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2026-06-25 21:31:19 +02:00 · 2026-06-25 21:00:54 +02:00 · 2026-06-25 20:35:34 +02:00
234 changed files with 3881 additions and 7731 deletions
@@ -1,4 +0,0 @@
-* Describe here the reasons behind the pull request.
-* Make sure you have read the CONTRIBUTING.md file.
-* Make sure any relevant documentation and tests have been added/updated.
-* Do not submit Draft pull requests unless previously asked/agreed.
@@ -42,11 +42,11 @@ jobs:
    env:
      ERLC_OPTS: "warnings_as_errors"
    steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
        with:
          persist-credentials: false

-      - uses: erlef/setup-beam@54075bcc5e249e4758d363f27d099f55d843f124 # v1.24.1
+      - uses: erlef/setup-beam@fc68ffb90438ef2936bbb3251622353b3dcb2f93 # v1.24.0
        with:
          otp-version: ${{ matrix.otp_version }}

@@ -123,11 +123,11 @@ jobs:
      - name: Configure Git
        run: git config --global core.autocrlf input

-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
        with:
          persist-credentials: false

-      - uses: erlef/setup-beam@54075bcc5e249e4758d363f27d099f55d843f124 # v1.24.1
+      - uses: erlef/setup-beam@fc68ffb90438ef2936bbb3251622353b3dcb2f93 # v1.24.0
        with:
          otp-version: ${{ matrix.otp_version }}

@@ -28,11 +28,11 @@ jobs:
            build-mode: none
    steps:
      - name: Checkout repository
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
        with:
          persist-credentials: false
      - name: Initialize CodeQL
-        uses: github/codeql-action/init@cdf488f595d80d6e07e03d4674febd5ab45fa938 # v4.37.9
+        uses: github/codeql-action/init@8aad20d150bbac5944a9f9d289da16a4b0d87c1e # v4.36.2
        with:
          languages: ${{ matrix.language }}
          build-mode: ${{ matrix.build-mode }}
@@ -48,8 +48,8 @@ jobs:
      security-events: write
    steps:
      - name: Checkout repository
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
        with:
          persist-credentials: false
      - name: Run zizmor
-        uses: zizmorcore/zizmor-action@3dc1ecc9bcb9e94e9b2c709687979e1298497054 # v0.6.2
+        uses: zizmorcore/zizmor-action@5f14fd08f7cf1cb1609c1e344975f152c7ee938d # v0.5.6
@@ -27,7 +27,7 @@ jobs:

      - name: Checkout project
        id: checkout
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
        with:
          persist-credentials: false

@@ -33,9 +33,9 @@ jobs:
      fail-fast: false

    steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
        with:
          persist-credentials: false

      - name: Run markdownlint-cli2
-        uses: DavidAnson/markdownlint-cli2-action@21c1be1b93ad9ed58fa840aacc3f279cde2a72ff # v24.2.0
+        uses: DavidAnson/markdownlint-cli2-action@ded1f9488f68a970bc66ea5619e13e9b52e601cd # v23.2.0
@@ -74,6 +74,6 @@ unless System.get_env("DRYRUN") do
    "api-username" => "Elixir"
  }

-  resp = Req.post!("https://forum.elixirforum.com/posts.json", {:json, post}, headers: headers)
+  resp = Req.post!("https://elixirforum.com/posts.json", {:json, post}, headers: headers)
  IO.puts("#{resp.status} Elixir Forum\n#{inspect(resp.body)}")
 end
@@ -89,9 +89,9 @@ runs:

    - name: Run OSS Review Toolkit
      id: ort
-      uses: oss-review-toolkit/ort-ci-github-action@086d928d24ef1653dc0777296b312fda5faaaf52 # v1.2.0
+      uses: oss-review-toolkit/ort-ci-github-action@1805edcf1f4f55f35ae6e4d2d9795ccfb29b6021 # v1.1.0
      with:
-        image: ghcr.io/oss-review-toolkit/ort:92.2.0
+        image: ghcr.io/oss-review-toolkit/ort-minimal:65.0.0
        run: >-
          labels,
          cache-dependencies,
@@ -107,6 +107,4 @@ runs:
        ort-cli-report-args: >-
          -O CycloneDX=output.file.formats=json,xml
          -O SpdxDocument=outputFileFormats=JSON,YAML
-        ort-cli-scan-args: >-
-          --scanners Provenant
        sw-version: "${{ inputs.version }}"
@@ -32,7 +32,7 @@ jobs:
      fail-fast: false

    steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
        with:
          persist-credentials: false

@@ -43,7 +43,7 @@ jobs:
            --draft \
            "$GITHUB_REF_NAME"

-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
        # zizmor: ignore[artipacked]
        if: github.ref_type == 'branch'

@@ -82,7 +82,7 @@ jobs:
            otp_version: "29.0"

    steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
        with:
          persist-credentials: false

@@ -145,7 +145,7 @@ jobs:

      - name: Log in to Azure
        if: ${{ matrix.flavor == 'windows' && vars.AZURE_TRUSTED_SIGNING_ACCOUNT_NAME }}
-        uses: azure/login@f5d393ae46f8fde4be8b75f32e3fc50e654ad0ca # v3.0.1
+        uses: azure/login@532459ea530d8321f2fb9bb10d1e0bcf23869a43 # v3.0.0
        with:
          client-id: ${{ secrets.AZURE_CLIENT_ID }}
          tenant-id: ${{ secrets.AZURE_TENANT_ID }}
@@ -205,7 +205,7 @@ jobs:

      - name: Checkout project
        id: checkout
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
        with:
          persist-credentials: false

@@ -17,11 +17,11 @@ jobs:
    name: Notify

    steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
        with:
          persist-credentials: false

-      - uses: erlef/setup-beam@54075bcc5e249e4758d363f27d099f55d843f124 # v1.24.1
+      - uses: erlef/setup-beam@fc68ffb90438ef2936bbb3251622353b3dcb2f93 # v1.24.0
        with:
          otp-version: "27.3"
          elixir-version: "1.18.3"
@@ -5,8 +5,7 @@
    "**/*.md"
  ],
  "ignores": [
-    ".git/**",
-    ".github/**"
+    ".git/**"
  ],
  "gitignore": true,
  "config": {
@@ -37,11 +37,6 @@ curations:
      comment: "Apply Trademark Policy to VERSION file"
      detected_license: "NONE"
      concluded_license: "Apache-2.0"
-    - path: ".github/pull_request_template.md"
-      reason: "NOT_DETECTED"
-      comment: "Apply default license to GitHub pull request template"
-      detected_license: "NONE"
-      concluded_license: "Apache-2.0"

    # Wrongly Identified
    - path: ".gitignore"
@@ -18,14 +18,10 @@

  * [Access] Add support for keyword lists in `Access.key/2` and `Access.key!/1`
  * [Code] Add support for the `:erlc_options` compiler option
-  * [Code.Formatter] Add a `:migrate_atom_interpolations` option
-  * [Kernel] Improve performance of type constructors and complex intersections
  * [Kernel] Warn on binary patterns with segments that are not byte-aligned
-  * [Kernel.ParallelCompiler] Add a hint when spawned processes cannot load modules defined during compilation
  * [Keyword] Optimize `Keyword.pop/3`, `Keyword.pop!/2`, and `Keyword.pop_lazy/3`
  * [List] Add `List.to_existing_atom/2` and `List.to_unsafe_atom/1`
  * [MapSet] Optimize `MapSet.symmetric_difference/2` when set sizes differ
-  * [Path] Add `Path.safe_join/2`
  * [Registry] Optimize exact key matching in lookups
  * [String] Optimize `String.bag_distance/2`
  * [String] Add `String.to_existing_atom/2` and `String.to_unsafe_atom/1`
@@ -39,58 +35,18 @@

 #### Elixir

-  * [Calendar] Fix `Calendar.strftime/3` formatting of negative years with `%y`
-  * [Calendar] Fix rounding for `:day`, `:hour`, and `:minute` units in `DateTime.diff/3`, `NaiveDateTime.diff/3`, and `Time.diff/3`
-  * [Calendar.ISO] Fix `Calendar.ISO.valid_time?/4` to reject non-integer microsecond precision
-  * [Calendar.ISO] Reject negative zero UTC offsets in basic formats
-  * [Code.Formatter] Fix rendering calls where `do` is followed by non-block keyword arguments
-  * [Code.Fragment] Fix cursor completion when operator keywords such as `in`, `when`, `and`, `or`, and `not` follow another operator
-  * [Date] Preserve the `:format` option in `Date.to_iso8601/2` with custom calendars
-  * [Date.Range] Fix slicing date ranges with stepped ranges
-  * [Duration] Reject duplicate seconds in `Duration.from_iso8601/1`
-  * [Enum] Fix `Enum.min/2,3` and `Enum.max/2,3` with custom sorters on ranges
-  * [IO.ANSI.Docs] Recognize additional punctuation delimiters when rendering Markdown
  * [Kernel] Fix expansion of rebound variables in bitstring size expressions
-  * [Kernel] Expand `defguard` macros separately in guard and body contexts, preserving `and`/`or` error semantics outside guards
-  * [Kernel] Fix inferred stacktrace types to allow arbitrary keyword metadata
-  * [Kernel] Fix inferred types for functions with non-returning clauses
-  * [Kernel] Fix map field type inference in the presence of empty map types
-  * [Kernel] Fix tuple fetch and deletion type operations across equivalent tuple types
  * [Kernel] Fix variables defined in one default argument leaking into subsequent default arguments
-  * [Kernel] Improve the error message for non-atom struct keys
-  * [Kernel] Raise when `|` is used in guards
  * [Kernel.Typespec] Preserve metadata when proxying to Elixir typespecs
-  * [Keyword] Delete duplicate keys when `Keyword.get_and_update/3` and `Keyword.get_and_update!/3` return `:pop`
-  * [Macro] Properly escape C1 control characters and Unicode noncharacters
-  * [NaiveDateTime] Fix `NaiveDateTime.diff/3` over-counting incomplete units
-  * [Range] Fix `Range.disjoint?/2` for ranges beyond floating-point precision
-  * [Range] Fix `Range.disjoint?/2` for single-element ranges with a negative step
-  * [String] Fix `String.reverse/1` grapheme ordering around invalid UTF-8 bytes
-  * [String] Return `1.0` from `String.bag_distance/2` for two empty strings
-  * [Time] Validate microseconds in `Time.from_seconds_after_midnight/3`

 #### ExUnit

-  * [ExUnit.Assertions] Fix `refute_in_delta/4` at the delta boundary and with negative deltas
-  * [ExUnit.CaptureIO] Stop `StringIO` processes when capturing a named device fails
-
-#### IEx
-
-  * [IEx.Autocomplete] Fix completion crashes on maps with non-atom keys
-  * [IEx.Evaluator] Recognize `**` and `not in` as continuation operators
-  * [IEx.Helpers] Fix `r/1` when multiple modules are defined in the same file
-  * [IEx.Helpers] Fix heap and stack memory calculations in `process_info/1`
+  * [ExUnit.CaptureLog] Fix the typespec for capture log options

 #### Mix

-  * [Mix] Prevent synchronization lock files from being overwritten with empty contents
-  * [Mix.Release] Accept chardata paths in `Mix.Release.make_boot_script/4`
  * [Mix.SCM.Git] Raise if Git refspecs start with `-`
-  * [mix deps] Recompile path and fetchable dependencies when one of the dependencies they were compiled with is removed
-  * [mix deps] Mark fetchable dependencies for compilation when their build exists but their SCM manifest is missing
  * [mix deps.compile] Preserve code paths and compiler options across OS partitions
-  * [mix format] Pass `:sigils` to plugins invoked for sigils, allowing nested sigils to be formatted
-  * [mix new] Avoid trailing whitespace in generated files

