives each stream element
-  and an accumulator. It must return a tuple, where the first element is a new
-  stream (often a list) or the atom `:halt`, and the second element is the
-  accumulator to be used by the next element, if any, in both cases.
+  It expects an accumulator and a function that receives two arguments,
+  the stream element and the updated accumulator. It must return a tuple,
+  where the first element is a new stream (often a list) or the atom `:halt`,
+  and the second element is the accumulator to be used by the next element.
 
   Note: this function is equivalent to `Enum.flat_map_reduce/3`, except this
   function does not return the accumulator once the stream is processed.
@@ -822,44 +862,72 @@ defmodule Stream do
       iex> Enum.to_list(stream)
       [1001, 1002, 1003]
 
+  `Stream.transform/5` further generalizes this function to allow wrapping
+  around resources.
   """
   @spec transform(Enumerable.t(), acc, fun) :: Enumerable.t()
         when fun: (element, acc -> {Enumerable.t(), acc} | {:halt, acc}),
              acc: any
   def transform(enum, acc, reducer) when is_function(reducer, 2) do
-    &do_transform(enum, fn -> acc end, reducer, &1, &2, nil)
+    &do_transform(enum, fn -> acc end, reducer, &1, &2, nil, fn acc -> acc end)
   end
 
   @doc """
-  Transforms an existing stream with function-based start and finish.
-
-  The accumulator is only calculated when transformation starts. It also
-  allows an after function to be given which is invoked when the stream
-  halts or completes.
+  Similar to `Stream.transform/5`, except `last_fun` is not supplied.
 
   This function can be seen as a combination of `Stream.resource/3` with
   `Stream.transform/3`.
   """
-  @spec transform(Enumerable.t(), (() -> acc), fun, (acc -> term)) :: Enumerable.t()
-        when fun: (element, acc -> {Enumerable.t(), acc} | {:halt, acc}),
+  @spec transform(Enumerable.t(), start_fun, reducer, after_fun) :: Enumerable.t()
+        when start_fun: (() -> acc),
+             reducer: (element, acc -> {Enumerable.t(), acc} | {:halt, acc}),
+             after_fun: (acc -> term),
              acc: any
   def transform(enum, start_fun, reducer, after_fun)
       when is_function(start_fun, 0) and is_function(reducer, 2) and is_function(after_fun, 1) do
-    &do_transform(enum, start_fun, reducer, &1, &2, after_fun)
+    &do_transform(enum, start_fun, reducer, &1, &2, nil, after_fun)
   end
 
-  defp do_transform(enumerables, user_acc, user, inner_acc, fun, after_fun) do
+  @doc """
+  Transforms an existing stream with function-based start, last, and after
+  callbacks.
+
+  Once transformation starts, `start_fun` is invoked to compute the initial
+  accumulator. Then, for each element in the enumerable, the `reducer` function
+  is invoked with the element and the accumulator, returning new elements and a
+  new accumulator, as in `transform/3`.
+
+  Once the collection is done, `last_fun` is invoked with the accumulator to
+  emit any remaining items. Then `after_fun` is invoked, to close any resource,
+  but not emitting any new items. `last_fun` is only invoked if the given
+  enumerable terminates successfully (either because it is done or it halted
+  itself). `after_fun` is always invoked, therefore `after_fun` must be the
+  one used for closing resources.
+  """
+  @spec transform(Enumerable.t(), start_fun, reducer, last_fun, after_fun) :: Enumerable.t()
+        when start_fun: (() -> acc),
+             reducer: (element, acc -> {Enumerable.t(), acc} | {:halt, acc}),
+             last_fun: (acc -> {Enumerable.t(), acc} | {:halt, acc}),
+             after_fun: (acc -> term),
+             acc: any
+  def transform(enum, start_fun, reducer, last_fun, after_fun)
+      when is_function(start_fun, 0) and is_function(reducer, 2) and is_function(last_fun, 1) and
+             is_function(after_fun, 1) do
+    &do_transform(enum, start_fun, reducer, &1, &2, last_fun, after_fun)
+  end
+
+  defp do_transform(enumerables, user_acc, user, inner_acc, fun, last_fun, after_fun) do
     inner = &do_transform_each(&1, &2, fun)
     step = &do_transform_step(&1, &2)
     next = &Enumerable.reduce(enumerables, &1, step)
-    funs = {user, fun, inner, after_fun}
+    funs = {user, fun, inner, last_fun, after_fun}
     do_transform(user_acc.(), :cont, next, inner_acc, funs)
   end
 
   defp do_transform(user_acc, _next_op, next, {:halt, inner_acc}, funs) do
-    {_, _, _, after_fun} = funs
+    {_, _, _, _, after_fun} = funs
     next.({:halt, []})
-    do_after(after_fun, user_acc)
+    after_fun.(user_acc)
     {:halted, inner_acc}
   end
 
@@ -867,72 +935,99 @@ defmodule Stream do
     {:suspended, inner_acc, &do_transform(user_acc, next_op, next, &1, funs)}
   end
 
-  defp do_transform(user_acc, :halt, _next, {_, inner_acc}, funs) do
-    {_, _, _, after_fun} = funs
-    do_after(after_fun, user_acc)
-    {:halted, inner_acc}
-  end
-
   defp do_transform(user_acc, :cont, next, inner_acc, funs) do
-    {_, _, _, after_fun} = funs
+    {_, _, _, _, after_fun} = funs
 
     try do
       next.({:cont, []})
     catch
       kind, reason ->
-        do_after(after_fun, user_acc)
+        after_fun.(user_acc)
         :erlang.raise(kind, reason, __STACKTRACE__)
     else
       {:suspended, vals, next} ->
         do_transform_user(:lists.reverse(vals), user_acc, :cont, next, inner_acc, funs)
 
       {_, vals} ->
-        do_transform_user(:lists.reverse(vals), user_acc, :halt, next, inner_acc, funs)
+        do_transform_user(:lists.reverse(vals), user_acc, :last, next, inner_acc, funs)
     end
   end
 
+  defp do_transform(user_acc, :last, next, inner_acc, funs) do
+    {_, _, _, last_fun, after_fun} = funs
+
+    if last_fun do
+      try do
+        last_fun.(user_acc)
+      catch
+        kind, reason ->
+          next.({:halt, []})
+          after_fun.(user_acc)
+          :erlang.raise(kind, reason, __STACKTRACE__)
+      else
+        result -> do_transform_result(result, [], :halt, next, inner_acc, funs)
+      end
+    else
+      do_transform(user_acc, :halt, next, inner_acc, funs)
+    end
+  end
+
+  defp do_transform(user_acc, :halt, _next, inner_acc, funs) do
+    {_, _, _, _, after_fun} = funs
+    after_fun.(user_acc)
+    {:halted, elem(inner_acc, 1)}
+  end
+
   defp do_transform_user([], user_acc, next_op, next, inner_acc, funs) do
     do_transform(user_acc, next_op, next, inner_acc, funs)
   end
 
   defp do_transform_user([val | vals], user_acc, next_op, next, inner_acc, funs) do
-    {user, fun, inner, after_fun} = funs
+    {user, _, _, _, after_fun} = funs
 
     try do
       user.(val, user_acc)
     catch
       kind, reason ->
         next.({:halt, []})
-        do_after(after_fun, user_acc)
+        after_fun.(user_acc)
         :erlang.raise(kind, reason, __STACKTRACE__)
     else
+      result -> do_transform_result(result, vals, next_op, next, inner_acc, funs)
+    end
+  end
+
+  defp do_transform_result(result, vals, next_op, next, inner_acc, funs) do
+    {_, fun, inner, _, after_fun} = funs
+
+    case result do
       {[], user_acc} ->
         do_transform_user(vals, user_acc, next_op, next, inner_acc, funs)
 
       {list, user_acc} when is_list(list) ->
         reduce = &Enumerable.List.reduce(list, &1, fun)
-        do_list_transform(vals, user_acc, next_op, next, inner_acc, reduce, funs)
+        do_transform_inner_list(vals, user_acc, next_op, next, inner_acc, reduce, funs)
 
       {:halt, user_acc} ->
         next.({:halt, []})
-        do_after(after_fun, user_acc)
+        after_fun.(user_acc)
         {:halted, elem(inner_acc, 1)}
 
       {other, user_acc} ->
         reduce = &Enumerable.reduce(other, &1, inner)
-        do_enum_transform(vals, user_acc, next_op, next, inner_acc, reduce, funs)
+        do_transform_inner_enum(vals, user_acc, next_op, next, inner_acc, reduce, funs)
     end
   end
 