 ### 3. Hard deprecations

@@ -55,7 +55,7 @@ To recompile all (including Erlang modules):
 make compile
 ```

-After your changes are done, run `make format` to guarantee
+After your changes are done, please remember to run `make format` to guarantee
 all files are properly formatted, then run the full suite with
 `make test`.

@@ -71,39 +71,44 @@ updating an existing checkout, run `make clean compile`. You can check
 [the official build status](https://github.com/elixir-lang/elixir/actions/workflows/ci.yml).
 More tasks can be found by reading the [Makefile](Makefile).

-## Sending a pull request
+We encourage contributors to write tests that capture both existing and newly
+introduced behavior, especially for bug fixes and major changes:

-Contributions are done [via pull request](https://help.github.com/articles/using-pull-requests/)
-and must include tests and other relevant proof of work:
-
-  * **Bug Fixes:** If you are fixing a bug, include a test that *fails* before
-    your change and *passes* afterward. This makes it easier to confirm that the
-    fix addresses the underlying issue and helps prevent regressions in the future.
+  * **Bug Fixes:** If you are fixing a bug, please try to include a test that
+    *fails* before your change and *passes* afterward. This makes it easier to
+    confirm that the fix addresses the underlying issue and helps prevent
+    regressions in the future.

  * **New Features or Major Changes:** If you are adding a new feature or making
-    major changes to existing functionality, please add assocaited tests. Aim to
-    have the best code coverage possible.
+    major changes to existing functionality, please add tests that cover the
+    major parts of that functionality. Aim to have the best code coverage possible.

-  * **Performance improvements:** For performance improvements, please include the
-    benchmark script, with inputs and results, in the pull request description.
-    We recommend using [benchee](https://github.com/bencheeorg/benchee).
+With tests running and passing, you are ready to contribute to Elixir and
+[send a pull request](https://help.github.com/articles/using-pull-requests/).
+We have saved some excellent pull requests we have received in the past in
+case you are looking for some examples:

-Here are some pull requests we have received in the past you can use as reference:
+  * [Implement Enum.member? - Pull request](https://github.com/elixir-lang/elixir/pull/992)

-  * [Implement Enum.member?](https://github.com/elixir-lang/elixir/pull/992)
+  * [Add String.valid? - Pull request](https://github.com/elixir-lang/elixir/pull/1058)

-  * [Add String.valid?](https://github.com/elixir-lang/elixir/pull/1058)
-
-  * [Implement capture_io for ExUnit](https://github.com/elixir-lang/elixir/pull/1059)
+  * [Implement capture_io for ExUnit - Pull request](https://github.com/elixir-lang/elixir/pull/1059)

 ## Reviewing changes

 Once a pull request is sent, the Elixir team will review your changes.
+We outline our process below to clarify the roles of everyone involved.
+
+All pull requests must be reviewed before being merged into the repository.
 If changes are necessary, the team will leave appropriate 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.

+The Elixir team may optionally assign someone to review a pull request.
+If someone is assigned, they must explicitly approve the code before
+another team member can merge it.
+
 When the review finishes, your pull request will be squashed and merged
 into the repository. If you have carefully organized your commits and
 believe they should be merged without squashing, please mention it in
@@ -112,7 +117,7 @@ a comment.
 ## Building documentation

 Building the documentation requires that [ExDoc](https://github.com/elixir-lang/ex_doc)
-is cloned and compiled alongside Elixir.
+is installed and built alongside Elixir.

 After cloning and compiling Elixir, run:

@@ -218,11 +223,10 @@ agents in Elixir spaces:
    use coding agents to implement it, as long as it follows the AI Contributions
    guidelines below.

-  * When automating AI usage on the Elixir codebase for performance improvements,
-    security fixes, or correctness changes to the compiler or type system, pair it
-    with a separate set of agents whose job is to argue against and try to invalidate
-    any proposed change. And treat their approval as advisory: a human must still
-    validate it before opening issues or pull requests.
+  * When automating AI usage on the Elixir codebase for performance improvements
+    or security fixes, pair it with a separate set of agents whose job is to argue
+    against and try to invalidate any proposed change. And treat their approval as
+    advisory: a human must still validate it before opening issues or pull requests.

 If any code is written by AI, then you must follow the guidelines below.

@@ -7,14 +7,14 @@
 <h1>
 <picture>
  <source media="(prefers-color-scheme: dark)" srcset="https://github.com/elixir-lang/elixir-lang.github.com/raw/main/images/logo/logo-dark.png">
-  <img alt="Elixir logo" src="https://github.com/elixir-lang/elixir-lang.github.com/raw/main/public/images/logo/logo.png" width="200">
+  <img alt="Elixir logo" src="https://github.com/elixir-lang/elixir-lang.github.com/raw/main/images/logo/logo.png" width="200">
 </picture>
 </h1>

 [![CI](https://github.com/elixir-lang/elixir/actions/workflows/ci.yml/badge.svg?branch=main)](https://github.com/elixir-lang/elixir/actions/workflows/ci.yml?query=branch%3Amain)
 [![OpenSSF Best Practices](https://www.bestpractices.dev/projects/10187/badge)](https://www.bestpractices.dev/projects/10187)

-Elixir is a programming language designed for building scalable
+Elixir is a dynamic, functional language designed for building scalable
 and maintainable applications.

 For more about Elixir, installation and documentation,
@@ -293,7 +293,7 @@ defmodule EEx do
      "foo baz"

  """
-  @spec eval_string(String.t(), Code.binding(), [compile_opt]) :: term()
+  @spec eval_string(String.t(), keyword, [compile_opt]) :: term()
  def eval_string(source, bindings \\ [], options \\ [])
      when is_binary(source) and is_list(bindings) and is_list(options) do
    compiled = compile_string(source, options)
@@ -315,7 +315,7 @@ defmodule EEx do
      #=> "foo baz"

  """
-  @spec eval_file(Path.t(), Code.binding(), [compile_opt]) :: String.t()
+  @spec eval_file(Path.t(), keyword, [compile_opt]) :: String.t()
  def eval_file(filename, bindings \\ [], options \\ [])
      when is_list(bindings) and is_list(options) do
    filename = IO.chardata_to_string(filename)
@@ -344,7 +344,6 @@ defmodule EEx do

  It returns `{:ok, [token]}` where a token is one of:

-    * `{:comment, content, %{column: column, line: line}}`
    * `{:text, content, %{column: column, line: line}}`
    * `{:expr, marker, content, %{column: column, line: line}}`
    * `{:start_expr, marker, content, %{column: column, line: line}}`
@@ -209,8 +209,11 @@ defmodule EEx.Compiler do
      {[{:end, _} | _], [{:stab_op, _, _} | _]} ->
        {:middle_expr, expr, %{}}

-      {_, [{:stab_op, _, _} | rev_tokens]} ->
-        if fn_before_end?(rev_tokens) do
+      {_, [{: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, %{}}
@@ -224,11 +227,6 @@ defmodule EEx.Compiler do
    end
  end

-  defp fn_before_end?([{:fn, _} | _]), do: true
-  defp fn_before_end?([{:end, _} | _]), do: false
-  defp fn_before_end?([_ | rev_tokens]), do: fn_before_end?(rev_tokens)
-  defp fn_before_end?([]), do: false
-
  defp drop_eol([{:eol, _} | rest]), do: drop_eol(rest)
  defp drop_eol(rest), do: rest

@@ -195,7 +195,7 @@ defmodule EEx.Engine do
  def handle_expr(state, "=", ast) do
    check_state!(state)
    %{binary: binary, dynamic: dynamic, vars_count: vars_count} = state
-    var = Macro.var(String.to_unsafe_atom("arg#{vars_count}"), __MODULE__)
+    var = Macro.var(:"arg#{vars_count}", __MODULE__)

    ast =
      quote do
@@ -10,8 +10,8 @@ defmodule Access do
  keys of any type in a data structure via the `data[key]` syntax.

  `Access` supports keyword lists (`Keyword`) and maps (`Map`) out
-  of the box. Keyword lists support only atom keys, while keys for maps
-  can be of any type. Both return `nil` if the key does not exist:
+  of the box. Keywords supports only atoms keys, keys for maps can
+  be of any type. Both return `nil` if the key does not exist:

      iex> keywords = [a: 1, b: 2]
      iex> keywords[:a]
@@ -33,7 +33,7 @@ defmodule Access do
      iex> keywords[:c][:unknown]
      nil

-  This works because accessing anything on a `nil` value returns
+  This works because accessing anything on a `nil` value, returns
  `nil` itself:

      iex> nil[:a]
@@ -917,7 +917,7 @@ defmodule Access do
      iex> pop_in(list, [Access.filter(&(&1.salary >= 20)), :name])
      {["francine"], [%{name: "john", salary: 10}, %{salary: 30}]}

-  When no match is found, an empty list is returned and the update function is never called:
+  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}]
      iex> get_in(list, [Access.filter(&(&1.salary >= 50)), :name])
@@ -934,7 +934,7 @@ defmodule Access do

  """
  @doc since: "1.6.0"
-  @spec filter((term -> as_boolean(term))) :: access_fun(data :: list, current_value :: list)
+  @spec filter((term -> boolean)) :: access_fun(data :: list, current_value :: list)
  def filter(func) when is_function(func) do
    fn op, data, next -> filter(op, data, func, next) end
  end
@@ -1035,12 +1035,12 @@ defmodule Access do
  end

  defp slice(:get_and_update, data, range, next) when is_list(data) do
-    %Range{first: first, last: last, step: step} = normalize_range(range, data)
+    range = normalize_range(range, data)

-    if first > last do
+    if range.first > range.last do
      {[], data}
    else
-      get_and_update_slice(data, first, last, step, next, [], [], 0)
+      get_and_update_slice(data, range, next, [], [], 0)
    end
  end

@@ -1145,23 +1145,21 @@ defmodule Access do

  defp normalize_range(range, _list), do: range

-  defp get_and_update_slice(rest, _first, last, _step, _next, updates, gets, index)
+  defp get_and_update_slice(rest, %Range{last: last}, _next, updates, gets, index)
       when index > last do
    {:lists.reverse(gets), :lists.reverse(updates, rest)}
  end

-  defp get_and_update_slice([head | rest], first, last, step, next, updates, gets, index) do
-    if index >= first and rem(index - first, step) == 0 do
+  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, first, last, step, next, updates, [head | gets], index + 1)
+          get_and_update_slice(rest, range, next, updates, [head | gets], index + 1)

        {get, update} ->
          get_and_update_slice(
            rest,
-            first,
-            last,
-            step,
+            range,
            next,
            [update | updates],
            [get | gets],
@@ -1169,11 +1167,11 @@ defmodule Access do
          )
      end
    else
-      get_and_update_slice(rest, first, last, step, next, [head | updates], gets, index + 1)
+      get_and_update_slice(rest, range, next, [head | updates], gets, index + 1)
    end
  end

-  defp get_and_update_slice([], _first, _last, _step, _next, updates, gets, _index) do
+  defp get_and_update_slice([], _range, _next, updates, gets, _index) do
    {:lists.reverse(gets), :lists.reverse(updates)}
  end

@@ -1200,7 +1198,7 @@ defmodule Access do
      iex> pop_in(list, [Access.find(&(&1.salary <= 40))])
      {%{name: "john", salary: 10}, [%{name: "francine", salary: 30}]}

-  When no match is found, nil is returned and the update function is never called:
+  When no match is found, nil is returned and the update function is never called

      iex> list = [%{name: "john", salary: 10}, %{name: "francine", salary: 30}]
      iex> get_in(list, [Access.find(&(&1.salary >= 50)), :name])
@@ -327,7 +327,7 @@ defmodule Agent do
  passing the agent state. The result of the function invocation is
  returned from this function.

-  `timeout` is a non-negative integer which specifies how many
+  `timeout` is an integer greater than zero which specifies how many
  milliseconds are allowed before the agent executes the function and returns
  the result value, or the atom `:infinity` to wait indefinitely. If no result
  is received within the specified time, the function call fails and the caller
@@ -366,7 +366,7 @@ defmodule Agent do
  elements, the first being the value to return (that is, the "get" value)
  and the second one being the new state of the agent.

-  `timeout` is a non-negative integer which specifies how many
+  `timeout` is an integer greater than zero which specifies how many
  milliseconds are allowed before the agent executes the function and returns
  the result value, or the atom `:infinity` to wait indefinitely. If no result
  is received within the specified time, the function call fails and the caller
@@ -407,7 +407,7 @@ defmodule Agent do

  This function always returns `:ok`.

-  `timeout` is a non-negative integer which specifies how many
+  `timeout` is an integer greater than zero which specifies how many
  milliseconds are allowed before the agent executes the function and returns
  the result value, or the atom `:infinity` to wait indefinitely. If no result
  is received within the specified time, the function call fails and the caller
@@ -996,7 +996,7 @@ defmodule Application do
  end

  @doc """
-  Gets the directory for `app`.
+  Gets the directory for app.

  This information is returned based on the code path. Here is an
  example:
@@ -1077,7 +1077,7 @@ defmodule Application do
  @doc """
  Formats the error reason returned by `start/2`,
  `ensure_started/2`, `stop/1`, `load/1` and `unload/1`,
-  and returns a string.
+  returns a string.
  """
  @spec format_error(any) :: String.t()
  def format_error(reason) do
@@ -187,21 +187,21 @@ defmodule Base do

  # For base64 standard, '/' (0x2F) sits exactly one below '0' (0x30), so we
  # extend the digit range to [0x2F, 0x39], which absorbs '/' into one range
-  # check — saves one singleton term. Trick lifted from
+  # check — saves one Mycroft singleton. Trick lifted from
  # https://lemire.me/blog/2025/04/13/detect-control-characters-quotes-and-backslashes-efficiently-using-swar/
  @swar_ge_slash 0x51515151515151

-  # base64's '+', '-' and '_' border no other range, so each is checked as the
-  # degenerate range [c, c]. Mycroft zero-byte detection is one operation
-  # cheaper per singleton but not exact per lane: subtracting 0x01..01 makes a
-  # zero lane borrow from the lane above it, and a lane holding 1 turns that
-  # borrow into 0xFF, so bytes equal to `c bxor 0x01` read as matches too.
-  @swar_ge_plus 0x55555555555555
-  @swar_gt_plus 0x54545454545454
-  @swar_ge_dash 0x53535353535353
-  @swar_gt_dash 0x52525252525252
-  @swar_ge_underscore 0x21212121212121
-  @swar_gt_underscore 0x20202020202020
+  # Mycroft zero-byte detection for base64 singletons (+, -, _).
+  # Per lane: high bit set iff `bxor(w, K*ones) - 0x01..01` has its high bit
+  # set, i.e. that byte's V value was 0 → original byte was K. Simplified
+  # (no `bnot V` term) — for ASCII-gated `w`, borrow-propagation false
+  # positives only occur for adjacent bytes that happen to equal `K xor 0x01`,
+  # which is outside the base64 alphabet, so it never matters here.
+  # Pattern follows https://github.com/elixir-lang/elixir/pull/15255.
+  @swar_mask01 0x01010101010101
+  @swar_plus_x7 0x2B2B2B2B2B2B2B
+  @swar_dash_x7 0x2D2D2D2D2D2D2D
+  @swar_under_x7 0x5F5F5F5F5F5F5F

  # Per-byte validity checks (used in both the SWAR clauses for the 8th byte
  # of each stride and in the body of the sub-8-byte tail clauses).
@@ -365,8 +365,8 @@ defmodule Base do

  # base64 SWAR word validity: 3 ranges (A-Z, a-z, 0-9) OR'd with singletons.
  # For base, the digit range is extended to [0x2F, 0x39] to absorb '/' as
-  # part of one range (Lemire merge), leaving only '+' as a singleton. For url,
-  # '-' and '_' are two more singletons.
+  # part of one range (Lemire merge), leaving only '+' as a Mycroft singleton.
+  # For url, the singletons '-' and '_' are detected via two Mycroft terms.
  defp valid_word64base?(w) do
    band(w, @swar_mask80) == 0 and
      band(
@@ -378,7 +378,7 @@ defmodule Base do
            ),
            bxor(w + @swar_ge_slash, w + @swar_gt_9)
          ),
-          bxor(w + @swar_ge_plus, w + @swar_gt_plus)
+          bxor(w, @swar_plus_x7) - @swar_mask01
        ),
        @swar_mask80
      ) == @swar_mask80
@@ -396,8 +396,8 @@ defmodule Base do
            bxor(w + @swar_ge_0, w + @swar_gt_9)
          ),
          bor(
-            bxor(w + @swar_ge_dash, w + @swar_gt_dash),
-            bxor(w + @swar_ge_underscore, w + @swar_gt_underscore)
+            bxor(w, @swar_dash_x7) - @swar_mask01,
+            bxor(w, @swar_under_x7) - @swar_mask01
          )
        ),
        @swar_mask80
@@ -436,7 +436,7 @@ defmodule Base do
  end

  for {base, alphabet} <- [upper: b16_alphabet, lower: to_lower_enc.(b16_alphabet)] do
-    name = String.to_unsafe_atom("encode16#{base}")
+    name = :"encode16#{base}"
    encoded = to_encode_list.(alphabet)

    @compile {:inline, [{name, 1}]}
@@ -536,7 +536,7 @@ defmodule Base do
    * `:lower` - only allows lower case characters
    * `:mixed` - allows mixed case characters

-  An `ArgumentError` exception is raised if the string has an odd length or
+  An `ArgumentError` exception is raised if the padding is incorrect or
  a non-alphabet character is present in the string.

  ## Examples
@@ -617,10 +617,10 @@ defmodule Base do
  upper = Enum.with_index(b16_alphabet)

  for {base, alphabet} <- [upper: upper, lower: to_lower_dec.(upper), mixed: to_mixed_dec.(upper)] do
-    decode_name = String.to_unsafe_atom("decode16#{base}!")
-    validate_name = String.to_unsafe_atom("validate16#{base}?")
-    valid_char_name = String.to_unsafe_atom("valid_char16#{base}?")
-    valid_word_name = String.to_unsafe_atom("valid_word16#{base}?")
+    decode_name = :"decode16#{base}!"
+    validate_name = :"validate16#{base}?"
+    valid_char_name = :"valid_char16#{base}?"
+    valid_word_name = :"valid_word16#{base}?"

    {min, decoded} = to_decode_list.(alphabet)

@@ -735,7 +735,7 @@ defmodule Base do
  end

  for {base, alphabet} <- [base: b64_alphabet, url: b64url_alphabet] do
-    name = String.to_unsafe_atom("encode64#{base}")
+    name = :"encode64#{base}"
    encoded = to_encode_list.(alphabet)

    @compile {:inline, [{name, 1}]}
@@ -1001,12 +1001,12 @@ defmodule Base do
  end

  for {base, alphabet} <- [base: b64_alphabet, url: b64url_alphabet] do
-    decode_name = String.to_unsafe_atom("decode64#{base}!")
+    decode_name = :"decode64#{base}!"

-    validate_name = String.to_unsafe_atom("validate64#{base}?")
-    validate_main_name = String.to_unsafe_atom("validate_main64#{validate_name}?")
-    valid_char_name = String.to_unsafe_atom("valid_char64#{base}?")
-    valid_word_name = String.to_unsafe_atom("valid_word64#{base}?")
+    validate_name = :"validate64#{base}?"
+    validate_main_name = :"validate_main64#{validate_name}?"
+    valid_char_name = :"valid_char64#{base}?"
+    valid_word_name = :"valid_word64#{base}?"
    {min, decoded} = alphabet |> Enum.with_index() |> to_decode_list.()

    # SWAR fast path: 7 bytes per stride, validated via `valid_word64<base>?`
@@ -1314,7 +1314,7 @@ defmodule Base do
        hexupper: b32hex_alphabet,
        hexlower: to_lower_enc.(b32hex_alphabet)
      ] do
-    name = String.to_unsafe_atom("encode32#{base}")
+    name = :"encode32#{base}"
    encoded = to_encode_list.(alphabet)

    @compile {:inline, [{name, 1}]}
@@ -1388,7 +1388,7 @@ defmodule Base do

  The values for `:case` can be:

-    * `:upper` - only allows upper case characters (default)
+    * `:upper` - only allows  upper case characters (default)
    * `:lower` - only allows lower case characters
    * `:mixed` - allows mixed case characters

@@ -1653,16 +1653,16 @@ defmodule Base do
        hexlower: to_lower_dec.(hexupper),
        hexmixed: to_mixed_dec.(hexupper)
      ] do
-    decode_name = String.to_unsafe_atom("decode32#{base}!")
-    validate_name = String.to_unsafe_atom("validate32#{base}?")
-    validate_main_name = String.to_unsafe_atom("validate_main32#{validate_name}?")
-    valid_char_name = String.to_unsafe_atom("valid_char32#{base}?")
+    decode_name = :"decode32#{base}!"
+    validate_name = :"validate32#{base}?"
+    validate_main_name = :"validate_main32#{validate_name}?"
+    valid_char_name = :"valid_char32#{base}?"
    {min, decoded} = to_decode_list.(alphabet)

    # SWAR fast path: 7 bytes per stride, validated via `valid_word32<base>?`
    # in the body. Tail leftover (1-6 bytes after a 7-byte stride hits an
    # 8-byte-multiple `main`) recurses through the single-byte clause.
-    valid_word_name = String.to_unsafe_atom("valid_word32#{base}?")
+    valid_word_name = :"valid_word32#{base}?"

    defp unquote(validate_main_name)(<<w::56, rest::binary>>),
      do: unquote(valid_word_name)(w) and unquote(validate_main_name)(rest)
@@ -106,7 +106,6 @@ defmodule Calendar do
  @typedoc "Any map or struct that contains the time fields."
  @type time :: %{
          optional(any) => any,
-          calendar: calendar,
          hour: hour,
          minute: minute,
          second: second,
@@ -296,7 +295,7 @@ defmodule Calendar do
  @callback time_from_day_fraction(day_fraction) :: {hour, minute, second, microsecond}

  @doc """
-  Defines the rollover moment for the calendar.
+  Define the rollover moment for the calendar.

  This is the moment, in your calendar, when the current day ends
  and the next day starts.
@@ -382,13 +381,13 @@ defmodule Calendar do
  @callback iso_days_to_end_of_day(iso_days) :: iso_days

  @doc """
-  Shifts date by the given duration according to its calendar.
+  Shifts date by given duration according to its calendar.
  """
  @doc since: "1.17.0"
  @callback shift_date(year, month, day, Duration.t()) :: {year, month, day}

  @doc """
-  Shifts naive datetime by the given duration according to its calendar.
+  Shifts naive datetime by given duration according to its calendar.
  """
  @doc since: "1.17.0"
  @callback shift_naive_datetime(
@@ -403,7 +402,7 @@ defmodule Calendar do
            ) :: {year, month, day, hour, minute, second, microsecond}

  @doc """
-  Shifts time by the given duration according to its calendar.
+  Shifts time by given duration according to its calendar.
  """
  @doc since: "1.17.0"
  @callback shift_time(hour, minute, second, microsecond, Duration.t()) ::
@@ -563,11 +562,11 @@ defmodule Calendar do
  P      | "am" or "pm" (noon is "pm", midnight as "am")                           | am, pm
  q      | Quarter                                                                 | 1, 2, 3, 4
  s      | Number of seconds since the Epoch, 1970-01-01 00:00:00+0000 (UTC)       | 1565888877
-  S      | Second                                                                  | 00, 59
+  S      | Second                                                                  | 00, 59, 60
  u      | Day of the week                                                         | 1 (Monday), 7 (Sunday)
  x      | Preferred date (without time) representation                            | 2018-10-17
  X      | Preferred time (without date) representation                            | 12:34:56
-  y      | Year as 2-digits                                                        | -01, 01, 86, 18
+  y      | Year as 2-digits                                                        | 01, 01, 86, 18
  Y      | Year                                                                    | -0001, 0001, 1986
  z      | +hhmm/-hhmm time zone offset from UTC (empty string if naive)           | +0300, -0530
  Z      | Time zone abbreviation (empty string if naive)                          | CET, BRST
@@ -624,7 +623,7 @@ defmodule Calendar do
      ...>)
      "серпень"

-    Microsecond formatting:
+   Microsecond formatting:

      iex> Calendar.strftime(~U[2019-08-26 13:52:06Z], "%y-%m-%d %H:%M:%S.%f")
      "19-08-26 13:52:06.0"
@@ -712,7 +711,7 @@ defmodule Calendar do

  # Literally just %
  defp format_modifiers("%" <> rest, width, pad, datetime, format_options, acc) do
-    parse(rest, datetime, format_options, [pad_leading_ascii("%", width, pad) | acc])
+    parse(rest, datetime, format_options, [pad_leading("%", width, pad) | acc])
  end

  # Abbreviated name of day
@@ -781,7 +780,7 @@ defmodule Calendar do

  # Day of the month
  defp format_modifiers("d" <> rest, width, pad, datetime, format_options, acc) do
-    result = datetime.day |> Integer.to_string() |> pad_leading_ascii(width, pad)
+    result = datetime.day |> Integer.to_string() |> pad_leading(width, pad)
    parse(rest, datetime, format_options, [result | acc])
  end

@@ -800,35 +799,31 @@ defmodule Calendar do

  # Hour using a 24-hour clock
  defp format_modifiers("H" <> rest, width, pad, datetime, format_options, acc) do
-    result = datetime.hour |> Integer.to_string() |> pad_leading_ascii(width, pad)
+    result = datetime.hour |> Integer.to_string() |> pad_leading(width, pad)
    parse(rest, datetime, format_options, [result | acc])
  end

  # Hour using a 12-hour clock
  defp format_modifiers("I" <> rest, width, pad, datetime, format_options, acc) do
-    result =
-      (rem(datetime.hour + 23, 12) + 1) |> Integer.to_string() |> pad_leading_ascii(width, pad)
-
+    result = (rem(datetime.hour + 23, 12) + 1) |> Integer.to_string() |> pad_leading(width, pad)
    parse(rest, datetime, format_options, [result | acc])
  end

  # Day of the year
  defp format_modifiers("j" <> rest, width, pad, datetime, format_options, acc) do
-    result =
-      datetime |> Date.day_of_year() |> Integer.to_string() |> pad_leading_ascii(width, pad)
-
+    result = datetime |> Date.day_of_year() |> Integer.to_string() |> pad_leading(width, pad)
    parse(rest, datetime, format_options, [result | acc])
  end

  # Month
  defp format_modifiers("m" <> rest, width, pad, datetime, format_options, acc) do
-    result = datetime.month |> Integer.to_string() |> pad_leading_ascii(width, pad)
+    result = datetime.month |> Integer.to_string() |> pad_leading(width, pad)
    parse(rest, datetime, format_options, [result | acc])
  end

  # Minute
  defp format_modifiers("M" <> rest, width, pad, datetime, format_options, acc) do
-    result = datetime.minute |> Integer.to_string() |> pad_leading_ascii(width, pad)
+    result = datetime.minute |> Integer.to_string() |> pad_leading(width, pad)
    parse(rest, datetime, format_options, [result | acc])
  end

@@ -856,23 +851,19 @@ defmodule Calendar do

  # Quarter
  defp format_modifiers("q" <> rest, width, pad, datetime, format_options, acc) do
-    result =
-      datetime |> Date.quarter_of_year() |> Integer.to_string() |> pad_leading_ascii(width, pad)
-
+    result = datetime |> Date.quarter_of_year() |> Integer.to_string() |> pad_leading(width, pad)
    parse(rest, datetime, format_options, [result | acc])
  end

  # Second
  defp format_modifiers("S" <> rest, width, pad, datetime, format_options, acc) do
-    result = datetime.second |> Integer.to_string() |> pad_leading_ascii(width, pad)
+    result = datetime.second |> Integer.to_string() |> pad_leading(width, pad)
    parse(rest, datetime, format_options, [result | acc])
  end

  # Day of the week
  defp format_modifiers("u" <> rest, width, pad, datetime, format_options, acc) do
-    result =
-      datetime |> Date.day_of_week() |> Integer.to_string() |> pad_leading_ascii(width, pad)
-
+    result = datetime |> Date.day_of_week() |> Integer.to_string() |> pad_leading(width, pad)
    parse(rest, datetime, format_options, [result | acc])
  end

@@ -922,25 +913,20 @@ defmodule Calendar do

  # Year as 2-digits
  defp format_modifiers("y" <> rest, width, pad, datetime, format_options, acc) do
-    result =
-      if datetime.year < 0 do
-        [?- | -datetime.year |> rem(100) |> Integer.to_string() |> pad_leading_ascii(width, pad)]
-      else
-        datetime.year |> rem(100) |> Integer.to_string() |> pad_leading_ascii(width, pad)
-      end
-
+    result = datetime.year |> rem(100) |> Integer.to_string() |> pad_leading(width, pad)
    parse(rest, datetime, format_options, [result | acc])
  end

  # Year
  defp format_modifiers("Y" <> rest, width, pad, datetime, format_options, acc) do
-    result =
+    {sign, year} =
      if datetime.year < 0 do
-        [?- | -datetime.year |> Integer.to_string() |> pad_leading_ascii(width, pad)]
+        {?-, -datetime.year}
      else
-        datetime.year |> Integer.to_string() |> pad_leading_ascii(width, pad)
+        {[], datetime.year}
      end

+    result = [sign | year |> Integer.to_string() |> pad_leading(width, pad)]
    parse(rest, datetime, format_options, [result | acc])
  end

@@ -987,7 +973,7 @@ defmodule Calendar do
      Integer.to_string(div(absolute_offset, 3600) * 100 + rem(div(absolute_offset, 60), 60))

    sign = if utc_offset + std_offset >= 0, do: "+", else: "-"
-    result = "#{sign}#{pad_leading_ascii(offset_number, width, pad)}"
+    result = "#{sign}#{pad_leading(offset_number, width, pad)}"
    parse(rest, datetime, format_options, [result | acc])
  end

@@ -1006,19 +992,13 @@ defmodule Calendar do
    raise ArgumentError, "invalid strftime format: %#{next}"
  end

-  defp pad_preferred(result, width, pad) do
-    result
-    |> IO.iodata_to_binary()
-    |> pad_leading(width, pad)
+  defp pad_preferred(result, width, pad) when length(result) < width do
+    pad_preferred([pad | result], width, pad)
  end

+  defp pad_preferred(result, _width, _pad), do: result
+
  defp pad_leading(string, count, padding) do
-    to_pad = count - String.length(string)
-    if to_pad > 0, do: do_pad_leading(to_pad, padding, string), else: string
-  end
-
-  # Similar to `pad_leading/3`, but only for strings that always ASCII-only
-  defp pad_leading_ascii(string, count, padding) do
    to_pad = count - byte_size(string)
    if to_pad > 0, do: do_pad_leading(to_pad, padding, string), else: string
  end
@@ -81,7 +81,7 @@ defmodule Date do

  Ranges of dates can be increasing (`first <= last`) and are
  always inclusive. For a decreasing range, use `range/3` with
-  a step of -1 as third argument.
+  a step of -1 as first argument.

  ## Examples

@@ -160,7 +160,7 @@ defmodule Date do
      ) do
    raise ArgumentError,
          "both dates must have matching calendar and the step must be a " <>
-            "non-zero integer, got: #{inspect(first)}, #{inspect(last)}, #{inspect(step)}"
+            "non-zero integer, got: #{inspect(first)}, #{inspect(last)}, #{step}"
  end

  defp range(first, first_days, last, last_days, calendar, step) do
@@ -422,7 +422,7 @@ defmodule Date do
  def to_iso8601(%{calendar: _} = date, format) when format in [:basic, :extended] do
    date
    |> convert!(Calendar.ISO)
-    |> to_iso8601(format)
+    |> to_iso8601()
  end

  @doc """
@@ -556,18 +556,14 @@ defmodule Date do
  """
  @doc since: "1.4.0"
  @spec compare(Calendar.date(), Calendar.date()) :: :lt | :eq | :gt
-  def compare(
-        %{year: year1, month: month1, day: day1, calendar: calendar},
-        %{year: year2, month: month2, day: day2, calendar: calendar}
-      ) do
-    cond do
-      year1 > year2 -> :gt
-      year1 < year2 -> :lt
-      month1 > month2 -> :gt
-      month1 < month2 -> :lt
-      day1 > day2 -> :gt
-      day1 < day2 -> :lt
-      true -> :eq
+  def compare(%{calendar: calendar} = date1, %{calendar: calendar} = date2) do
+    %{year: year1, month: month1, day: day1} = date1
+    %{year: year2, month: month2, day: day2} = date2
+
+    case {{year1, month1, day1}, {year2, month2, day2}} do
+      {first, second} when first > second -> :gt
+      {first, second} when first < second -> :lt
+      _ -> :eq
    end
  end

@@ -1051,7 +1047,7 @@ defmodule Date do
  @doc """
  Calculates the quarter of the year of a given `date`.

-  Returns the quarter of the year as an integer. For the ISO 8601
+  Returns the day of the year as an integer. For the ISO 8601
  calendar (the default), it is an integer from 1 to 4.

  ## Examples
@@ -37,19 +37,21 @@ defmodule Date.Range do
            first_in_iso_days: first_days,
            last_in_iso_days: last_days,
            step: step
-          },
+          } = range,
          %Date{calendar: calendar} = date
        ) do
      {days, _} = Date.to_iso_days(date)

-      in_range? =
-        if step > 0 do
-          first_days <= days and days <= last_days and rem(days - first_days, step) == 0
-        else
-          last_days <= days and days <= first_days and rem(days - first_days, step) == 0
-        end
+      cond do
+        empty?(range) ->
+          {:ok, false}

-      {:ok, in_range?}
+        first_days <= last_days ->
+          {:ok, first_days <= days and days <= last_days and rem(days - first_days, step) == 0}
+
+        true ->
+          {:ok, last_days <= days and days <= first_days and rem(days - first_days, step) == 0}
+      end
    end

    def member?(%Date.Range{step: _}, _) do
@@ -86,7 +88,7 @@ defmodule Date.Range do
            step: step
          } = range
        ) do
-      {:ok, size(range), &slice(first + &1 * step, step * &3, &2, calendar)}
+      {:ok, size(range), &slice(first + &1 * step, step + &3 - 1, &2, calendar)}
    end

    # TODO: Remove me on v2.0
@@ -183,7 +185,7 @@ defmodule Date.Range do
           last_in_iso_days: last_days,
           step: step
         }),
-         do: div(last_days - first_days, step) + 1
+         do: abs(div(last_days - first_days, step)) + 1

    # TODO: Remove me on v2.0
    defp size(
@@ -193,6 +195,33 @@ defmodule Date.Range do
      step = if first_days <= last_days, do: 1, else: -1
      size(Map.put(date_range, :step, step))
    end
+
+    defp empty?(%Date.Range{
+           first_in_iso_days: first_days,
+           last_in_iso_days: last_days,
+           step: step
+         })
+         when step > 0 and first_days > last_days,
+         do: true
+
+    defp empty?(%Date.Range{
+           first_in_iso_days: first_days,
+           last_in_iso_days: last_days,
+           step: step
+         })
+         when step < 0 and first_days < last_days,
+         do: true
+
+    defp empty?(%Date.Range{step: _}), do: false
+
+    # TODO: Remove me on v2.0
+    defp empty?(
+           %{__struct__: Date.Range, first_in_iso_days: first_days, last_in_iso_days: last_days} =
+             date_range
+         ) do
+      step = if first_days <= last_days, do: 1, else: -1
+      empty?(Map.put(date_range, :step, step))
+    end
  end

  defimpl Inspect do
@@ -180,7 +180,7 @@ defmodule DateTime do
  since v1.15.0.

  The default unit if none gets passed is `:native`,
-  which results in a default resolution of microseconds.
+  which results on a default resolution of microseconds.

  ## Examples

@@ -720,9 +720,6 @@ defmodule DateTime do
  Other time zone databases can be passed as argument or set globally.
  See the "Time zone database" section in the module docs.

-  Shifting to the `"Etc/UTC"` time zone always succeeds without
-  consulting the `time_zone_database`.
-
  ## Examples

      iex> {:ok, pacific_datetime} = DateTime.shift_zone(~U[2018-07-16 10:00:00Z], "America/Los_Angeles", FakeTimeZoneDatabase)
@@ -756,28 +753,6 @@ defmodule DateTime do
    |> shift_zone_for_iso_days_utc(calendar, precision, time_zone, time_zone_database)
  end

-  defp shift_zone_for_iso_days_utc(iso_days_utc, calendar, precision, "Etc/UTC", _time_zone_db) do
-    {year, month, day, hour, minute, second, {microsecond, _}} =
-      calendar.naive_datetime_from_iso_days(iso_days_utc)
-
-    datetime = %DateTime{
-      calendar: calendar,
-      year: year,
-      month: month,
-      day: day,
-      hour: hour,
-      minute: minute,
-      second: second,
-      microsecond: {microsecond, precision},
-      std_offset: 0,
-      utc_offset: 0,
-      zone_abbr: "UTC",
-      time_zone: "Etc/UTC"
-    }
-
-    {:ok, datetime}
-  end
-
  defp shift_zone_for_iso_days_utc(iso_days_utc, calendar, precision, time_zone, time_zone_db) do
    case time_zone_db.time_zone_period_from_utc_iso_days(iso_days_utc, time_zone) do
      {:ok, %{std_offset: std_offset, utc_offset: utc_offset, zone_abbr: zone_abbr}} ->
@@ -1202,7 +1177,7 @@ defmodule DateTime do
    datetime
    |> to_iso_days()
    # Subtract total original offset in order to get UTC and add the new offset
-    |> Calendar.ISO.add_time_unit_to_iso_days(offset - total_offset, :second)
+    |> Calendar.ISO.add_day_fraction_to_iso_days(offset - total_offset, 86400)
    |> calendar.naive_datetime_from_iso_days()
  end

@@ -1321,9 +1296,9 @@ defmodule DateTime do
  end

  @doc """
-  Converts a number of Gregorian seconds to a `DateTime` struct.
+  Converts a number of gregorian seconds to a `DateTime` struct.

-  The returned `DateTime` will have `UTC` timezone, if you want another timezone, please use
+  The returned `DateTime` will have `UTC` timezone, if you want other timezone, please use
  `DateTime.shift_zone/3`.

  ## Examples
@@ -1366,7 +1341,7 @@ defmodule DateTime do
  end

  @doc """
-  Converts a `DateTime` struct to a number of Gregorian seconds and microseconds.
+  Converts a `DateTime` struct to a number of gregorian seconds and microseconds.

  ## Examples

@@ -1601,15 +1576,15 @@ defmodule DateTime do
  def diff(datetime1, datetime2, unit \\ :second)

  def diff(datetime1, datetime2, :day) do
-    diff(datetime1, datetime2, :microsecond) |> div(86_400_000_000)
+    diff(datetime1, datetime2, :second) |> div(86400)
  end

  def diff(datetime1, datetime2, :hour) do
-    diff(datetime1, datetime2, :microsecond) |> div(3_600_000_000)
+    diff(datetime1, datetime2, :second) |> div(3600)
  end

  def diff(datetime1, datetime2, :minute) do
-    diff(datetime1, datetime2, :microsecond) |> div(60_000_000)
+    diff(datetime1, datetime2, :second) |> div(60)
  end

  def diff(
@@ -1651,9 +1626,6 @@ defmodule DateTime do
  all converted to microseconds. Negative values will move backwards
  in time and the default precision is `:second`.

-  If the datetime is in the `"Etc/UTC"` time zone, this function
-  always succeeds without consulting the `time_zone_database`.
-
  This function relies on a contiguous representation of time,
  ignoring timezone changes. For example, if you add one day when there
  are summer time/daylight saving time changes, it will also change the
@@ -1772,9 +1744,6 @@ defmodule DateTime do

  Allowed units are: `:year`, `:month`, `:week`, `:day`, `:hour`, `:minute`, `:second`, `:microsecond`.

-  If the datetime is in the `"Etc/UTC"` time zone, this function
-  always succeeds without consulting the `time_zone_database`.
-
  This operation is equivalent to shifting the datetime wall clock
  (in other words, the value as someone in that timezone would see
  on their watch), then applying the time zone offset to convert it
@@ -1843,6 +1812,44 @@ defmodule DateTime do
  @spec shift(Calendar.datetime(), Duration.duration(), Calendar.time_zone_database()) :: t
  def shift(datetime, duration, time_zone_database \\ Calendar.get_time_zone_database())

+  def shift(%{calendar: calendar, time_zone: "Etc/UTC"} = datetime, duration, _time_zone_database) do
+    %{
+      year: year,
+      month: month,
+      day: day,
+      hour: hour,
+      minute: minute,
+      second: second,
+      microsecond: microsecond
+    } = datetime
+
+    {year, month, day, hour, minute, second, microsecond} =
+      calendar.shift_naive_datetime(
+        year,
+        month,
+        day,
+        hour,
+        minute,
+        second,
+        microsecond,
+        __duration__!(duration)
+      )
+
+    %DateTime{
+      year: year,
+      month: month,
+      day: day,
+      hour: hour,
+      minute: minute,
+      second: second,
+      microsecond: microsecond,
+      time_zone: "Etc/UTC",
+      zone_abbr: "UTC",
+      std_offset: 0,
+      utc_offset: 0
+    }
+  end
+
  def shift(%{calendar: calendar} = datetime, duration, time_zone_database) do
    %{
      year: year,
@@ -2053,12 +2060,11 @@ defmodule DateTime do
  end

  defp apply_tz_offset(iso_days, offset) do
-    Calendar.ISO.add_time_unit_to_iso_days(iso_days, -offset, :second)
+    Calendar.ISO.add_day_fraction_to_iso_days(iso_days, -offset, 86400)
  end

  defp from_map(%{} = datetime_map) do
    %DateTime{
-      calendar: datetime_map.calendar,
      year: datetime_map.year,
      month: datetime_map.month,
      day: datetime_map.day,
@@ -72,7 +72,7 @@ defmodule Duration do

  However, once again, it is important to remember that shifting a duration is not
  arithmetic, so you may want to use the functions in this module depending on what
-  you want to achieve. Compare the results of both examples below:
+  you to achieve. Compare the results of both examples below:

      # Adding one month after the other
      iex> date = ~D[2016-01-31]
@@ -129,16 +129,6 @@ defmodule Duration do
            second: 0,
            microsecond: {0, 0}

-  @typedoc """
-  The microsecond component of a duration.
-
-  Unlike `t:Calendar.microsecond/0`, the value may be negative, as
-  durations may represent negative amounts of time. The precision is
-  an integer from 0 to 6 holding the number of significant digits,
-  as in the calendar types.
-  """
-  @type microsecond :: {value :: integer, precision :: 0..6}
-
  @typedoc """
  The duration struct type.
  """
@@ -150,7 +140,7 @@ defmodule Duration do
          hour: integer,
          minute: integer,
          second: integer,
-          microsecond: microsecond()
+          microsecond: Calendar.microsecond()
        }

  @typedoc """
@@ -164,7 +154,7 @@ defmodule Duration do
          | {:hour, integer}
          | {:minute, integer}
          | {:second, integer}
-          | {:microsecond, microsecond()}
+          | {:microsecond, Calendar.microsecond()}

  @typedoc """
  The duration type specifies a `%Duration{}` struct or a keyword list of valid duration unit pairs.
@@ -33,9 +33,8 @@ defmodule Calendar.ISO do
  you to format datetimes however else you desire.

  Elixir does not support reduced accuracy formats (for example, a date without
-  the day component) nor decimal precisions in components other than seconds
-  (such as `10:01,5`). Fractional seconds are supported and truncated to
-  microsecond precision.
+  the day component) nor decimal precisions in the lowest component (such as
+  `10:01:25,5`).

  #### Examples

@@ -82,11 +81,6 @@ defmodule Calendar.ISO do
      iex> Calendar.ISO.parse_time("23")
      {:error, :invalid_format}

-  A decimal fraction is accepted on seconds, but not on any other component:
-
-      iex> Calendar.ISO.parse_time("10:01:25,5")
-      {:ok, {10, 1, 25, {500000, 1}}}
-
  ### Extensions

  The parser and formatter adopt one ISO 8601 extension: extended year notation.
@@ -423,13 +417,16 @@ defmodule Calendar.ISO do
  @spec parse_date(String.t(), format) ::
          {:ok, {year, month, day}}
          | {:error, atom}
-  def parse_date("-" <> string, format) when is_format(format),
+  def parse_date(string, format) when is_binary(string) and is_format(format),
+    do: parse_date_guarded(string, format)
+
+  defp parse_date_guarded("-" <> string, format),
    do: do_parse_date(string, -1, format)

-  def parse_date("+" <> string, format) when is_format(format),
+  defp parse_date_guarded("+" <> string, format),
    do: do_parse_date(string, 1, format)

-  def parse_date(string, format) when is_binary(string) and is_format(format),
+  defp parse_date_guarded(string, format),
    do: do_parse_date(string, 1, format)

  defp do_parse_date(unquote(match_basic_date), multiplier, :basic) when unquote(guard_date) do
@@ -505,13 +502,16 @@ defmodule Calendar.ISO do
  @spec parse_naive_datetime(String.t(), format) ::
          {:ok, {year, month, day, hour, minute, second, microsecond}}
          | {:error, atom}
-  def parse_naive_datetime("-" <> string, format) when is_format(format),
+  def parse_naive_datetime(string, format) when is_binary(string) and is_format(format),
+    do: parse_naive_datetime_guarded(string, format)
+
+  defp parse_naive_datetime_guarded("-" <> string, format),
    do: do_parse_naive_datetime(string, -1, format)

-  def parse_naive_datetime("+" <> string, format) when is_format(format),
+  defp parse_naive_datetime_guarded("+" <> string, format),
    do: do_parse_naive_datetime(string, 1, format)

-  def parse_naive_datetime(string, format) when is_binary(string) and is_format(format),
+  defp parse_naive_datetime_guarded(string, format),
    do: do_parse_naive_datetime(string, 1, format)

  defp do_parse_naive_datetime(
@@ -606,13 +606,16 @@ defmodule Calendar.ISO do
  @spec parse_utc_datetime(String.t(), format) ::
          {:ok, {year, month, day, hour, minute, second, microsecond}, utc_offset}
          | {:error, atom}
-  def parse_utc_datetime("-" <> string, format) when is_format(format),
+  def parse_utc_datetime(string, format) when is_binary(string) and is_format(format),
+    do: parse_utc_datetime_guarded(string, format)
+
+  defp parse_utc_datetime_guarded("-" <> string, format),
    do: do_parse_utc_datetime(string, -1, format)

-  def parse_utc_datetime("+" <> string, format) when is_format(format),
+  defp parse_utc_datetime_guarded("+" <> string, format),
    do: do_parse_utc_datetime(string, 1, format)

-  def parse_utc_datetime(string, format) when is_binary(string) and is_format(format),
+  defp parse_utc_datetime_guarded(string, format),
    do: do_parse_utc_datetime(string, 1, format)

  defp do_parse_utc_datetime(
@@ -663,7 +666,7 @@ defmodule Calendar.ISO do
          day_fraction = time_to_day_fraction(hour, minute, second, {0, 0})

          {{year, month, day}, {hour, minute, second, _}} =
-            case add_time_unit_to_iso_days({0, day_fraction}, -offset, :second) do
+            case add_day_fraction_to_iso_days({0, day_fraction}, -offset, 86_400) do
              {0, day_fraction} ->
                {{year, month, day}, time_from_day_fraction(day_fraction)}

@@ -680,73 +683,75 @@ defmodule Calendar.ISO do
  end

  @doc """
-  Parses an ISO 8601 formatted duration string to a list of `Duration` compatible unit pairs.
+  Parses an ISO 8601 formatted duration string to a list of `Duration` compabitble unit pairs.

  See `Duration.from_iso8601/1`.
  """
  @doc since: "1.17.0"
  @spec parse_duration(String.t()) :: {:ok, [Duration.unit_pair()]} | {:error, atom}
  def parse_duration("P" <> string) when byte_size(string) > 0 do
-    parse_duration_date(string, 1, [], 0)
+    parse_duration_date(string, [], year: ?Y, month: ?M, week: ?W, day: ?D)
  end

  def parse_duration("+P" <> string) when byte_size(string) > 0 do
-    parse_duration_date(string, 1, [], 0)
+    parse_duration_date(string, [], year: ?Y, month: ?M, week: ?W, day: ?D)
  end

  def parse_duration("-P" <> string) when byte_size(string) > 0 do
-    parse_duration_date(string, -1, [], 0)
+    with {:ok, fields} <- parse_duration_date(string, [], year: ?Y, month: ?M, week: ?W, day: ?D) do
+      {:ok,
+       Enum.map(fields, fn
+         {:microsecond, {value, precision}} -> {:microsecond, {-value, precision}}
+         {unit, value} -> {unit, -value}
+       end)}
+    end
  end

  def parse_duration(_) do
    {:error, :invalid_duration}
  end

-  defp parse_duration_date("", _sign, acc, _min_position), do: {:ok, acc}
+  defp parse_duration_date("", acc, _allowed), do: {:ok, acc}

-  defp parse_duration_date("T" <> string, sign, acc, _min_position)
-       when byte_size(string) > 0 do
-    parse_duration_time(string, sign, acc, 0)
+  defp parse_duration_date("T" <> string, acc, _allowed) when byte_size(string) > 0 do
+    parse_duration_time(string, acc, hour: ?H, minute: ?M, second: ?S)
  end

-  defp parse_duration_date(string, sign, acc, min_position) do
-    with {integer, <<unit, rest::binary>>} <- Integer.parse(string),
-         {key, next_min_position} <- find_date_unit(min_position, unit) do
-      parse_duration_date(rest, sign, [{key, integer * sign} | acc], next_min_position)
+  defp parse_duration_date(string, acc, allowed) do
+    with {integer, <<next, rest::binary>>} <- Integer.parse(string),
+         {key, allowed} <- find_unit(allowed, next) do
+      parse_duration_date(rest, [{key, integer} | acc], allowed)
    else
      _ -> {:error, :invalid_date_component}
    end
  end

-  defp parse_duration_time("", _sign, acc, _min_position), do: {:ok, acc}
+  defp parse_duration_time("", acc, _allowed), do: {:ok, acc}

-  defp parse_duration_time(string, sign, acc, min_position) do
+  defp parse_duration_time(string, acc, allowed) do
    case Integer.parse(string) do
      {second, <<delimiter, _::binary>> = rest} when delimiter in [?., ?,] ->
-        with {:second, _next_min_position} <- find_time_unit(min_position, ?S),
-             {{ms, precision}, "S"} <- parse_microsecond(rest) do
-          ms =
-            case string do
-              "-" <> _ ->
-                -ms
+        case parse_microsecond(rest) do
+          {{ms, precision}, "S"} ->
+            ms =
+              case string do
+                "-" <> _ ->
+                  -ms

-              _ ->
-                ms
-            end
+                _ ->
+                  ms
+              end
+
+            {:ok, [second: second, microsecond: {ms, precision}] ++ acc}

-          {:ok, [second: second * sign, microsecond: {ms * sign, precision}] ++ acc}
-        else
          _ ->
            {:error, :invalid_time_component}
        end

-      {integer, <<unit, rest::binary>>} ->
-        case find_time_unit(min_position, unit) do
-          {key, next_min_position} ->
-            parse_duration_time(rest, sign, [{key, integer * sign} | acc], next_min_position)
-
-          false ->
-            {:error, :invalid_time_component}
+      {integer, <<next, rest::binary>>} ->
+        case find_unit(allowed, next) do
+          {key, allowed} -> parse_duration_time(rest, [{key, integer} | acc], allowed)
+          false -> {:error, :invalid_time_component}
        end

      _ ->
@@ -754,17 +759,9 @@ defmodule Calendar.ISO do
    end
  end

-  # The minimum position is the earliest unit still allowed, or one past the end.
-  defp find_date_unit(min_position, ?Y) when min_position <= 0, do: {:year, 1}
-  defp find_date_unit(min_position, ?M) when min_position <= 1, do: {:month, 2}
-  defp find_date_unit(min_position, ?W) when min_position <= 2, do: {:week, 3}
-  defp find_date_unit(min_position, ?D) when min_position <= 3, do: {:day, 4}
-  defp find_date_unit(_min_position, _unit), do: false
-
-  defp find_time_unit(min_position, ?H) when min_position <= 0, do: {:hour, 1}
-  defp find_time_unit(min_position, ?M) when min_position <= 1, do: {:minute, 2}
-  defp find_time_unit(min_position, ?S) when min_position <= 2, do: {:second, 3}
-  defp find_time_unit(_min_position, _unit), do: false
+  defp find_unit([{key, unit} | rest], unit), do: {key, rest}
+  defp find_unit([_ | rest], unit), do: find_unit(rest, unit)
+  defp find_unit([], _unit), do: false

  @doc """
  Returns the `t:Calendar.iso_days/0` format of the specified date.
@@ -1137,11 +1134,6 @@ defmodule Calendar.ISO do

  It is an integer from 1 to 4.

-  In the ISO calendar, the quarter is determined solely by the month, so the `year`
-  and `day` arguments are ignored. Combination of `year`, `month`, and `day` is not
-  validated as a valid date, unlike in `day_of_year/3`. Use `valid_date?/3` when
-  full date validation is required.
-
  ## Examples

      iex> Calendar.ISO.quarter_of_year(2016, 1, 31)
@@ -1184,7 +1176,7 @@ defmodule Calendar.ISO do
  @doc since: "1.8.0"
  @spec year_of_era(year) :: {1..10_000, era}
  def year_of_era(year) when is_year_CE(year), do: {year, 1}
-  def year_of_era(year) when is_year_BCE(year), do: {1 - year, 0}
+  def year_of_era(year) when is_year_BCE(year), do: {abs(year) + 1, 0}

  @doc """
  Calendar callback to compute the year and era from the
@@ -1237,7 +1229,7 @@ defmodule Calendar.ISO do
  end

  def day_of_era(year, month, day) when is_year_BCE(year) do
-    day = @iso_epoch - date_to_iso_days(year, month, day)
+    day = abs(date_to_iso_days(year, month, day) - @iso_epoch)
    {day, 0}
  end

@@ -1464,7 +1456,7 @@ defmodule Calendar.ISO do
  @doc """
  Converts the given naive_datetime into a iodata.

-  See `naive_datetime_to_string/8` for more information.
+  See `naive_datetime_to_iodata/8` for more information.

  ## Examples

@@ -1589,7 +1581,7 @@ defmodule Calendar.ISO do
  @doc """
  Converts the given datetime into a iodata.

-  See `datetime_to_string/12` for more information.
+  See `datetime_to_iodata/12` for more information.

  ## Examples

@@ -1693,7 +1685,7 @@ defmodule Calendar.ISO do
  end

  @doc """
-  Determines if the time given is valid.
+  Determines if the date given is valid according to the proleptic Gregorian calendar.

  Leap seconds are not supported by the built-in Calendar.ISO.

@@ -1713,7 +1705,7 @@ defmodule Calendar.ISO do
          boolean
  def valid_time?(hour, minute, second, {ms_value, ms_precision} = _microsecond)
      when is_integer(hour) and is_integer(minute) and is_integer(second) and is_integer(ms_value) and
-             is_integer(ms_precision) do
+             is_integer(ms_value) do
    is_hour(hour) and is_minute(minute) and is_second(second) and
      is_microsecond(ms_value, ms_precision)
  end
@@ -1846,9 +1838,6 @@ defmodule Calendar.ISO do
    shift_options = shift_datetime_options(duration)

    Enum.reduce(shift_options, {year, month, day, hour, minute, second, microsecond}, fn
-      {:microsecond, {0, _}}, naive_datetime ->
-        naive_datetime
-
      {_, 0}, naive_datetime ->
        naive_datetime

@@ -1878,9 +1867,6 @@ defmodule Calendar.ISO do
    shift_options = shift_time_options(duration)

    Enum.reduce(shift_options, {hour, minute, second, microsecond}, fn
-      {:microsecond, {0, _}}, time ->
-        time
-
      {_, 0}, time ->
        time

@@ -1943,7 +1929,8 @@ defmodule Calendar.ISO do

  def shift_time_unit({_days, _day_fraction} = iso_days, value, unit)
      when unit in [:second, :millisecond, :microsecond, :nanosecond] or is_integer(unit) do
-    add_time_unit_to_iso_days(iso_days, value, unit)
+    ppd = System.convert_time_unit(86_400, :second, unit)
+    add_day_fraction_to_iso_days(iso_days, value, ppd)
  end

  defp shift_time_unit_values({0, _}, {_, original_precision}) do
@@ -2024,8 +2011,8 @@ defmodule Calendar.ISO do
    total = System.convert_time_unit(integer, unit, :microsecond)

    if total in @unix_range_microseconds do
-      {seconds, microseconds} = div_rem(total, @microseconds_per_second)
-      seconds = @unix_epoch + seconds
+      microseconds = Integer.mod(total, @microseconds_per_second)
+      seconds = @unix_epoch + floor_div_positive_divisor(total, @microseconds_per_second)
      precision = precision_for_unit(unit)
      {date, time} = iso_seconds_to_datetime(seconds)
      {:ok, date, time, {microseconds, precision}}
@@ -2046,27 +2033,38 @@ defmodule Calendar.ISO do
    end
  end

-  defp parse_microsecond("." <> rest), do: parse_microsecond(rest, rest, 0)
-  defp parse_microsecond("," <> rest), do: parse_microsecond(rest, rest, 0)
-  defp parse_microsecond(rest), do: {{0, 0}, rest}
+  defp parse_microsecond("." <> rest) do
+    case parse_microsecond(rest, 0, []) do
+      {[], 0, _} ->
+        :error

-  # Digits past the sixth are consumed but do not contribute to the value.
-  defp parse_microsecond(<<head, tail::binary>>, digits, 6) when head in ?0..?9,
-    do: parse_microsecond(tail, digits, 6)
+      {microsecond, precision, rest} ->
+        scale = scale_factor(precision)
+        {{:erlang.list_to_integer(microsecond) * scale, precision}, rest}
+    end
+  end

-  defp parse_microsecond(<<head, tail::binary>>, digits, precision) when head in ?0..?9,
-    do: parse_microsecond(tail, digits, precision + 1)
+  defp parse_microsecond("," <> rest) do
+    parse_microsecond("." <> rest)
+  end

-  defp parse_microsecond(_rest, _digits, 0), do: :error
+  defp parse_microsecond(rest) do
+    {{0, 0}, rest}
+  end

-  defp parse_microsecond(rest, digits, precision) do
-    scale = scale_factor(precision)
-    microsecond = :erlang.binary_to_integer(:binary.part(digits, 0, precision)) * scale
-    {{microsecond, precision}, rest}
+  defp parse_microsecond(<<head, tail::binary>>, 6, acc) when head in ?0..?9,
+    do: parse_microsecond(tail, 6, acc)
+
+  defp parse_microsecond(<<head, tail::binary>>, precision, acc) when head in ?0..?9,
+    do: parse_microsecond(tail, precision + 1, [head | acc])
+
+  defp parse_microsecond(rest, precision, acc) do
+    {:lists.reverse(acc), precision, rest}
  end

  defp parse_offset(""), do: {nil, ""}
  defp parse_offset("Z"), do: {0, ""}
+  defp parse_offset("-00:00"), do: :error

  defp parse_offset(<<?+, h1, h2, ?:, m1, m2, rest::binary>>),
    do: parse_offset(1, h1, h2, m1, m2, rest)
@@ -2089,8 +2087,7 @@ defmodule Calendar.ISO do
         true <- m1 in ?0..?5 and m2 in ?0..?9,
         hour = (h1 - ?0) * 10 + h2 - ?0,
         min = (m1 - ?0) * 10 + m2 - ?0,
-         true <- hour < 24,
-         true <- sign == 1 or hour != 0 or min != 0 do
+         true <- hour < 24 do
      {(hour * 60 + min) * 60 * sign, rest}
    else
      _ -> :error
@@ -2106,43 +2103,10 @@ defmodule Calendar.ISO do
  end

  @doc false
-  def iso_days_to_unit(iso_days, :second) do
-    floor_div_positive_divisor(iso_days_to_microseconds(iso_days), @microseconds_per_second)
-  end
-
-  def iso_days_to_unit(iso_days, :millisecond) do
-    floor_div_positive_divisor(iso_days_to_microseconds(iso_days), 1_000)
-  end
-
-  def iso_days_to_unit(iso_days, :microsecond) do
-    iso_days_to_microseconds(iso_days)
-  end
-
-  def iso_days_to_unit(iso_days, unit) do
-    System.convert_time_unit(iso_days_to_microseconds(iso_days), :microsecond, unit)
-  end
-
-  defp iso_days_to_microseconds({days, {parts, ppd}}) do
-    days * @parts_per_day + divide_by_parts_per_day(parts, ppd)
-  end
-
-  @doc false
-  def add_time_unit_to_iso_days(iso_days, add, :second) do
-    add_day_fraction_to_iso_days(iso_days, add * @microseconds_per_second, @parts_per_day)
-  end
-
-  def add_time_unit_to_iso_days(iso_days, add, :millisecond) do
-    add_day_fraction_to_iso_days(iso_days, add * 1_000, @parts_per_day)
-  end
-
-  def add_time_unit_to_iso_days(iso_days, add, :microsecond) do
-    add_day_fraction_to_iso_days(iso_days, add, @parts_per_day)
-  end
-
-  def add_time_unit_to_iso_days(iso_days, add, unit)
-      when unit == :nanosecond or is_integer(unit) do
-    ppd = System.convert_time_unit(@seconds_per_day, :second, unit)
-    add_day_fraction_to_iso_days(iso_days, add, ppd)
+  def iso_days_to_unit({days, {parts, ppd}}, unit) do
+    day_microseconds = days * @parts_per_day
+    microseconds = divide_by_parts_per_day(parts, ppd)
+    System.convert_time_unit(day_microseconds + microseconds, :microsecond, unit)
  end

  @doc false
@@ -164,7 +164,7 @@ defmodule NaiveDateTime do
  Returns the "local time" for the machine the Elixir program is running on.

  WARNING: This function can cause insidious bugs. It depends on the time zone
-  configuration at run time. This can change and be set to a time zone that has
+  configuration at run time. This can changed and be set to a time zone that has
  daylight saving jumps (spring forward or fall back).

  This function can be used to display what the time is right now for the time
@@ -541,15 +541,15 @@ defmodule NaiveDateTime do
  def diff(naive_datetime1, naive_datetime2, unit \\ :second)

  def diff(naive_datetime1, naive_datetime2, :day) do
-    diff(naive_datetime1, naive_datetime2, :microsecond) |> div(86_400_000_000)
+    diff(naive_datetime1, naive_datetime2, :second) |> div(86400)
  end

  def diff(naive_datetime1, naive_datetime2, :hour) do
-    diff(naive_datetime1, naive_datetime2, :microsecond) |> div(3_600_000_000)
+    diff(naive_datetime1, naive_datetime2, :second) |> div(3600)
  end

  def diff(naive_datetime1, naive_datetime2, :minute) do
-    diff(naive_datetime1, naive_datetime2, :microsecond) |> div(60_000_000)
+    diff(naive_datetime1, naive_datetime2, :second) |> div(60)
  end

  def diff(
@@ -570,11 +570,9 @@ defmodule NaiveDateTime do
            "unsupported time unit. Expected :day, :hour, :minute, :second, :millisecond, :microsecond, :nanosecond, or a positive integer, got #{inspect(unit)}"
    end

-    diff_microsecond =
-      (naive_datetime1 |> to_iso_days() |> Calendar.ISO.iso_days_to_unit(:microsecond)) -
-        (naive_datetime2 |> to_iso_days() |> Calendar.ISO.iso_days_to_unit(:microsecond))
-
-    System.convert_time_unit(diff_microsecond, :microsecond, unit)
+    units1 = naive_datetime1 |> to_iso_days() |> Calendar.ISO.iso_days_to_unit(unit)
+    units2 = naive_datetime2 |> to_iso_days() |> Calendar.ISO.iso_days_to_unit(unit)
+    units1 - units2
  end

  @doc """
@@ -674,7 +672,7 @@ defmodule NaiveDateTime do

  """
  @doc since: "1.6.0"
-  @spec truncate(Calendar.naive_datetime(), :microsecond | :millisecond | :second) :: t()
+  @spec truncate(t(), :microsecond | :millisecond | :second) :: t()
  def truncate(%NaiveDateTime{microsecond: microsecond} = naive_datetime, precision) do
    %{naive_datetime | microsecond: Calendar.truncate(microsecond, precision)}
  end
@@ -62,7 +62,7 @@ defmodule Time do

  You can pass a time unit to automatically truncate the resulting time.

-  The default unit if none gets passed is `:native` which results in a default resolution of microseconds.
+  The default unit if none gets passed is `:native` which results on a default resolution of microseconds.

  ## Examples

@@ -146,9 +146,8 @@ defmodule Time do
      iex> Time.new(23, 59, 59, 1_000_000)
      {:error, :invalid_time}

-  Invalid precision:
-
-      iex> Time.new(23, 59, 59, {999_999, 10})
+      # Invalid precision
+      Time.new(23, 59, 59, {999_999, 10})
      {:error, :invalid_time}

  """
@@ -467,12 +466,8 @@ defmodule Time do
          Calendar.microsecond(),
          Calendar.calendar()
        ) :: t
-  def from_seconds_after_midnight(
-        seconds,
-        {microsecond, precision} \\ {0, 0},
-        calendar \\ Calendar.ISO
-      )
-      when is_integer(seconds) and microsecond in 0..999_999 and precision in 0..6 do
+  def from_seconds_after_midnight(seconds, microsecond \\ {0, 0}, calendar \\ Calendar.ISO)
+      when is_integer(seconds) do
    seconds_in_day = Integer.mod(seconds, @seconds_per_day)

    {hour, minute, second, {_, _}} =
@@ -483,7 +478,7 @@ defmodule Time do
      hour: hour,
      minute: minute,
      second: second,
-      microsecond: {microsecond, precision}
+      microsecond: microsecond
    }
  end

@@ -501,7 +496,7 @@ defmodule Time do

  """
  @doc since: "1.11.0"
-  @spec to_seconds_after_midnight(Calendar.time()) :: {non_neg_integer(), non_neg_integer()}
+  @spec to_seconds_after_midnight(Calendar.time()) :: {integer(), non_neg_integer()}
  def to_seconds_after_midnight(%{microsecond: {microsecond, _precision}} = time) do
    iso_days = {0, to_day_fraction(time)}
    {Calendar.ISO.iso_days_to_unit(iso_days, :second), microsecond}
@@ -694,7 +689,7 @@ defmodule Time do
  @doc """
  Compares two time structs.

-  Returns `:gt` if the first time is later than the second
+  Returns `:gt` if first time is later than the second
  and `:lt` for vice versa. If the two times are equal
  `:eq` is returned.

@@ -720,32 +715,14 @@ defmodule Time do
  """
  @doc since: "1.4.0"
  @spec compare(Calendar.time(), Calendar.time()) :: :lt | :eq | :gt
-  def compare(
-        %{
-          hour: hour1,
-          minute: minute1,
-          second: second1,
-          microsecond: {microsecond1, _},
-          calendar: calendar
-        },
-        %{
-          hour: hour2,
-          minute: minute2,
-          second: second2,
-          microsecond: {microsecond2, _},
-          calendar: calendar
-        }
-      ) do
-    cond do
-      hour1 > hour2 -> :gt
-      hour1 < hour2 -> :lt
-      minute1 > minute2 -> :gt
-      minute1 < minute2 -> :lt
-      second1 > second2 -> :gt
-      second1 < second2 -> :lt
-      microsecond1 > microsecond2 -> :gt
-      microsecond1 < microsecond2 -> :lt
-      true -> :eq
+  def compare(%{calendar: calendar} = time1, %{calendar: calendar} = time2) do
+    %{hour: hour1, minute: minute1, second: second1, microsecond: {microsecond1, _}} = time1
+    %{hour: hour2, minute: minute2, second: second2, microsecond: {microsecond2, _}} = time2
+
+    case {{hour1, minute1, second1, microsecond1}, {hour2, minute2, second2, microsecond2}} do
+      {first, second} when first > second -> :gt
+      {first, second} when first < second -> :lt
+      _ -> :eq
    end
  end

@@ -924,11 +901,11 @@ defmodule Time do
  def diff(time1, time2, unit \\ :second)

  def diff(time1, time2, :hour) do
-    diff(time1, time2, :microsecond) |> div(3_600_000_000)
+    diff(time1, time2, :second) |> div(3600)
  end

  def diff(time1, time2, :minute) do
-    diff(time1, time2, :microsecond) |> div(60_000_000)
+    diff(time1, time2, :second) |> div(60)
  end

  def diff(
@@ -50,7 +50,7 @@ defmodule Code do

  You can use `ensure_loaded/1` (as well as `ensure_loaded?/1` and
  `ensure_loaded!/1`) to check if a module is loaded before using it and
-  act accordingly.
+  act.

  ## `ensure_compiled/1` and `ensure_compiled!/1`

@@ -258,7 +258,6 @@ defmodule Code do
          | {:locals_without_parens, keyword()}
          | {:force_do_end_blocks, boolean()}
          | {:migrate, boolean()}
-          | {:migrate_atom_interpolations, boolean()}
          | {:migrate_bitstring_modifiers, boolean()}
          | {:migrate_call_parens_on_pipe, boolean()}
          | {:migrate_charlists_as_sigils, boolean()}
@@ -273,7 +272,6 @@ defmodule Code do
          | {:escape, boolean()}
          | {:locals_without_parens, keyword()}
          | {:comments, [term()]}
-          | {:syntax_colors, [{Inspect.Opts.color_key(), IO.ANSI.ansidata()}]}

  @typedoc """
  Options for parsing functions that convert strings to quoted expressions.
@@ -287,7 +285,7 @@ defmodule Code do
          unescape: boolean(),
          existing_atoms_only: boolean(),
          token_metadata: boolean(),
-          literal_encoder: (term(), Macro.metadata() -> {:ok, Macro.t()} | {:error, binary()}),
+          literal_encoder: (term(), Macro.metadata() -> term()),
          static_atoms_encoder: (binary(), Macro.metadata() -> {:ok, term()} | {:error, binary()}),
          emit_warnings: boolean()
        ]
@@ -415,7 +413,7 @@ defmodule Code do
      operations.

  """
-  @spec append_path(Path.t(), cache: boolean()) :: boolean()
+  @spec append_path(Path.t(), cache: boolean()) :: true | false
  def append_path(path, opts \\ []) do
    apply(:code, :add_pathz, [to_charlist(Path.expand(path)) | cache(opts)]) == true
  end
@@ -554,7 +552,8 @@ defmodule Code do
  This is the list of directories the Erlang VM uses for finding
  module code. The list of files is managed per Erlang VM node.

-  All paths are expanded with `Path.expand/1` before being deleted.
+  The path is expanded with `Path.expand/1` before being deleted. If the
+  path does not exist, this function returns `false`.
  """
  @doc since: "1.15.0"
  @spec delete_paths([Path.t()]) :: :ok
@@ -768,12 +767,6 @@ defmodule Code do
    * `:migrate` (since v1.18.0) - when `true`, sets all other migration options
      to `true` by default. Defaults to `false`.

-    * `:migrate_atom_interpolations` (since v1.21.0) - when `true`, rewrites
-      deprecated atom interpolations to explicit calls to `String.to_unsafe_atom/1`.
-      For example, `:"foo_#{bar}"` becomes `String.to_unsafe_atom("foo_#{bar}")`.
-      Interpolated keywords like `["foo_#{bar}": 1]` are **not** migrated.
-      Defaults to the value of the `:migrate` option. This option changes the AST.
-
    * `:migrate_bitstring_modifiers` (since v1.18.0) - when `true`,
      removes unnecessary parentheses in known bitstring
      [modifiers](`<<>>/1`), for example `<<foo::binary()>>`
@@ -1298,9 +1291,9 @@ defmodule Code do
    * `:literal_encoder` (since v1.10.0) - how to encode literals in the AST.
      It must be a function that receives two arguments, the literal and its
      metadata, and it must return `{:ok, ast :: Macro.t}` or
-      `{:error, reason :: binary}`. If you return anything other than the literal
+      `{:error, reason :: binary}`. If you return anything than the literal
      itself as the `term`, then the AST is no longer valid. This option
-      may still be useful for textual analysis of the source code.
+      may still useful for textual analysis of the source code.

    * `:static_atoms_encoder` - the static atom encoder function, see
      "The `:static_atoms_encoder` function" section below. Note this
@@ -1394,15 +1387,12 @@ defmodule Code do
  while preserving information like comments and literals position.

  Returns `{:ok, quoted_form, comments}` if it succeeds,
-  `{:error, {location, error, token}}` otherwise, where `location`
-  is keyword metadata containing the line and column of the error.
+  `{:error, {line, error, token}}` otherwise.

  Comments are maps with the following fields:

    * `:line` - The line number of the source code

-    * `:column` - The column number of the source code
-
    * `:text` - The full text of the comment, including the leading `#`

    * `:previous_eol_count` - How many end of lines there are between the comment and the previous AST node or comment
@@ -1457,9 +1447,7 @@ defmodule Code do

  Returns the AST and a list of comments if it succeeds, raises an exception
  otherwise. The exception is a `TokenMissingError` in case a token is missing
-  (usually because the expression is incomplete), `MismatchedDelimiterError`
-  (in case of mismatched opening and closing delimiters) and `SyntaxError`
-  otherwise.
+  (usually because the expression is incomplete), `SyntaxError` otherwise.

  Check `string_to_quoted/2` for options information.
  """
@@ -1562,13 +1550,9 @@ defmodule Code do
      `string_to_quoted/2`, setting this option to `false` will prevent it from
      escaping the sequences twice. Defaults to `true`.

-    * `:syntax_colors` - a keyword list of colors the output is colorized.
-      See `Inspect.Opts` for more information.
-
  See `format_string!/2` for the full list of formatting options including
-  `:file`, `:line`, `:locals_without_parens`, `:force_do_end_blocks`, and all
-  migration options like `:migrate_charlists_as_sigils`. Note `:line_length`
-  does not apply here.
+  `:file`, `:line`, `:line_length`, `:locals_without_parens`, `:force_do_end_blocks`,
+  `:syntax_colors`, and all migration options like `:migrate_charlists_as_sigils`.
  """
  @doc since: "1.13.0"
  @spec quoted_to_algebra(Macro.t(), [format_opt() | quoted_to_algebra_opt()]) ::
@@ -1688,7 +1672,7 @@ defmodule Code do
  @doc """
  Stores all given compilation options.

-  Changing the compilation options affects all processes
+  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`.
@@ -1752,7 +1736,7 @@ defmodule Code do
  @doc """
  Stores a compilation option.

-  Changing the compilation options affects all processes running in a
+  Changing the compilation options affect all processes running in a
  given Erlang VM node.

  Available options are:
@@ -1768,7 +1752,7 @@ defmodule Code do
      remove the `:debug_info` while deploying, tools like `mix release`
      already do such by default.

-      Other environments, such as `mix test`, automatically disable this
+      Other environments, such as `mix test`, automatically disables this
      via the `:test_elixirc_options` project configuration, as there is
      typically no need to store debug chunks for test files.

@@ -1786,13 +1770,13 @@ defmodule Code do
    * `:ignore_module_conflict` - when `true`, does not warn when a module has
      already been defined. Defaults to `false`.

-    * `:infer_signatures` (since v1.18.0) - a list of applications whose modules
-      should be used during type inference. When `false`, it disables module-local
+    * `:infer_signatures` (since v1.18.0) - a list of applications of which modules
+      should be using during type inference. When `false`, it disables module-local
      signature inference used when type checking remote calls to the compiled
      module. Type checking will be executed regardless of the value of this option.
      Mix projects will set this option to your dependencies list in dev/prod, and
      it will disable this option during test (as there is typically no need to infer
-      signatures for test files). Outside of Mix projects, it defaults to `[:elixir]`.
+      signature for test files). Outside of Mix projects, it defaults to `[:elixir]`.

    * `:module_definition` (since v1.20.0) - stores if the module definition should
      be `:compiled` (the default) or `:interpreted`. Note this does not affect the
@@ -1815,7 +1799,7 @@ defmodule Code do

    * `:on_undefined_variable` (since v1.15.0) - either `:raise` or `:warn`.
      When `:raise` (the default), undefined variables will trigger a compilation
-      error. You may set it to `:warn` if you want undefined variables to
+      error. You may be set it to `:warn` if you want undefined variables to
      emit a warning and expand as to a local call to the zero-arity function
      of the same name (for example, `node` would be expanded as `node()`).
      This `:warn` behavior only exists for compatibility reasons when working
@@ -2150,7 +2134,7 @@ defmodule Code do
  If the module being checked is currently in a compiler deadlock,
  this function returns `{:error, :unavailable}`. Unavailable doesn't
  necessarily mean the module doesn't exist, just that it is not currently
-  available, but it may (or may not) become available in the future.
+  available, but it (or may not) become available in the future.

  Therefore, if you can only continue if the module is available, use
  `ensure_compiled!/1` instead. In particular, do not do this:
@@ -195,7 +195,6 @@ defmodule Code.Formatter do
    file = Keyword.get(opts, :file, nil)
    sigils = Keyword.get(opts, :sigils, [])
    migrate = Keyword.get(opts, :migrate, false)
-    migrate_atom_interpolations = Keyword.get(opts, :migrate_atom_interpolations, migrate)
    migrate_bitstring_modifiers = Keyword.get(opts, :migrate_bitstring_modifiers, migrate)
    migrate_call_parens_on_pipe = Keyword.get(opts, :migrate_call_parens_on_pipe, migrate)
    migrate_charlists_as_sigils = Keyword.get(opts, :migrate_charlists_as_sigils, migrate)
@@ -224,7 +223,6 @@ defmodule Code.Formatter do
      comments: comments,
      sigils: sigils,
      file: file,
-      migrate_atom_interpolations: migrate_atom_interpolations,
      migrate_bitstring_modifiers: migrate_bitstring_modifiers,
      migrate_call_parens_on_pipe: migrate_call_parens_on_pipe,
      migrate_charlists_as_sigils: migrate_charlists_as_sigils,
@@ -336,20 +334,14 @@ defmodule Code.Formatter do
  end

  defp quoted_to_algebra(
-         {{:., _, [:erlang, :binary_to_atom]}, _, [{:<<>>, _, entries} = bitstring, :utf8]} =
-           quoted,
+         {{:., _, [:erlang, :binary_to_atom]}, _, [{:<<>>, _, entries}, :utf8]} = quoted,
         context,
         state
       ) do
-    cond do
-      not interpolated?(entries) ->
-        remote_to_algebra(quoted, context, state)
-
-      state.migrate_atom_interpolations ->
-        quoted_to_algebra(quote(do: String.to_unsafe_atom(unquote(bitstring))), context, state)
-
-      true ->
-        interpolation_to_algebra(entries, @double_quote, state, ":\"", @double_quote)
+    if interpolated?(entries) do
+      interpolation_to_algebra(entries, @double_quote, state, ":\"", @double_quote)
+    else
+      remote_to_algebra(quoted, context, state)
    end
  end

@@ -1704,7 +1696,7 @@ defmodule Code.Formatter do
    iodata |> IO.iodata_to_binary() |> string() |> color_doc(:atom, inspect_opts)
  end

-  defp integer_to_algebra(text, inspect_opts) do
+  defp integer_to_algebra(text, inspect_otps) do
    case text do
      <<?0, ?x, rest::binary>> ->
        "0x" <> String.upcase(rest)
@@ -1718,15 +1710,15 @@ defmodule Code.Formatter do
      decimal ->
        insert_underscores(decimal)
    end
-    |> color_doc(:number, inspect_opts)
+    |> color_doc(:number, inspect_otps)
  end

-  defp float_to_algebra(text, inspect_opts) do
+  defp float_to_algebra(text, inspect_otps) do
    [int_part, decimal_part] = :binary.split(text, ".")
    decimal_part = String.downcase(decimal_part)

    string = insert_underscores(int_part) <> "." <> decimal_part
-    color_doc(string, :number, inspect_opts)
+    color_doc(string, :number, inspect_otps)
  end

  defp insert_underscores("-" <> digits) do
@@ -27,8 +27,7 @@ defmodule Code.Fragment do
          column: pos_integer(),
          columns: boolean(),
          token_metadata: boolean(),
-          literal_encoder: (term(), Macro.metadata() -> {:ok, Macro.t()} | {:error, binary()}),
-          preserve_sigils: boolean(),
+          literal_encoder: (term(), Macro.metadata() -> term()),
          trailing_fragment: String.t()
        ]

@@ -36,7 +35,7 @@ defmodule Code.Fragment do
  Returns the list of lines in the given string, preserving their line endings.

  Only the line endings recognized by the Elixir compiler are
-  considered, namely `\r\n` and `\n`. If you would like to retrieve
+  considered, namely `\r\n` and `\n`. If you would like the retrieve
  lines without their line endings, use `String.split(string, ["\r\n", "\n"])`.

  ## Examples
@@ -52,7 +51,6 @@ defmodule Code.Fragment do

  """
  @doc since: "1.19.0"
-  @spec lines(String.t()) :: [String.t()]
  def lines(string) do
    lines(string, <<>>)
  end
@@ -142,9 +140,6 @@ defmodule Code.Fragment do
    * `{:anonymous_call, inside_caller}` - the context is an anonymous
      call, such as `fun.(` and `@fun.(`.

-    * `{:capture_arg, charlist}` - the context is a capture argument,
-      such as `&1`
-
    * `{:module_attribute, charlist}` - the context is a module attribute,
      such as `@hello_wor`

@@ -162,8 +157,8 @@ defmodule Code.Fragment do
    * `:none` - no context possible

    * `{:sigil, charlist}` - the context is a sigil. It may be either the beginning
-      of a sigil, such as `~` or `~s`. Operators starting with `~`, such as
-      `~>` and `~>>`, are returned as :operator contexts
+      of a sigil, such as `~` or `~s`, or an operator starting with `~`, such as
+      `~>` and `~>>`

    * `{: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
@@ -662,7 +657,7 @@ defmodule Code.Fragment do
      iex> Code.Fragment.surround_context("foo", {1, 1})
      %{begin: {1, 1}, context: {:local_or_var, ~c"foo"}, end: {1, 4}}

-  ## Differences from `cursor_context/2`
+  ## Differences to `cursor_context/2`

  Because `surround_context/3` attempts to capture complex expressions,
  it has some differences to `cursor_context/2`:
@@ -676,7 +671,7 @@ defmodule Code.Fragment do
      be a local or variable

    * `@` when not followed by any identifier is returned as `{:operator, ~c"@"}`
-      (in contrast to `{:module_attribute, ~c""}` in `cursor_context/2`)
+      (in contrast to `{:module_attribute, ~c""}` in `cursor_context/2`

    * This function never returns empty sigils `{:sigil, ~c""}` or empty structs
      `{:struct, ~c""}` as context
@@ -150,20 +150,20 @@ defmodule Code.Identifier do
    <<acc::binary, char::utf8>>
  end

-  defp escape_char(char, acc) when char < 0x80 do
+  defp escape_char(char, acc) when char < 0x100 do
    <<a::4, b::4>> = <<char::8>>
    <<acc::binary, ?\\, ?x, to_hex(a), to_hex(b)>>
  end

  defp escape_char(char, acc) when char < 0x10000 do
    <<a::4, b::4, c::4, d::4>> = <<char::16>>
-    <<acc::binary, ?\\, ?u, to_hex(a), to_hex(b), to_hex(c), to_hex(d)>>
+    <<acc::binary, ?\\, ?x, ?{, to_hex(a), to_hex(b), to_hex(c), to_hex(d), ?}>>
  end

  defp escape_char(char, acc) when char < 0x1000000 do
    <<a::4, b::4, c::4, d::4, e::4, f::4>> = <<char::24>>

-    <<acc::binary, ?\\, ?u, ?{, to_hex(a), to_hex(b), to_hex(c), to_hex(d), to_hex(e), to_hex(f),
+    <<acc::binary, ?\\, ?x, ?{, to_hex(a), to_hex(b), to_hex(c), to_hex(d), to_hex(e), to_hex(f),
      ?}>>
  end

@@ -4,8 +4,6 @@
 defmodule Code.Normalizer do
  @moduledoc false

-  @do_end_keywords [:rescue, :catch, :else, :after]
-
  defguard is_literal(x)
           when is_integer(x) or
                  is_float(x) or
@@ -70,7 +68,7 @@ defmodule Code.Normalizer do

  # Bit containers
  defp do_normalize({:<<>>, _, args} = quoted, state) when is_list(args) do
-    normalize_bitstring(quoted, state, state.escape)
+    normalize_bitstring(quoted, state, false)
  end

  # Atoms with interpolations
@@ -184,8 +182,7 @@ defmodule Code.Normalizer do
        |> patch_meta_line(state.parent_meta)
        |> Keyword.put_new(:delimiter, "\"")

-      string = normalize_bitstring(string, %{state | parent_meta: meta}, false)
-      {sigil, meta, [string, modifiers]}
+      {sigil, meta, [do_normalize(string, %{state | parent_meta: meta}), modifiers]}
    else
      _ ->
        normalize_call(quoted, state)
@@ -349,20 +346,18 @@ defmodule Code.Normalizer do
        args = normalize_args(args, %{state | parent_meta: meta})
        {form, meta, args}

-      Keyword.has_key?(meta, :do) and kw_blocks?(last) ->
+      Keyword.has_key?(meta, :do) ->
        # def foo do :ok end
        # def foo, do: :ok
        normalize_kw_blocks(form, meta, args, state)

-      match?([{:do, _} | _], last) and kw_blocks?(last) ->
+      match?([{:do, _} | _], last) and Keyword.keyword?(last) ->
        # Non normalized kw blocks
        line = state.parent_meta[:line] || meta[:line]
        meta = meta ++ [do: [line: line], end: [line: line]]
        normalize_kw_blocks(form, meta, args, state)

      true ->
-        # The formatter renders do-end blocks from the meta alone
-        meta = Keyword.drop(meta, [:do, :end])
        args = normalize_args(args, %{state | parent_meta: meta})
        {last_arg, leading_args} = List.pop_at(args, -1, [])

@@ -401,22 +396,12 @@ defmodule Code.Normalizer do
  defp block_keyword?([]), do: true
  defp block_keyword?(_), do: false

-  # Anything after the do block that is not a block keyword makes it a keyword list
-  defp kw_blocks?([{:do, _} | rest] = kw) do
-    Keyword.keyword?(kw) and Enum.all?(rest, &match?({key, _} when key in @do_end_keywords, &1))
-  end
-
-  defp kw_blocks?([{{:__block__, _, [:do]}, _} | rest]) do
-    Enum.all?(rest, &match?({{:__block__, _, [key]}, _} when key in @do_end_keywords, &1))
-  end
-
-  defp kw_blocks?(_), do: false
-
  defp allow_keyword?(:when, 2), do: true
  defp allow_keyword?(:{}, _), do: false
  defp allow_keyword?(op, arity), do: not is_atom(op) or not Macro.operator?(op, arity)

  defp normalize_bitstring({:<<>>, meta, parts}, state, escape_interpolation) do
+    parts = maybe_add_trailing_newline(meta, parts, state)
    meta = patch_meta_line(meta, state.parent_meta)

    parts =
@@ -435,7 +420,6 @@ defmodule Code.Normalizer do
        end)
      end

-    parts = maybe_add_trailing_newline(meta, parts, state)
    {:<<>>, meta, parts}
  end

@@ -80,8 +80,7 @@ defmodule Code.Typespec do
  Returns all types available from the module's BEAM code.

  The result is returned as a list of tuples where the first
-  element is the type (`:typep`, `:type`, `:opaque` and, on Erlang/OTP 28+,