-  defp do_list_transform(vals, user_acc, next_op, next, inner_acc, reduce, funs) do
-    {_, _, _, after_fun} = funs
+  defp do_transform_inner_list(vals, user_acc, next_op, next, inner_acc, reduce, funs) do
+    {_, _, _, _, after_fun} = funs
 
     try do
       reduce.(inner_acc)
     catch
       kind, reason ->
         next.({:halt, []})
-        do_after(after_fun, user_acc)
+        after_fun.(user_acc)
         :erlang.raise(kind, reason, __STACKTRACE__)
     else
       {:done, acc} ->
@@ -940,24 +1035,24 @@ defmodule Stream do
 
       {:halted, acc} ->
         next.({:halt, []})
-        do_after(after_fun, user_acc)
+        after_fun.(user_acc)
         {:halted, acc}
 
       {:suspended, acc, continuation} ->
-        resume = &do_list_transform(vals, user_acc, next_op, next, &1, continuation, funs)
+        resume = &do_transform_inner_list(vals, user_acc, next_op, next, &1, continuation, funs)
         {:suspended, acc, resume}
     end
   end
 
-  defp do_enum_transform(vals, user_acc, next_op, next, {op, inner_acc}, reduce, funs) do
-    {_, _, _, after_fun} = funs
+  defp do_transform_inner_enum(vals, user_acc, next_op, next, {op, inner_acc}, reduce, funs) do
+    {_, _, _, _, after_fun} = funs
 
     try do
       reduce.({op, [:outer | inner_acc]})
     catch
       kind, reason ->
         next.({:halt, []})
-        do_after(after_fun, user_acc)
+        after_fun.(user_acc)
         :erlang.raise(kind, reason, __STACKTRACE__)
     else
       # Only take into account outer halts when the op is not halt itself.
@@ -967,21 +1062,18 @@ defmodule Stream do
 
       {:halted, [_ | acc]} ->
         next.({:halt, []})
-        do_after(after_fun, user_acc)
+        after_fun.(user_acc)
         {:halted, acc}
 
       {:done, [_ | acc]} ->
         do_transform_user(vals, user_acc, next_op, next, {:cont, acc}, funs)
 
       {:suspended, [_ | acc], continuation} ->
-        resume = &do_enum_transform(vals, user_acc, next_op, next, &1, continuation, funs)
+        resume = &do_transform_inner_enum(vals, user_acc, next_op, next, &1, continuation, funs)
         {:suspended, acc, resume}
     end
   end
 
-  defp do_after(nil, _user_acc), do: :ok
-  defp do_after(fun, user_acc), do: fun.(user_acc)
-
   defp do_transform_each(x, [:outer | acc], f) do
     case f.(x, acc) do
       {:halt, res} -> {:halt, [:inner | res]}
@@ -1188,7 +1280,7 @@ defmodule Stream do
   enumerable, transforming them with the `zip_fun` function as it goes.
 
   The first element from each of the enums in `enumerables` will be put into a list which is then passed to
-  the 1-arity `zip_fun` function. Then, the second elements from each of the enums are put into a list and passed to
+  the one-arity `zip_fun` function. Then, the second elements from each of the enums are put into a list and passed to
   `zip_fun`, and so on until any one of the enums in `enumerables` completes.
 
   Returns a new enumerable with the results of calling `zip_fun`.

lib/elixir/lib/string.ex

@@ -17,6 +17,9 @@ defmodule String do
       iex> "hello" <> " " <> "world"
       "hello world"
 
+  The functions in this module act according to
+  [The Unicode Standard, Version 14.0.0](http://www.unicode.org/versions/Unicode14.0.0/).
+
   ## Interpolation
 
   Strings in Elixir also support interpolation. This allows
@@ -37,7 +40,7 @@ defmodule String do
       "2 + 2 = 4"
 
   In case the value you want to interpolate cannot be
-  converted to a string, because it doesn't have an human
+  converted to a string, because it doesn't have a human
   textual representation, a protocol error will be raised.
 
   ## Escape characters
@@ -45,6 +48,7 @@ defmodule String do
   Besides allowing double-quotes to be escaped with a backslash,
   strings also support the following escape characters:
 
+    * `\0` - Null byte
     * `\a` - Bell
     * `\b` - Backspace
     * `\t` - Horizontal tab
@@ -53,7 +57,9 @@ defmodule String do
     * `\f` - Form feed
     * `\r` - Carriage return
     * `\e` - Command Escape
+    * `\s` - Space
     * `\#` - Returns the `#` character itself, skipping interpolation
+    * `\\` - Single backslash
     * `\xNN` - A byte represented by the hexadecimal `NN`
     * `\uNNNN` - A Unicode code point represented by `NNNN`
 
@@ -66,29 +72,82 @@ defmodule String do
   low-level manipulations of string, so let's explore them in
   detail next.
 
-  ## Code points and grapheme cluster
+  ## Unicode and code points
 
-  The functions in this module act according to
-  [The Unicode Standard, Version 14.0.0](http://www.unicode.org/versions/Unicode14.0.0/).
+  In order to facilitate meaningful communication between computers
+  across multiple languages, a standard is required so that the ones
+  and zeros on one machine mean the same thing when they are transmitted
+  to another. The Unicode Standard acts as an official registry of
+  virtually all the characters we know: this includes characters from
+  classical and historical texts, emoji, and formatting and control
+  characters as well.
 
-  As per the standard, a code point is a single Unicode Character,
-  which may be represented by one or more bytes.
+  Unicode organizes all of the characters in its repertoire into code
+  charts, and each character is given a unique numerical index. This
+  numerical index is known as a Code Point.
 
-  For example, although the code point "é" is a single character,
-  its underlying representation uses two bytes:
+  In Elixir you can use a `?` in front of a character literal to reveal
+  its code point:
 
-      iex> String.length("é")
-      1
-      iex> byte_size("é")
-      2
+      iex> ?a
+      97
+      iex> ?ł
+      322
 
-  Furthermore, this module also presents the concept of grapheme cluster
-  (from now on referenced as graphemes). Graphemes can consist of multiple
-  code points that may be perceived as a single character by readers. For
-  example, "é" can be represented either as a single "e with acute" code point
-  or as the letter "e" followed by a "combining acute accent" (two code points):
+  Note that most Unicode code charts will refer to a code point by its
+  hexadecimal (hex) representation, e.g. `97` translates to `0061` in hex,
+  and we can represent any Unicode character in an Elixir string by
+  using the `\u` escape character followed by its code point number:
+
+      iex> "\u0061" === "a"
+      true
+      iex> 0x0061 = 97 = ?a
+      97
+
+  The hex representation will also help you look up information about a
+  code point, e.g. [https://codepoints.net/U+0061](https://codepoints.net/U+0061)
+  has a data sheet all about the lower case `a`, a.k.a. code point 97.
+  Remember you can get the hex presentation of a number by calling
+  `Integer.to_string/2`:
+
+      iex> Integer.to_string(?a, 16)
+      "61"
+
+  ## UTF-8 encoded and encodings
+
+  Now that we understand what the Unicode standard is and what code points
+  are, we can finally talk about encodings. Whereas the code point is **what**
+  we store, an encoding deals with **how** we store it: encoding is an
+  implementation. In other words, we need a mechanism to convert the code
+  point numbers into bytes so they can be stored in memory, written to disk, and such.
+
+  Elixir uses UTF-8 to encode its strings, which means that code points are
+  encoded as a series of 8-bit bytes. UTF-8 is a **variable width** character
+  encoding that uses one to four bytes to store each code point. It is capable
+  of encoding all valid Unicode code points. Let's see an example:
+
+      iex> string = "héllo"
+      "héllo"
+      iex> String.length(string)
+      5
+      iex> byte_size(string)
+      6
+
+  Although the string above has 5 characters, it uses 6 bytes, as two bytes
+  are used to represent the character `é`.
+
+  ## Grapheme clusters
+
+  This module also works with the concept of grapheme cluster
+  (from now on referenced as graphemes). Graphemes can consist
+  of multiple code points that may be perceived as a single character
+  by readers. For example, "é" can be represented either as a single
+  "e with acute" code point, as seen above in the string `"héllo"`,
+  or as the letter "e" followed by a "combining acute accent"
+  (two code points):
 
       iex> string = "\u0065\u0301"
+      "é"
       iex> byte_size(string)
       3
       iex> String.length(string)
@@ -98,14 +157,13 @@ defmodule String do
       iex> String.graphemes(string)
       ["é"]
 
-  Although the example above is made of two characters, it is
-  perceived by users as one.
+  Although it looks visually the same as before, the example above
+  is made of two characters, it is perceived by users as one.
 