-  `:nominal`).
+  element is the type (`:typep`, `:type` and `:opaque`).

  The module must have a corresponding BEAM file which can be
  located by the runtime system. The types will be in the Erlang
@@ -96,10 +95,9 @@ defmodule Code.Typespec do

        types =
          for {:attribute, _, kind, {name, _, args} = type} <- abstract_code,
-              kind in [:opaque, :type, :nominal] do
+              kind in [:opaque, :type] do
            cond do
              kind == :opaque -> {:opaque, type}
-              kind == :nominal -> {:nominal, type}
              {name, length(args)} in exported_types -> {:type, type}
              true -> {:typep, type}
            end
@@ -119,7 +117,7 @@ defmodule Code.Typespec do
  element is spec name and arity and the second is the spec.

  The module must have a corresponding BEAM file which can be
-  located by the runtime system. The specs will be in the Erlang
+  located by the runtime system. The types will be in the Erlang
  Abstract Format.
  """
  @spec fetch_specs(module | binary) :: {:ok, [tuple]} | :error
@@ -137,10 +135,10 @@ defmodule Code.Typespec do
  Returns all callbacks available from the module's BEAM code.

  The result is returned as a list of tuples where the first
-  element is the callback name and arity and the second is the callback.
+  element is spec name and arity and the second is the spec.

  The module must have a corresponding BEAM file
-  which can be located by the runtime system. The callbacks will be
+  which can be located by the runtime system. The types will be
  in the Erlang Abstract Format.
  """
  @spec fetch_callbacks(module | binary) :: {:ok, [tuple]} | :error
@@ -193,8 +191,8 @@ defmodule Code.Typespec do

  ## To AST conversion

-  defp collect_vars({:ann_type, _anno, [_var, type]}) do
-    collect_vars(type)
+  defp collect_vars({:ann_type, _anno, args}) when is_list(args) do
+    []
  end

  defp collect_vars({:type, _anno, _kind, args}) when is_list(args) do
@@ -152,7 +152,6 @@ defmodule Config do

  """
  @doc since: "1.9.0"
-  @spec config(atom(), keyword()) :: keyword()
  def config(root_key, opts) when is_atom(root_key) and is_list(opts) do
    if not Keyword.keyword?(opts) do
      raise ArgumentError, "config/2 expected a keyword list, got: #{inspect(opts)}"
@@ -199,7 +198,6 @@ defmodule Config do

  """
  @doc since: "1.9.0"
-  @spec config(atom(), atom(), term()) :: keyword()
  def config(root_key, key, opts) when is_atom(root_key) and is_atom(key) do
    get_config!()
    |> __merge__([{root_key, [{key, opts}]}])
@@ -227,7 +225,6 @@ defmodule Config do

  """
  @doc since: "1.18.0"
-  @spec read_config(atom()) :: keyword() | nil
  def read_config(root_key) when is_atom(root_key) do
    get_config!()[root_key]
  end
@@ -236,7 +233,7 @@ defmodule Config do
  Returns the environment this configuration file is executed on.

  In Mix projects this function returns the environment this configuration
-  file is executed on.
+  file is executed on. 
  In releases, returns the `MIX_ENV` specified when running `mix release`.

  This is most often used to execute conditional code:
@@ -287,8 +284,8 @@ defmodule Config do

  In case the file doesn't exist, an error is raised.

-  If the file is relative, it will be expanded relative to the
-  directory of the current configuration file.
+  If file is a relative, it will be expanded relatively to the
+  directory the current configuration file is in.

  ## Examples

@@ -25,7 +25,7 @@ defmodule Config.Provider do
  For example, imagine you want to list some basic configuration
  on Mix's built-in `config/runtime.exs` file, but you also want
  to support additional configuration files. To do so, you can add
-  this inside the `def project` portion of your `mix.exs`:
+  this inside the `def project` portion of  your `mix.exs`:

      releases: [
        demo: [
@@ -16,7 +16,7 @@ defmodule Config.Reader do

  For example, if you expect the target system to have a config file
  in an absolute path, you can add this inside the `def project` portion
-  of your `mix.exs`:
+  of  your `mix.exs`:

      releases: [
        demo: [
@@ -618,7 +618,7 @@ defmodule Enum do
          acc,
          (element, acc -> {:cont, chunk, acc} | {:cont, acc} | {:halt, acc}),
          (acc -> {:cont, chunk, acc} | {:cont, acc})
-        ) :: [chunk]
+        ) :: Enumerable.t()
        when chunk: any
  def chunk_while(enumerable, acc, chunk_fun, after_fun) do
    {_, {res, acc}} =
@@ -666,7 +666,7 @@ defmodule Enum do
      [1, [2], 3, 4, 5, 6]

  """
-  @spec concat(Enumerable.t(Enumerable.t(elem))) :: [elem] when elem: term
+  @spec concat(t) :: t
  def concat(enumerables)

  def concat(list) when is_list(list) do
@@ -681,8 +681,8 @@ defmodule Enum do
  Concatenates the enumerable on the `right` with the enumerable on the
  `left`.

-  This function behaves similarly to the `++/2` operator with proper
-  lists, but applied to enumerables.
+  This function produces the same result as the `++/2` operator
+  for lists.

  ## Examples

@@ -693,7 +693,7 @@ defmodule Enum do
      [1, 2, 3, 4, 5, 6]

  """
-  @spec concat(Enumerable.t(elem), Enumerable.t(elem)) :: [elem] when elem: term
+  @spec concat(t, t) :: t
  def concat(left, right) when is_list(left) and is_list(right) do
    left ++ right
  end
@@ -859,10 +859,6 @@ defmodule Enum do

  """
  @spec dedup_by(t, (element -> term)) :: list
-  def dedup_by([head | tail], fun) do
-    dedup_by_list(tail, fun, fun.(head), [head])
-  end
-
  def dedup_by(enumerable, fun) do
    {list, _} = reduce(enumerable, {[], []}, R.dedup(fun))
    :lists.reverse(list)
@@ -907,7 +903,7 @@ defmodule Enum do

  def drop(enumerable, amount) when is_integer(amount) and amount < 0 do
    {count, fun} = slice_count_and_fun(enumerable, 1)
-    amount = amount + count
+    amount = Kernel.min(amount + count, count)

    if amount > 0 do
      fun.(0, amount, 1)
@@ -2233,19 +2229,14 @@ defmodule Enum do
      nil

  """
-  @spec min_max(t, (element, element -> boolean) | module()) :: {min :: element, max :: element}
-  @spec min_max(t, (-> empty_result)) :: {min :: element, max :: element} | empty_result
-        when empty_result: any
+  @spec min_max(t, (element, element -> boolean) | module()) :: {element, element}
+  @spec min_max(t, (-> empty_result)) :: {element, element} | empty_result when empty_result: any
  @spec min_max(t, (element, element -> boolean) | module(), (-> empty_result)) ::
-          {min :: element, max :: element} | empty_result
+          {element, element} | empty_result
        when empty_result: any

  def min_max(enumerable, sorter_or_empty_fallback \\ fn -> raise Enum.EmptyError end)

-  def min_max(list = [_ | _], empty_fallback) when is_function(empty_fallback, 0) do
-    min_max_list(list)
-  end
-
  def min_max(first..last//step = range, empty_fallback)
      when is_function(empty_fallback, 0) do
    case Range.size(range) do
@@ -2352,14 +2343,14 @@ defmodule Enum do

  """
  @spec min_max_by(t, (element -> any), (element, element -> boolean) | module()) ::
-          {min :: element, max :: element} | empty_result
+          {element, element} | empty_result
        when empty_result: any
  @spec min_max_by(
          t,
          (element -> any),
          (element, element -> boolean) | module(),
          (-> empty_result)
-        ) :: {min :: element, max :: element} | empty_result
+        ) :: {element, element} | empty_result
        when empty_result: any
  def min_max_by(
        enumerable,
@@ -2403,18 +2394,6 @@ defmodule Enum do

  defp min_max_sort_fun(module) when is_atom(module), do: &(module.compare(&1, &2) == :lt)

-  defp min_max_list([h | t]), do: min_max_list(t, h, h)
-
-  defp min_max_list([h | t], min, max) do
-    cond do
-      h < min -> min_max_list(t, h, max)
-      max < h -> min_max_list(t, min, h)
-      true -> min_max_list(t, min, max)
-    end
-  end
-
-  defp min_max_list([], min, max), do: {min, max}
-
  @doc """
  Splits the `enumerable` in two lists according to the given function `fun`.

@@ -2692,7 +2671,7 @@ defmodule Enum do
      5050

  """
-  @spec reduce_while(t, acc, (element, acc -> {:cont, acc} | {:halt, acc})) :: acc
+  @spec reduce_while(t, any, (element, any -> {:cont, any} | {:halt, any})) :: any
  def reduce_while(enumerable, acc, fun) do
    Enumerable.reduce(enumerable, {:cont, acc}, fun) |> elem(1)
  end
@@ -2935,7 +2914,8 @@ defmodule Enum do
  end

  defp slide_list_middle(list, 0, last, start_to_middle) do
-    slide_list_last(list, last + 1, [], start_to_middle)
+    {slid_range, tail} = slide_list_last(list, last + 1, [])
+    slid_range ++ :lists.reverse(start_to_middle, tail)
  end

  # You asked for a middle index off the end of the list... you get what we've got
@@ -2943,16 +2923,16 @@ defmodule Enum do
    :lists.reverse(acc)
  end

-  defp slide_list_last([h | t], last, acc, start_to_middle) when last > 0 do
-    slide_list_last(t, last - 1, [h | acc], start_to_middle)
+  defp slide_list_last([h | t], last, acc) when last > 0 do
+    slide_list_last(t, last - 1, [h | acc])
  end

-  defp slide_list_last(rest, 0, acc, start_to_middle) do
-    :lists.reverse(acc, :lists.reverse(start_to_middle, rest))
+  defp slide_list_last(rest, 0, acc) do
+    {:lists.reverse(acc), rest}
  end

-  defp slide_list_last([], _, acc, start_to_middle) do
-    :lists.reverse(acc, :lists.reverse(start_to_middle))
+  defp slide_list_last([], _, acc) do
+    {:lists.reverse(acc), []}
  end

  @doc """
@@ -4218,7 +4198,7 @@ defmodule Enum do

  `zip_with/2` can be used to transpose lists of lists:

-      iex> Enum.zip_with([[1, 2], [3, 4]], & &1)
+      iex> Enum.zip_with([[1, 2,], [3, 4]], & &1)
      [[1, 3], [2, 4]]

  """
@@ -4329,24 +4309,11 @@ defmodule Enum do
        empty.()

      _ ->
-        # The endpoint shortcut is only valid for sorters consistent with
-        # the natural integer order of the range elements, which is known
-        # to hold for the default sorters; any other sorter traverses the
-        # elements, seeded with the first one since the range is not empty
-        if fun == (&<=/2) or fun == (&>=/2) do
-          last = last - rem(last - first, step)
+        last = last - rem(last - first, step)

-          case fun.(first, last) do
-            true -> first
-            false -> last
-          end
-        else
-          reduce_range(first + step, last, step, first, fn element, acc ->
-            case fun.(acc, element) do
-              true -> acc
-              false -> element
-            end
-          end)
+        case fun.(first, last) do
+          true -> first
+          false -> last
        end
    end
  end
@@ -4449,9 +4416,10 @@ defmodule Enum do
  ## any?/2 all?/2

  defp predicate_list([h | t], initial, fun) do
-    case !!fun.(h) do
-      ^initial -> predicate_list(t, initial, fun)
-      _ -> not initial
+    if !!fun.(h) == initial do
+      predicate_list(t, initial, fun)
+    else
+      not initial
    end
  end

@@ -4462,9 +4430,10 @@ defmodule Enum do
  defp predicate_range(first, last, step, initial, fun)
       when step > 0 and first <= last
       when step < 0 and first >= last do
-    case !!fun.(first) do
-      ^initial -> predicate_range(first + step, last, step, initial, fun)
-      _ -> not initial
+    if !!fun.(first) == initial do
+      predicate_range(first + step, last, step, initial, fun)
+    else
+      not initial
    end
  end

@@ -4547,17 +4516,6 @@ defmodule Enum do
  defp dedup_list([value | tail]), do: [value | dedup_list(tail)]
  defp dedup_list([]), do: []

-  ## dedup_by
-
-  defp dedup_by_list([head | tail], fun, prev, acc) do
-    case fun.(head) do
-      ^prev -> dedup_by_list(tail, fun, prev, acc)
-      new_val -> dedup_by_list(tail, fun, new_val, [head | acc])
-    end
-  end
-
-  defp dedup_by_list([], _fun, _prev, acc), do: :lists.reverse(acc)
-
  ## drop

  defp drop_list(list, 0), do: list
@@ -2376,7 +2376,7 @@ defmodule File.Error do
  @moduledoc """
  An exception that is raised when a file operation fails.

-  For example, this exception is raised, when trying to read a nonexistent file:
+  For example, this exception is raised, when trying to read a non existent file:

      iex> File.read!("nonexistent_file.txt")
      ** (File.Error) could not read file "nonexistent_file.txt": no such file or directory
@@ -2409,7 +2409,7 @@ defmodule File.CopyError do
  @moduledoc """
  An exception that is raised when copying a file fails.

-  For example, this exception is raised when trying to copy to a file or directory that isn't present:
+  For example, this exception is raised when trying to copy to file or directory that isn't present:

      iex> File.cp_r!("non_existent", "source_dir/subdir")
      ** (File.CopyError) could not copy recursively from "non_existent" to "source_dir/subdir". non_existent: no such file or directory
@@ -2477,7 +2477,7 @@ defmodule File.LinkError do
  @moduledoc """
  An exception that is raised when linking a file fails.

-  For example, this exception is raised when trying to link to a file that isn't present:
+  For example, this exception is raised when trying to link to file that isn't present:

      iex> File.ln!("existing.txt", "link.txt")
      ** (File.LinkError) could not create hard link from "link.txt" to "existing.txt": no such file or directory
@@ -897,7 +897,7 @@ defmodule File do
      File.copy("non_existing.txt", "copy.txt")
      #=> {:error, :enoent}
  """
-  @spec copy(Path.t() | io_device, Path.t() | io_device, non_neg_integer | :infinity) ::
+  @spec copy(Path.t() | io_device, Path.t() | io_device, pos_integer | :infinity) ::
          {:ok, non_neg_integer} | {:error, posix | :badarg | :terminated}
  def copy(source, destination, bytes_count \\ :infinity) do
    source = normalize_path_or_io_device(source)
@@ -918,7 +918,7 @@ defmodule File do
      File.copy!("non_existing.txt", "copy.txt")
      ** (File.CopyError) could not copy from "non_existing.txt" to "copy.txt": no such file or directory
  """
-  @spec copy!(Path.t() | io_device, Path.t() | io_device, non_neg_integer | :infinity) ::
+  @spec copy!(Path.t() | io_device, Path.t() | io_device, pos_integer | :infinity) ::
          non_neg_integer
  def copy!(source, destination, bytes_count \\ :infinity) do
    case copy(source, destination, bytes_count) do
@@ -1362,8 +1362,9 @@ defmodule File do
  end

  defp copy_file_mode(src, dest) do
-    with {:ok, src_fileinfo} <- stat(src) do
-      chmod(dest, src_fileinfo.mode)
+    with {:ok, dest_fileinfo} <- stat(dest),
+         {:ok, src_fileinfo} <- stat(src) do
+      write_stat(dest, %{dest_fileinfo | mode: src_fileinfo.mode})
    end
  end

@@ -2220,7 +2221,7 @@ defmodule File do
  type. If you pass, for example, `[encoding: :utf8]` or
  `[encoding: {:utf16, :little}]` in the modes parameter, the underlying stream
  will use `IO.write/2` and the `String.Chars` protocol to convert the data.
-  See `IO.binwrite/2` and `IO.write/2`.
+  See `IO.binwrite/2` and `IO.write/2` .

  One may also consider passing the `:delayed_write` option if the stream
  is meant to be written to under a tight loop.
@@ -18,13 +18,7 @@ defmodule File.Stream do

  defstruct path: nil, modes: [], line_or_bytes: :line, raw: true, node: nil

-  @type t :: %__MODULE__{
-          path: Path.t(),
-          modes: [term()],
-          line_or_bytes: :line | pos_integer(),
-          raw: boolean(),
-          node: node()
-        }
+  @type t :: %__MODULE__{}

  @doc false
  def __build__(path, line_or_bytes, modes) do
@@ -25,7 +25,7 @@ defmodule Float do
  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.
+  to Elixir, they are a property of floating point representation itself.

  For example, the numbers 0.1 and 0.01 are two of them, what means the result
  of squaring 0.1 does not give 0.01 neither the closest representable. Here is
@@ -167,73 +167,40 @@ defmodule Float do
    parse_unsigned(binary)
  end

-  defp parse_unsigned(<<digit, rest::binary>> = binary) when digit in ?0..?9,
-    do: parse_mantissa(binary, rest, false)
+  defp parse_unsigned(<<digit, rest::binary>>) when digit in ?0..?9,
+    do: parse_unsigned(rest, false, false, [digit])

  defp parse_unsigned(binary) when is_binary(binary), do: :error

-  defp parse_mantissa(binary, <<digit, rest::binary>>, dot?) when digit in ?0..?9,
-    do: parse_mantissa(binary, rest, dot?)
+  defp parse_unsigned(<<digit, rest::binary>>, dot?, e?, acc) when digit in ?0..?9,
+    do: parse_unsigned(rest, dot?, e?, [digit | acc])

-  defp parse_mantissa(binary, <<?., digit, rest::binary>>, false) when digit in ?0..?9,
-    do: parse_mantissa(binary, rest, true)
+  defp parse_unsigned(<<?., digit, rest::binary>>, false, false, acc) when digit in ?0..?9,
+    do: parse_unsigned(rest, true, false, [digit, ?. | acc])

-  defp parse_mantissa(binary, <<exp_marker, digit, rest::binary>> = tail, dot?)
+  defp parse_unsigned(<<exp_marker, digit, rest::binary>>, dot?, false, acc)
       when exp_marker in ~c"eE" and digit in ?0..?9,
-       do: parse_exponent(binary, byte_size(binary) - byte_size(tail), rest, dot?)
+       do: parse_unsigned(rest, true, true, [digit, ?e | add_dot(acc, dot?)])

-  defp parse_mantissa(binary, <<exp_marker, sign, digit, rest::binary>> = tail, dot?)
+  defp parse_unsigned(<<exp_marker, sign, digit, rest::binary>>, dot?, false, acc)
       when exp_marker in ~c"eE" and sign in ~c"-+" and digit in ?0..?9,
-       do: parse_exponent(binary, byte_size(binary) - byte_size(tail), rest, dot?)
+       do: parse_unsigned(rest, true, true, [digit, sign, ?e | add_dot(acc, dot?)])

-  defp parse_mantissa(binary, rest, dot?), do: finish_mantissa(binary, rest, dot?)
-
-  defp parse_exponent(binary, exp_pos, <<digit, rest::binary>>, dot?) when digit in ?0..?9,
-    do: parse_exponent(binary, exp_pos, rest, dot?)
-
-  defp parse_exponent(binary, exp_pos, rest, dot?),
-    do: finish_exponent(binary, exp_pos, rest, dot?)
-
-  defp finish_mantissa(binary, rest, _dot? = true) do
-    {:erlang.binary_to_float(consumed(binary, rest)), rest}
+  # :erlang.binary_to_float/1 can raise an ArgumentError if the e exponent is too big. For example,
+  # "1.0e400". Because of this, we rescue the ArgumentError here and return an error.
+  defp parse_unsigned(rest, dot?, _, acc) do
+    acc
+    |> add_dot(dot?)
+    |> :lists.reverse()
+    |> :erlang.list_to_float()
  rescue
    ArgumentError -> :error
+  else
+    float -> {float, rest}
  end

-  # Bare integer: * 1.0 casts to the nearest float without building a new binary,
-  # and raises ArithmeticError on overflow (for example a 400-digit integer).
-  defp finish_mantissa(binary, rest, _dot? = false) do
-    {:erlang.binary_to_integer(consumed(binary, rest)) * 1.0, rest}
-  rescue
-    ArithmeticError -> :error
-  end
-
-  # binary_to_float/1 raises ArgumentError when the exponent is too big, e.g. "1.0e400".
-  defp finish_exponent(binary, _exp_pos, rest, _dot? = true) do
-    {:erlang.binary_to_float(consumed(binary, rest)), rest}
-  rescue
-    ArgumentError -> :error
-  end
-
-  # No decimal point, so ".0" is spliced in before the exponent (at exp_pos) to
-  # form a valid float literal.
-  defp finish_exponent(binary, exp_pos, rest, _dot? = false) do
-    len = byte_size(binary) - byte_size(rest)
-
-    literal =
-      IO.iodata_to_binary([
-        :binary.part(binary, 0, exp_pos),
-        ".0",
-        :binary.part(binary, exp_pos, len - exp_pos)
-      ])
-
-    {:erlang.binary_to_float(literal), rest}
-  rescue
-    ArgumentError -> :error
-  end
-
-  defp consumed(binary, ""), do: binary
-  defp consumed(binary, rest), do: :binary.part(binary, 0, byte_size(binary) - byte_size(rest))
+  defp add_dot(acc, true), do: acc
+  defp add_dot(acc, false), do: [?0, ?. | acc]

  @doc """
  Rounds a float to the largest float less than or equal to `number`.
@@ -286,7 +253,7 @@ defmodule Float do
  @doc """
  Rounds a float to the smallest float greater than or equal to `number`.

-  `ceil/2` also accepts a precision to round a floating-point value up
+  `ceil/2` also accepts a precision to round a floating-point value down
  to an arbitrary number of fractional digits (between 0 and 15).

  The operation is performed on the binary floating point, without a
@@ -355,7 +322,7 @@ defmodule Float do
  and therefore the number above is internally represented as 5.567499999,
  which explains the behavior above. If you want exact rounding for decimals,
  you must use a decimal library. The behavior above is also in accordance
-  with reference implementations, such as "Correctly Rounded Binary-Decimal and
+  to reference implementations, such as "Correctly Rounded Binary-Decimal and
  Decimal-Binary Conversions" by David M. Gay.

  ## Examples
@@ -379,7 +346,7 @@ defmodule Float do
  @spec round(float, precision_range) :: float
  def round(float, precision \\ 0)

-  def round(float, 0) when float === 0.0 or float === -0.0, do: float
+  def round(float, 0) when float == 0.0, do: float

  def round(float, 0) when is_float(float) do
    case :erlang.round(float) * 1.0 do
@@ -705,7 +672,7 @@ defmodule Float do
  end

  defp invalid_precision_message(precision) do
-    "precision #{inspect(precision)} is out of valid range of #{inspect(@precision_range)}"
+    "precision #{precision} is out of valid range of #{inspect(@precision_range)}"
  end

  defp expand_compact([{:compact, false} | t]), do: expand_compact(t)
@@ -69,6 +69,7 @@ defmodule Function do
          | :name
          | :new_index
          | :new_uniq
+          | :pid
          | :type
          | :uniq

@@ -111,6 +112,8 @@ defmodule Function do
  When `fun` is an anonymous function (that is, the type is `:local`), the following
  additional keys are returned:

+    * `:pid` - PID of the process that originally created the function.
+
    * `:index` - (integer) an index into the module function table.

    * `:new_index` - (integer) an index into the module function table.
@@ -156,7 +159,7 @@ defmodule Function do
  `:module`, `:name`, `:arity`, `:env`, or `:type`.

  For anonymous functions, there is also information about any of the
-  atoms `:index`, `:new_index`, `:new_uniq`, and `:uniq`.
+  atoms `:index`, `:new_index`, `:new_uniq`, `:uniq`, and `:pid`.
  For a named function, the value of any of these items is always the
  atom `:undefined`.

@@ -176,6 +179,8 @@ defmodule Function do
      iex> fun = &String.length/1
      iex> Function.info(fun, :name)
      {:name, :length}
+      iex> Function.info(fun, :pid)
+      {:pid, :undefined}

  """
  @doc since: "1.7.0"
@@ -1158,7 +1158,7 @@ defmodule GenServer do

  ## Timeouts

-  `timeout` is a non-negative integer which specifies how many
+  `timeout` is an integer greater than zero which specifies how many
  milliseconds to wait for a reply, or the atom `:infinity` to wait
  indefinitely. The default value is `5000`. If no reply is received within
  the specified time, the function call fails and the caller exits. If the
@@ -92,7 +92,7 @@ defprotocol Inspect do
      end

      inspect(%Point{x: 1})
-      #=> %Point{x: 1, y: 0}
+      %Point{x: 1, y: 0}

  ## Custom implementation

@@ -387,20 +387,13 @@ defimpl Inspect, for: List do
    close = color_doc("]", :list, opts)

    cond do
-      (lists == :as_charlists and unicode_list?(term, printable_limit)) or
-          (lists == :infer and List.ascii_printable?(term, printable_limit)) ->
-        {split, tail} =
-          if is_integer(printable_limit) do
-            case Enum.split(term, printable_limit) do
-              {split, []} -> {split, []}
-              {split, _} -> {split, " ++ ..."}
-            end
-          else
-            {term, []}
+      lists == :as_charlists or (lists == :infer and List.ascii_printable?(term, printable_limit)) ->
+        inspected =
+          case Identifier.escape(IO.chardata_to_string(term), ?", printable_limit) do
+            {escaped, ""} -> [?~, ?c, ?", escaped, ?"]
+            {escaped, _} -> [?~, ?c, ?", escaped, ?", " ++ ..."]
          end

-        {escaped, _} = Identifier.escape(IO.chardata_to_string(split), ?")
-        inspected = [?~, ?c, ?", escaped, ?" | tail]
        color_doc(IO.iodata_to_binary(inspected), :charlist, opts)

      keyword?(term) ->
@@ -414,19 +407,6 @@ defimpl Inspect, for: List do
    end
  end

-  defp unicode_list?(_, 0), do: true
-
-  defp unicode_list?([char | rest], counter)
-       when char in 0..0xD7FF or char in 0xE000..0x10FFFF,
-       do: unicode_list?(rest, decrement(counter))
-
-  defp unicode_list?([], _counter), do: true
-  defp unicode_list?(_, _counter), do: false
-
-  @compile {:inline, decrement: 1}
-  defp decrement(:infinity), do: :infinity
-  defp decrement(counter), do: counter - 1
-
  @doc false
  def keyword({key, value}, opts) do
    key = color_doc(Macro.inspect_atom(:key, key), :atom, opts)
@@ -436,8 +416,8 @@ defimpl Inspect, for: List do

  @doc false
  def keyword?([{key, _value} | rest]) when is_atom(key) do
-    case Atom.to_string(key) do
-      "Elixir." <> _ -> false
+    case Atom.to_charlist(key) do
+      [?E, ?l, ?i, ?x, ?i, ?r, ?.] ++ _ -> false
      _ -> keyword?(rest)
    end
  end
@@ -21,8 +21,8 @@ defmodule Inspect.Opts do
      is `:decimal` and if it is printable, otherwise in bit syntax. See
      `String.printable?/1` to learn when a string is printable.

-    * `:charlists` - when `:as_charlists` all charlists will be printed as charlists,
-      non-printable code points will be escaped. Other lists will be printed as lists.
+    * `:charlists` - when `:as_charlists` all lists will be printed as charlists,
+      non-printable elements will be escaped.

      When `:as_lists` all lists will be printed as lists.

@@ -108,7 +108,7 @@ defmodule Integer do
  defguard is_even(integer) when is_integer(integer) and (integer &&& 1) == 0

  @doc """
-  Computes `base` raised to the power of `exponent`.
+  Computes `base` raised to power of `exponent`.

  Both `base` and `exponent` must be integers.
  The exponent must be zero or positive.
@@ -545,10 +545,10 @@ defmodule Integer do
  @doc since: "1.12.0"
  @spec extended_gcd(integer, integer) :: {non_neg_integer, integer, integer}
  def extended_gcd(0, 0), do: {0, 0, 0}
-  def extended_gcd(0, b) when is_integer(b) and b > 0, do: {b, 0, 1}
-  def extended_gcd(0, b) when is_integer(b) and b < 0, do: {-b, 0, -1}
-  def extended_gcd(a, 0) when is_integer(a) and a > 0, do: {a, 1, 0}
-  def extended_gcd(a, 0) when is_integer(a) and a < 0, do: {-a, -1, 0}
+  def extended_gcd(0, b) when b > 0, do: {b, 0, 1}
+  def extended_gcd(0, b) when b < 0, do: {-b, 0, -1}
+  def extended_gcd(a, 0) when a > 0, do: {a, 1, 0}
+  def extended_gcd(a, 0) when a < 0, do: {-a, -1, 0}

  def extended_gcd(integer1, integer2) when is_integer(integer1) and is_integer(integer2) do
    extended_gcd(integer2, integer1, 0, 1, 1, 0)
@@ -128,7 +128,7 @@ defmodule IO do
  @type nodata :: {:error, term} | :eof
  @type chardata :: String.t() | maybe_improper_list(char | chardata, String.t() | [])

-  @type inspect_opts :: [Inspect.Opts.new_opt() | {:label, String.Chars.t()}]
+  @type inspect_opts :: [Inspect.Opts.new_opt() | {:label, term}]

  @typedoc """
  Stacktrace information as keyword options for `warn/2`.
@@ -152,9 +152,9 @@ defmodule IO do

  The `device` is iterated as specified by the `line_or_chars` argument:

-    * if `line_or_chars` is an integer, it is the number of Unicode
-      code points to be retrieved for devices open in Unicode/utf8 mode.
-      Otherwise, it is the number of raw bytes to be retrieved.
+    * if `line_or_chars` is an integer, it represents a number of bytes. The device is
+      iterated by that number of bytes. This should be the preferred mode for reading
+      non-textual inputs.

    * if `line_or_chars` is `:line`, the device is iterated line by line.
      CRLF newlines  ("\r\n") are automatically normalized to "\n".
@@ -521,7 +521,7 @@ defmodule IO do
  end

  @doc """
-  Gets a number of characters from IO device `:stdio`.
+  Gets a number of bytes from IO device `:stdio`.

  If `:stdio` is a Unicode device, `count` implies
  the number of Unicode code points to be retrieved.
@@ -549,7 +549,7 @@ defmodule IO do
  end

  @doc """
-  Gets a number of characters from the IO `device`.
+  Gets a number of bytes from the IO `device`.

  If the IO `device` is a Unicode device, `count` implies
  the number of Unicode code points to be retrieved.
@@ -111,15 +111,13 @@ defmodule IO.ANSI do
  end

  defsequence = fn name, code, terminator ->
-    sequence = "\e[#{code}#{terminator}"
-
    @spec unquote(name)() :: String.t()
    def unquote(name)() do
-      unquote(sequence)
+      "\e[#{unquote(code)}#{unquote(terminator)}"
    end

    defp format_sequence(unquote(name)) do
-      unquote(sequence)
+      unquote(name)()
    end
  end

@@ -161,7 +159,7 @@ defmodule IO.ANSI do

  for font_n <- [1, 2, 3, 4, 5, 6, 7, 8, 9] do
    @doc "Sets alternative font #{font_n}."
-    defsequence.(String.to_unsafe_atom("font_#{font_n}"), font_n + 10, "m")
+    defsequence.(:"font_#{font_n}", font_n + 10, "m")
  end

  @doc "Normal color or intensity."
@@ -195,13 +193,13 @@ defmodule IO.ANSI do
    defsequence.(color, code + 30, "m")

    @doc "Sets foreground color to light #{color}."
-    defsequence.(String.to_unsafe_atom("light_#{color}"), code + 90, "m")
+    defsequence.(:"light_#{color}", code + 90, "m")

    @doc "Sets background color to #{color}."
-    defsequence.(String.to_unsafe_atom("#{color}_background"), code + 40, "m")
+    defsequence.(:"#{color}_background", code + 40, "m")

    @doc "Sets background color to light #{color}."
-    defsequence.(String.to_unsafe_atom("light_#{color}_background"), code + 100, "m")
+    defsequence.(:"light_#{color}_background", code + 100, "m")
  end

  @doc "Default text color."
@@ -673,7 +673,7 @@ defmodule IO.ANSI.Docs do

  # Characters that can mark the beginning or the end of a word.
  # Only support the most common ones at this moment.
-  @delimiters [?\s, ?', ?", ?!, ??, ?,, ?:, ?;, ?/, ?@, ?#, ?$, ?%, ?^, ?&] ++
+  @delimiters [?\s, ?', ?", ?!, ?@, ?#, ?$, ?%, ?^, ?&] ++
                [?-, ?+, ?(, ?), ?[, ?], ?{, ?}, ?<, ?>, ?.]

  ### Inline start
@@ -31,7 +31,7 @@ defmodule IO.Stream do
  @type t :: %__MODULE__{
          device: IO.device(),
          raw: boolean(),
-          line_or_bytes: :line | pos_integer()
+          line_or_bytes: :line | non_neg_integer()
        }

  @doc false
@@ -175,7 +175,6 @@ defimpl JSON.Encoder, for: Map do

  # Erlang supports only numbers, binaries, and atoms as keys,
  # we support anything that implements the String.Chars protocol.
-  @compile inline: [key: 2]
  defp key(key, encoder) when is_atom(key), do: encoder.(Atom.to_string(key), encoder)
  defp key(key, encoder) when is_binary(key), do: encoder.(key, encoder)
  defp key(key, encoder), do: encoder.(String.Chars.to_string(key), encoder)
@@ -142,7 +142,7 @@ defmodule Kernel do
    * [Patterns and guards](patterns-and-guards.md) - an introduction to patterns,
      guards, and extensions
    * [Syntax reference](syntax-reference.md) - the language syntax reference
-    * [Typespecs reference](typespecs.md) - types and function specifications, including list of types
+    * [Typespecs reference](typespecs.md)- types and function specifications, including list of types
    * [Unicode syntax](unicode-syntax.md) - outlines Elixir support for Unicode

  ## Guards
@@ -3088,7 +3088,7 @@ defmodule Kernel do
  @doc """
  Pops a key from the given nested structure.

-  Uses the `Access` behaviour to traverse the structures
+  Uses the `Access` protocol to traverse the structures
  according to the given `keys`, unless the `key` is a
  function. If the key is a function, it will be invoked
  as specified in `get_and_update_in/3`.
@@ -4960,7 +4960,6 @@ defmodule Kernel do

  """
  @doc since: "1.14.0"
-  @spec binary_slice(binary, integer, non_neg_integer) :: binary
  def binary_slice(binary, start, size)
      when is_binary(binary) and is_integer(start) and is_integer(size) and size >= 0 do
    total = byte_size(binary)
@@ -5034,7 +5033,6 @@ defmodule Kernel do

  """
  @doc since: "1.14.0"
-  @spec binary_slice(binary, Range.t()) :: binary
  def binary_slice(binary, first..last//step)
      when is_binary(binary) and step > 0 do
    total = byte_size(binary)
@@ -5149,7 +5147,7 @@ defmodule Kernel do
  warning saying that a module has been redefined.

  There are some modules that Elixir does not currently implement but it
-  may implement in the future. Those modules are reserved and defining
+  may be implement in the future. Those modules are reserved and defining
  them will result in a compilation error:

      defmodule Any do
@@ -5562,7 +5560,7 @@ defmodule Kernel do
  when the struct is printed:

      defmodule User do
-        @derive {Inspect, only: [:name]}
+        @derive {Inspect, only: :name}
        defstruct name: nil, age: nil
      end

@@ -5589,9 +5587,6 @@ defmodule Kernel do
        defstruct name: nil, age: 10 + 11
      end

-  `@enforce_keys` must be set to an atom or a list of unique atoms,
-  all of which must name fields defined by `defstruct/1`
-
  Now trying to build a struct without the name key will fail:

      %User{age: 21}
@@ -6382,7 +6377,7 @@ defmodule Kernel do

  ### Passing timeouts

-  You can also pass timeouts directly to this function, that is, milliseconds or
+  You can also pass timeouts directly to this functions, that is, milliseconds or
  the atom `:infinity`. In this case, this function just returns the given argument.

  ## Examples
@@ -49,7 +49,7 @@ defmodule Kernel.CLI do

  @doc """
  Runs the given function by catching any failure
-  and printing them to stderr. `at_exit` hooks are
+  and printing them to stdout. `at_exit` hooks are
  also invoked before exiting.

  This function is used by Elixir's CLI and also
@@ -206,7 +206,7 @@ defmodule Kernel.CLI do
  end

  @elixir_internals [:elixir, :elixir_aliases, :elixir_clauses, :elixir_compiler, :elixir_def] ++
-                      [:elixir_dispatch, :elixir_expand, :elixir_lexical] ++
+                      [:elixir_def, :elixir_dispatch, :elixir_expand, :elixir_lexical] ++
                      [:elixir_map, :elixir_module] ++
                      [:elixir_erl, :elixir_erl_clauses, :elixir_erl_compiler, :elixir_erl_pass] ++
                      [Kernel.ErrorHandler, Module.ParallelChecker]
@@ -344,7 +344,7 @@ defmodule Kernel.CLI do
    parse_argv(t, %{config | verbose_compile: true})
  end

-  defp parse_argv([~c"--profile", ~c"time" | t], %{mode: :elixirc} = config) do
+  defp parse_argv([~c"--profile", "time" | t], %{mode: :elixirc} = config) do
    parse_argv(t, %{config | profile: :time})
  end

@@ -23,7 +23,7 @@ defmodule Kernel.LexicalTracker do

  @doc """
  Invoked during module expansion to annotate a require
-  that must be warned if unused.
+  must be warned if unused.
  """
  def warn_require(pid, meta, module, alias) do
    :gen_server.cast(pid, {:warn_require, module, meta, alias})
@@ -32,7 +32,7 @@ defmodule Kernel.LexicalTracker do

  @doc """
  Invoked during module expansion to annotate an alias
-  that must be warned if unused.
+  must be warned if unused.
  """
  def warn_alias(pid, meta, alias, module) do
    :gen_server.cast(pid, {:warn_alias, alias, meta})
@@ -41,7 +41,7 @@ defmodule Kernel.LexicalTracker do

  @doc """
  Invoked during module expansion to annotate an import
-  that must be warned if unused.
+  must be warned if unused.
  """
  def warn_import(pid, module) do
    :gen_server.cast(pid, {:warn_import, module})
@@ -25,8 +25,8 @@ defmodule Kernel.ParallelCompiler do
          each_long_compilation: (Path.t() -> term()) | (Path.t(), pid() -> term()),
          each_long_verification: (module() -> term()) | (module(), pid() -> term()),
          each_module: (Path.t(), module(), binary() -> term()),
-          each_cycle: (-> {:compile, [Path.t()], [Code.diagnostic(:warning)]}
-                          | {:runtime, [{module(), Path.t()}], [Code.diagnostic(:warning)]}),
+          each_cycle: (-> {:compile, [module()], [Code.diagnostic(:warning)]}
+                          | {:runtime, [module()], [Code.diagnostic(:warning)]}),
          long_compilation_threshold: pos_integer(),
          long_verification_threshold: pos_integer(),
          verification: boolean(),
@@ -100,8 +100,6 @@ defmodule Kernel.ParallelCompiler do
  This function allows a developer to perform such tasks.
  """
  @doc since: "1.16.0"
-  @spec pmap(Enumerable.t(input), (input -> output)) :: [output]
-        when input: term, output: term
  def pmap(collection, fun) when is_function(fun, 1) do
    ref = make_ref()

@@ -173,25 +171,25 @@ defmodule Kernel.ParallelCompiler do

    * `:each_long_verification` (since v1.19.0) - for each file that takes more
      than a given timeout (see the `:long_verification_threshold` option) to
-      verify, invoke this callback passing the module as its argument (and
+      compile, invoke this callback passing the module as its argument (and
      optionally the PID of the process verifying the module)

    * `:each_module` - for each module compiled, invokes the callback passing
      the file, module and the module bytecode

-    * `:each_cycle` - invoked after each compilation cycle and should return one
-      of the following values:
+    * `:each_cycle` - after the given files are compiled, invokes this function
+      that should return the following values:
      * `{:compile, modules, warnings}` - to continue compilation with a list of
-        further module files to compile
+        further modules to compile
      * `{:runtime, modules, warnings}` - to stop compilation and verify the list
-        of `{module, path}` pairs because dependent modules have changed
+        of modules because dependent modules have changed

    * `:long_compilation_threshold` - the timeout (in seconds) to check for files
      taking too long to compile. For each file that exceeds the threshold, the
      `:each_long_compilation` callback is invoked. Defaults to `10` seconds.

    * `:long_verification_threshold` (since v1.19.0) - the timeout (in seconds) to
-      check for modules taking too long to verify. For each module that exceeds the
+      check for modules taking too long to compile. For each module that exceeds the
      threshold, the `:each_long_verification` callback is invoked. Defaults to
      `10` seconds.

@@ -214,7 +212,7 @@ defmodule Kernel.ParallelCompiler do

    * `:return_diagnostics` (since v1.15.0) - returns maps with information instead of
      a list of warnings and returns diagnostics as maps instead of tuples.
-      This option must be set to true, except for backward compatibility reasons.
+      This option must be set to true, except for backwards compatibibility reasons.

    * `:max_concurrency` - the maximum number of files to compile in parallel.
      Setting this option to 1 will compile files sequentially.
@@ -271,7 +269,7 @@ defmodule Kernel.ParallelCompiler do

    * `:return_diagnostics` (since v1.15.0) - returns maps with information instead of
      a list of warnings and returns diagnostics as maps instead of tuples.
-      This option must be set to true, except for backward compatibility reasons.
+      This option must be set to true, except for backwards compatibibility reasons.

  """
  @doc since: "1.6.0"
@@ -768,8 +768,8 @@ defmodule Kernel.SpecialForms do
  It is used in typespecs to specify the type of a variable,
  function or of a type itself:

-      @type num :: integer | float
-      @spec add(num, num) :: num
+      @type number :: integer | float
+      @spec add(number, number) :: number

  It may also be used in bit strings to specify the type
  of a given bit segment:
@@ -1333,9 +1333,9 @@ defmodule Kernel.SpecialForms do
        sum(1, value, 3)
      end

-  However, the code above does not work as expected, because this
-  injects the representation of the `value` variable,
-  not its contents:
+
+  Which the argument for the `:sum` function call is not the
+  expected result:

      {:sum, [], [1, {:value, [], Elixir}, 3]}

@@ -2077,9 +2077,9 @@ defmodule Kernel.SpecialForms do
      iex> try do
      ...>   1 / 0
      ...> rescue
-      ...>   x in [ArithmeticError] -> {:rescued, Exception.message(x)}
+      ...>   x in [ArithmeticError] -> [:rescued, is_exception(x)]
      ...> end
-      {:rescued, "bad argument in arithmetic expression"}
+      [:rescued, true]

  Rescue different errors with separate clauses:

@@ -686,13 +686,6 @@ defmodule Kernel.Typespec do
    {{:type, location(meta), :range, [left, right]}, state}
  end

-  defp typespec({:..//, _meta, [_first, _last, _step]} = range, _vars, caller, _state) do
-    compile_error(
-      caller,
-      "ranges with steps are not supported in typespecs, got: #{Macro.to_string(range)}"
-    )
-  end
-
  # Handle special forms
  defp typespec({:__MODULE__, _, atom}, vars, caller, state) when is_atom(atom) do
    typespec(caller.module, vars, caller, state)
@@ -162,8 +162,16 @@ defmodule Kernel.Utils do
    # TODO: Make it raise on v2.0
    warn_on_duplicate_struct_key(:lists.keysort(1, fields), env)

-    field_map = :maps.from_list(fields)
-    struct = :maps.put(:__struct__, module, field_map)
+    foreach = fn
+      key when is_atom(key) ->
+        :ok
+
+      key ->
+        raise ArgumentError, "keys given to @enforce_keys must be atoms, got: #{inspect(key)}"
+    end
+
+    :lists.foreach(foreach, enforce_keys)
+    struct = :maps.from_list([__struct__: module] ++ fields)
    escaped_struct = :elixir_quote.escape(struct, {:struct, module}, false)

    body =
@@ -207,7 +215,7 @@ defmodule Kernel.Utils do
          end
      end

-    case enforce_keys -- :maps.keys(field_map) do
+    case enforce_keys -- :maps.keys(struct) do
      [] ->
        mapper = fn {key, val} ->
          %{field: key, default: val, required: :lists.member(key, enforce_keys)}
@@ -217,9 +225,10 @@ defmodule Kernel.Utils do
        derive = :lists.map(fn {_, value} -> value end, :ets.take(bag, {:accumulate, :derive}))
        {struct, :lists.reverse(derive), escaped_struct, quote(do: kv), body}

-      invalid_keys ->
+      error_keys ->
        raise ArgumentError,
-              "unknown or duplicate keys given to @enforce_keys, got: #{inspect(invalid_keys)}"
+              "@enforce_keys required keys (#{inspect(error_keys)}) that are not defined in defstruct: " <>
+                "#{inspect(fields)}"
    end
  end

@@ -38,7 +38,7 @@ defmodule Keyword do

  ## Duplicate keys and ordering

-  A keyword list may have duplicate keys so it is not strictly a key-value
+  A keyword may have duplicate keys so it is not strictly a key-value
  data type. However, most of the functions in this module work on a
  key-value structure and behave similar to the functions you would
  find in the `Map` module. For example, `Keyword.get/3` will get the first
@@ -517,7 +517,7 @@ defmodule Keyword do
        {get, :lists.reverse(acc, [{key, value} | delete(t, key)])}

      :pop ->
-        {current, :lists.reverse(acc, delete(t, key))}
+        {current, :lists.reverse(acc, t)}

      other ->
        raise "the given function must return a two-element tuple or :pop, got: #{inspect(other)}"
@@ -583,7 +583,7 @@ defmodule Keyword do
        {get, :lists.reverse(acc, [{key, value} | delete(t, key)])}

      :pop ->
-        {value, :lists.reverse(acc, delete(t, key))}
+        {value, :lists.reverse(acc, t)}

      other ->
        raise "the given function must return a two-element tuple or :pop, got: #{inspect(other)}"
@@ -1323,8 +1323,7 @@ defmodule Keyword do
  @doc """
  Drops the given `keys` from the keyword list.

-  If a key occurs multiple times, all of its entries are removed when that key
-  is included in `keys`.
+  Removes duplicate keys from the new keyword list.

  ## Examples

@@ -1434,7 +1433,7 @@ defmodule Keyword do
    do: {values, acc}

  @doc """
-  Lazily returns the first value for `key` and removes all associated entries in the keyword list.
+  Lazily returns and removes all values associated with `key` in the keyword list.

  This is useful if the default value is very expensive to calculate or
  generally difficult to set up and tear down again.
@@ -311,6 +311,9 @@ defmodule List do
      iex> List.first!([1, 2, 3])
      1

+      iex> List.first!([])
+      ** (ArgumentError) attempted to get the first element of an empty list
+
  """
  @doc since: "1.20.0"
  @spec first!([elem, ...]) :: elem when elem: var
@@ -363,6 +366,9 @@ defmodule List do
      iex> List.last!([1, 2, 3])
      3

+      iex> List.last!([])
+      ** (ArgumentError) attempted to get the last element of an empty list
+
  """
  @doc since: "1.20.0"
  @spec last!([elem, ...]) :: elem when elem: var
@@ -429,7 +435,7 @@ defmodule List do

  """
  @doc since: "1.13.0"
-  @spec keyfind!([tuple], any, non_neg_integer) :: tuple
+  @spec keyfind!([tuple], any, non_neg_integer) :: any
  def keyfind!(list, key, position) when is_integer(position) do
    :lists.keyfind(key, position + 1, list) ||
      raise KeyError,
@@ -514,8 +520,8 @@ defmodule List do

  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 the third
-  argument or any module that implements a `compare/2` function. For example,
+  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:
@@ -655,7 +661,7 @@ defmodule List do
  end

  @doc """
-  Wraps `term` in a list if it is not a list.
+  Wraps `term` in a list if this is not list.

  If `term` is already a list, it returns the list.
  If `term` is `nil`, it returns an empty list.
@@ -954,12 +960,9 @@ defmodule List do
  @spec pop_at(list, integer, any) :: {any, list}
  def pop_at(list, index, default \\ nil) when is_integer(index) do
    if index < 0 do
-      case length(list) + index do
-        index when index < 0 -> {default, list}
-        index -> do_pop_at(list, index, default, [], list)
-      end
+      do_pop_at(list, length(list) + index, default, [])
    else
-      do_pop_at(list, index, default, [], list)
+      do_pop_at(list, index, default, [])
    end
  end

@@ -1027,23 +1030,11 @@ defmodule List do
  end

  @doc """
-  Converts a charlist to an existing atom or creates a new one.
+  Converts a charlist to an atom.

  Elixir supports conversions from charlists which contain any Unicode
  code point.

-  > #### Dynamic Atom Creation {: .warning}
-  >
-  > This function creates atoms dynamically and atoms are
-  > not garbage-collected. Therefore, `charlist` should not be an
-  > untrusted value, such as input received from a socket or during
-  > a web request. Consider using `to_existing_atom/1` instead.
-
-  By default, the maximum number of atoms is `1_048_576`. This limit
-  can be raised or lowered using the VM option `+t`.
-
-  The maximum atom size is 255 Unicode code points.
-
  Inlined by the compiler.

  ## Examples
@@ -1148,7 +1139,7 @@ defmodule List do
      2.2017764

  """
-  @spec to_float(nonempty_charlist) :: float
+  @spec to_float(charlist) :: float
  def to_float(charlist) do
    :erlang.list_to_float(charlist)
  end
@@ -1164,7 +1155,7 @@ defmodule List do
      123

  """
-  @spec to_integer(nonempty_charlist) :: integer
+  @spec to_integer(charlist) :: integer
  def to_integer(charlist) do
    :erlang.list_to_integer(charlist)
  end
@@ -1182,7 +1173,7 @@ defmodule List do
      1023

  """
-  @spec to_integer(nonempty_charlist, 2..36) :: integer
+  @spec to_integer(charlist, 2..36) :: integer
  def to_integer(charlist, base) do
    :erlang.list_to_integer(charlist, base)
  end
@@ -1251,7 +1242,7 @@ defmodule List do

        Please check the given list or call inspect/1 to get the list representation, got:

-        #{inspect(list, charlists: :as_lists)}
+        #{inspect(list)}
        """
    else
      result when is_binary(result) ->
@@ -1303,7 +1294,7 @@ defmodule List do

        Please check the given list or call inspect/1 to get the list representation, got:

-        #{inspect(list, charlists: :as_lists)}
+        #{inspect(list)}
        """
    else
      result when is_list(result) ->
@@ -1368,13 +1359,13 @@ defmodule List do

  defp myers_difference_with_diff_script(list1, list2, diff_script) do
    path = {0, list1, list2, []}
-    find_script(0, [path], diff_script)
+    find_script(0, length(list1) + length(list2), [path], diff_script)
  end

-  defp find_script(envelope, paths, diff_script) do
+  defp find_script(envelope, max, paths, diff_script) do
    case each_diagonal(-envelope, envelope, paths, [], diff_script) do
      {:done, edits} -> compact_reverse(edits, [])
-      {:next, paths} -> find_script(envelope + 1, paths, diff_script)
+      {:next, paths} -> find_script(envelope + 1, max, paths, diff_script)
    end
  end

@@ -1519,16 +1510,15 @@ defmodule List do

  # pop_at

-  # The original list is returned when the index is out of bounds
-  defp do_pop_at([], _index, default, _acc, original) do
-    {default, original}
+  defp do_pop_at([], _index, default, acc) do
+    {default, :lists.reverse(acc)}
  end

-  defp do_pop_at([head | tail], 0, _default, acc, _original) do
+  defp do_pop_at([head | tail], 0, _default, acc) do
    {head, :lists.reverse(acc, tail)}
  end

-  defp do_pop_at([head | tail], index, default, acc, original) do
-    do_pop_at(tail, index - 1, default, [head | acc], original)
+  defp do_pop_at([head | tail], index, default, acc) do
+    do_pop_at(tail, index - 1, default, [head | acc])
  end
 end
@@ -166,7 +166,7 @@ defmodule Macro do
      of a `__block__` or the right side of `->`. The last expression of the
      block does not have metadata if it is not followed by an end of line
      character (either a newline or `;`). This entry may appear multiple times
-      in the same metadata if the expression is surrounded by parens
+      in the same metadata if the expression is surround by parens

    * `:format` - set to `:keyword` when an atom is defined as a keyword.
      It may also be set to `:atom` to distinguish `nil`, `false`, and `true`
@@ -235,7 +235,7 @@ defmodule Macro do
  `div/2` function, so that the AST for that function will become `{:div, [],
  [100, 5]}` (`div(100, 5)`).
  """
-  @spec unpipe(t()) :: [{t(), non_neg_integer}]
+  @spec unpipe(t()) :: [t()]
  def unpipe(expr) do
    :lists.reverse(unpipe(expr, []))
  end
@@ -518,7 +518,7 @@ defmodule Macro do
  @doc since: "1.11.3"
  @spec generate_unique_arguments(0, context :: atom) :: []
  @spec generate_unique_arguments(pos_integer, context) ::
-          [{atom, metadata(), context}, ...]
+          [{atom, [counter: integer], context}, ...]
        when context: atom
  def generate_unique_arguments(amount, context),
    do: generate_arguments(amount, context, &unique_var/2)
@@ -576,7 +576,7 @@ defmodule Macro do

  """
  @doc since: "1.11.3"
-  @spec unique_var(var, context) :: {var, metadata(), context}
+  @spec unique_var(var, context) :: {var, [counter: integer], context}
        when var: atom, context: atom
  def unique_var(var, context) when is_atom(var) and is_atom(context) do
    {var, [counter: :elixir_module.next_counter(context)], context}
@@ -690,39 +690,7 @@ defmodule Macro do
  """
  @spec prewalk(t, (t -> t)) :: t
  def prewalk(ast, fun) when is_function(fun, 1) do
-    do_prewalk(fun.(ast), fun)
-  end
-
-  # Mirrors do_traverse/4 with an always-pre fun and no accumulator,
-  # avoiding the wrapper closures and tuple threading of traverse/4.
-  # Each clause dispatches on the already-transformed node, so fun's
-  # rewrites are descended into, exactly as in traverse/4.
-  defp do_prewalk({form, meta, args}, fun) when is_atom(form) do
-    {form, meta, do_prewalk_args(args, fun)}
-  end
-
-  defp do_prewalk({form, meta, args}, fun) do
-    form = do_prewalk(fun.(form), fun)
-    {form, meta, do_prewalk_args(args, fun)}
-  end
-
-  defp do_prewalk({left, right}, fun) do
-    left = do_prewalk(fun.(left), fun)
-    {left, do_prewalk(fun.(right), fun)}
-  end
-
-  defp do_prewalk(list, fun) when is_list(list) do
-    do_prewalk_args(list, fun)
-  end
-
-  defp do_prewalk(x, _fun) do
-    x
-  end
-
-  defp do_prewalk_args(args, _fun) when is_atom(args), do: args
-
-  defp do_prewalk_args(args, fun) when is_list(args) do
-    :lists.map(fn x -> do_prewalk(fun.(x), fun) end, args)
+    elem(prewalk(ast, nil, fn x, nil -> {fun.(x), nil} end), 0)
  end

  @doc """
@@ -760,41 +728,11 @@ defmodule Macro do
  """
  @spec postwalk(t, (t -> t)) :: t
  def postwalk(ast, fun) when is_function(fun, 1) do
-    do_postwalk(ast, fun)
-  end
-
-  # Mirrors do_traverse/4 with an always-post fun and no accumulator,
-  # avoiding the wrapper closures and tuple threading of traverse/4
-  defp do_postwalk({form, meta, args}, fun) when is_atom(form) do
-    fun.({form, meta, do_postwalk_args(args, fun)})
-  end
-
-  defp do_postwalk({form, meta, args}, fun) do
-    form = do_postwalk(form, fun)
-    fun.({form, meta, do_postwalk_args(args, fun)})
-  end
-
-  defp do_postwalk({left, right}, fun) do
-    left = do_postwalk(left, fun)
-    fun.({left, do_postwalk(right, fun)})
-  end
-
-  defp do_postwalk(list, fun) when is_list(list) do
-    fun.(do_postwalk_args(list, fun))
-  end
-
-  defp do_postwalk(x, fun) do
-    fun.(x)
-  end
-
-  defp do_postwalk_args(args, _fun) when is_atom(args), do: args
-
-  defp do_postwalk_args(args, fun) when is_list(args) do
-    :lists.map(fn x -> do_postwalk(x, fun) end, args)
+    elem(postwalk(ast, nil, fn x, nil -> {fun.(x), nil} end), 0)
  end

  @doc """
-  This function behaves like `prewalk/3`, but performs a depth-first,
+  This functions behaves like `prewalk/3`, but performs a depth-first,
  post-order traversal of quoted expressions using an accumulator.
  """
  @spec postwalk(t, any, (t, any -> {t, any})) :: {t, any}
@@ -1002,7 +940,7 @@ defmodule Macro do

  This is useful when a struct needs to be expanded at
  compilation time and the struct being expanded may or may
-  not have been compiled (including structs defined
+  not have been compiled (including structs in the defined
  under the module being compiled). For compiled modules,
  it will invoke `module.__info__(:struct)`.

@@ -1096,7 +1034,7 @@ defmodule Macro do
  defp find_invalid(other), do: {:error, other}

  @doc """
-  Returns an enumerable that traverses the `ast` in depth-first,
+  Returns an enumerable that traverses the  `ast` in depth-first,
  pre-order traversal.

  ## Examples
@@ -1154,7 +1092,7 @@ defmodule Macro do
  end

  @doc """
-  Returns an enumerable that traverses the `ast` in depth-first,
+  Returns an enumerable that traverses the  `ast` in depth-first,
  post-order traversal.

  ## Examples
@@ -1257,15 +1195,14 @@ defmodule Macro do
  The mapping function receives an integer representing the code point
  of the character it wants to unescape. There are also the special atoms
  `:newline`, `:unicode`, and `:hex`, which control newline, unicode,
-  and escaping respectively, and for which the mapping function must return
-  a boolean.
+  and escaping respectively.

  Here is the default mapping function implemented by Elixir:

      def unescape_map(:newline), do: true
      def unescape_map(:unicode), do: true
      def unescape_map(:hex), do: true
-      def unescape_map(?0), do: 0
+      def unescape_map(?0), do: ?0
      def unescape_map(?a), do: ?\a
      def unescape_map(?b), do: ?\b
      def unescape_map(?d), do: ?\d
@@ -1288,11 +1225,7 @@ defmodule Macro do
      Macro.unescape_string("example\\n", &unescape_map(&1))

  """
-  @spec unescape_string(
-          String.t(),
-          (non_neg_integer | :newline | :unicode | :hex ->
-             non_neg_integer | boolean)
-        ) :: String.t()
+  @spec unescape_string(String.t(), (non_neg_integer -> non_neg_integer | false)) :: String.t()
  def unescape_string(string, map) do
    :elixir_interpolation.unescape_string(string, map)
  end
@@ -1807,9 +1740,9 @@ defmodule Macro do

  defp kw_blocks_to_string(kw, fun) do
    Enum.reduce(unquote(kw_keywords), " ", fn x, acc ->
-      case Keyword.fetch(kw, x) do
-        {:ok, value} -> acc <> kw_block_to_string(x, value, fun)
-        :error -> acc
+      case Keyword.has_key?(kw, x) do
+        true -> acc <> kw_block_to_string(x, Keyword.get(kw, x), fun)
+        false -> acc
      end
    end) <> "end"
  end
@@ -1923,7 +1856,6 @@ defmodule Macro do
  definition compile-time, and you can use `Macro.expand/2`.
  """
  @doc since: "1.16.0"
-  @spec compile_apply(module(), atom(), [term()], Macro.Env.t()) :: term()
  def compile_apply(mod, fun, args, caller) do
    :elixir_env.trace({:remote_function, [], mod, fun, length(args)}, %{caller | function: nil})
    Kernel.apply(mod, fun, args)
@@ -2048,9 +1980,10 @@ defmodule Macro do

  defp do_expand_once({{:., _, [{:__ENV__, _, atom}, field]}, _, []} = original, env)
       when is_atom(atom) and is_atom(field) and env.context != :match do
-    case Map.fetch(env, field) do
-      {:ok, value} -> {maybe_escape_map(value), true}
-      :error -> {original, false}
+    if Map.has_key?(env, field) do
+      {maybe_escape_map(Map.get(env, field)), true}
+    else
+      {original, false}
    end
  end

@@ -2188,9 +2121,6 @@ defmodule Macro do
  def quoted_literal?({:__aliases__, _, args}),
    do: quoted_literal?(args)

-  def quoted_literal?({:__block__, _, [wrapped]}),
-    do: quoted_literal?(wrapped)
-
  def quoted_literal?({:%, _, [left, right]}),
    do: quoted_literal?(left) and quoted_literal?(right)

@@ -2570,7 +2500,7 @@ defmodule Macro do

  ### As a remote call

-  Inspect an atom as the function name of a remote call.
+  Inspect an atom the function name of a remote call.

      iex> Macro.inspect_atom(:remote_call, :foo)
      "foo"
@@ -2691,76 +2621,54 @@ defmodule Macro do
        :unquoted_operator

      true ->
-        classify_binary(Atom.to_string(atom), atom)
-    end
-  end
+        charlist = Atom.to_charlist(atom)

-  # ASCII identifiers and aliases are recognized on the binary to avoid building a
-  # charlist and running the (unicode aware) tokenizer, which dominates the cost of
-  # classifying keyword list, map and struct keys.
-  defp classify_binary(<<char, rest::binary>>, atom)
-       when char >= ?a and char <= ?z
-       when char == ?_ do
-    if valid_identifier_rest?(rest), do: :identifier, else: classify_with_tokenizer(atom)
-  end
+        if valid_alias?(charlist) do
+          :alias
+        else
+          case :elixir_config.identifier_tokenizer().tokenize(charlist) do
+            {kind, _acc, [], _, _, special} ->
+              cond do
+                kind != :identifier or :lists.member(:at, special) ->
+                  :not_callable

-  defp classify_binary("Elixir" <> rest, atom) do
-    if valid_alias_piece?(rest), do: :alias, else: classify_with_tokenizer(atom)
-  end
+                # identifier_tokenizer used to return errors for non-nfc, but
+                # now it nfc-normalizes everything. However, lack of nfc is
+                # still a good reason to quote an atom when printing.
+                :lists.member(:nfkc, special) ->
+                  :other

-  defp classify_binary(_binary, atom), do: classify_with_tokenizer(atom)
+                true ->
+                  :identifier
+              end

-  defp classify_with_tokenizer(atom) do
-    case :elixir_config.identifier_tokenizer().tokenize(Atom.to_charlist(atom)) do
-      {kind, _acc, [], _, _, special} ->
-        cond do
-          kind != :identifier or :lists.member(:at, special) ->
-            :not_callable
-
-          # identifier_tokenizer used to return errors for non-nfc, but
-          # now it nfc-normalizes everything. However, lack of nfc is
-          # still a good reason to quote an atom when printing.
-          :lists.member(:nfkc, special) ->
-            :other
-
-          true ->
-            :identifier
+            _ ->
+              :other
+          end
        end
-
-      _ ->
-        :other
    end
  end

-  defp valid_identifier_rest?(<<char, rest::binary>>)
-       when char >= ?a and char <= ?z
-       when char >= ?A and char <= ?Z
-       when char >= ?0 and char <= ?9
-       when char == ?_ do
-    valid_identifier_rest?(rest)
-  end
+  defp valid_alias?([?E, ?l, ?i, ?x, ?i, ?r] ++ rest), do: valid_alias_piece?(rest)
+  defp valid_alias?(_other), do: false

-  defp valid_identifier_rest?(<<char>>) when char == ?? when char == ?!, do: true
-  defp valid_identifier_rest?(<<>>), do: true
-  defp valid_identifier_rest?(_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?(<<?., char, rest::binary>>) when char >= ?A and char <= ?Z,
-    do: valid_alias_piece_rest?(rest)
-
-  defp valid_alias_piece?(<<>>), do: true
+  defp valid_alias_piece?([]), do: true
  defp valid_alias_piece?(_other), do: false

-  # A helper returning the rest of the binary would build a sub binary per piece,
-  # so branch back into valid_alias_piece?/1 to keep the match context.
-  defp valid_alias_piece_rest?(<<char, rest::binary>>)
+  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
-    valid_alias_piece_rest?(rest)
+    trim_leading_while_valid_identifier(rest)
  end

-  defp valid_alias_piece_rest?(other), do: valid_alias_piece?(other)
+  defp trim_leading_while_valid_identifier(other) do
+    other
+  end

  @doc """
  Default backend for `Kernel.dbg/2`.
@@ -3046,8 +2954,6 @@ defmodule Macro do
  @doc false
  def __dbg__(to_debug, header, options) do
    {print_location?, options} = Keyword.pop(options, :print_location, true)
-    syntax_colors = if IO.ANSI.enabled?(), do: IO.ANSI.syntax_colors(), else: []
-    options = Keyword.merge([width: 80, pretty: true, syntax_colors: syntax_colors], options)
    ansi_enabled? = options[:syntax_colors] != []

    if print_location? and is_binary(header) do
@@ -3055,6 +2961,8 @@ defmodule Macro do
      :ok = IO.write(IO.ANSI.format(formatted, ansi_enabled?))
    end

+    syntax_colors = if IO.ANSI.enabled?(), do: IO.ANSI.syntax_colors(), else: []
+    options = Keyword.merge([width: 80, pretty: true, syntax_colors: syntax_colors], options)
    {formatted, result} = dbg_format_ast_to_debug(to_debug, options)
    :ok = IO.write(IO.ANSI.format([formatted, ?\n], ansi_enabled?))
    result
@@ -203,7 +203,7 @@ defmodule Macro.Env do
  Returns a keyword list containing the file and line
  information as keys.
  """
-  @spec location(t) :: [file: file, line: line]
+  @spec location(t) :: keyword
  def location(env)

  def location(%{__struct__: Macro.Env, file: file, line: line}) do
@@ -213,13 +213,13 @@ defmodule Macro.Env do
  @doc false
  @deprecated "Use Macro.Env.expand_alias/4 instead"
  def fetch_alias(%{__struct__: Macro.Env, aliases: aliases}, atom) when is_atom(atom),
-    do: Keyword.fetch(aliases, String.to_unsafe_atom("Elixir.#{atom}"))
+    do: Keyword.fetch(aliases, :"Elixir.#{atom}")

  @doc false
  @deprecated "Use Macro.Env.expand_alias/4 instead"
  def fetch_macro_alias(%{__struct__: Macro.Env, macro_aliases: aliases}, atom)
      when is_atom(atom),
-      do: Keyword.fetch(aliases, String.to_unsafe_atom("Elixir.#{atom}"))
+      do: Keyword.fetch(aliases, :"Elixir.#{atom}")

  @doc """
  Returns the modules from which the given `{name, arity}` was
@@ -234,7 +234,7 @@ defmodule Macro.Env do
  > This function does not emit compiler tracing events,
  > which may block the compiler from correctly tracking
  > dependencies. Use this function for reflection purposes
-  > but do not use it to expand imports into qualified
+  > but to do not use it to expand imports into qualified
  > calls. Instead, use `expand_import/5`.

  ## Examples
@@ -345,7 +345,7 @@ defmodule Macro.Env do

  ## Additional options

-  It accepts the same options as `Kernel.SpecialForms.require/2` plus:
+  It accepts the same options as `Kernel.SpecialForm.require/2` plus:

    * #{trace_option}

@@ -386,7 +386,7 @@ defmodule Macro.Env do

  ## Additional options

-  It accepts the same options as `Kernel.SpecialForms.import/2` plus:
+  It accepts the same options as `Kernel.SpecialForm.import/2` plus:

    * `:emit_warnings` - emit warnings found when defining imports

@@ -394,7 +394,7 @@ defmodule Macro.Env do

    * `:info_callback` - a function to use instead of `c:Module.__info__/1`.
      The function will be invoked with `:functions` or `:macros` argument.
-      It has to return a list of `{function, arity}` key-value pairs.
+      It has to return a list of `{function, arity}` key value pairs.
      If it fails, it defaults to using module metadata based on `module_info/1`.

  ## Examples
@@ -406,7 +406,7 @@ defmodule Macro.Env do
      iex> Macro.Env.lookup_import(env, {:flatten, 1})
      [{:function, List}]

-  It accepts the same options as `Kernel.SpecialForms.import/2`:
+  It accepts the same options as `Kernel.SpecialForm.import/2`:

      iex> env = __ENV__
      iex> Macro.Env.lookup_import(env, {:is_odd, 1})
@@ -448,7 +448,7 @@ defmodule Macro.Env do

  ## Additional options

-  It accepts the same options as `Kernel.SpecialForms.alias/2` plus:
+  It accepts the same options as `Kernel.SpecialForm.alias/2` plus:

    * #{trace_option}

@@ -700,7 +700,7 @@ defmodule Macro.Env do
  @doc """
  Returns the environment stacktrace.
  """
-  @spec stacktrace(t) :: [{module, atom, arity, keyword}]
+  @spec stacktrace(t) :: list
  def stacktrace(%{__struct__: Macro.Env} = env) do
    cond do
      is_nil(env.module) ->
@@ -201,7 +201,7 @@ defmodule Map do
      %{}

  """
-  @spec new :: %{}
+  @spec new :: map
  def new, do: %{}

  @doc """
@@ -51,15 +51,6 @@ defmodule MapSet do
  that they share many properties, including logarithmic time complexity. Erlang
  `:sets` (version 2) are implemented on top of maps, so see the documentation
  for `Map` for more information on its execution time complexity.
-
-  > #### Dialyzer opaqueness warnings {: .warning}
-  >
-  > `MapSet` internally relies on the `:sets` module which uses
-  > opaque types. This might cause Dialyzer to report opaqueness violations.
-  > These can be silenced by setting the following module attribute: 
-  >   
-  >     @dialyzer :no_opaque
-
  """

  @type value :: term
@@ -210,7 +201,7 @@ defmodule MapSet do
  Checks if two sets are equal.

  The comparison between elements is done using `===/2`,
-  which means a set with `1` is not equivalent to a set with
+  which a set with `1` is not equivalent to a set with
  `1.0`.

  ## Examples
@@ -349,7 +340,7 @@ defmodule MapSet do
  > 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 set at the end using `MapSet.new/1`.
+  > a map at the end using `MapSet.new/1`.

  ## Examples

@@ -405,15 +396,15 @@ defmodule MapSet do
      iex> while_false
      MapSet.new([1, 3])

-      iex> {while_true, while_false} = MapSet.split_with(MapSet.new([10, 20, 60, 70]), fn v -> v > 50 end)
+      iex> {while_true, while_false} = MapSet.split_with(MapSet.new(), fn {_k, v} -> v > 50 end)
      iex> while_true
-      MapSet.new([60, 70])
+      MapSet.new([])
      iex> while_false
-      MapSet.new([10, 20])
+      MapSet.new([])

  """
  @doc since: "1.15.0"
-  @spec split_with(t(a), (a -> as_boolean(term))) :: {t(a), t(a)} when a: value
+  @spec split_with(MapSet.t(), (term() -> as_boolean(term))) :: {MapSet.t(), MapSet.t()}
  def split_with(%MapSet{map: map}, fun) when is_function(fun, 1) do
    {while_true, while_false} = Map.split_with(map, fn {key, _} -> fun.(key) end)
    {%MapSet{map: while_true}, %MapSet{map: while_false}}
@@ -754,7 +754,7 @@ defmodule Module do

  """
  @doc since: "1.12.0"
-  @spec reserved_attributes() :: %{optional(atom()) => %{doc: binary()}}
+  @spec reserved_attributes() :: map
  def reserved_attributes() do
    %{
      after_compile: %{
@@ -1192,7 +1192,7 @@ defmodule Module do
  defp expand_key(key, counters) do
    case counters do
      %{^key => count} when is_integer(count) and count >= 1 ->
-        {{String.to_unsafe_atom("#{key}#{count}"), [], Elixir}, Map.put(counters, key, count - 1)}
+        {{:"#{key}#{count}", [], Elixir}, Map.put(counters, key, count - 1)}

      _ ->
        {{key, [], Elixir}, counters}
@@ -1225,8 +1225,7 @@ defmodule Module do
  defp merge_signature({var, _, _} = older, {var, _, _}, _), do: older

  # Otherwise, returns a generic guess
-  defp merge_signature({_, meta, _}, _newer, i),
-    do: {String.to_unsafe_atom("arg#{i}"), meta, Elixir}
+  defp merge_signature({_, meta, _}, _newer, i), do: {:"arg#{i}", meta, Elixir}

  @doc """
  Checks if the module defines the given function or macro.
@@ -68,37 +68,17 @@ defmodule Module.ParallelChecker do
  def spawn({pid, {checker, table}}, module, module_map, signatures, beam_location, log?) do
    # Protocols may have been consolidated. So if we know their beam location,
    # we discard their module map on purpose and start from file.
-    if beam_location != [] and Keyword.has_key?(module_map.attributes, :__protocol__) do
-      spawn_and_register_cache(pid, checker, table, module, List.to_string(beam_location), log?)
-    else
-      {mode, module_tuple} = cache_from_module_map(table, module_map, signatures)
-      ref = make_ref()
-      spawned = spawn_checker(ref, pid, checker, table, module, module_tuple, log?)
-      register_cache_and_checker(checker, mode, module, spawned, ref)
-      :ok
-    end
-  end
-
-  defp spawn_checker(ref, pid, checker, table, module, module_tuple, log?) do
-    spawn(fn ->
-      mon_ref = Process.monitor(pid)
-
-      receive do
-        {^ref, :check, profile} ->
-          # Set the compiler info so we can collect warnings
-          Process.link(pid)
-          :erlang.put(:elixir_compiler_info, {pid, self()})
-          {warnings, errors} = check_module(module_tuple, {checker, table}, log?, profile)
-          send(pid, {__MODULE__, module, warnings, errors})
-          send(checker, {__MODULE__, :checked, ref})
-
-        {:DOWN, ^mon_ref, _, _, _} ->
-          :ok
+    info =
+      if beam_location != [] and Keyword.has_key?(module_map.attributes, :__protocol__) do
+        List.to_string(beam_location)
+      else
+        cache_from_module_map(table, module_map, signatures)
      end
-    end)
+
+    inner_spawn(pid, checker, table, module, info, log?)
  end

-  defp spawn_and_register_cache(pid, checker, table, module, info, log?) do
+  defp inner_spawn(pid, checker, table, module, info, log?) do
    ref = make_ref()

    spawned =
@@ -109,28 +89,48 @@ defmodule Module.ParallelChecker do
          {^ref, :cache} ->
            Process.link(pid)

-            location =
-              case :code.which(module) do
-                [_ | _] = path -> path
-                _ -> info
+            {mode, module_tuple} =
+              cond do
+                is_binary(info) ->
+                  location =
+                    case :code.which(module) do
+                      [_ | _] = path -> path
+                      _ -> info
+                    end
+
+                  with {:ok, binary} <- File.read(location),
+                       {:ok,
+                        {_, [{:debug_info, {:debug_info_v1, backend, data}}, {~c"ExCk", checker}]}} <-
+                         :beam_lib.chunks(binary, [:debug_info, ~c"ExCk"]),
+                       {:ok, module_map} <- backend.debug_info(:elixir_v1, module, data, []),
+                       {@elixir_checker_version, contents} <- :erlang.binary_to_term(checker) do
+                    {cache_chunk(table, module, contents), module_map_to_module_tuple(module_map)}
+                  else
+                    _ -> {:uncached, nil}
+                  end
+
+                is_tuple(info) ->
+                  info
              end

-            with {:ok, binary} <- File.read(location),
-                 {:ok, {_, [{:debug_info, {:debug_info_v1, backend, data}}, {~c"ExCk", exck}]}} <-
-                   :beam_lib.chunks(binary, [:debug_info, ~c"ExCk"]),
-                 {:ok, module_map} <- backend.debug_info(:elixir_v1, module, data, []),
-                 {@elixir_checker_version, contents} <- :erlang.binary_to_term(exck) do
-              mode = cache_chunk(table, module, contents)
-              module_tuple = module_map_to_module_tuple(module_map)
-              spawned = spawn_checker(ref, pid, checker, table, module, module_tuple, log?)
-              :ets.insert(table, {module, mode})
-              send(checker, {__MODULE__, :cached, module, spawned, ref})
-            else
-              _ ->
-                # Nothing to check, so we notify everyone we are done
-                :ets.insert(table, {module, :uncached})
-                send(checker, {__MODULE__, :cached, module, nil, ref})
-                send(pid, {__MODULE__, module, [], []})
+            # We only make the module available now, so they are not visible during inference
+            :ets.insert(table, {module, mode})
+            send(checker, {ref, :cached})
+
+            receive do
+              {^ref, :check, profile} ->
+                # Set the compiler info so we can collect warnings
+                :erlang.put(:elixir_compiler_info, {pid, self()})
+
+                {warnings, errors} =
+                  if module_tuple do
+                    check_module(module_tuple, {checker, table}, log?, profile)
+                  else
+                    {[], []}
+                  end
+
+                send(pid, {__MODULE__, module, warnings, errors})
+                send(checker, {__MODULE__, :done, module})
            end

          {:DOWN, ^mon_ref, _, _, _} ->
@@ -138,7 +138,7 @@ defmodule Module.ParallelChecker do
        end
      end)

-    register_cache(checker, module, spawned, ref)
+    register(checker, module, spawned, ref)
    :ok
  end

@@ -192,7 +192,7 @@ defmodule Module.ParallelChecker do
    log? = not match?({_, false}, value)

    for {module, file} <- runtime_files do
-      spawn_and_register_cache(self(), checker, table, module, file, log?)
+      inner_spawn(self(), checker, table, module, file, log?)
    end

    count = :gen_server.call(checker, :start, :infinity)
@@ -533,12 +533,8 @@ defmodule Module.ParallelChecker do
    :gen_server.call(server, {:unlock, module, mode}, :infinity)
  end

-  defp register_cache_and_checker(server, mode, module, pid, ref) do
-    :gen_server.cast(server, {:register_cache_and_checker, mode, module, pid, ref})
-  end
-
-  defp register_cache(server, module, pid, ref) do
-    :gen_server.cast(server, {:register_cache, module, pid, ref})
+  defp register(server, module, pid, ref) do
+    :gen_server.cast(server, {:register, module, pid, ref})
  end

  ## Server callbacks
@@ -581,8 +577,7 @@ defmodule Module.ParallelChecker do

    state = %{
      waiting: %{},
-      caches: [],
-      checkers: [],
+      modules: [],
      spawned: %{},
      schedulers: schedulers,
      threshold: threshold,
@@ -595,9 +590,20 @@ defmodule Module.ParallelChecker do
    :gen_server.enter_loop(__MODULE__, [], state)
  end

-  def handle_call(:start, _from, %{caches: caches, protocols: protocols, table: table} = state) do
+  def handle_call(:start, _from, %{modules: modules, protocols: protocols, table: table} = state) do
    :ets.insert(table, Enum.map(protocols, &{&1, :uncached}))
-    {:reply, length(caches), run_caches(%{state | protocols: []})}
+
+    for {_module, pid, ref} <- modules do
+      send(pid, {ref, :cache})
+    end
+
+    for {_module, _pid, ref} <- modules do
+      receive do
+        {^ref, :cached} -> :ok
+      end
+    end
+
+    {:reply, length(modules), run_checkers(%{state | protocols: []})}
  end

  def handle_call({:lock, module}, from, %{waiting: waiting} = state) do
@@ -627,21 +633,10 @@ defmodule Module.ParallelChecker do
    {:noreply, state}
  end

-  def handle_info({__MODULE__, :cached, module, pid, ref}, state) do
-    {_nil, spawned} = Map.pop(state.spawned, ref)
-
-    state =
-      if pid do
-        %{state | spawned: spawned, checkers: [{module, pid, ref} | state.checkers]}
-      else
-        %{state | spawned: spawned}
-      end
-
-    {:noreply, run_caches(state)}
-  end
-
-  def handle_info({__MODULE__, :checked, ref}, state) do
-    {timer, spawned} = Map.pop(state.spawned, ref)
+  def handle_info({__MODULE__, :done, module}, state) do
+    # Unfortunately we cannot assume uniqueness because the same module
+    # may be defined by mistake several times
+    {timer, spawned} = Map.pop(state.spawned, module)
    timer && Process.cancel_timer(timer)
    {:noreply, run_checkers(%{state | spawned: spawned})}
  end
@@ -650,41 +645,11 @@ defmodule Module.ParallelChecker do
    {:stop, :normal, state}
  end

-  def handle_cast({:register_cache, module, pid, ref}, %{caches: caches} = state) do
-    {:noreply, %{state | caches: [{module, pid, ref} | caches]}}
+  def handle_cast({:register, module, pid, ref}, %{modules: modules} = state) do
+    {:noreply, %{state | modules: [{module, pid, ref} | modules]}}
  end

-  def handle_cast(
-        {:register_cache_and_checker, mode, module, pid, ref},
-        %{caches: caches, checkers: checkers} = state
-      ) do
-    {:noreply,
-     %{state | caches: [{module, mode} | caches], checkers: [{module, pid, ref} | checkers]}}
-  end
-
-  defp run_caches(%{caches: [], spawned: spawned} = state) do
-    if spawned == %{}, do: run_checkers(state), else: state
-  end
-
-  defp run_caches(%{spawned: spawned, schedulers: schedulers} = state)
-       when map_size(spawned) >= schedulers do
-    state
-  end
-
-  defp run_caches(%{caches: [cache | caches]} = state) do
-    case cache do
-      {_module, pid, ref} ->
-        send(pid, {ref, :cache})
-        spawned = Map.put(state.spawned, ref, nil)
-        run_caches(%{state | caches: caches, spawned: spawned})
-
-      {module, mode} ->
-        :ets.insert(state.table, {module, mode})
-        run_caches(%{state | caches: caches})
-    end
-  end
-
-  defp run_checkers(%{checkers: []} = state) do
+  defp run_checkers(%{modules: []} = state) do
    state
  end

@@ -693,11 +658,11 @@ defmodule Module.ParallelChecker do
    state
  end

-  defp run_checkers(%{checkers: [{module, pid, ref} | checkers]} = state) do
+  defp run_checkers(%{modules: [{module, pid, ref} | modules]} = state) do
    send(pid, {ref, :check, state.profile})
    timer = :erlang.send_after(state.threshold, self(), {__MODULE__, :timeout, module, pid})
-    spawned = Map.put(state.spawned, ref, timer)
-    run_checkers(%{state | checkers: checkers, spawned: spawned})
+    spawned = Map.put(state.spawned, module, timer)
+    run_checkers(%{state | modules: modules, spawned: spawned})
  end

  defp profile(module, :time, fun) do
@@ -232,7 +232,7 @@ defmodule Module.Types do

    context =
      Enum.reduce(defs, context(), fn {fun_arity, _kind, meta, _clauses} = def, context ->
-        # Optimized version of finder, since we already have the definition
+        # Optimized version of finder, since we already the definition
        finder = fn _ -> default_domain(:dynamic, def, fun_arity, impl) end
        {_kind, _inferred, context} = local_handler(meta, fun_arity, stack, context, finder)
        context
@@ -251,23 +251,27 @@ defmodule Module.Types do
      context ->
        {_kind, info, mapping} = Map.fetch!(context.local_sigs, fun_arity)

-        {used_indexes, unused_indexes} =
-          Enum.reduce(mapping, {[], []}, fn {clause_index, type_index},
-                                            {used_indexes, unused_indexes} ->
-            if type_index in pending and not skip_unused_clause?(info, type_index) do
-              {used_indexes, [clause_index | unused_indexes]}
-            else
-              {[clause_index | used_indexes], unused_indexes}
-            end
+        if pending != [] do
+          {used_indexes, unused_indexes} =
+            Enum.reduce(mapping, {[], []}, fn {clause_index, type_index},
+                                              {used_indexes, unused_indexes} ->
+              if type_index in pending and not skip_unused_clause?(info, type_index) do
+                {used_indexes, [clause_index | unused_indexes]}
+              else
+                {[clause_index | used_indexes], unused_indexes}
+              end
+            end)
+
+          unused_indexes = Enum.uniq(unused_indexes) -- used_indexes
+
+          Enum.reduce(unused_indexes, context, fn clause_index, context ->
+            {meta, _args, _guards, _body} = Enum.fetch!(clauses, clause_index)
+            stack = %{stack | function: fun_arity} |> with_file_meta(meta)
+            Helpers.warn(__MODULE__, {:unused_clause, kind, fun_arity}, meta, stack, context)
          end)
-
-        unused_indexes = Enum.uniq(unused_indexes) -- used_indexes
-
-        Enum.reduce(unused_indexes, context, fn clause_index, context ->
-          {meta, _args, _guards, _body} = Enum.fetch!(clauses, clause_index)
-          stack = %{stack | function: fun_arity} |> with_file_meta(meta)
-          Helpers.warn(__MODULE__, {:unused_clause, kind, fun_arity}, meta, stack, context)
-        end)
+        else
+          context
+        end
    end
  end

@@ -394,15 +398,16 @@ defmodule Module.Types do
  end

  defp infer_local_handler(clauses, base_info, kind, fun, expected, stack, context) do
-    {_, clauses_types, clauses_context} =
-      Enum.reduce(clauses, {Pattern.init_previous(), [], context}, fn
-        {meta, args, guards, body}, {previous, inferred, acc_context} ->
+    {_, _, _, domain, mapping, clauses_types, clauses_context} =
+      Enum.reduce(clauses, {0, 0, Pattern.init_previous(), [], [], [], context}, fn
+        {meta, args, guards, body},
+        {index, total, previous, domain, mapping, inferred, acc_context} ->
          stack = with_file_meta(stack, meta)
          fresh_context = fresh_context(acc_context)
          info = {base_info, args, guards}

          try do
-            {trees, precise?, head_no_previous_args_types, previous, head_context} =
+            {trees, _precise?, head_no_previous_args_types, previous, head_context} =
              Pattern.of_head(args, guards, expected, previous, info, meta, stack, fresh_context)

            {return_type, context} =
@@ -410,88 +415,42 @@ defmodule Module.Types do

            args_types = Pattern.of_domain(trees, stack, context)

-            head_args_types =
-              case inferred do
-                [] -> nil
-                _ -> Pattern.of_domain(trees, stack, head_context)
+            {type_index, inferred} =
+              add_inferred(inferred, args_types, return_type, total - 1, [])
+
+            domain =
+              case domain do
+                [] ->
+                  args_types
+
+                _ ->
+                  head_args_types = Pattern.of_domain(trees, stack, head_context)
+                  compute_domain(args_types, head_args_types, head_no_previous_args_types, domain)
              end

-            args_triplet = {args_types, head_args_types, head_no_previous_args_types}
-            inferred = [{args_triplet, return_type, precise?} | inferred]
-            {previous, inferred, context}
+            if type_index == -1 do
+              mapping = [{index, total} | mapping]
+              {index + 1, total + 1, previous, domain, mapping, inferred, context}
+            else
+              mapping = [{index, type_index} | mapping]
+              {index + 1, total, previous, domain, mapping, inferred, context}
+            end
          rescue
            e ->
              internal_error!(e, __STACKTRACE__, kind, meta, fun, args, guards, body, stack)
          end
      end)

-    {clauses_types, mapping, domain} =