-  Graphemes can also be two characters that are interpreted
-  as one by some languages. For example, some languages may
-  consider "ch" as a single character. However, since this
-  information depends on the locale, it is not taken into account
-  by this module.
+  Graphemes can also be two characters that are interpreted as one
+  by some languages. For example, some languages may consider "ch"
+  as a single character. However, since this information depends on
+  the locale, it is not taken into account by this module.
 
   In general, the functions in this module rely on the Unicode
   Standard, but do not contain any of the locale specific behaviour.
@@ -135,98 +193,31 @@ defmodule String do
     * Plus a number of functions for working with binaries (bytes)
       in the [`:binary` module](`:binary`)
 
-  There are many situations where using the `String` module can
-  be avoided in favor of binary functions or pattern matching.
-  For example, imagine you have a string `prefix` and you want to
-  remove this prefix from another string named `full`.
+  A `utf8` modifier is also available inside the binary syntax `<<>>`.
+  It can be used to match code points out of a binary/string:
 
-  One may be tempted to write:
+      iex> <<eacute::utf8>> = "é"
+      iex> eacute
+      233
 
-      iex> take_prefix = fn full, prefix ->
-      ...>   base = String.length(prefix)
-      ...>   String.slice(full, base, String.length(full) - base)
-      ...> end
-      iex> take_prefix.("Mr. John", "Mr. ")
-      "John"
+  You can also fully convert a string into a list of integer code points,
+  known as "charlists" in Elixir, by calling `String.to_charlist/1`:
 
-  Although the function above works, it performs poorly. To
-  calculate the length of the string, we need to traverse it
-  fully, so we traverse both `prefix` and `full` strings, then
-  slice the `full` one, traversing it again.
+      iex> String.to_charlist("héllo")
+      [104, 233, 108, 108, 111]
 
-  A first attempt at improving it could be with ranges:
+  If you would rather see the underlying bytes of a string, instead of
+  its codepoints, a common trick is to concatenate the null byte `<<0>>`
+  to it:
 
-      iex> take_prefix = fn full, prefix ->
-      ...>   base = String.length(prefix)
-      ...>   String.slice(full, base..-1)
-      ...> end
-      iex> take_prefix.("Mr. John", "Mr. ")
-      "John"
+      iex> "héllo" <> <<0>>
+      <<104, 195, 169, 108, 108, 111, 0>>
 
-  While this is much better (we don't traverse `full` twice),
-  it could still be improved. In this case, since we want to
-  extract a substring from a string, we can use `Kernel.byte_size/1`
-  and `Kernel.binary_part/3` as there is no chance we will slice in
-  the middle of a code point made of more than one byte:
+  Alternatively, you can view a string's binary representation by
+  passing an option to `IO.inspect/2`:
 
-      iex> take_prefix = fn full, prefix ->
-      ...>   base = byte_size(prefix)
-      ...>   binary_part(full, base, byte_size(full) - base)
-      ...> end
-      iex> take_prefix.("Mr. John", "Mr. ")
-      "John"
-
-  Or simply use pattern matching:
-
-      iex> take_prefix = fn full, prefix ->
-      ...>   base = byte_size(prefix)
-      ...>   <<_::binary-size(base), rest::binary>> = full
-      ...>   rest
-      ...> end
-      iex> take_prefix.("Mr. John", "Mr. ")
-      "John"
-
-  On the other hand, if you want to dynamically slice a string
-  based on an integer value, then using `String.slice/3` is the
-  best option as it guarantees we won't incorrectly split a valid
-  code point into multiple bytes.
-
-  ## Integer code points
-
-  Although code points are represented as integers, this module
-  represents code points in their encoded format as strings.
-  For example:
-
-      iex> String.codepoints("olá")
-      ["o", "l", "á"]
-
-  There are a couple of ways to retrieve the character code point.
-  One may use the `?` construct:
-
-      iex> ?o
-      111
-
-      iex> ?á
-      225
-
-  Or also via pattern matching:
-
-      iex> <<aacute::utf8>> = "á"
-      iex> aacute
-      225
-
-  As we have seen above, code points can be inserted into
-  a string by their hexadecimal code:
-
-      iex> "ol\u00E1"
-      "olá"
-
-  Finally, to convert a String into a list of integer
-  code points, known as "charlists" in Elixir, you can call
-  `String.to_charlist`:
-
-      iex> String.to_charlist("olá")
-      [111, 108, 225]
+      IO.inspect("héllo", binaries: :as_binaries)
+      #=> <<104, 195, 169, 108, 108, 111>>
 
   ## Self-synchronization
 
@@ -283,8 +274,23 @@ defmodule String do
   @typedoc "Multiple code points that may be perceived as a single character by readers"
   @type grapheme :: t
 
-  @typedoc "Pattern used in functions like `replace/4` and `split/3`"
-  @type pattern :: t | [t] | :binary.cp()
+  @typedoc """
+  Pattern used in functions like `replace/4` and `split/3`.
+
+  It must be one of:
+
+    * a string
+    * an empty list
+    * a list containing non-empty strings
+    * a compiled search pattern created by `:binary.compile_pattern/1`
+
+  """
+  # TODO: Replace "nonempty_binary :: <<_::8, _::_*8>>" with "nonempty_binary()"
+  # when minimum requirement is >= OTP 24.
+  @type pattern ::
+          t()
+          | [nonempty_binary :: <<_::8, _::_*8>>]
+          | (compiled_search_pattern :: :binary.cp())
 
   @conditional_mappings [:greek, :turkic]
 
@@ -486,6 +492,14 @@ defmodule String do
     end
   end
 
+  def split(string, [], options) when is_binary(string) and is_list(options) do
+    if string == "" and Keyword.get(options, :trim, false) do
+      []
+    else
+      [string]
+    end
+  end
+
   def split(string, pattern, options) when is_binary(string) and is_list(options) do
     parts = Keyword.get(options, :parts, :infinity)
     trim = Keyword.get(options, :trim, false)
@@ -575,6 +589,14 @@ defmodule String do
     end
   end
 
+  def splitter(string, [], options) when is_binary(string) and is_list(options) do
+    if string == "" and Keyword.get(options, :trim, false) do
+      Stream.duplicate(string, 0)
+    else
+      Stream.duplicate(string, 1)
+    end
+  end
+
   def splitter(string, pattern, options) when is_binary(string) and is_list(options) do
     pattern = maybe_compile_pattern(pattern)
     trim = Keyword.get(options, :trim, false)
@@ -962,6 +984,8 @@ defmodule String do
       iex> String.replace_leading("hello hello world", "hello ", "ola ")
       "ola ola world"
 
+  This function can replace across grapheme boundaries. See `replace/3`
+  for more information and examples.
   """
   @spec replace_leading(t, t, t) :: t
   def replace_leading(string, match, replacement)
@@ -1019,6 +1043,8 @@ defmodule String do
       iex> String.replace_trailing("hello world world", " world", " mundo")
       "hello mundo mundo"
 
+  This function can replace across grapheme boundaries. See `replace/3`
+  for more information and examples.
   """
   @spec replace_trailing(t, t, t) :: t
   def replace_trailing(string, match, replacement)
@@ -1079,6 +1105,8 @@ defmodule String do
       iex> String.replace_prefix("world", "", "hello ")
       "hello world"
 
+  This function can replace across grapheme boundaries. See `replace/3`
+  for more information and examples.
   """
   @spec replace_prefix(t, t, t) :: t
   def replace_prefix(string, match, replacement)
@@ -1119,6 +1147,8 @@ defmodule String do
       iex> String.replace_suffix("hello", "", " world")
       "hello world"
 
+  This function can replace across grapheme boundaries. See `replace/3`
+  for more information and examples.
   """
   @spec replace_suffix(t, t, t) :: t
   def replace_suffix(string, match, replacement)
@@ -1472,6 +1502,20 @@ defmodule String do
       iex> String.replace("ELIXIR", "", "")
       "ELIXIR"
 
+  Be aware that this function can replace within or across grapheme boundaries.
+  For example, take the grapheme "é" which is made of the characters
+  "e" and the acute accent. The following will replace only the letter "e",
+  moving the accent to the letter "o":
+
+      iex> String.replace(String.normalize("é", :nfd), "e", "o")
+      "ó"
+
+  However, if "é" is represented by the single character "e with acute"
+  accent, then it won't be replaced at all:
+
+      iex> String.replace(String.normalize("é", :nfc), "e", "o")
+      "é"
+
   """
   @spec replace(t, pattern | Regex.t(), t | (t -> t | iodata), keyword) :: t
   def replace(subject, pattern, replacement, options \\ [])
@@ -1489,6 +1533,10 @@ defmodule String do
     subject
   end
 
+  defp replace_guarded(subject, [], _, _) do
+    subject
+  end
+
   defp replace_guarded(subject, "", replacement_binary, options)
        when is_binary(replacement_binary) do
     if Keyword.get(options, :global, true) do
@@ -2027,7 +2075,8 @@ defmodule String do
 
   Remember this function works with Unicode graphemes and considers
   the slices to represent grapheme offsets. If you want to split
-  on raw bytes, check `Kernel.binary_part/3` instead.
+  on raw bytes, check `Kernel.binary_part/3` or `Kernel.binary_slice/3`
+  instead.
 