-      clauses_types
-      |> Enum.reverse()
-      |> group_clauses()
-
    domain =
      case clauses_types do
        [_] -> nil
        _ -> domain
      end

-    inferred = {:infer, domain, clauses_types}
+    inferred = {:infer, domain, Enum.reverse(clauses_types)}
    {inferred, mapping, restore_context(clauses_context, context)}
  end

-  defp group_clauses(clauses) do
-    {_, all_clauses, filtered_clauses, non_empty?} =
-      Enum.reduce(clauses, {0, [], [], false}, fn
-        {_args_triplet, return, precise?} = clause,
-        {index, all_clauses, filtered_clauses, non_empty?} ->
-          empty? = Descr.empty?(return)
-          indexed_clause = {clause, index}
-
-          filtered_clauses =
-            if precise? and empty? do
-              filtered_clauses
-            else
-              [indexed_clause | filtered_clauses]
-            end
-
-          {index + 1, [indexed_clause | all_clauses], filtered_clauses, non_empty? or not empty?}
-      end)
-
-    clauses =
-      if non_empty? do
-        Enum.reverse(filtered_clauses)
-      else
-        Enum.reverse(all_clauses)
-      end
-
-    [
-      {{{args, _head_args, _head_no_previous_args}, _return, _precise?}, _index}
-      | clauses_tail
-    ] = clauses
-
-    domain =
-      Enum.reduce(clauses_tail, args, fn
-        {{{args, head_args, head_no_previous_args}, _return, _precise?}, _index}, domain ->
-          compute_domain(args, head_args, head_no_previous_args, domain)
-      end)
-
-    {_, mapping, inferred} =
-      Enum.reduce(clauses, {0, [], []}, fn
-        {{{args, _head_args, _head_no_previous_args}, return, _precise?}, index},
-        {total, mapping, inferred} ->
-          {type_index, inferred} = add_inferred(inferred, args, return, total - 1, [])
-
-          if type_index == -1 do
-            {total + 1, [{index, total} | mapping], inferred}
-          else
-            {total, [{index, type_index} | mapping], inferred}
-          end
-      end)
-
-    {Enum.reverse(inferred), mapping, domain}
-  end
-
  defp compute_domain(
         [arg | args_types],
         [head_arg | head_args_types],
@@ -40,13 +40,7 @@ defmodule Module.Types.Apply do
  fas = list(tuple([atom(), integer()]))

  struct_info =
-    list(
-      closed_map(
-        default: {term(), true},
-        field: {atom(), false},
-        required: {boolean(), true}
-      )
-    )
+    list(closed_map(default: if_set(term()), field: atom(), required: if_set(boolean())))

  shared_info = [
    attributes: list(tuple([atom(), list(term())])),
@@ -118,15 +112,7 @@ defmodule Module.Types.Apply do

  args_or_arity = opt_union(list(term()), integer())
  args_or_none = opt_union(list(term()), atom([:none]))
-  custom_info_key = opt_difference(atom(), atom([:file, :line, :error_info]))
-
-  extra_info =
-    list(
-      tuple([atom([:file]), opt_union(list(integer()), binary())])
-      |> opt_union(tuple([atom([:line]), integer()]))
-      |> opt_union(tuple([atom([:error_info]), open_map()]))
-      |> opt_union(tuple([custom_info_key, term()]))
-    )
+  extra_info = kw.(file: list(integer()), line: integer(), error_info: open_map())

  raise_stacktrace =
    list(
@@ -151,8 +137,6 @@ defmodule Module.Types.Apply do
      {[atom([left]), atom([right])], atom([left or right])}
    end

-  non_empty_tuple = opt_difference(open_tuple([]), tuple([]))
-
  for {mod, fun, clauses} <- [
        # :binary
        {:binary, :copy, [{[binary(), integer()], binary()}]},
@@ -230,38 +214,35 @@ defmodule Module.Types.Apply do
        {:erlang, :spawn_link, [{mfargs, pid()}]},
        {:erlang, :spawn_monitor, [{[fun(0)], tuple([pid(), reference()])}]},
        {:erlang, :spawn_monitor, [{mfargs, tuple([pid(), reference()])}]},
-        {:erlang, :split_binary,
-         [
-           {[binary(), integer()], tuple([binary(), binary()])},
-           {[bitstring_no_binary(), integer()], tuple([binary(), bitstring_no_binary()])}
-         ]},
+        {:erlang, :split_binary, [{[binary(), integer()], tuple([binary(), binary()])}]},
        {:erlang, :tuple_size, [{[open_tuple([])], integer()}]},
        {:erlang, :trunc, [{[opt_union(integer(), float())], integer()}]},
+
+        # TODO: Replace term()/dynamic() by parametric types
        {:erlang, :++,
         [
           {[empty_list(), term()], dynamic(term())},
           {[non_empty_list(term()), term()], dynamic(non_empty_list(term(), term()))}
         ]},
        {:erlang, :--, [{[list(term()), list(term())], dynamic(list(term()))}]},
-        {:erlang, :delete_element, [{[integer(), non_empty_tuple], dynamic(open_tuple([]))}]},
+        {:erlang, :delete_element, [{[integer(), open_tuple([])], dynamic(open_tuple([]))}]},
        {:erlang, :hd, [{[non_empty_list(term(), term())], dynamic()}]},
-        {:erlang, :element, [{[integer(), non_empty_tuple], dynamic()}]},
+        {:erlang, :element, [{[integer(), open_tuple([])], dynamic()}]},
        {:erlang, :insert_element,
-         [{[integer(), open_tuple([]), term()], dynamic(non_empty_tuple)}]},
+         [{[integer(), open_tuple([]), term()], dynamic(open_tuple([]))}]},
        {:erlang, :list_to_tuple, [{[list(term())], dynamic(open_tuple([]))}]},
        {:erlang, :map_get, [{[term(), open_map()], term()}]},
        {:erlang, :max, [{[term(), term()], dynamic()}]},
        {:erlang, :min, [{[term(), term()], dynamic()}]},
        {:erlang, :send, [{[send_destination, term()], dynamic()}]},
-        {:erlang, :setelement,
-         [{[integer(), non_empty_tuple, term()], dynamic(non_empty_tuple)}]},
+        {:erlang, :setelement, [{[integer(), open_tuple([]), term()], dynamic(open_tuple([]))}]},
        {:erlang, :tl, [{[non_empty_list(term(), term())], dynamic()}]},
        {:erlang, :tuple_to_list, [{[open_tuple([])], dynamic(list(term()))}]},

        ## Kernel
-        {Kernel, :elem, [{[non_empty_tuple, integer()], dynamic()}]},
+        {Kernel, :elem, [{[open_tuple([]), integer()], dynamic()}]},
        {Kernel, :is_map_key, [{[open_map(), term()], boolean()}]},
-        {Kernel, :put_elem, [{[non_empty_tuple, integer(), term()], dynamic(non_empty_tuple)}]},
+        {Kernel, :put_elem, [{[open_tuple([]), integer(), term()], dynamic(open_tuple([]))}]},

        ## Lists
        {:lists, :member,
@@ -275,8 +256,7 @@ defmodule Module.Types.Apply do
        {Map, :fetch,
         [{[open_map(), term()], tuple([atom([:ok]), term()]) |> opt_union(atom([:error]))}]},
        {Map, :fetch!, [{[open_map(), term()], term()}]},
-        {Map, :from_struct,
-         [{[open_map(__struct__: {atom(), false})], open_map(__struct__: {none(), true})}]},
+        {Map, :from_struct, [{[open_map()], open_map(__struct__: not_set())}]},
        {Map, :get, [{[open_map(), term()], term()}]},
        {Map, :get, [{[open_map(), term(), term()], term()}]},
        {Map, :get_lazy, [{[open_map(), term(), fun(0)], term()}]},
@@ -293,9 +273,9 @@ defmodule Module.Types.Apply do
        {Map, :replace_lazy, [{[open_map(), term(), fun(1)], open_map()}]},
        {Map, :update, [{[open_map(), term(), term(), fun(1)], open_map()}]},
        {Map, :update!, [{[open_map(), term(), fun(1)], open_map()}]},
-        {Tuple, :delete_at, [{[non_empty_tuple, integer()], dynamic(open_tuple([]))}]},
+        {Tuple, :delete_at, [{[open_tuple([]), integer()], dynamic(open_tuple([]))}]},
        {Tuple, :duplicate, [{[term(), integer()], tuple()}]},
-        {Tuple, :insert_at, [{[open_tuple([]), integer(), term()], dynamic(non_empty_tuple)}]},
+        {Tuple, :insert_at, [{[open_tuple([]), integer(), term()], dynamic(open_tuple([]))}]},
        {:maps, :from_keys, [{[list(term()), term()], open_map()}]},
        {:maps, :find,
         [{[term(), open_map()], tuple([atom([:ok]), term()]) |> opt_union(atom([:error]))}]},
@@ -466,14 +446,9 @@ defmodule Module.Types.Apply do
    #     a and not number(), b and not number() -> a and b
    #
    # However, during inference, we type it as `a, b -> a and b` only.
-    # Either argument may be discarded based on term ordering, so the result's
-    # expected type cannot be used to refine either argument. The result itself
-    # flows directly to the consumer, so it can still be contextually refined.
-    {left_type, context} = of_fun.(left, term(), expr, stack, context)
-    {right_type, context} = of_fun.(right, term(), expr, stack, context)
+    {left_type, context} = of_fun.(left, expected, expr, stack, context)
+    {right_type, context} = of_fun.(right, expected, expr, stack, context)
    result = opt_union(left_type, right_type)
-    refined_result = opt_intersection(result, expected)
-    result = if empty?(refined_result), do: result, else: refined_result

    if error = mismatched_ordered_comparison(left_type, right_type, stack) do
      remote_error(error, :erlang, name, 2, expr, stack, context)
@@ -1017,71 +992,61 @@ defmodule Module.Types.Apply do
    info =
      {:strong, [term(), open_map()],
       [
-         {[term(), open_map([{key, {term(), false}}])], atom([true])},
-         {[term(), open_map([{key, {none(), true}}])], atom([false])}
+         {[term(), open_map([{key, term()}])], atom([true])},
+         {[term(), open_map([{key, not_set()}])], atom([false])}
       ]}

    {info, filter_domain(info, expected, 2), context}
  end

-  def remote_domain(:maps, :is_key, [key, map], expected, meta, stack, context)
-      when is_atom(key) do
-    remote_domain(:erlang, :is_map_key, [key, map], expected, meta, stack, context)
-  end
-
  def remote_domain(Kernel, :is_map_key, [_map, key], expected, _meta, _stack, context)
      when is_atom(key) do
    info =
      {:strong, [open_map(), term()],
       [
-         {[open_map([{key, {term(), false}}]), term()], atom([true])},
-         {[open_map([{key, {none(), true}}]), term()], atom([false])}
+         {[open_map([{key, term()}]), term()], atom([true])},
+         {[open_map([{key, not_set()}]), term()], atom([false])}
       ]}

    {info, filter_domain(info, expected, 2), context}
  end

-  def remote_domain(Map, :has_key?, [map, key], expected, meta, stack, context)
-      when is_atom(key) do
-    remote_domain(Kernel, :is_map_key, [map, key], expected, meta, stack, context)
-  end
-
  def remote_domain(:erlang, :map_get, [key, _], expected, _meta, _stack, context)
      when is_atom(key) do
-    domain = [term(), open_map([{key, {expected, false}}])]
+    domain = [term(), open_map([{key, expected}])]
    {{:strong, nil, [{domain, term()}]}, domain, context}
  end

  def remote_domain(Map, :fetch!, [_, key], expected, _meta, _stack, context) when is_atom(key) do
-    domain = [open_map([{key, {expected, false}}]), term()]
+    domain = [open_map([{key, expected}]), term()]
    {{:strong, nil, [{domain, term()}]}, domain, context}
  end

  def remote_domain(:maps, :get, [key, _], expected, _meta, _stack, context) when is_atom(key) do
-    domain = [term(), open_map([{key, {expected, false}}])]
+    domain = [term(), open_map([{key, expected}])]
    {{:strong, nil, [{domain, term()}]}, domain, context}
  end

  def remote_domain(Map, :replace!, [_, key, _], _expected, _meta, _stack, context)
      when is_atom(key) do
-    domain = [open_map([{key, {term(), false}}]), term(), term()]
+    domain = [open_map([{key, term()}]), term(), term()]
    {{:strong, nil, [{domain, open_map()}]}, domain, context}
  end

  def remote_domain(:maps, :update, [key, _, _], _expected, _meta, _stack, context)
      when is_atom(key) do
-    domain = [term(), term(), open_map([{key, {term(), false}}])]
+    domain = [term(), term(), open_map([{key, term()}])]
    {{:strong, nil, [{domain, open_map()}]}, domain, context}
  end

  def remote_domain(Map, :pop!, [_, key], _expected, _meta, _stack, context) when is_atom(key) do
-    domain = [open_map([{key, {term(), false}}]), term()]
+    domain = [open_map([{key, term()}]), term()]
    {{:strong, nil, [{domain, tuple([term(), open_map()])}]}, domain, context}
  end

  def remote_domain(Map, :update!, [_, key, _], _expected, _meta, _stack, context)
      when is_atom(key) do
-    domain = [open_map([{key, {term(), false}}]), term(), fun(1)]
+    domain = [open_map([{key, term()}]), term(), fun(1)]
    {{:strong, nil, [{domain, open_map()}]}, domain, context}
  end

@@ -1121,10 +1086,6 @@ defmodule Module.Types.Apply do
    end
  end

-  defp remote_apply(:erlang, :element, info, [_index, tuple] = args_types, stack) do
-    remote_apply_tuple_element(info, args_types, tuple, stack)
-  end
-
  defp remote_apply(:erlang, :map_get, _info, [key, map] = args_types, stack) do
    case map_get(map, key) do
      {:ok, value} -> {:ok, return(value, args_types, stack)}
@@ -1133,13 +1094,6 @@ defmodule Module.Types.Apply do
    end
  end

-  defp remote_apply(:erlang, :send, info, [_dest, message] = args_types, stack) do
-    case remote_apply(info, args_types, stack) do
-      {:ok, _type} -> {:ok, return(message, args_types, stack)}
-      other -> other
-    end
-  end
-
  defp remote_apply(:erlang, :tl, _info, [list], stack) do
    case list_tl(list) do
      {:ok, value_type} -> {:ok, return(value_type, [list], stack)}
@@ -1147,58 +1101,19 @@ defmodule Module.Types.Apply do
    end
  end

-  defp remote_apply(:erlang, :++, _info, [left, right], stack) do
-    # TODO: remove once we add parametric types, this will just be:
-    # empty_list(), a -> a
-    # non_empty_list(elem), a -> non_empty_list(elem, a)
-    case list_of(left) do
-      {empty_list?, list_of} ->
-        left_result =
-          if empty_list? do
-            right
-          else
-            none()
-          end
-
-        right_result =
-          if list_of do
-            non_empty_list(list_of, right)
-          else
-            none()
-          end
-
-        {:ok, return(opt_union(left_result, right_result), [left, right], stack)}
-
-      :badproperlist ->
-        {:error, badremote(:erlang, :++, [left, right])}
-    end
-  end
-
-  defp remote_apply(Kernel, :elem, info, [tuple, _index] = args_types, stack) do
-    remote_apply_tuple_element(info, args_types, tuple, stack)
-  end
-
  @struct_key atom([:__struct__])
  @nil_atom atom([nil])

-  defp remote_apply(Map, :from_struct, info, [map] = args_types, stack) do
-    case remote_apply(info, args_types, stack) do
-      {:ok, _type} ->
-        case map_update(map, @struct_key, none(), true, false, true) do
-          {_value, descr, _errors} ->
-            {:ok, return(descr, args_types, stack)}
-
-          _ ->
-            {:error, badremote(Map, :from_struct, args_types)}
-        end
-
-      other ->
-        other
+  defp remote_apply(Map, :from_struct, _info, [map] = args_types, stack) do
+    case map_update(map, @struct_key, not_set(), false, true) do
+      {_value, descr, _errors} -> {:ok, return(descr, args_types, stack)}
+      :badmap -> {:error, badremote(Map, :from_struct, args_types)}
+      {:error, _errors} -> {:ok, map}
    end
  end

  defp remote_apply(Map, :delete, _info, [map, key] = args_types, stack) do
-    case map_update(map, key, none(), true, false, true) do
+    case map_update(map, key, not_set(), false, true) do
      {_value, descr, _errors} -> {:ok, return(descr, args_types, stack)}
      :badmap -> {:error, badremote(Map, :delete, args_types)}
      {:error, _errors} -> {:ok, map}
@@ -1275,7 +1190,7 @@ defmodule Module.Types.Apply do
        _ -> args_types
      end

-    case map_update(map, key, none(), true, true, false) do
+    case map_update(map, key, not_set(), true, false) do
      {value, descr, _errors} ->
        value = opt_union(value, default)
        {:ok, return(tuple([value, descr]), args_types, stack)}
@@ -1291,7 +1206,7 @@ defmodule Module.Types.Apply do
  defp remote_apply(Map, :pop_lazy, _info, [map, key, fun] = args_types, stack) do
    case fun_apply(fun, []) do
      {:ok, default} ->
-        case map_update(map, key, none(), true, true, false) do
+        case map_update(map, key, not_set(), true, false) do
          {value, descr, _errors} ->
            value = opt_union(value, default)
            {:ok, return(tuple([value, descr]), args_types, stack)}
@@ -1309,7 +1224,7 @@ defmodule Module.Types.Apply do
  end

  defp remote_apply(Map, :put, _info, [map, key, value] = args_types, stack) do
-    case map_update(map, key, value, false, false, true) do
+    case map_update(map, key, value, false, true) do
      {_value, descr, _errors} -> {:ok, return(descr, args_types, stack)}
      :badmap -> {:error, badremote(Map, :put, args_types)}
      {:error, _errors} -> {:ok, map}
@@ -1317,7 +1232,7 @@ defmodule Module.Types.Apply do
  end

  defp remote_apply(Map, :pop!, _info, [map, key] = args_types, stack) do
-    case map_update(map, key, none(), true, true, false) do
+    case map_update(map, key, not_set(), true, false) do
      {value, descr, _errors} -> {:ok, return(tuple([value, descr]), args_types, stack)}
      :badmap -> {:error, badremote(Map, :pop!, args_types)}
      {:error, _errors} -> {:error, {:badkeydomain, map, key, "raise"}}
@@ -1325,7 +1240,7 @@ defmodule Module.Types.Apply do
  end

  defp remote_apply(Map, :replace, _info, [map, key, value] = args_types, stack) do
-    fun = fn _value, optional? -> {value, optional?} end
+    fun = fn optional?, _type -> if optional?, do: if_set(value), else: value end

    case map_update_fun(map, key, fun, false, false) do
      {_value, descr, _errors} -> {:ok, return(descr, args_types, stack)}
@@ -1335,7 +1250,7 @@ defmodule Module.Types.Apply do
  end

  defp remote_apply(Map, :replace!, _info, [map, key, value] = args_types, stack) do
-    fun = fn _value, optional? -> {value, optional?} end
+    fun = fn optional?, _type -> if optional?, do: if_set(value), else: value end

    case map_update_fun(map, key, fun, false, false) do
      {_value, descr, _errors} -> {:ok, return(descr, args_types, stack)}
@@ -1362,12 +1277,12 @@ defmodule Module.Types.Apply do
          _ -> map
        end

-      fun_apply = fn arg_type, optional? ->
+      fun_apply = fn optional?, arg_type ->
        if empty?(arg_type) do
-          {default, false}
+          default
        else
          case fun_apply(fun, [arg_type]) do
-            {:ok, res} -> {if(optional?, do: opt_union(res, default), else: res), false}
+            {:ok, res} -> if optional?, do: opt_union(res, default), else: res
            reason -> throw({:badapply, reason, [arg_type]})
          end
        end
@@ -1411,6 +1326,7 @@ defmodule Module.Types.Apply do
        if key_type == dynamic() or key_type == term() do
          {:ok, return(open_map(), args_types, stack)}
        else
+          value_type = if_set(value_type)
          domain_keys = to_domain_keys(key_type)

          keys =
@@ -1419,13 +1335,7 @@ defmodule Module.Types.Apply do
              _ -> [domain_keys]
            end

-          map =
-            closed_map(
-              Enum.map(keys, fn
-                key when is_atom(key) -> {key, {value_type, true}}
-                key -> {key, value_type}
-              end)
-            )
+          map = closed_map(Enum.map(keys, &{&1, value_type}))

          map_and_maybe_empty_map =
            case empty_list? do
@@ -1457,7 +1367,7 @@ defmodule Module.Types.Apply do
  end

  defp remote_apply(:maps, :put, _info, [key, value, map] = args_types, stack) do
-    case map_update(map, key, value, false, false, true) do
+    case map_update(map, key, value, false, true) do
      {_value, descr, _errors} -> {:ok, return(descr, args_types, stack)}
      :badmap -> {:error, badremote(:maps, :put, args_types)}
      {:error, _errors} -> {:ok, map}
@@ -1465,7 +1375,7 @@ defmodule Module.Types.Apply do
  end

  defp remote_apply(:maps, :remove, _info, [key, map] = args_types, stack) do
-    case map_update(map, key, none(), true, false, true) do
+    case map_update(map, key, not_set(), false, true) do
      {_value, descr, _errors} -> {:ok, return(descr, args_types, stack)}
      :badmap -> {:error, badremote(:maps, :remove, args_types)}
      {:error, _errors} -> {:ok, map}
@@ -1473,7 +1383,7 @@ defmodule Module.Types.Apply do
  end

  defp remote_apply(:maps, :take, _info, [key, map] = args_types, stack) do
-    case map_update(map, key, none(), true, true, false) do
+    case map_update(map, key, not_set(), true, false) do
      {value, descr, _errors} ->
        result = opt_union(tuple([value, descr]), atom([:error]))
        {:ok, return(result, args_types, stack)}
@@ -1494,7 +1404,7 @@ defmodule Module.Types.Apply do
  end

  defp remote_apply(:maps, :update, _info, [key, value, map] = args_types, stack) do
-    fun = fn _value, optional? -> {value, optional?} end
+    fun = fn optional?, _type -> if optional?, do: if_set(value), else: value end

    case map_update_fun(map, key, fun, false, false) do
      {_value, descr, _errors} -> {:ok, return(descr, args_types, stack)}
@@ -1512,22 +1422,13 @@ defmodule Module.Types.Apply do

  defp remote_apply(mod, :to_existing_atom, info, [_string, list] = args_types, stack)
       when mod in [String, List] do
-    # TODO: remove once we add parametric types, this will just be:
+    # TODO remove once we add parametric types, this will just be:
    # binary(), non_empty_list(a) -> a when a: atom()

    case remote_apply(info, args_types, stack) do
      {:ok, _} ->
-        # If list is a dynamic type, remote_apply only guarantees compatibility,
-        # and therefore we may still have improper lists or lists of dynamic().
-        # Note we cannot have static empty lists, as those would fail on remote_apply,
-        # but we can have dynamic empty lists (which we should ignore)
-        case list_of(list) do
-          {_empty_list, refined_atom} when is_descr(refined_atom) ->
-            {:ok, return(opt_intersection(refined_atom, atom()), args_types, stack)}
-
-          :badproperlist ->
-            {:error, badremote(mod, :to_existing_atom, args_types)}
-        end
+        {false, refined_atom} = list_of(list)
+        {:ok, refined_atom}

      other ->
        other
@@ -1538,21 +1439,6 @@ defmodule Module.Types.Apply do
    remote_apply(info, args_types, stack)
  end

-  defp remote_apply_tuple_element(info, args_types, tuple, stack) do
-    # TODO: Convert this into a regular type signature {...a} and not {}, integer -> a
-    with {:ok, fallback} <- remote_apply(info, args_types, stack) do
-      case tuple_values(tuple) do
-        :badtuple ->
-          # This is not virtually possible, since remote apply validates the arguments.
-          # So returning the fallback is acceptable.
-          {:ok, fallback}
-
-        values ->
-          {:ok, return(values, args_types, stack)}
-      end
-    end
-  end
-
  defp remote_apply(:none, _args_types, _stack) do
    {:ok, dynamic()}
  end
@@ -1880,8 +1766,8 @@ defmodule Module.Types.Apply do

  defp map_put_new(map, key, value, name, args_types, stack) do
    fun = fn
-      type, true -> {opt_union(type, value), false}
-      type, false -> {if(empty?(type), do: value, else: type), false}
+      true, type -> opt_union(type, value)
+      false, type -> if empty?(type), do: value, else: type
    end

    case map_update_fun(map, key, fun, false, true) do
@@ -1899,9 +1785,9 @@ defmodule Module.Types.Apply do
          _ -> map
        end

-      fun_apply = fn arg_type, optional? ->
+      fun_apply = fn optional?, arg_type ->
        case fun_apply(fun, [arg_type]) do
-          {:ok, res} -> {res, optional?}
+          {:ok, res} -> if optional?, do: if_set(res), else: res
          reason -> throw({:badapply, reason, [arg_type]})
        end
      end
@@ -11,44 +11,40 @@ defmodule Module.Types.Expr do
  14 = length(Macro.Env.__info__(:struct))

  aliases = list(tuple([atom(), atom()]))
-  macro_aliases = list(tuple([atom(), tuple([term(), atom()])]))
  functions_and_macros = list(tuple([atom(), list(tuple([atom(), integer()]))]))
  list_of_modules = list(atom())

  @try_catch atom([:error, :exit, :throw])

  @caller closed_map(
-            __struct__: {atom([Macro.Env]), false},
-            aliases: {aliases, false},
-            context: {atom([:match, :guard, nil]), false},
-            context_modules: {list_of_modules, false},
-            file: {binary(), false},
-            function: {opt_union(tuple([atom(), integer()]), atom([nil])), false},
-            functions: {functions_and_macros, false},
-            lexical_tracker: {opt_union(pid(), atom([nil])), false},
-            line: {integer(), false},
-            macro_aliases: {macro_aliases, false},
-            macros: {functions_and_macros, false},
-            module: {atom(), false},
-            requires: {list_of_modules, false},
-            tracers: {list_of_modules, false},
-            versioned_vars: {open_map(), false}
+            __struct__: atom([Macro.Env]),
+            aliases: aliases,
+            context: atom([:match, :guard, nil]),
+            context_modules: list_of_modules,
+            file: binary(),
+            function: opt_union(tuple([atom(), integer()]), atom([nil])),
+            functions: functions_and_macros,
+            lexical_tracker: opt_union(pid(), atom([nil])),
+            line: integer(),
+            macro_aliases: aliases,
+            macros: functions_and_macros,
+            module: atom(),
+            requires: list_of_modules,
+            tracers: list_of_modules,
+            versioned_vars: open_map()
          )

  # We do not make exception dynamic on purpose. If you do a blank rescue,
  # then we will assume you need to statically handle all possible exceptions.
-  @exception open_map(__struct__: {atom(), false}, __exception__: {term(), false})
+  @exception open_map(__struct__: atom(), __exception__: term())

  args_or_arity = opt_union(list(term()), integer())

-  custom_info_key = opt_difference(atom(), atom([:file, :line, :error_info]))
-
  extra_info =
    list(
-      tuple([atom([:file]), opt_union(list(integer()), binary())])
+      tuple([atom([:file]), list(integer())])
      |> opt_union(tuple([atom([:line]), integer()]))
      |> opt_union(tuple([atom([:error_info]), open_map()]))
-      |> opt_union(tuple([custom_info_key, term()]))
    )

  @stacktrace list(
@@ -186,7 +182,7 @@ defmodule Module.Types.Expr do
    expected_pairs =
      Enum.flat_map(pairs_types, fn {key_type, _value_type} ->
        case atom_fetch(key_type) do
-          {:finite, [key]} -> [{key, {term(), false}}]
+          {:finite, [key]} -> [{key, term()}]
          _ -> []
        end
      end)
@@ -625,41 +621,34 @@ defmodule Module.Types.Expr do
      else
        # TODO: Use the collectable protocol for the output
        into = Keyword.get(opts, :into, [])
+        {into_type, into_kind, context} = for_into(into, meta, stack, context)

-        {into_kinds, into_type, expected, context} =
-          for_into(into, meta, expected, stack, context)
-
-        {block_type, context} = of_expr(block, expected, block, stack, context)
-
-        result_type =
-          if :non_empty_list in into_kinds do
-            opt_union(into_type, non_empty_list(block_type))
-          else
-            into_type
-          end
-
-        {result_type, context} =
-          if :bitstring in into_kinds do
+        case into_kind do
+          :bitstring ->
+            {block_type, context} = of_expr(block, bitstring(), block, stack, context)
            intersection = opt_intersection(block_type, bitstring())

-            # TODO: currently if :into is a binary, then we expect the body
-            # to return a binary, even if the binary is a gradual type. This
-            # is ok for now because we only check for bitstring if the type
-            # is a subset of empty_list() or bitstring(), but we may want to
-            # relax in the future.
            if empty?(intersection) do
              error = {:badbitbody, block_type, block, context}
              {error_type(), error(__MODULE__, error, meta, stack, context)}
            else
-              # If into_type is a binary but the block is a bitstring_no_binary(),
-              # then the result may be a bitstring_no_binary().
-              {opt_union(intersection, result_type), context}
+              {opt_union(into_type, intersection), context}
            end
-          else
-            {result_type, context}
-          end

-        {if(gradual?(into_type), do: dynamic(result_type), else: result_type), context}
+          :non_empty_list ->
+            expected =
+              case list_hd(expected) do
+                {:ok, head} -> head
+                _ -> term()
+              end
+
+            {block_type, context} = of_expr(block, expected, block, stack, context)
+            {opt_union(into_type, non_empty_list(block_type)), context}
+
+          :none ->
+            {_, context} = of_expr(block, term(), block, stack, context)
+            {into_type, context}
+        end
        |> dynamic_unless_static(stack)
      end
    end)
@@ -702,9 +691,7 @@ defmodule Module.Types.Expr do
  def of_expr({{:., _, [callee, key_or_fun]}, meta, []} = call, expected, expr, stack, context)
      when not is_atom(callee) and is_atom(key_or_fun) do
    if Keyword.get(meta, :no_parens, false) do
-      {type, context} =
-        of_expr(callee, open_map([{key_or_fun, {expected, false}}]), expr, stack, context)
-
+      {type, context} = of_expr(callee, open_map([{key_or_fun, expected}]), expr, stack, context)
      Of.map_fetch(call, type, key_or_fun, stack, context)
    else
      {type, context} = of_expr(callee, atom(), call, stack, context)
@@ -765,7 +752,7 @@ defmodule Module.Types.Expr do
  defp of_tuple([elem | elems], index, acc, expected, expr, stack, context) do
    expr_expected =
      case tuple_fetch(expected, index) do
-        {_optional?, type} -> type
+        {_, type} -> type
        _ -> term()
      end

@@ -780,7 +767,7 @@ defmodule Module.Types.Expr do
  ## Try

  defp of_rescue(var, exceptions, expr, info, meta, stack, context) do
-    args = [__exception__: {term(), false}]
+    args = [__exception__: term()]

    {structs, context} =
      Enum.map_reduce(exceptions, context, fn exception, context ->
@@ -846,20 +833,13 @@ defmodule Module.Types.Expr do

  @into_compile opt_union(bitstring(), empty_list())

-  defp maybe_list_hd_or_term(expected) do
-    case list_hd(expected) do
-      {:ok, head} -> head
-      _ -> term()
-    end
-  end
+  defp for_into([], _meta, _stack, context),
+    do: {empty_list(), :non_empty_list, context}

-  defp for_into([], _meta, expected, _stack, context),
-    do: {[:non_empty_list], empty_list(), maybe_list_hd_or_term(expected), context}
+  defp for_into(binary, _meta, _stack, context) when is_binary(binary),
+    do: {binary(), :bitstring, context}

-  defp for_into(binary, _meta, _expected, _stack, context) when is_binary(binary),
-    do: {[:bitstring], binary(), bitstring(), context}
-
-  defp for_into(into, meta, expected, stack, context) do
+  defp for_into(into, meta, stack, context) do
    meta =
      case into do
        {_, meta, _} -> meta
@@ -876,26 +856,24 @@ defmodule Module.Types.Expr do
    # We use subtype? instead of compatible because we want to handle
    # only bitstring/list, even if a dynamic with something else is given.
    if subtype?(type, @into_compile) do
-      cond do
-        bitstring_type?(type) ->
-          kinds = if empty_list_type?(type), do: [:bitstring, :non_empty_list], else: [:bitstring]
-          # A comprehension may concatenate the block an arbitrary number of times.
-          # Even if both the initial value and each block are unaligned bitstrings,
-          # repeated concatenation may eventually produce an aligned binary.
-          {kinds, opt_union(binary(), type), bitstring(), context}
+      case {bitstring_type?(type), empty_list_type?(type)} do
+        # If they can be both be true, then we don't know
+        # what the contents of the block are for
+        {true, true} ->
+          type = opt_union(bitstring(), list(term()))
+          {if(gradual?(type), do: dynamic(type), else: type), :none, context}

-        empty_list_type?(type) ->
-          {[:non_empty_list], type, maybe_list_hd_or_term(expected), context}
+        {false, true} ->
+          {type, :non_empty_list, context}

-        # The type is empty...
-        true ->
-          {[], type, term(), context}
+        {true, false} ->
+          {type, :bitstring, context}
      end
    else
      {_type, context} =
        Apply.remote_apply(info, Collectable, :into, [type], expr, stack, context)

-      {[], dynamic(), term(), context}
+      {dynamic(), :none, context}
    end
  end

@@ -1068,7 +1046,7 @@ defmodule Module.Types.Expr do
    do: [{args, return}]

  defp literal_map_update(descr, key_descr, value_descr) do
-    case map_update(descr, key_descr, value_descr, false, false, false) do
+    case map_update(descr, key_descr, value_descr, false, false) do
      {_type, descr, []} -> {:ok, descr}
      {_, _, [error | _]} -> error
      :badmap -> :badmap
@@ -265,7 +265,7 @@ defmodule Module.Types.Of do
    {Function, fun()},
    {Integer, integer()},
    {List, opt_union(empty_list(), non_empty_list(term(), term()))},
-    {Map, open_map(__struct__: {Module.Types.Descr.opt_negation(atom()), true})},
+    {Map, open_map(__struct__: if_set(Module.Types.Descr.opt_negation(atom())))},
    {Port, port()},
    {PID, pid()},
    {Reference, reference()},
@@ -294,7 +294,7 @@ defmodule Module.Types.Of do
    if info = mode == :closed && Code.ensure_loaded?(struct) && struct.__info__(:struct) do
      struct_type(struct, info)
    else
-      open_map(__struct__: {atom([struct]), false})
+      open_map(__struct__: atom([struct]))
    end
  end

@@ -365,7 +365,7 @@ defmodule Module.Types.Of do
                # Because a multiple key may override single keys, we can only
                # collect single keys while there are no multiples.
                [key] when multiple == [] ->
-                  {dynamic?, domain, [{key, {value_type, false}} | single], multiple}
+                  {dynamic?, domain, [{key, value_type} | single], multiple}

                _ ->
                  {dynamic?, domain, single, [{pos, value_type} | multiple]}
@@ -381,10 +381,8 @@ defmodule Module.Types.Of do
          closed_map(non_multiple)

        [{keys, type} | tail] ->
-          products = cartesian_map(tail)
-
-          for key <- keys, product <- products do
-            closed_map(non_multiple ++ [{key, {type, false}} | product])
+          for key <- keys, t <- cartesian_map(tail) do
+            closed_map(non_multiple ++ [{key, type} | t])
          end
          |> Enum.reduce(&opt_union/2)
      end
@@ -393,11 +391,7 @@ defmodule Module.Types.Of do
  end

  defp union_negated([], new_type, single, multiple) do
-    single =
-      Enum.map(single, fn
-        {key, {old_type, optional?}} ->
-          {key, {opt_union(old_type, new_type), optional?}}
-      end)
+    single = Enum.map(single, fn {key, old_type} -> {key, opt_union(old_type, new_type)} end)

    multiple =
      Enum.map(multiple, fn {keys, old_type} -> {keys, opt_union(old_type, new_type)} end)
@@ -407,13 +401,12 @@ defmodule Module.Types.Of do

  defp union_negated(negated, new_type, single, multiple) do
    {single, matched} =
-      Enum.map_reduce(single, [], fn
-        {key, {old_type, optional?}}, matched ->
-          if key in negated do
-            {{key, {old_type, optional?}}, [key | matched]}
-          else
-            {{key, {opt_union(old_type, new_type), optional?}}, matched}
-          end
+      Enum.map_reduce(single, [], fn {key, old_type}, matched ->
+        if key in negated do
+          {{key, old_type}, [key | matched]}
+        else
+          {{key, opt_union(old_type, new_type)}, matched}
+        end
      end)

    multiple =
@@ -421,7 +414,7 @@ defmodule Module.Types.Of do
        {keys, opt_union(old_type, new_type)}
      end)

-    {Enum.map(negated -- matched, fn key -> {key, {none(), true}} end) ++ single, multiple}
+    {Enum.map(negated -- matched, fn key -> {key, not_set()} end) ++ single, multiple}
  end

  defp pairs(pairs, expected, stack, context, of_fun) do
@@ -430,7 +423,7 @@ defmodule Module.Types.Of do

      expected_value_type =
        with {[key], [], []} <- pos_neg_domain,
-             {_optional?, expected_value_type} <- map_fetch_key(expected, key) do
+             {_, expected_value_type} <- map_fetch_key(expected, key) do
          expected_value_type
        else
          _ -> term()
@@ -465,8 +458,7 @@ defmodule Module.Types.Of do
        [[]]

      [{keys, type} | tail] ->
-        products = cartesian_map(tail)
-        for key <- keys, product <- products, do: [{key, {type, false}} | product]
+        for key <- keys, t <- cartesian_map(tail), do: [{key, type} | t]
    end
  end

@@ -488,15 +480,15 @@ defmodule Module.Types.Of do
        Enum.map_reduce(args, context, fn {key, value}, context when is_atom(key) ->
          value_type =
            case map_fetch_key(expected, key) do
-              {_optional?, expected_value_type} -> expected_value_type
+              {_, expected_value_type} -> expected_value_type
              _ -> term()
            end

          {type, context} = of_fun.(value, value_type, stack, context)
-          {{key, {type, false}}, context}
+          {{key, type}, context}
        end)

-      {closed_map([__struct__: {atom([struct]), false}] ++ args_types), context}
+      {closed_map([{:__struct__, atom([struct])} | args_types]), context}
    end
  end

@@ -535,16 +527,9 @@ defmodule Module.Types.Of do
  # we introduce typed structs. They are only used by exceptions.
  def struct_type(struct, info, args_types \\ []) do
    term = dynamic()
-    pairs = for %{field: field} <- info, do: {field, {term, false}}
-    pairs = [{:__struct__, {atom([struct]), false}} | pairs]
-
-    pairs =
-      if args_types == [] do
-        pairs
-      else
-        pairs ++ args_types
-      end
-
+    pairs = for %{field: field} <- info, do: {field, term}
+    pairs = [{:__struct__, atom([struct])} | pairs]
+    pairs = if args_types == [], do: pairs, else: pairs ++ args_types
    closed_map(pairs)
  end

@@ -534,18 +534,14 @@ defmodule Module.Types.Pattern do

  defp of_pattern_tree({:open_map, static, dynamic}, stack, context) do
    dynamic =
-      Enum.map(dynamic, fn {key, value} ->
-        {key, {of_pattern_tree(value, stack, context), false}}
-      end)
+      Enum.map(dynamic, fn {key, value} -> {key, of_pattern_tree(value, stack, context)} end)

    open_map(static ++ dynamic)
  end

  defp of_pattern_tree({:closed_map, static, dynamic}, stack, context) do
    dynamic =
-      Enum.map(dynamic, fn {key, value} ->
-        {key, {of_pattern_tree(value, stack, context), false}}
-      end)
+      Enum.map(dynamic, fn {key, value} -> {key, of_pattern_tree(value, stack, context)} end)

    closed_map(static ++ dynamic)
  end
@@ -725,20 +721,20 @@ defmodule Module.Types.Pattern do

      pairs = Map.new(pairs)
      term = term()
-      static = [__struct__: {atom([struct]), false}]
+      static = [__struct__: atom([struct])]
      dynamic = []

      {static, dynamic} =
        Enum.reduce(info, {static, dynamic}, fn %{field: field}, {static, dynamic} ->
          case pairs do
            %{^field => value_type} when is_descr(value_type) ->
-              {[{field, {value_type, false}} | static], dynamic}
+              {[{field, value_type} | static], dynamic}

            %{^field => value_type} ->
              {static, [{field, value_type} | dynamic]}

            _ ->
-              {[{field, {term, false}} | static], dynamic}
+              {[{field, term} | static], dynamic}
          end
        end)

@@ -776,9 +772,7 @@ defmodule Module.Types.Pattern do
    {refined, context} = of_match_var(var, atom(), expr, stack, context)

    if compatible?(refined, atom()) do
-      fields = [__struct__: {refined, false}]
-      precise? = match?({:_, _, _}, var) or singleton?(refined)
-      of_open_map(args, precise?, fields, [], path, stack, context)
+      of_open_map(args, singleton?(refined), [__struct__: refined], [], path, stack, context)
    else
      error = {:badstruct, refined, expr, context}
      {error_type(), false, error(__MODULE__, error, meta, stack, context)}
@@ -812,12 +806,8 @@ defmodule Module.Types.Pattern do
    version = Keyword.fetch!(meta, :version)

    case Enum.reverse(reverse_path) do
-      [%{root: :key} | _] ->
-        {Of.var(var, context), false, context}
-
-      path ->
-        precise? = singleton?(context.vars[version].type)
-        {{:var, version}, precise?, of_shared_var(var, version, true, path, context)}
+      [%{root: :key} | _] -> {Of.var(var, context), false, context}
+      path -> {{:var, version}, false, of_shared_var(var, version, true, path, context)}
    end
  end

@@ -871,7 +861,7 @@ defmodule Module.Types.Pattern do
          precise? = precise? and value_precise?

          if is_descr(value_type) do
-            {precise?, [{key, {value_type, false}} | static], dynamic, context}
+            {precise?, [{key, value_type} | static], dynamic, context}
          else
            {precise?, static, [{key, value_type} | dynamic], context}
          end
@@ -1175,7 +1165,7 @@ defmodule Module.Types.Pattern do
  # var.field
  def of_guard({{:., _, [callee, key]}, _, []} = map_fetch, expected, expr, stack, context)
      when not is_atom(callee) do
-    {type, context} = of_guard(callee, open_map([{key, {expected, false}}]), expr, stack, context)
+    {type, context} = of_guard(callee, open_map([{key, expected}]), expr, stack, context)
    Of.map_fetch(map_fetch, type, key, stack, context)
  end

@@ -1402,7 +1392,7 @@ defmodule Module.Types.Pattern do
    Apply.remote(:erlang, fun, args, expected, call, stack, context, &of_guard/5)