   ## Examples
 
@@ -2040,19 +2089,19 @@ defmodule String do
       iex> String.slice("elixir", 10, 3)
       ""
 
+  If the start position is negative, it is normalized
+  against the string length and clamped to 0:
+
       iex> String.slice("elixir", -4, 4)
       "ixir"
 
       iex> String.slice("elixir", -10, 3)
-      ""
+      "eli"
 
-      iex> String.slice("a", 0, 1500)
-      "a"
+  If start is more than the string length, an empty
+  string is returned:
 
-      iex> String.slice("a", 1, 1500)
-      ""
-
-      iex> String.slice("a", 2, 1500)
+      iex> String.slice("elixir", 10, 1500)
       ""
 
   """
@@ -2071,12 +2120,8 @@ defmodule String do
   def slice(string, start, length)
       when is_binary(string) and is_integer(start) and is_integer(length) and start < 0 and
              length >= 0 do
-    start = length(string) + start
-
-    case start >= 0 do
-      true -> do_slice(string, start, length)
-      false -> ""
-    end
+    start = max(length(string) + start, 0)
+    do_slice(string, start, length)
   end
 
   defp do_slice(string, start, length) do
@@ -2100,42 +2145,48 @@ defmodule String do
 
   Remember this function works with Unicode graphemes and considers
   the slices to represent grapheme offsets. If you want to split
-  on raw bytes, check `Kernel.binary_part/3` instead.
+  on raw bytes, check `Kernel.binary_part/3` or
+  `Kernel.binary_slice/2` instead
 
   ## Examples
 
       iex> String.slice("elixir", 1..3)
       "lix"
-
       iex> String.slice("elixir", 1..10)
       "lixir"
 
       iex> String.slice("elixir", -4..-1)
       "ixir"
-
       iex> String.slice("elixir", -4..6)
       "ixir"
+      iex> String.slice("elixir", -100..100)
+      "elixir"
 
   For ranges where `start > stop`, you need to explicitly
   mark them as increasing:
 
       iex> String.slice("elixir", 2..-1//1)
       "ixir"
-
       iex> String.slice("elixir", 1..-2//1)
       "lixi"
 
-  If values are out of bounds, it returns an empty string:
+  You can use `../0` as a shortcut for `0..-1//1`, which returns
+  the whole string as is:
+
+      iex> String.slice("elixir", ..)
+      "elixir"
+
+  The step can be any positive number. For example, to
+  get every 2 characters of the string:
+
+      iex> String.slice("elixir", 0..-1//2)
+      "eii"
+
+  If the first position is after the string ends or after
+  the last position of the range, it returns an empty string:
 
       iex> String.slice("elixir", 10..3)
       ""
-
-      iex> String.slice("elixir", -10..-7)
-      ""
-
-      iex> String.slice("a", 0..1500)
-      "a"
-
       iex> String.slice("a", 1..1500)
       ""
 
@@ -2143,16 +2194,16 @@ defmodule String do
   @spec slice(t, Range.t()) :: t
   def slice(string, first..last//step = range) when is_binary(string) do
     # TODO: Deprecate negative steps on Elixir v1.16
-    # TODO: There are two features we can add to slicing ranges:
-    # 1. We can allow the step to be any positive number
-    # 2. We can allow slice and reverse at the same time. However, we can't
-    #    implement so right now. First we will have to raise if a decreasing
-    #    range is given on Elixir v2.0.
-    if step == 1 or (step == -1 and first > last) do
-      slice_range(string, first, last)
-    else
-      raise ArgumentError,
-            "String.slice/2 does not accept ranges with custom steps, got: #{inspect(range)}"
+    cond do
+      step > 0 ->
+        slice_range(string, first, last, step)
+
+      step == -1 and first > last ->
+        slice_range(string, first, last, 1)
+
+      true ->
+        raise ArgumentError,
+              "String.slice/2 does not accept ranges with negative steps, got: #{inspect(range)}"
     end
   end
 
@@ -2163,45 +2214,95 @@ defmodule String do
     slice(string, Map.put(range, :step, step))
   end
 
-  defp slice_range("", _, _), do: ""
+  defp slice_range("", _, _, _), do: ""
 
-  defp slice_range(string, first, -1) when first >= 0 do
-    left = byte_size_remaining_at(string, first)
-    binary_part(string, byte_size(string) - left, left)
+  defp slice_range(_string, first, last, _step) when first >= 0 and last >= 0 and first > last do
+    ""
   end
 
-  defp slice_range(string, first, last) when first >= 0 and last >= 0 do
-    if last >= first do
-      slice(string, first, last - first + 1)
-    else
-      ""
+  defp slice_range(string, first, last, step) when first >= 0 do
+    from_start = byte_size_remaining_at(string, first)
+    rest = binary_part(string, byte_size(string) - from_start, from_start)
+
+    cond do
+      last == -1 ->
+        slice_every(rest, byte_size(rest), step)
+
+      last >= 0 and step == 1 ->
+        from_end = byte_size_remaining_at(rest, last - first + 1)
+        binary_part(rest, 0, from_start - from_end)
+
+      last >= 0 ->
+        slice_every(rest, last - first + 1, step)
+
+      true ->
+        rest
+        |> slice_range_negative(0, last)
+        |> slice_every(byte_size(string), step)
     end
   end
 
-  defp slice_range(string, first, last) do
-    {bytes, length} = acc_bytes(:unicode_util.gc(string), [], 0)
-    first = add_if_negative(first, length)
+  defp slice_range(string, first, last, step) do
+    string
+    |> slice_range_negative(first, last)
+    |> slice_every(byte_size(string), step)
+  end
+
+  defp slice_range_negative(string, first, last) do
+    {reversed_bytes, length} = acc_bytes(string, [], 0)
+    first = add_if_negative(first, length) |> max(0)
     last = add_if_negative(last, length)
 
-    if first < 0 or first > last or first > length do
+    if first > last or first > length do
       ""
     else
       last = min(last + 1, length)
-      bytes = Enum.drop(bytes, length - last)
-      first = last - first
-      {length_bytes, start_bytes} = split_bytes(bytes, 0, first)
+      reversed_bytes = Enum.drop(reversed_bytes, length - last)
+      {length_bytes, start_bytes} = split_bytes(reversed_bytes, 0, last - first)
       binary_part(string, start_bytes, length_bytes)
     end
   end
 
-  defp acc_bytes([gc | rest], bytes, length),
-    do: acc_bytes(:unicode_util.gc(rest), [grapheme_byte_size(gc) | bytes], length + 1)
+  defp slice_every(string, _count, 1), do: string
+  defp slice_every(string, count, step), do: slice_every(string, count, step, [])
 
-  defp acc_bytes([], bytes, length),
-    do: {bytes, length}
+  defp slice_every(string, count, to_drop, acc) when count > 0 do
+    case :unicode_util.gc(string) do
+      [current | rest] ->
+        rest
+        |> drop(to_drop)
+        |> slice_every(count - to_drop, to_drop, [current | acc])
 
-  defp acc_bytes({:error, <<_, rest::bits>>}, bytes, length),
-    do: acc_bytes(:unicode_util.gc(rest), [1 | bytes], length + 1)
+      [] ->
+        reverse_characters_to_binary(acc)
+
+      {:error, <<byte, rest::bits>>} ->
+        reverse_characters_to_binary(acc) <>
+          <<byte>> <> slice_every(drop(rest, to_drop), count - to_drop, to_drop, [])
+    end
+  end
+
+  defp slice_every(_string, _count, _to_drop, acc) do
+    reverse_characters_to_binary(acc)
+  end
+
+  defp drop(string, 1), do: string
+
+  defp drop(string, count) do
+    case :unicode_util.gc(string) do
+      [_ | rest] -> drop(rest, count - 1)
+      [] -> ""
+      {:error, <<_, rest::bits>>} -> drop(rest, count - 1)
+    end
+  end
+
+  defp acc_bytes(string, bytes, length) do
+    case :unicode_util.gc(string) do
+      [gc | rest] -> acc_bytes(rest, [grapheme_byte_size(gc) | bytes], length + 1)
+      [] -> {bytes, length}
+      {:error, <<_, rest::bits>>} -> acc_bytes(rest, [1 | bytes], length + 1)
+    end
+  end
 
   defp add_if_negative(value, to_add) when value < 0, do: value + to_add
   defp add_if_negative(value, _to_add), do: value
@@ -2225,12 +2326,6 @@ defmodule String do
       iex> String.starts_with?("elixir", ["erlang", "ruby"])
       false
 
-  A compiled pattern can also be given:
-
-      iex> pattern = :binary.compile_pattern(["erlang", "elixir"])
-      iex> String.starts_with?("elixir", pattern)
-      true
-
   An empty string will always match:
 
       iex> String.starts_with?("elixir", "")
@@ -2238,8 +2333,16 @@ defmodule String do
       iex> String.starts_with?("elixir", ["", "other"])
       true
 
+  An empty list will never match:
+
+      iex> String.starts_with?("elixir", [])
+      false
+
+      iex> String.starts_with?("", [])
+      false
+
   """
-  @spec starts_with?(t, pattern) :: boolean
+  @spec starts_with?(t, t | [t]) :: boolean
   def starts_with?(string, prefix) when is_binary(string) and is_binary(prefix) do
     starts_with_string?(string, byte_size(string), prefix)
   end
@@ -2250,6 +2353,7 @@ defmodule String do
   end
 
   def starts_with?(string, prefix) when is_binary(string) do
+    IO.warn("compiled patterns are deprecated in starts_with?")
     Kernel.match?({0, _}, :binary.match(string, prefix))
   end
 
@@ -2318,7 +2422,7 @@ defmodule String do
       iex> String.match?("bar", ~r/foo/)
       false
 
-  Elixir also provides `Kernel.=~/2` and `Regex.match?/2` as
+  Elixir also provides text-based match operator `=~/2` and function `Regex.match?/2` as
   alternatives to test strings against regular expressions.
   """
   @spec match?(t, Regex.t()) :: boolean
@@ -2327,10 +2431,16 @@ defmodule String do
   end
 
   @doc """
-  Checks if `string` contains any of the given `contents`.
+  Searches if `string` contains any of the given `contents`.
 
   `contents` can be either a string, a list of strings,
-  or a compiled pattern.
+  or a compiled pattern. If `contents` is a list, this
+  function will search if any of the strings in `contents`
+  are part of `string`.
+
+  > Note: if you want to check if `string` is listed in `contents`,
+  > where `contents` is a list, use `Enum.member?(contents, string)`
+  > instead.
 
   ## Examples
 
@@ -2354,6 +2464,14 @@ defmodule String do
       iex> String.contains?("elixir of life", ["", "other"])
       true
 
+  An empty list will never match:
+
+      iex> String.contains?("elixir of life", [])
+      false
+
+      iex> String.contains?("", [])
+      false
+
   Be aware that this function can match within or across grapheme boundaries.
   For example, take the grapheme "é" which is made of the characters
   "e" and the acute accent. The following returns `true`:
@@ -2368,19 +2486,29 @@ defmodule String do
       false
 
   """
-  @spec contains?(t, pattern) :: boolean
-  def contains?(string, []) when is_binary(string) do
-    false
-  end
-
+  @spec contains?(t, [t] | pattern) :: boolean
   def contains?(string, contents) when is_binary(string) and is_list(contents) do
-    "" in contents or :binary.match(string, contents) != :nomatch
+    list_contains?(string, byte_size(string), contents, [])
   end
 
   def contains?(string, contents) when is_binary(string) do
     "" == contents or :binary.match(string, contents) != :nomatch
   end
 
+  defp list_contains?(string, size, [head | tail], acc) do
+    case byte_size(head) do
+      0 -> true
+      head_size when head_size > size -> list_contains?(string, size, tail, acc)
+      _ -> list_contains?(string, size, tail, [head | acc])
+    end
+  end
+
+  defp list_contains?(_string, _size, [], []),
+    do: false
+
+  defp list_contains?(string, _size, [], contents),
+    do: :binary.match(string, contents) != :nomatch
+
   @doc """
   Converts a string into a charlist.
 
@@ -2441,9 +2569,19 @@ defmodule String do
   Converts a string to an existing atom.
 
   The maximum atom size is of 255 Unicode code points.
+  Raises an `ArgumentError` if the atom does not exist.
 
   Inlined by the compiler.
 
+  > #### Atoms and modules {: .info}
+  >
+  > Since Elixir is a compiled language, the atoms defined in a module
+  > will only exist after said module is loaded, which typically happens
+  > whenever a function in the module is executed. Therefore, it is
+  > generally recommended to call `String.to_existing_atom/1` only to
+  > convert atoms defined within the module making the function call
+  > to `to_existing_atom/1`.
+
   ## Examples
 
       iex> _ = :my_atom
@@ -2723,12 +2861,16 @@ defmodule String do
             graphemes_and_length: 1,
             reverse_characters_to_binary: 1}
 
-  defp byte_size_remaining_at(binary, 0) do
-    byte_size(binary)
+  defp byte_size_unicode(binary) when is_binary(binary), do: byte_size(binary)
+  defp byte_size_unicode([head]), do: byte_size_unicode(head)
+  defp byte_size_unicode([head | tail]), do: byte_size_unicode(head) + byte_size_unicode(tail)
+
+  defp byte_size_remaining_at(unicode, 0) do
+    byte_size_unicode(unicode)
   end
 
-  defp byte_size_remaining_at(binary, n) do
-    case :unicode_util.gc(binary) do
+  defp byte_size_remaining_at(unicode, n) do
+    case :unicode_util.gc(unicode) do
       [_] -> 0
       [_ | rest] -> byte_size_remaining_at(rest, n - 1)
       [] -> 0
@@ -2736,7 +2878,7 @@ defmodule String do
     end
   end
 
-  defp codepoint_byte_size(cp) when cp <= 0x00FF, do: 1
+  defp codepoint_byte_size(cp) when cp <= 0x007F, do: 1
   defp codepoint_byte_size(cp) when cp <= 0x07FF, do: 2
   defp codepoint_byte_size(cp) when cp <= 0xFFFF, do: 3
   defp codepoint_byte_size(_), do: 4

lib/elixir/lib/string_io.ex

@@ -13,7 +13,10 @@ defmodule StringIO do
 
   """
 
-  use GenServer
+  # We're implementing the GenServer behaviour instead of using the
+  # `use GenServer` macro, because we don't want the `child_spec/1`
+  # function as it doesn't make sense to be started under a supervisor.
+  @behaviour GenServer
 
   @doc ~S"""
   Creates an IO device.
@@ -287,7 +290,7 @@ defmodule StringIO do
         {:ok, %{state | output: state.output <> string}}
 
       {_, _, _} ->
-        {{:error, req}, state}
+        {{:error, {:no_translation, encoding, state.encoding}}, state}
     end
   rescue
     ArgumentError -> {{:error, req}, state}
@@ -407,7 +410,6 @@ defmodule StringIO do
     end
   end
 
-  defp binary_to_list(data, _) when is_list(data), do: data
   defp binary_to_list(data, :unicode) when is_binary(data), do: String.to_charlist(data)
   defp binary_to_list(data, :latin1) when is_binary(data), do: :erlang.binary_to_list(data)
 
@@ -415,7 +417,7 @@ defmodule StringIO do
   defp list_to_binary(data, :unicode) when is_list(data), do: List.to_string(data)
   defp list_to_binary(data, :latin1) when is_list(data), do: :erlang.list_to_binary(data)
 
-  # From https://erlang.org/doc/apps/stdlib/io_protocol.html: result can be any
+  # From https://www.erlang.org/doc/apps/stdlib/io_protocol.html: result can be any
   # Erlang term, but if it is a list(), the I/O server can convert it to a binary().
   defp get_until_result(data, encoding) when is_list(data), do: list_to_binary(data, encoding)
   defp get_until_result(data, _), do: data

lib/elixir/lib/supervisor.ex

@@ -7,7 +7,7 @@ defmodule Supervisor do
   process structure called a *supervision tree*. Supervision trees provide
   fault-tolerance and encapsulate how our applications start and shutdown.
 
-  A supervisor may be started directly with a list of children via
+  A supervisor may be started directly with a list of child specifications via
   `start_link/2` or you may define a module-based supervisor that implements
   the required callbacks. The sections below use `start_link/2` to start
   supervisors in most examples, but it also includes a specific section
@@ -16,48 +16,55 @@ defmodule Supervisor do
   ## Examples
 
   In order to start a supervisor, we need to first define a child process
-  that will be supervised. As an example, we will define a GenServer that
-  represents a stack:
+  that will be supervised. As an example, we will define a `GenServer`,
+  a generic server, that keeps a counter. Other processes can then send
+  messages to this process to read the counter and bump its value.
 
-      defmodule Stack do
+  > Note: in practice you would not define a counter as a GenServer. Instead,
+  > if you need a counter, you would pass it around as inputs and outputs to
+  > the functions that need it. The reason we picked a counter in this example
+  > is due to its simplicity, as it allows us to focus on how supervisors work.
+
+      defmodule Counter do
         use GenServer
 
-        def start_link(state) do
-          GenServer.start_link(__MODULE__, state, name: __MODULE__)
+        def start_link(arg) when is_integer(arg) do
+          GenServer.start_link(__MODULE__, arg, name: __MODULE__)
         end
 
         ## Callbacks
 
         @impl true
-        def init(stack) do
-          {:ok, stack}
+        def init(counter) do
+          {:ok, counter}
         end
 
         @impl true
-        def handle_call(:pop, _from, [head | tail]) do
-          {:reply, head, tail}
+        def handle_call(:get, _from, counter) do
+          {:reply, counter, counter}
         end
 
-        @impl true
-        def handle_cast({:push, head}, tail) do
-          {:noreply, [head | tail]}
+        def handle_call({:bump, value}, _from, counter) do
+          {:reply, counter, counter + value}
         end
       end
 
-  The stack is a small wrapper around lists. It allows us to put
-  an element on the top of the stack, by prepending to the list,
-  and to get the top of the stack by pattern matching.
+  The `Counter` receives an argument on `start_link`. This argument
+  is passed to the `init/1` callback which becomes the initial value
+  of the counter. Our counter handles two operations (known as calls):
+  `:get`, to get the current counter value, and `:bump`, that bumps
+  the counter by the given `value` and returns the old counter.
 
   We can now start a supervisor that will start and supervise our
-  stack process. The first step is to define a list of **child
+  counter process. The first step is to define a list of **child
   specifications** that control how each child behaves. Each child
   specification is a map, as shown below:
 
       children = [
-        # The Stack is a child started via Stack.start_link([:hello])
+        # The Counter is a child started via Counter.start_link(0)
         %{
-          id: Stack,
-          start: {Stack, :start_link, [[:hello]]}
+          id: Counter,
+          start: {Counter, :start_link, [0]}
         }
       ]
 
@@ -69,30 +76,30 @@ defmodule Supervisor do
       #=> %{active: 1, specs: 1, supervisors: 0, workers: 1}
 
   Note that when starting the GenServer, we are registering it
-  with name `Stack`, which allows us to call it directly and get
-  what is on the stack:
+  with name `Counter` via the `name: __MODULE__` option. This allows
+  us to call it directly and get its value:
 
-      GenServer.call(Stack, :pop)
-      #=> :hello
+      GenServer.call(Counter, :get)
+      #=> 0
 
-      GenServer.cast(Stack, {:push, :world})
-      #=> :ok
+      GenServer.cast(Counter, {:bump, 3})
+      #=> 0
 
-      GenServer.call(Stack, :pop)
-      #=> :world
+      GenServer.call(Counter, :get)
+      #=> 3
 
-  However, there is a bug in our stack server. If we call `:pop` and
-  the stack is empty, it is going to crash because no clause matches:
+  However, there is a bug in our counter server. If we call `:bump` with
+  a non-numeric value, it is going to crash:
 
-      GenServer.call(Stack, :pop)
-      ** (exit) exited in: GenServer.call(Stack, :pop, 5000)
+      GenServer.call(Counter, {:bump, "oops"})
+      ** (exit) exited in: GenServer.call(Counter, {:bump, "oops"}, 5000)
 
   Luckily, since the server is being supervised by a supervisor, the
-  supervisor will automatically start a new one, with the initial stack
-  of `[:hello]`:
+  supervisor will automatically start a new one, reset back to its initial
+  value of `0`:
 
-      GenServer.call(Stack, :pop)
-      #=> :hello
+      GenServer.call(Counter, :get)
+      #=> 0
 
   Supervisors support different strategies; in the example above, we
   have chosen `:one_for_one`. Furthermore, each supervisor can have many
@@ -111,10 +118,11 @@ defmodule Supervisor do
   The child specification is a map containing up to 6 elements. The first two keys
   in the following list are required, and the remaining ones are optional:
 
-    * `:id` - any term used to identify the child specification
-      internally by the supervisor; defaults to the given module.
-      In the case of conflicting `:id` values, the supervisor will refuse
-      to initialize and require explicit IDs. This key is required.
+    * `:id` - any term used to identify the child specification internally by
+      the supervisor; defaults to the given module. This key is required.
+      For supervisors, in the case of conflicting `:id` values, the supervisor
+      will refuse to initialize and require explicit IDs. This is not the case
+      for [dynamic supervisors](`DynamicSupervisor`) though.
 
     * `:start` - a tuple with the module-function-args to be invoked
       to start the child process. This key is required.
@@ -131,8 +139,11 @@ defmodule Supervisor do
     * `:type` - specifies that the child process is a `:worker` or a
       `:supervisor`. This key is optional and defaults to `:worker`.
 
-  There is a sixth key, `:modules`, which is optional and is rarely changed.
-  It is set automatically based on the `:start` value.
+    * `:modules` - a list of modules used by hot code upgrade mechanisms
+      to determine which processes are using certain modules. It is typically
+      set to the callback module of behaviours like `GenServer`, `Supervisor`,
+      and such. It is set automatically based on the `:start` value and it is rarely
+      changed in practice.
 
   Let's understand what the `:shutdown` and `:restart` options control.
 
@@ -183,154 +194,100 @@ defmodule Supervisor do
   For a more complete understanding of the exit reasons and their
   impact, see the "Exit reasons and restarts" section.
 
-  ## child_spec/1
+  ## `child_spec/1` function
 
-  When starting a supervisor, we pass a list of child specifications. Those
+  When starting a supervisor, we may pass a list of child specifications. Those
   specifications are maps that tell how the supervisor should start, stop and
   restart each of its children:
 
       %{
-        id: Stack,
-        start: {Stack, :start_link, [[:hello]]}
+        id: Counter,
+        start: {Counter, :start_link, [0]}
       }
 
-  The map above defines a child with `:id` of `Stack` that is started
-  by calling `Stack.start_link([:hello])`.
+  The map above defines a child with `:id` of `Counter` that is started
+  by calling `Counter.start_link(0)`.
 
-  However, specifying the child specification for each child as a map can be
-  quite error prone, as we may change the Stack implementation and forget to
-  update its specification. That's why Elixir allows you to pass a tuple with
+  However, defining the child specification for each child as a map can be
+  quite error prone, as we may change the `Counter` implementation and forget
+  to update its specification. That's why Elixir allows you to pass a tuple with
   the module name and the `start_link` argument instead of the specification:
 
       children = [
-        {Stack, [:hello]}
+        {Counter, 0}
       ]
 
-  The supervisor will then invoke `Stack.child_spec([:hello])` to retrieve a
-  child specification. Now the `Stack` module is responsible for building its
-  own specification, for example, we could write:
+  The supervisor will then invoke `Counter.child_spec(0)` to retrieve a child
+  specification. Now the `Counter` module is responsible for building its own
+  specification, for example, we could write:
 
       def child_spec(arg) do
         %{
-          id: Stack,
-          start: {Stack, :start_link, [arg]}
+          id: Counter,
+          start: {Counter, :start_link, [arg]}
         }
       end
 
-  Luckily for us, `use GenServer` already defines a `Stack.child_spec/1`
-  exactly like above. If you need to customize the `GenServer`, you can
-  pass the options directly to `use GenServer`:
+  Luckily for us, `use GenServer` already defines a `Counter.child_spec/1`
+  exactly like above, so you don't need to write the definition above yourself.
+  If you want to customize the automatically generated `child_spec/1` function,
+  you can pass the options directly to `use GenServer`:
 
       use GenServer, restart: :transient
 
-  Finally, note it is also possible to simply pass the `Stack` module as
+  Finally, note it is also possible to simply pass the `Counter` module as
   a child:
 
       children = [
-        Stack
+        Counter
       ]
 
-  When only the module name is given, it is equivalent to `{Stack, []}`.
-  By replacing the map specification by `{Stack, [:hello]}` or `Stack`, we keep
-  the child specification encapsulated in the `Stack` module, using the default
-  implementation defined by `use GenServer`. We can now share our `Stack` worker
-  with other developers and they can add it directly to their supervision tree
-  without worrying about the low-level details of the worker.
+  When only the module name is given, it is equivalent to `{Counter, []}`,
+  which in our case would be invalid, which is why we always pass the initial
+  counter explicitly.
 
-  Overall, the child specification can be one of the following:
+  By replacing the child specification with `{Counter, 0}`, we keep it
+  encapsulated in the `Counter` module. We could now share our
+  `Counter` implementation with other developers and they can add it directly
+  to their supervision tree without worrying about the low-level details of
+  the counter.
+
+  Overall, a child specification can be one of the following:
 
     * a map representing the child specification itself - as outlined in the
       "Child specification" section
-    * a tuple with a module as first element and the start argument as second -
-      such as `{Stack, [:hello]}`. In this case, `Stack.child_spec([:hello])`
-      is called to retrieve the child specification
-    * a module - such as `Stack`. In this case, `Stack.child_spec([])`
-      is called to retrieve the child specification
 
-  If you need to convert a tuple or a module child specification to a map or
-  modify a child specification, you can use the `Supervisor.child_spec/2` function.
-  For example, to run the stack with a different `:id` and a `:shutdown` value of
+    * a tuple with a module as first element and the start argument as second -
+      such as `{Counter, 0}`. In this case, `Counter.child_spec(0)` is called
+      to retrieve the child specification
+
+    * a module - such as `Counter`. In this case, `Counter.child_spec([])`
+      would be called, which is invalid for the counter, but it is useful in
+      many other cases, especially when you want to pass a list of options
+      to the child process
+
+  If you need to convert a `{module, arg}` tuple or a module child specification to a
+  [child specification](`t:child_spec/0`) or modify a child specification itself,
+  you can use the `Supervisor.child_spec/2` function.
+  For example, to run the counter with a different `:id` and a `:shutdown` value of
   10 seconds (10_000 milliseconds):
 
       children = [
-        Supervisor.child_spec({Stack, [:hello]}, id: MyStack, shutdown: 10_000)
+        Supervisor.child_spec({Counter, 0}, id: MyCounter, shutdown: 10_000)
       ]
 
-  ## Module-based supervisors
-
-  In the example above, a supervisor was started by passing the supervision
-  structure to `start_link/2`. However, supervisors can also be created by
-  explicitly defining a supervision module:
-
-      defmodule MyApp.Supervisor do
-        # Automatically defines child_spec/1
-        use Supervisor
-
-        def start_link(init_arg) do
-          Supervisor.start_link(__MODULE__, init_arg, name: __MODULE__)
-        end
-
-        @impl true
-        def init(_init_arg) do
-          children = [
-            {Stack, [:hello]}
-          ]
-
-          Supervisor.init(children, strategy: :one_for_one)
-        end
-      end
-
-  The difference between the two approaches is that a module-based
-  supervisor gives you more direct control over how the supervisor
-  is initialized. Instead of calling `Supervisor.start_link/2` with
-  a list of children that are automatically initialized, we manually
-  initialize the children by calling `Supervisor.init/2` inside its
-  `c:init/1` callback.
-
-  `use Supervisor` also defines a `child_spec/1` function which allows
-  us to run `MyApp.Supervisor` as a child of another supervisor or
-  at the top of your supervision tree as:
-
-      children = [
-        MyApp.Supervisor
-      ]
-
-      Supervisor.start_link(children, strategy: :one_for_one)
-
-  A general guideline is to use the supervisor without a callback
-  module only at the top of your supervision tree, generally in the
-  `c:Application.start/2` callback. We recommend using module-based
-  supervisors for any other supervisor in your application, so they
-  can run as a child of another supervisor in the tree. The `child_spec/1`
-  generated automatically by `Supervisor` can be customized with the
-  following options:
-
-    * `:id` - the child specification identifier, defaults to the current module
-    * `:restart` - when the supervisor should be restarted, defaults to `:permanent`
-
-  The `@doc` annotation immediately preceding `use Supervisor` will be
-  attached to the generated `child_spec/1` function.
-
-  ## `start_link/2`, `init/2`, and strategies
+  ## Supervisor strategies and options
 
   So far we have started the supervisor passing a single child as a tuple
   as well as a strategy called `:one_for_one`:
 
       children = [
-        {Stack, [:hello]}
+        {Counter, 0}
       ]
 
       Supervisor.start_link(children, strategy: :one_for_one)
 
-  or from inside the `c:init/1` callback:
-
-      children = [
-        {Stack, [:hello]}
-      ]
-
-      Supervisor.init(children, strategy: :one_for_one)
-
-  The first argument given to `start_link/2` and `init/2` is a list of child
+  The first argument given to `start_link/2` is a list of child
   specifications as defined in the "child_spec/1" section above.
 
   The second argument is a keyword list of options:
@@ -368,13 +325,69 @@ defmodule Supervisor do
   In the above, process termination refers to unsuccessful termination, which
   is determined by the `:restart` option.
 
-  To dynamically supervise children, see `DynamicSupervisor`.
+  To efficiently supervise children started dynamically, see `DynamicSupervisor`.
 
   ### Name registration
 
   A supervisor is bound to the same name registration rules as a `GenServer`.
   Read more about these rules in the documentation for `GenServer`.
 
+  ## Module-based supervisors
+
+  In the example so far, the supervisor was started by passing the supervision
+  structure to `start_link/2`. However, supervisors can also be created by
+  explicitly defining a supervision module:
+
+      defmodule MyApp.Supervisor do
+        # Automatically defines child_spec/1
+        use Supervisor
+
+        def start_link(init_arg) do
+          Supervisor.start_link(__MODULE__, init_arg, name: __MODULE__)
+        end
+
+        @impl true
+        def init(_init_arg) do
+          children = [
+            {Counter, 0}
+          ]
+
+          Supervisor.init(children, strategy: :one_for_one)
+        end
+      end
+
+  The difference between the two approaches is that a module-based
+  supervisor gives you more direct control over how the supervisor
+  is initialized. Instead of calling `Supervisor.start_link/2` with
+  a list of child specifications that are automatically initialized, we manually
+  initialize the children by calling `Supervisor.init/2` inside its
+  `c:init/1` callback. `Supervisor.init/2` accepts the same `:strategy`,
+  `:max_restarts`, and `:max_seconds` options as `start_link/2`.
+
+  `use Supervisor` also defines a `child_spec/1` function which allows
+  us to run `MyApp.Supervisor` as a child of another supervisor or
+  at the top of your supervision tree as:
+
+      children = [
+        MyApp.Supervisor
+      ]
+
+      Supervisor.start_link(children, strategy: :one_for_one)
+
+  A general guideline is to use the supervisor without a callback
+  module only at the top of your supervision tree, generally in the
+  `c:Application.start/2` callback. We recommend using module-based
+  supervisors for any other supervisor in your application, so they
+  can run as a child of another supervisor in the tree. The `child_spec/1`
+  generated automatically by `Supervisor` can be customized with the
+  following options:
+
+    * `:id` - the child specification identifier, defaults to the current module
+    * `:restart` - when the supervisor should be restarted, defaults to `:permanent`
+
+  The `@doc` annotation immediately preceding `use Supervisor` will be
+  attached to the generated `child_spec/1` function.
+
   ## Start and shutdown
 
   When the supervisor starts, it traverses all child specifications and
@@ -474,7 +487,8 @@ defmodule Supervisor do
   init callback to return the proper supervision flags.
   """
   @callback init(init_arg :: term) ::
-              {:ok, {:supervisor.sup_flags(), [:supervisor.child_spec()]}}
+              {:ok,
+               {sup_flags(), [child_spec() | (old_erlang_child_spec :: :supervisor.child_spec())]}}
               | :ignore
 
   @typedoc "Return values of `start_link` functions"
@@ -489,14 +503,27 @@ defmodule Supervisor do
           | {:ok, child, info :: term}
           | {:error, {:already_started, child} | :already_present | term}
 
+  @typedoc """
+  A child process.
+
+  It can be a PID when the child process was started, or `:undefined` when
+  the child was created by a [dynamic supervisor](`DynamicSupervisor`).
+  """
   @type child :: pid | :undefined
 
-  @typedoc "The Supervisor name"
+  @typedoc "The supervisor name"
   @type name :: atom | {:global, term} | {:via, module, term}
 
   @typedoc "Option values used by the `start*` functions"
   @type option :: {:name, name}
 
+  @typedoc "The supervisor flags returned on init"
+  @type sup_flags() :: %{
+          strategy: strategy(),
+          intensity: non_neg_integer(),
+          period: pos_integer()
+        }
+
   @typedoc "The supervisor reference"
   @type supervisor :: pid | name | {atom, node}
 
@@ -506,35 +533,62 @@ defmodule Supervisor do
           | {:max_restarts, non_neg_integer}
           | {:max_seconds, pos_integer}
 
+  @typedoc "Supported restart options"
+  @type restart :: :permanent | :transient | :temporary
+
+  # TODO: Update :shutdown to "timeout() | :brutal_kill" when we require Erlang/OTP 24.
+  #       Additionally apply https://github.com/elixir-lang/elixir/pull/11836
+  @typedoc "Supported shutdown options"
+  @type shutdown :: pos_integer() | :infinity | :brutal_kill
+
   @typedoc "Supported strategies"
   @type strategy :: :one_for_one | :one_for_all | :rest_for_one
 
+  @typedoc """
+  Supervisor type.
+
+  Whether the supervisor is a worker or a supervisor.
+  """
+  @type type :: :worker | :supervisor
+
   # Note we have inlined all types for readability
-  @typedoc "The supervisor specification"
+  @typedoc """
+  The supervisor child specification.
+
+  It defines how the supervisor should start, stop and restart each of its children.
+  """
   @type child_spec :: %{
           required(:id) => atom() | term(),
-          required(:start) => {module(), atom(), [term()]},
-          optional(:restart) => :permanent | :transient | :temporary,
-          optional(:shutdown) => timeout() | :brutal_kill,
-          optional(:type) => :worker | :supervisor,
+          required(:start) => {module(), function_name :: atom(), args :: [term()]},
+          optional(:restart) => restart(),
+          optional(:shutdown) => shutdown(),
+          optional(:type) => type(),
           optional(:modules) => [module()] | :dynamic
         }
 
   @doc """
   Starts a supervisor with the given children.
 
-  The children is a list of modules, two-element tuples with module and
-  arguments or a map with the child specification. A strategy is required
-  to be provided through the `:strategy` option. See
-  "start_link/2, init/2, and strategies" for examples and other options.
+  `children` is a list of the following forms:
+
+    * a [child specification](`t:child_spec/0`)
+
+    * a module, where `module.child_spec([])` will be invoked to retrieve
+      its child specification
+
+    * a two-element tuple in the shape of `{module, arg}`, where `module.child_spec(arg)`
+      will be invoked to retrieve its child specification
+
+  A strategy is required to be provided through the `:strategy` option. See
+  "Supervisor strategies and options" for examples and other options.
 
   The options can also be used to register a supervisor name.
   The supported values are described under the "Name registration"
   section in the `GenServer` module docs.
 
-  If the supervisor and its child processes are successfully spawned
+  If the supervisor and all child processes are successfully spawned
   (if the start function of each child process returns `{:ok, child}`,
-  `{:ok, child, info}`, or `:ignore`) this function returns
+  `{:ok, child, info}`, or `:ignore`), this function returns
   `{:ok, pid}`, where `pid` is the PID of the supervisor. If the supervisor
   is given a name and a process with the specified name already exists,
   the function returns `{:error, {:already_started, pid}}`, where `pid`
@@ -549,20 +603,26 @@ defmodule Supervisor do
   process and exits not only on crashes but also if the parent process exits
   with `:normal` reason.
   """
-  @spec start_link([:supervisor.child_spec() | {module, term} | module], [option | init_option]) ::
-          {:ok, pid} | {:error, {:already_started, pid} | {:shutdown, term} | term}
+  @spec start_link(
+          [
+            child_spec()
+            | {module, term}
+            | module
+            | (old_erlang_child_spec :: :supervisor.child_spec())
+          ],
+          [option | init_option]
+        ) :: {:ok, pid} | {:error, {:already_started, pid} | {:shutdown, term} | term}
   def start_link(children, options) when is_list(children) do
     {sup_opts, start_opts} = Keyword.split(options, [:strategy, :max_seconds, :max_restarts])
     start_link(Supervisor.Default, init(children, sup_opts), start_opts)
   end
 
   @doc """
-  Receives a list of `children` to initialize and a set of `options`.
+  Receives a list of child specifications to initialize and a set of `options`.
 
   This is typically invoked at the end of the `c:init/1` callback of
-  module-based supervisors. See the sections "Module-based supervisors"
-  and "start_link/2, init/2, and strategies" in the module
-  documentation for more information.
+  module-based supervisors. See the sections "Supervisor strategies and options" and
+  "Module-based supervisors" in the module documentation for more information.
 
   This function returns a tuple containing the supervisor
   flags and child specifications.
@@ -571,7 +631,7 @@ defmodule Supervisor do
 
       def init(_init_arg) do
         children = [
-          {Stack, [:hello]}
+          {Counter, 0}
         ]
 
         Supervisor.init(children, strategy: :one_for_one)
@@ -593,7 +653,17 @@ defmodule Supervisor do
   description of the available strategies.
   """
   @doc since: "1.5.0"
-  @spec init([:supervisor.child_spec() | {module, term} | module], [init_option]) :: {:ok, tuple}
+  @spec init(
+          [
+            child_spec()
+            | {module, term}
+            | module
+            | (old_erlang_child_spec :: :supervisor.child_spec())
+          ],
+          [init_option]
+        ) ::
+          {:ok,
+           {sup_flags(), [child_spec() | (old_erlang_child_spec :: :supervisor.child_spec())]}}
   def init(children, options) when is_list(children) and is_list(options) do
     strategy =
       case options[:strategy] do
@@ -699,10 +769,14 @@ defmodule Supervisor do
   @doc """
   Builds and overrides a child specification.
 
-  Similar to `start_link/2` and `init/2`, it expects a
-  `module`, `{module, arg}` or a map as the child specification.
-  If a module is given, the specification is retrieved by calling
-  `module.child_spec(arg)`.
+  Similar to `start_link/2` and `init/2`, it expects a module, `{module, arg}`,
+  or a [child specification](`t:child_spec/0`).
+
+  If a two-element tuple in the shape of `{module, arg}` is given,
+  the child specification is retrieved by calling `module.child_spec(arg)`.
+
+  If a module is given, the child specification is retrieved by calling
+  `module.child_spec([])`.
 
   After the child specification is retrieved, the fields on `overrides`
   are directly applied on the child spec. If `overrides` has keys that
@@ -760,8 +834,8 @@ defmodule Supervisor do
   section in the `GenServer` module docs.
   """
 
-  # It is important to keep the 2-arity spec because it is a catch
-  # all to start_link(children, options).
+  # It is important to keep the two-arity spec because it is a catch-all
+  # to start_link(children, options).
   @spec start_link(module, term) :: on_start
   @spec start_link(module, term, [option]) :: on_start
   def start_link(module, init_arg, options \\ []) when is_list(options) do
@@ -816,7 +890,13 @@ defmodule Supervisor do
   returns `{:error, error}` where `error` is a term containing information about
   the error and child specification.
   """
-  @spec start_child(supervisor, :supervisor.child_spec() | {module, term} | module) ::
+  @spec start_child(
+          supervisor,
+          child_spec()
+          | {module, term}
+          | module
+          | (old_erlang_child_spec :: :supervisor.child_spec())
+        ) ::
           on_start_child
   def start_child(supervisor, {_, _, _, _, _, _} = child_spec) do
     call(supervisor, {:start_child, child_spec})
@@ -960,7 +1040,7 @@ defmodule Supervisor do
           workers: non_neg_integer
         }
   def count_children(supervisor) do
-    call(supervisor, :count_children) |> Map.new()
+    call(supervisor, :count_children) |> :maps.from_list()
   end
 
   @doc """