  end

-  defp unpack_op({{:., _, [_mod, fun]}, _, [left, right]}, fun, acc) do
+  defp unpack_op({{:., _, [:erlang, fun]}, _, [left, right]}, fun, acc) do
    unpack_op(left, fun, unpack_op(right, fun, acc))
  end

@@ -39,7 +39,7 @@ defmodule Node do
  Currently supported options are:

  * `:name_domain` - determines the host name part of the node name. If `:longnames`,
-    fully qualified domain names will be used, which is also the default.
+    fully qualified domain names will be   used which also is the default.
    If `:shortnames`, only the short name of the host will be used.

  * `:net_ticktime` - The tick time to use in seconds. Defaults to the value of the
@@ -47,7 +47,7 @@ defmodule Node do
    See [the `kernel` documentation](https://www.erlang.org/doc/apps/kernel/kernel_app.html)
    for more information.

-  * `:net_tickintensity` - The tick intensity to use. Defaults to the value of the
+  * `net_tickintensity` - The tick intensity to use. Defaults to the value of the
    `net_tickintensity` configuration under Erlang's `kernel` application.
    See [the `kernel` documentation](https://www.erlang.org/doc/apps/kernel/kernel_app.html)
    for more information.
@@ -338,6 +338,8 @@ defmodule Node do

  The default node is `Node.self/0`, the local node. If `node` is the local node,
  the function also sets the cookie of all other unknown nodes to `cookie`.
+
+  This function will raise `FunctionClauseError` if the given `node` is not alive.
  """
  @spec set_cookie(t, atom) :: true
  def set_cookie(node \\ Node.self(), cookie) when is_atom(cookie) do
@@ -43,7 +43,7 @@ defmodule OptionParser do

  defmodule ParseError do
    @moduledoc """
-    An exception raised when parsing an option fails.
+    An exception raised when parsing option fails.

    For example, see `OptionParser.parse!/2`.
    """
@@ -387,7 +387,7 @@ defmodule OptionParser do
        do_parse(rest, config, new_opts, args, invalid, all?)

      {:invalid, option, value, rest} ->
-        # the option exists but it has wrong value
+        # the option exist but it has wrong value
        do_parse(rest, config, opts, args, [{option, value} | invalid], all?)

      {:undefined, option, _value, rest} ->
@@ -463,7 +463,7 @@ defmodule OptionParser do
  defp next_with_config(["--" <> option | rest], config) do
    {option, value} = split_option(option)

-    if String.contains?(option, "_") do
+    if String.contains?(option, ["_"]) do
      {:undefined, "--" <> option, value, rest}
    else
      tagged = tag_option(option, config)
@@ -699,32 +699,6 @@ defmodule Path do
    end
  end

-  @doc """
-  Safely joins two paths.
-
-  Returns `{:ok, path}` if `right` is safe to append to `left`, or `:error`
-  otherwise. See `safe_relative/2` for the exact safety rules applied to `right`.
-
-  ## Examples
-
-      iex> Path.safe_join("foo", "bar")
-      {:ok, "foo/bar"}
-
-      iex> Path.safe_join("foo", "../bar")
-      :error
-
-      iex> Path.safe_join("foo", "/bar")
-      :error
-
-  """
-  @doc since: "1.21.0"
-  @spec safe_join(t, t) :: {:ok, t} | :error
-  def safe_join(left, right) do
-    with {:ok, right} <- safe_relative(right, left) do
-      {:ok, join(left, right)}
-    end
-  end
-
  @doc ~S"""
  Splits the path into a list at the path separator.

@@ -61,7 +61,7 @@ defmodule Port do
    * `{pid, {:connect, new_pid}}` - sets the `new_pid` as the new owner of
      the port. Once a port is opened, the port is linked and connected to the
      caller process and communication to the port only happens through the
-      connected process. This message makes `new_pid` the new connected process.
+      connected process. This message makes `new_pid` the new connected processes.
      Unless the port is dead, the port will reply to the old owner with
      `{port, :connected}`. See `connect/2`.

@@ -88,10 +88,10 @@ defmodule Port do
  > On Unix systems, arguments are passed to a new operating system
  > process as an array of strings but on Windows it is up to the child
  > process to parse them and some Windows programs may apply their own
-  > rules, which are inconsistent with the standard C runtime `argv` parsing.
+  > rules, which are inconsistent with the standard C runtime `argv` parsing
  >
-  > This is particularly troublesome when invoking `.bat`, `.cmd`, or `.com`
-  > files as these run implicitly through `cmd.exe`, whose argument parsing is
+  > This is particularly troublesome when invoking `.bat` or `.com` files
+  > as these run implicitly through `cmd.exe`, whose argument parsing is
  > vulnerable to malicious input and can be used to run arbitrary shell
  > commands.
  >
@@ -99,7 +99,7 @@ defmodule Port do
  > files or `.com` applications, you must not pass untrusted input as
  > arguments to the program. You may avoid accidentally executing them
  > by explicitly passing the extension of the program you want to run,
-  > such as `.exe`, and double-checking the program is indeed not a batch
+  > such as `.exe`, and double check the program is indeed not a batch
  > file or `.com` application.
  >
  > This affects both `spawn` and `spawn_executable`.
@@ -156,7 +156,7 @@ defmodule Port do

  We do not always have control over how third-party software terminates.
  If necessary, one workaround is to wrap the child application in a script that
-  checks whether stdin has been closed. Here is such a script that has been
+  checks whether stdin has been closed.  Here is such a script that has been
  verified to work on bash shells:

      #!/usr/bin/env bash
@@ -79,11 +79,10 @@ defmodule Process do
  @typedoc """
  A process destination.

-  A remote or local PID, a local port, a process alias, a locally registered name,
-  or a tuple in the form of `{registered_name, node}` for a registered name at
-  another node.
+  A remote or local PID, a local port, a locally registered name, or a tuple in
+  the form of `{registered_name, node}` for a registered name at another node.
  """
-  @type dest :: pid | port | alias | (registered_name :: atom) | {registered_name :: atom, node}
+  @type dest :: pid | port | (registered_name :: atom) | {registered_name :: atom, node}

  @doc """
  Tells whether the given process is alive on the local node.
@@ -227,7 +226,7 @@ defmodule Process do
  >
  > The functions `Kernel.exit/1` and `Process.exit/2` are
  > named similarly but provide very different functionalities. The
-  > `Kernel.exit/1` function should be used when the intent is to stop the current
+  > `Kernel:exit/1` function should be used when the intent is to stop the current
  > process while `Process.exit/2` should be used when the intent is to send an
  > exit signal to another process. Note also that `Kernel.exit/1` can be caught
  > with `try/1` while `Process.exit/2` can only be handled by trapping exits and
@@ -340,7 +339,7 @@ defmodule Process do
  @doc """
  Sends a message to the given `dest`.

-  `dest` may be a remote or local PID, a local port, a process alias, a locally
+  `dest` may be a remote or local PID, a local port, a locally
  registered name, or a tuple in the form of `{registered_name, node}` for a
  registered name at another node.

@@ -831,16 +830,12 @@ defmodule Process do

  Inlined by the compiler.
  """
-  @spec flag(:async_dist, boolean) :: boolean
  @spec flag(:error_handler, module) :: module
-  @spec flag(:fullsweep_after, non_neg_integer) :: non_neg_integer
  @spec flag(:max_heap_size, heap_size) :: heap_size
  # :off_heap | :on_heap twice because :erlang.message_queue_data() is not exported
  @spec flag(:message_queue_data, :off_heap | :on_heap) :: :off_heap | :on_heap
  @spec flag(:min_bin_vheap_size, non_neg_integer) :: non_neg_integer
  @spec flag(:min_heap_size, non_neg_integer) :: non_neg_integer
-  @spec flag(:monitor_nodes, term) :: term
-  @spec flag({:monitor_nodes, term}, term) :: term
  @spec flag(:priority, priority_level) :: priority_level
  @spec flag(:save_calls, 0..10_000) :: 0..10_000
  @spec flag(:sensitive, boolean) :: boolean
@@ -1007,7 +1002,7 @@ defmodule Process do
  end

  @doc """
-  Adds a descriptive term to the current process.
+  Add a descriptive term to the current process.

  The term does not need to be unique, and will be shown in Observer and in
  crash logs.
@@ -215,7 +215,7 @@ defmodule Protocol do
        ...
      end

-  If you are using `Mix.install/2`, you can do so by passing the `consolidate_protocols`
+  If you are using `Mix.install/2`, you can do by passing the `consolidate_protocols`
  option:

      Mix.install(
@@ -691,7 +691,7 @@ defmodule Protocol do
          structs_domain =
            case structs do
              [] -> Descr.none()
-              _ -> Descr.open_map(__struct__: {Descr.atom(structs), false})
+              _ -> Descr.open_map(__struct__: Descr.atom(structs))
            end

          domain =
@@ -258,7 +258,7 @@ defmodule Range do
  def size(range)
  def size(first..last//step) when step > 0 and first > last, do: 0
  def size(first..last//step) when step < 0 and first < last, do: 0
-  def size(first..last//step), do: div(last - first, step) + 1
+  def size(first..last//step), do: abs(div(last - first, step)) + 1

  # TODO: Remove me on v2.0
  def size(%{__struct__: Range, first: first, last: last} = range) do
@@ -476,8 +476,8 @@ defmodule Range do
  """
  @doc since: "1.8.0"
  @spec disjoint?(t, t) :: boolean
-  def disjoint?(first1..last1//step1, first2..last2//step2) do
-    if empty?(first1, last1, step1) or empty?(first2, last2, step2) do
+  def disjoint?(first1..last1//step1 = range1, first2..last2//step2 = range2) do
+    if size(range1) == 0 or size(range2) == 0 do
      true
    else
      {first1, last1, step1} = normalize(first1, last1, step1)
@@ -487,7 +487,7 @@ defmodule Range do
        last2 < first1 or last1 < first2 ->
          true

-        step1 == 1 and step2 == 1 ->
+        abs(step1) == 1 and abs(step2) == 1 ->
          false

        true ->
@@ -498,9 +498,9 @@ defmodule Range do

          if rem(first2 - first1, gcd) == 0 do
            c = first1 - first2 + step2 - step1
-            t1 = Integer.floor_div(-c * u, step2)
-            t2 = Integer.floor_div(-c * v, step1)
-            t = max(t1 + 1, t2 + 1)
+            t1 = -c / step2 * u
+            t2 = -c / step1 * v
+            t = max(floor(t1) + 1, floor(t2) + 1)
            x = div(c * u + t * step2, gcd) - 1
            y = div(c * v + t * step1, gcd) - 1

@@ -513,20 +513,9 @@ defmodule Range do
    end
  end

-  @compile inline: [empty?: 3, normalize: 3]
-  defp empty?(first, last, step) do
-    case step > 0 do
-      true -> first > last
-      false -> first < last
-    end
-  end
-
+  @compile inline: [normalize: 3]
  defp normalize(first, last, step) when first > last,
-    do: {first - div(first - last, step) * step, first, -step}
-
-  # A single-element range holds the same element regardless of the step, so
-  # make the step positive to keep the progression in disjoint?/2 increasing.
-  defp normalize(first, last, step) when first == last, do: {first, last, abs(step)}
+    do: {first - abs(div(first - last, step) * step), first, -step}

  defp normalize(first, last, step), do: {first, last, step}

@@ -340,7 +340,7 @@ defmodule Record do
    fields
  end

-  # Normalizes record fields to have default values.
+  # Normalizes of record fields to have default values.
  defp fields(kind, fields) do
    normalizer_fun = fn
      {key, value} when is_atom(key) ->
@@ -615,8 +615,8 @@ defmodule Regex do
  defp safe_run(%Regex{re_pattern: re_pattern} = regex, string, options) do
    # TODO: Remove me when Erlang/OTP 28+ is required
    # This allows regexes precompiled on Erlang/OTP 27- to work on Erlang/OTP 28+
-    with {:re_pattern, _, _, _, <<_::bitstring>>} <- re_pattern,
-         true <- :erlang.system_info(:otp_release) >= [?2, ?8] do
+    with true <- :erlang.system_info(:otp_release) >= [?2, ?8],
+         {:re_pattern, _, _, _, <<_::bitstring>>} <- re_pattern do
      %Regex{source: source, opts: compile_opts} = regex
      :re.run(string, source, compile_opts ++ options)
    else
@@ -22,7 +22,7 @@ defmodule Registry do
  implementation. We explore some of those use cases below.

  The registry may also be transparently partitioned with the `:partitions` option,
-  which provides more scalable behavior for running registries in highly concurrent
+  which provides more scalable behavior for running registries on highly concurrent
  environments with thousands or millions of entries.

  ## Using in `:via`
@@ -79,7 +79,7 @@ defmodule Registry do

  `Registry` has a dispatch mechanism that allows developers to implement custom
  dispatch logic triggered from the caller. For example, let's say we have a
-  duplicate registry started as follows:
+  duplicate registry started as so:

      {:ok, _} = Registry.start_link(keys: :duplicate, name: Registry.DispatcherTest)

@@ -172,7 +172,7 @@ defmodule Registry do
  the cost of delayed unsubscription. For example, if a process crashes,
  its keys are automatically removed from the registry but the change may
  not propagate immediately. This means certain operations may return processes
-  that are already dead. When this can happen, it will be explicitly stated
+  that are already dead. When such may happen, it will be explicitly stated
  in the function documentation.

  However, keep in mind those cases are typically not an issue. After all, a
@@ -218,7 +218,7 @@ defmodule Registry do
  @typedoc "A list of guards to be evaluated when matching on objects in a registry"
  @type guards :: [guard]

-  @typedoc "A pattern used to represent the output format part of a match spec"
+  @typedoc "A pattern used to representing the output format part of a match spec"
  @type body :: [term]

  @typedoc "A full match spec used when selecting objects in the registry"
@@ -230,7 +230,6 @@ defmodule Registry do
          | {:name, registry}
          | {:partitions, pos_integer}
          | {:listeners, [atom]}
-          | {:compressed, boolean}
          | {:meta, [{meta_key, meta_value}]}

  @typedoc """
@@ -240,8 +239,8 @@ defmodule Registry do
  """
  @typedoc since: "1.15.0"
  @type listener_message ::
-          {:register, registry, key, pid, value}
-          | {:unregister, registry, key, pid}
+          {:register, registry, key, registry_partition :: pid, value}
+          | {:unregister, registry, key, registry_partition :: pid}

  @typedoc """
  Options used for `dispatch/4`.
@@ -347,7 +346,7 @@ defmodule Registry do

  The registry requires the following keys:

-    * `:keys` - controls whether keys are `:unique`, `:duplicate`,
+    * `:keys` - chooses if keys are `:unique`, `:duplicate`,
      `{:duplicate, :key}`, or `{:duplicate, :pid}`
    * `:name` - the name of the registry and its tables

@@ -358,8 +357,6 @@ defmodule Registry do
      and unregister events. The registered process must be monitored by the
      listener if the listener wants to be notified if the registered process
      crashes. Messages sent to listeners are of type `t:listener_message/0`.
-    * `:compressed` - turns on compression for registry's keys ETS tables, reducing
-      memory usage at the cost of additional CPU usage. Defaults to `false`.
    * `:meta` - a keyword list of metadata to be attached to the registry.

  For `:duplicate` registries, you can specify the partitioning strategy
@@ -639,7 +636,7 @@ defmodule Registry do
  @doc """
  Finds the `{pid, value}` pair for the given `key` in `registry` in no particular order.

-  Returns an empty list if there is no match.
+  An empty list if there is no match.

  For unique registries, a single partition lookup is necessary. For
  duplicate registries, all partitions must be looked up.
@@ -737,7 +734,7 @@ defmodule Registry do

  This function is useful only when spawning processes is not an option,
  for example, when copying the data to another process could be too
-  expensive, or when the work must be done within the current process
+  expensive. Or when the work must be done within the current process
  for other reasons. In such cases, this function provides a scalable
  mechanism for managing locks on top of the registry's infrastructure.

@@ -751,7 +748,6 @@ defmodule Registry do

  """
  @doc since: "1.18.0"
-  @spec lock(registry, term, (-> result)) :: result when result: var
  def lock(registry, lock_key, function)
      when is_atom(registry) and is_function(function, 0) do
    {_kind, partitions, _, pid_ets, _} = info!(registry)
@@ -772,7 +768,7 @@ defmodule Registry do
  For example the `$1 > 1` guard condition would be expressed as the `{:>, :"$1", 1}` tuple.
  Please note that guard conditions will work only for assigned
  variables like `:"$1"`, `:"$2"`, and so forth.
-  Avoid using of special match variables `:"$_"` and `:"$$"`, because they might not work as expected.
+  Avoid usage of special match variables `:"$_"` and `:"$$"`, because it might not work as expected.

  An empty list will be returned if there is no match.

@@ -842,7 +838,7 @@ defmodule Registry do
      iex> Registry.keys(Registry.UniqueKeysTest, self())
      ["hello"]

-  This is possible for duplicate registries though:
+  Such is possible for duplicate registries though:

      iex> Registry.start_link(keys: :duplicate, name: Registry.DuplicateKeysTest)
      iex> Registry.keys(Registry.DuplicateKeysTest, self())
@@ -1464,12 +1460,12 @@ defmodule Registry do
  end

  @doc """
-  Selects key, pid, and values registered using full match specs.
+  Select key, pid, and values registered using full match specs.

-  The `spec` consists of a list of three-part tuples, in the shape of `[{match_pattern, guards, body}]`.
+  The `spec` consists of a list of three part tuples, in the shape of `[{match_pattern, guards, body}]`.

  The first part, the match pattern, must be a tuple that will match the structure of the
-  data stored in the registry, which is `{key, pid, value}`. The atom `:_` can be used to
+  the data stored in the registry, which is `{key, pid, value}`. The atom `:_` can be used to
  ignore a given value or tuple element, while the atom `:"$1"` can be used to temporarily
  assign part of pattern to a variable for a subsequent comparison. This can be combined
  like `{:"$1", :_, :_}`.
@@ -1481,7 +1477,7 @@ defmodule Registry do
  variables like `:"$1"`, `:"$2"`, and so forth.

  The third part, the body, is a list of shapes of the returned entries. Like guards, you have access to
-  assigned variables like `:"$1"`, which you can combine with hard-coded values to freely shape entries.
+  assigned variables like `:"$1"`, which you can combine with hard-coded values to freely shape entries
  Note that tuples have to be wrapped in an additional tuple. To get a result format like
  `%{key: key, pid: pid, value: value}`, assuming you bound those variables in order in the match part,
  you would provide a body like `[%{key: :"$1", pid: :"$2", value: :"$3"}]`. Like guards, you can use
@@ -1823,7 +1819,7 @@ defmodule Registry.Partition do
  @key_info -2

  @doc """
-  Returns the name of the key partition table.
+  Returns the name of key partition table.
  """
  @spec key_name(atom, non_neg_integer) :: atom
  def key_name(registry, partition) do
@@ -1831,7 +1827,7 @@ defmodule Registry.Partition do
  end

  @doc """
-  Returns the name of the pid partition table.
+  Returns the name of pid partition table.
  """
  @spec pid_name(atom, non_neg_integer) :: atom
  def pid_name(name, partition) do
@@ -1848,7 +1844,7 @@ defmodule Registry.Partition do
  end

  @doc """
-  Runs the function with a lock.
+  Runs function with a lock.
  """
  def lock(pid, key, lock) do
    ref = GenServer.call(pid, {:lock, key})
@@ -234,12 +234,12 @@ defmodule String do
  to the definition of the encoding) is encountered, only one
  code point needs to be rejected.

-  Most functions in this module perform self-synchronization too.
-  For example, `downcase/1` will return a downcased string, with
-  any invalid codepoints preserved at their location.
+  This module relies on this behavior to ignore such invalid
+  characters. For example, `length/1` will return
+  a correct result even if an invalid code point is fed into it.

  In other words, this module expects invalid data to be detected
-  at the boundary, typically when retrieving data from the external source.
+  elsewhere, usually when retrieving data from the external source.
  For example, a driver that reads strings from a database will be
  responsible to check the validity of the encoding. `String.chunk/2`
  can be used for breaking a string into valid and invalid parts.
@@ -935,28 +935,18 @@ defmodule String do
  end

  def upcase(string, :ascii) when is_binary(string) do
-    upcase_ascii(string, string, 0)
+    IO.iodata_to_binary(upcase_ascii(string))
  end

  def upcase(string, mode) when is_binary(string) and mode in @conditional_mappings do
    String.Unicode.upcase(string, [], mode)
  end

-  defp upcase_ascii(<<char, rest::bits>>, original, skip) when char >= ?a and char <= ?z do
-    prefix = binary_part(original, 0, skip)
-    upcase_ascii(rest, <<prefix::binary, char - 32>>)
-  end
+  defp upcase_ascii(<<char, rest::bits>>) when char >= ?a and char <= ?z,
+    do: [char - 32 | upcase_ascii(rest)]

-  defp upcase_ascii(<<_char, rest::bits>>, original, skip),
-    do: upcase_ascii(rest, original, skip + 1)
-
-  defp upcase_ascii(<<>>, original, _skip), do: original
-
-  defp upcase_ascii(<<char, rest::bits>>, acc) when char >= ?a and char <= ?z,
-    do: upcase_ascii(rest, <<acc::binary, char - 32>>)
-
-  defp upcase_ascii(<<char, rest::bits>>, acc), do: upcase_ascii(rest, <<acc::binary, char>>)
-  defp upcase_ascii(<<>>, acc), do: acc
+  defp upcase_ascii(<<char, rest::bits>>), do: [char | upcase_ascii(rest)]
+  defp upcase_ascii(<<>>), do: []

  @doc """
  Converts all characters in the given string to lowercase according to `mode`.
@@ -1015,32 +1005,18 @@ defmodule String do
  end

  def downcase(string, :ascii) when is_binary(string) do
-    downcase_ascii(string, string, 0)
-  end
-
-  def downcase(string, :greek) when is_binary(string) do
-    String.Unicode.downcase_greek(string, [])
+    IO.iodata_to_binary(downcase_ascii(string))
  end

  def downcase(string, mode) when is_binary(string) and mode in @conditional_mappings do
    String.Unicode.downcase(string, [], mode)
  end

-  defp downcase_ascii(<<char, rest::bits>>, original, skip) when char >= ?A and char <= ?Z do
-    prefix = binary_part(original, 0, skip)
-    downcase_ascii(rest, <<prefix::binary, char + 32>>)
-  end
+  defp downcase_ascii(<<char, rest::bits>>) when char >= ?A and char <= ?Z,
+    do: [char + 32 | downcase_ascii(rest)]

-  defp downcase_ascii(<<_char, rest::bits>>, original, skip),
-    do: downcase_ascii(rest, original, skip + 1)
-
-  defp downcase_ascii(<<>>, original, _skip), do: original
-
-  defp downcase_ascii(<<char, rest::bits>>, acc) when char >= ?A and char <= ?Z,
-    do: downcase_ascii(rest, <<acc::binary, char + 32>>)
-
-  defp downcase_ascii(<<char, rest::bits>>, acc), do: downcase_ascii(rest, <<acc::binary, char>>)
-  defp downcase_ascii(<<>>, acc), do: acc
+  defp downcase_ascii(<<char, rest::bits>>), do: [char | downcase_ascii(rest)]
+  defp downcase_ascii(<<>>), do: []

  @doc """
  Converts the first character in the given string to
@@ -1082,39 +1058,19 @@ defmodule String do
  @letter_I_dot_above <<0x0130::utf8>>

  def capitalize(<<@letter_i, right::binary>>, mode) do
-    capitalized = if mode == :turkic, do: @letter_I_dot_above, else: @letter_I
-    capitalized <> downcase_after_capitalize(right, mode, ?i)
+    if(mode == :turkic, do: @letter_I_dot_above, else: @letter_I) <> downcase(right, mode)
  end

  def capitalize(string, mode) when is_binary(string) do
    case :unicode_util.gc(string) do
-      [gc] ->
-        grapheme_to_binary(:string.titlecase([gc]))
-
-      [gc, rest] ->
-        grapheme_to_binary(:string.titlecase([gc])) <>
-          downcase_after_capitalize(rest, mode, gc)
-
-      [gc | rest] ->
-        grapheme_to_binary(:string.titlecase([gc])) <>
-          downcase_after_capitalize(rest, mode, gc)
-
-      [] ->
-        ""
-
-      {:error, <<byte, rest::bits>>} ->
-        <<byte>> <> downcase(rest, mode)
+      [gc] -> grapheme_to_binary(:string.titlecase([gc]))
+      [gc, rest] -> grapheme_to_binary(:string.titlecase([gc])) <> downcase(rest, mode)
+      [gc | rest] -> grapheme_to_binary(:string.titlecase([gc])) <> downcase(rest, mode)
+      [] -> ""
+      {:error, <<byte, rest::bits>>} -> <<byte>> <> downcase(rest, mode)
    end
  end

-  defp downcase_after_capitalize(rest, :greek, gc) do
-    String.Unicode.downcase_greek(rest, [], grapheme_to_binary(gc))
-  end
-
-  defp downcase_after_capitalize(rest, mode, _gc) do
-    downcase(rest, mode)
-  end
-
  @doc false
  @deprecated "Use String.trim_trailing/1 instead"
  defdelegate rstrip(binary), to: String.Break, as: :trim_trailing
@@ -1126,7 +1082,7 @@ defmodule String do
  end

  @doc """
-  Replaces all leading occurrences of `match` by `replacement` in `string`.
+  Replaces all leading occurrences of `match` by `replacement` of `match` in `string`.

  Returns the string untouched if there are no occurrences.

@@ -1770,7 +1726,7 @@ defmodule String do
  end

  defp do_replace(subject, [], _, n) do
-    binary_part(subject, n, byte_size(subject) - n)
+    [binary_part(subject, n, byte_size(subject) - n)]
  end

  defp do_replace(subject, [{start, length} | matches], replacement, n) do
@@ -1828,7 +1784,7 @@ defmodule String do
    do: :unicode.characters_to_binary(acc)

  defp do_reverse({:error, <<byte, rest::bits>>}, acc),
-    do: do_reverse(:unicode_util.gc(rest), []) <> <<byte>> <> :unicode.characters_to_binary(acc)
+    do: :unicode.characters_to_binary(acc) <> <<byte>> <> do_reverse(:unicode_util.gc(rest), [])

  @doc """
  Returns a string `subject` repeated `n` times.
@@ -2454,7 +2410,7 @@ defmodule String do
      ""

  """
-  @spec slice(t, integer, non_neg_integer) :: t
+  @spec slice(t, integer, non_neg_integer) :: grapheme

  def slice(_, _, 0) do
    ""
@@ -3015,17 +2971,15 @@ defmodule String do
  @doc """
  Converts a string to an existing atom or creates a new one.

-  > #### Dynamic Atom Creation {: .warning}
-  >
-  > This function creates atoms dynamically and atoms are
-  > not garbage-collected. Therefore, `string` should not be an
-  > untrusted value, such as input received from a socket or during
-  > a web request. Consider using `to_existing_atom/1` instead.
+  Warning: this function creates atoms dynamically and atoms are
+  not garbage-collected. Therefore, `string` should not be an
+  untrusted value, such as input received from a socket or during
+  a web request. Consider using `to_existing_atom/1` instead.

  By default, the maximum number of atoms is `1_048_576`. This limit
  can be raised or lowered using the VM option `+t`.

-  The maximum atom size is 255 Unicode code points.
+  The maximum atom size is of 255 Unicode code points.

  Inlined by the compiler.

@@ -3047,7 +3001,7 @@ defmodule String do

  If the list of expected atoms is known upfront, prefer `to_existing_atom/2`.

-  The maximum atom size is 255 Unicode code points.
+  The maximum atom size is of 255 Unicode code points.
  Raises an `ArgumentError` if the atom does not exist.

  Inlined by the compiler.
@@ -3214,13 +3168,10 @@ defmodule String do
      0.75
      iex> String.bag_distance("abcd", "abcd")
      1.0
-      iex> String.bag_distance("", "")
-      1.0

  """
  @spec bag_distance(t, t) :: float
  @doc since: "1.8.0"
-  def bag_distance("", ""), do: 1.0
  def bag_distance(_string, ""), do: 0.0
  def bag_distance("", _string), do: 0.0

@@ -88,7 +88,7 @@ defmodule StringIO do
  If options are provided, the result will be `{:ok, pid}`, returning the
  IO device created. The option `:capture_prompt`, when set to `true`, causes
  prompts (which are specified as arguments to `IO.get*` functions) to be
-  included in the device's output. See `open/3` for the list of supported
+  included in the device's output. See `options/3` for the list of supported
  options.

  If a function is provided, the device will be created and sent to the
@@ -1026,10 +1026,10 @@ defmodule System do
  > On Unix systems, arguments are passed to a new operating system
  > process as an array of strings but on Windows it is up to the child
  > process to parse them and some Windows programs may apply their own
-  > rules, which are inconsistent with the standard C runtime `argv` parsing.
+  > rules, which are inconsistent with the standard C runtime `argv` parsing
  >
-  > This is particularly troublesome when invoking `.bat`, `.cmd`, or `.com`
-  > files as these run implicitly through `cmd.exe`, whose argument parsing is
+  > This is particularly troublesome when invoking `.bat` or `.com` files
+  > as these run implicitly through `cmd.exe`, whose argument parsing is
  > vulnerable to malicious input and can be used to run arbitrary shell
  > commands.
  >
@@ -1037,7 +1037,7 @@ defmodule System do
  > files or `.com` applications, you must not pass untrusted input as
  > arguments to the program. You may avoid accidentally executing them
  > by explicitly passing the extension of the program you want to run,
-  > such as `.exe`, and double-checking the program is indeed not a batch
+  > such as `.exe`, and double check the program is indeed not a batch
  > file or `.com` application.

  ## Options
@@ -1248,10 +1248,9 @@ defmodule Task do
        {ref, nil}
      end)

-    ref_count = map_size(refs)
    on_timeout = Keyword.get(opts, :on_timeout, :nothing)
    timeout = Keyword.get(opts, :timeout, 5_000)
-    limit = min(Keyword.get(opts, :limit, ref_count), ref_count)
+    limit = Keyword.get(opts, :limit, map_size(refs))
    timeout_ref = make_ref()

    timer_ref =
@@ -123,8 +123,7 @@ defmodule Task.Supervised do
              args: args,
              reason: {log_value(kind, value), __STACKTRACE__},
              # using :proc_lib over Process because we want the :undefined default, not nil
-              process_label: :proc_lib.get_label(self()),
-              orphan_compiler_module?: orphan_compiler_module?(kind, value)
+              process_label: :proc_lib.get_label(self())
            }
          },
          %{
@@ -139,23 +138,6 @@ defmodule Task.Supervised do
    end
  end

-  defp orphan_compiler_module?(kind, reason) do
-    with :error <- kind,
-         :undef <- reason,
-         {:error_handler, :error_handler} <- :erlang.process_info(self(), :error_handler),
-         {:parent, parent} <- :erlang.process_info(self(), :parent),
-         {:error_handler, Kernel.ErrorHandler} <-
-           (try do
-              :erlang.process_info(parent, :error_handler)
-            rescue
-              _ -> nil
-            end) do
-      true
-    else
-      _ -> false
-    end
-  end
-
  defp exit_reason(:error, reason, stacktrace), do: {reason, stacktrace}
  defp exit_reason(:exit, reason, _stacktrace), do: reason
  defp exit_reason(:throw, reason, stacktrace), do: {{:nocatch, reason}, stacktrace}
@@ -335,8 +317,8 @@ defmodule Task.Supervised do
      # this response when the replying task dies (we'll see this in the :down
      # message).
      {{^monitor_ref, position}, reply} ->
-        %{^position => {:running, _element}} = waiting
-        waiting = Map.put(waiting, position, {:ok, reply})
+        %{^position => {pid, :running, _element}} = waiting
+        waiting = Map.put(waiting, position, {pid, {:ok, reply}})
        stream_reduce({:cont, acc}, max, spawned, delivered, waiting, next, config)

      # The task at position "position" died for some reason. We check if it
@@ -349,18 +331,18 @@ defmodule Task.Supervised do
          case waiting do
            # If the task replied, we don't care whether it went down for timeout
            # or for normal reasons.
-            %{^position => {:ok, _} = ok} ->
+            %{^position => {_, {:ok, _} = ok}} ->
              ok

            # If the task exited by itself before replying, we emit {:exit, reason}.
-            %{^position => {:running, element}}
+            %{^position => {_, :running, element}}
            when kind == :down ->
              if zip_input_on_exit?, do: {:exit, {element, reason}}, else: {:exit, reason}

            # If the task timed out before replying, we either exit (on_timeout: :exit)
            # or emit {:exit, :timeout} (on_timeout: :kill_task) (note the task is already
            # dead at this point).
-            %{^position => {:running, element}}
+            %{^position => {_, :running, element}}
            when kind == :timed_out ->
              if on_timeout == :exit do
                stream_cleanup_inbox(monitor_pid, monitor_ref)
@@ -488,7 +470,7 @@ defmodule Task.Supervised do
    end
  end

-  # This function spawns a task for the given "value", and stores it as running
+  # This function spawns a task for the given "value", and puts the pid of this
  # new task in the map of "waiting" tasks, which is returned.
  defp stream_spawn(value, spawned, waiting, config) do
    %{
@@ -507,7 +489,7 @@ defmodule Task.Supervised do
        mfa_with_value = normalize_mfa_with_arg(mfa, value)
        send(pid, {self(), {monitor_ref, spawned}, self(), callers, mfa_with_value})
        stored_value = if zip_input_on_exit?, do: value, else: nil
-        Map.put(waiting, spawned, {:running, stored_value})
+        Map.put(waiting, spawned, {pid, :running, stored_value})

      {:max_children, ^monitor_ref} ->
        stream_close(config)
@@ -132,12 +132,10 @@ defmodule Tuple do
  """
  @doc since: "1.12.0"
  @spec sum(tuple) :: number()
-  def sum(tuple), do: sum(tuple, 1, tuple_size(tuple) + 1, 0)
+  def sum(tuple), do: sum(tuple, tuple_size(tuple))

-  defp sum(_tuple, top, top, acc), do: acc
-
-  defp sum(tuple, index, top, acc),
-    do: sum(tuple, index + 1, top, acc + :erlang.element(index, tuple))
+  defp sum(_tuple, 0), do: 0
+  defp sum(tuple, index), do: :erlang.element(index, tuple) + sum(tuple, index - 1)

  @doc """
  Computes a product of tuple elements.
@@ -153,12 +151,10 @@ defmodule Tuple do
  """
  @doc since: "1.12.0"
  @spec product(tuple) :: number()
-  def product(tuple), do: product(tuple, 1, tuple_size(tuple) + 1, 1)
+  def product(tuple), do: product(tuple, tuple_size(tuple))

-  defp product(_tuple, top, top, acc), do: acc
-
-  defp product(tuple, index, top, acc),
-    do: product(tuple, index + 1, top, acc * :erlang.element(index, tuple))
+  defp product(_tuple, 0), do: 1
+  defp product(tuple, index), do: :erlang.element(index, tuple) * product(tuple, index - 1)

  @doc """
  Converts a tuple to a list.
@@ -168,8 +168,8 @@ defmodule URI do
  end

  defp encode_kv_pair({key, value}, :rfc3986) do
-    encode_unreserved(Kernel.to_string(key), :percent) <>
-      "=" <> encode_unreserved(Kernel.to_string(value), :percent)
+    encode(Kernel.to_string(key), &char_unreserved?/1) <>
+      "=" <> encode(Kernel.to_string(value), &char_unreserved?/1)
  end

  defp encode_kv_pair({key, value}, :www_form) do
@@ -340,10 +340,6 @@ defmodule URI do
    character in @reserved_characters
  end

-  defguardp unreserved_char?(character)
-            when character in ?0..?9 or character in ?a..?z or character in ?A..?Z or
-                   character in ~c"~_-."
-
  @doc """
  Checks if `character` is an unreserved one in a URI.

@@ -361,7 +357,7 @@ defmodule URI do
  """
  @spec char_unreserved?(byte) :: boolean
  def char_unreserved?(character) do
-    unreserved_char?(character)
+    character in ?0..?9 or character in ?a..?z or character in ?A..?Z or character in ~c"~_-."
  end

  @doc """
@@ -436,31 +432,15 @@ defmodule URI do

  """
  @spec encode_www_form(binary) :: binary
-  def encode_www_form(<<>>), do: ""
-
  def encode_www_form(string) when is_binary(string) do
-    encode_unreserved(string, "", :www_form)
+    for <<byte <- string>>, into: "" do
+      case percent(byte, &char_unreserved?/1) do
+        "%20" -> "+"
+        percent -> percent
+      end
+    end
  end

-  # Matching upfront keeps the empty case from allocating the accumulator.
-  defp encode_unreserved(<<>>, _mode), do: ""
-
-  defp encode_unreserved(string, mode), do: encode_unreserved(string, "", mode)
-
-  defp encode_unreserved(<<?\s, rest::binary>>, acc, :www_form) do
-    encode_unreserved(rest, <<acc::binary, ?+>>, :www_form)
-  end
-
-  defp encode_unreserved(<<byte, rest::binary>>, acc, mode) when unreserved_char?(byte) do
-    encode_unreserved(rest, <<acc::binary, byte>>, mode)
-  end
-
-  defp encode_unreserved(<<byte, rest::binary>>, acc, mode) do
-    encode_unreserved(rest, <<acc::binary, ?%, hex(bsr(byte, 4)), hex(band(byte, 15))>>, mode)
-  end
-
-  defp encode_unreserved(<<>>, acc, _mode), do: acc
-
  defp percent(char, predicate) do
    if predicate.(char) do
      <<char>>
@@ -1059,11 +1039,11 @@ defmodule URI do
    %{uri | query: query}
  end

-  def append_query(%URI{query: current} = uri, query) when is_binary(query) do
-    if String.ends_with?(current, "&") do
-      %{uri | query: current <> query}
+  def append_query(%URI{} = uri, query) when is_binary(query) do
+    if String.ends_with?(uri.query, "&") do
+      %{uri | query: uri.query <> query}
    else
-      %{uri | query: current <> "&" <> query}
+      %{uri | query: uri.query <> "&" <> query}
    end
  end

@@ -81,10 +81,8 @@ defmodule Version do
  allowing us to express `~> 2.1` or `~> 2.1-dev`, something that wouldn't be allowed
  when using the common comparison operators.

-  When the `:allow_pre` option is set `false` in `Version.match?/3`, a pre-release
-  version will not match the `~>`, `>`, and `>=` operators unless the operand is
-  itself a pre-release version. The `<` and `<=` operators are not affected by
-  `:allow_pre` and always match according to precedence.
+  When the `:allow_pre` option is set `false` in `Version.match?/3`, the requirement
+  will not match a pre-release version unless the operand is a pre-release version.
  The default is to always allow pre-releases but note that in
  Hex `:allow_pre` is set to `false`. See the table below for examples.

@@ -101,7 +99,6 @@ defmodule Version do
  `>= 2.1.0`     | `2.2.0-dev` | `true`            | `true`
  `>= 2.1.0`     | `2.2.0-dev` | `false`           | `false`
  `>= 2.1.0-dev` | `2.2.6-dev` | `true` or `false` | `true`
-  `< 2.2.0`      | `2.1.0-dev` | `true` or `false` | `true`

  """

@@ -285,9 +282,8 @@ defmodule Version do

  ## Options

-    * `:allow_pre` (boolean) - when `false`, pre-release versions will not match the
-      `~>`, `>`, and `>=` operators unless the operand is a pre-release version;
-      the `<` and `<=` operators are not affected. Defaults to `true`.
+    * `:allow_pre` (boolean) - when `false`, pre-release versions will not match
+      unless the operand is a pre-release version. Defaults to `true`.
      For examples, please refer to the table above under the "Requirements" section.

  ## Examples
@@ -362,21 +358,11 @@ defmodule Version do

  """
  @spec compare(version, version) :: :gt | :eq | :lt
-  def compare(
-        %Version{major: major1, minor: minor1, patch: patch1, pre: pre1},
-        %Version{major: major2, minor: minor2, patch: patch2, pre: pre2}
-      ) do
-    do_compare(major1, minor1, patch1, pre1, major2, minor2, patch2, pre2)
-  end
-
  def compare(version1, version2) do
-    {major1, minor1, patch1, pre1, _} = to_matchable(version1, true)
-    {major2, minor2, patch2, pre2, _} = to_matchable(version2, true)
-
-    do_compare(major1, minor1, patch1, pre1, major2, minor2, patch2, pre2)
+    do_compare(to_matchable(version1, true), to_matchable(version2, true))
  end

-  defp do_compare(major1, minor1, patch1, pre1, major2, minor2, patch2, pre2) do
+  defp do_compare({major1, minor1, patch1, pre1, _}, {major2, minor2, patch2, pre2, _}) do
    cond do
      major1 > major2 -> :gt
      major1 < major2 -> :lt
@@ -643,17 +629,17 @@ defmodule Version do
    defp require_digits(string) do
      if leading_zero?(string) or byte_size(string) > @max_numeric_component_digits,
        do: :error,
-        else: parse_digits(string)
+        else: parse_digits(string, "")
    end

    defp leading_zero?(<<?0, _, _::binary>>), do: true
    defp leading_zero?(_), do: false

-    defp parse_digits(<<>>), do: :error
+    defp parse_digits(<<char, rest::binary>>, acc) when char in ?0..?9,
+      do: parse_digits(rest, <<acc::binary, char>>)

-    defp parse_digits(string) do
-      if all_digits?(string), do: {:ok, :erlang.binary_to_integer(string)}, else: :error
-    end
+    defp parse_digits(<<>>, acc) when byte_size(acc) > 0, do: {:ok, String.to_integer(acc)}
+    defp parse_digits(_, _acc), do: :error

    defp maybe_patch(patch, approximate?)
    defp maybe_patch(nil, true), do: {:ok, nil}
@@ -677,7 +663,7 @@ defmodule Version do
    end

    defp convert_parts_to_integer([part | rest], acc) do
-      case parse_digits(part) do
+      case parse_digits(part, "") do
        {:ok, integer} ->
          if leading_zero?(part) do
            :error
@@ -197,7 +197,7 @@ iex> MyRequestHandler.parse(%{"status" => "status_not_seen_anywhere", "message"

 By explicitly listing all supported statuses, you guarantee that only a limited number of conversions may happen, and that all expected atoms already exist within the system.

-An alternative is to use pattern matching and explicitly convert each string to its respective atom. This is useful when you need additional logic on different branches:
+An alternative is to use pattern matching and explicitly convert each string to its respective atom. This is useful when you need additional logic on differnt branches:

 ```elixir
 defmodule MyRequestHandler do
@@ -200,7 +200,7 @@ This anti-pattern is of special importance to library authors and whenever writi

  * some frameworks, such as [Phoenix](https://phoenixframework.org), allow developers to raise exceptions in their code and uses a protocol to convert these exceptions into semantic HTTP responses

-In cases where you have a complex algorithm and you must abort in the middle of a computation, you may use `throw` to abort and handle it with a `try/catch`, which was designed explicitly for this purpose. However, you must always catch what you throw, it must never be exposed as part of your library definition.
+This anti-pattern was formerly known as [Using exceptions for control-flow](https://github.com/lucasvegi/Elixir-Code-Smells#using-exceptions-for-control-flow).

 ## Primitive obsession

@@ -380,11 +380,9 @@ If you really need to define modules dynamically, you can do so via meta-program
 defmodule MyMacro do
  defmacro call_examples(parts) do
    for part <- parts do
-      module = Module.concat(OtherModule, part)
-
      quote do
        # This builds OtherModule.Foo at compile-time
-        unquote(module).example()
+        OtherModule.unquote(part).example()
      end
    end
  end
@@ -144,7 +144,7 @@ iex> C.update(agent)

 # state of shared information
 iex> D.get(agent)
-[:atom_value | %{a: 123}]
+[:atom_value, %{a: 123}]
 ```

 For a `GenServer` and other behaviours, this anti-pattern will manifest when scattering calls to `GenServer.call/3` and `GenServer.cast/2` throughout multiple modules, instead of encapsulating all the interaction with the `GenServer` in a single place.
@@ -279,7 +279,7 @@ defmodule Counter do

  @doc "Bumps the value of the given counter."
  def bump(name \\ __MODULE__, value) do
-    Agent.get_and_update(name, fn state -> {state, value + state} end)
+    Agent.get_and_update(fn state -> {state, value + state} end)
  end
 end
 ```
@@ -689,14 +689,14 @@ iex> Enum.map_join(cart, ", ", & &1.fruit)
 "apple, banana, orange"
 ```

-### [`intersperse(enum, separator)`](`Enum.intersperse/2`)
+### [`intersperse(enum, separator \\ "")`](`Enum.intersperse/2`)

 ```elixir
 iex> Enum.intersperse(["apple", "banana", "orange"], ", ")
 ["apple", ", ", "banana", ", ", "orange"]
 ```

-### [`map_intersperse(enum, separator, mapper)`](`Enum.map_intersperse/3`)
+### [`map_intersperse(enum, separator \\ "", mapper)`](`Enum.map_intersperse/3`)

 ```elixir
 iex> Enum.map_intersperse(cart, ", ", & &1.fruit)
@@ -976,7 +976,7 @@ iex> Enum.chunk_every(cart, 2)
 ]
 ```

-### [`chunk_every(enum, count, step, leftover \\ [])`](`Enum.chunk_every/4`)
+### [`chunk_every(enum, count, step, leftover \\ [])`](`Enum.chunk_every/2`)

 ```elixir
 iex> Enum.chunk_every(cart, 2, 2, [:elements, :to_complete])
@@ -1019,7 +1019,7 @@ iex> Enum.zip(fruits, counts)

 See `Enum.zip/1` for zipping many collections at once.

-### [`zip_with(enum1, enum2, fun)`](`Enum.zip_with/3`)
+### [`zip_with(enum1, enum2, fun)`](`Enum.zip_with/2`)

 ```elixir
 iex> fruits = ["apple", "banana", "orange"]
@@ -184,6 +184,8 @@ iex> :zlib.uncompress(compressed)

 If you want to get deeper into Erlang, here's a list of online resources that cover Erlang's fundamentals and its more advanced features:

+  * This [Erlang Syntax: A Crash Course](https://elixir-lang.org/crash-course.html) provides a concise intro to Erlang's syntax. Each code snippet is accompanied by equivalent code in Elixir. This is an opportunity for you to not only get some exposure to Erlang's syntax but also review what you learned about Elixir.
+
  * Erlang's official website has a short [tutorial](https://www.erlang.org/course). There is a chapter with pictures briefly describing Erlang's primitives for [concurrent programming](https://www.erlang.org/course/concurrent_programming.html).

  * [Learn You Some Erlang for Great Good!](https://learnyousomeerlang.com/) is an excellent introduction to Erlang, its design principles, standard library, best practices, and much more. Once you have read through the crash course mentioned above, you'll be able to safely skip the first couple of chapters in the book that mostly deal with the syntax. When you reach [The Hitchhiker's Guide to Concurrency](https://learnyousomeerlang.com/the-hitchhikers-guide-to-concurrency) chapter, that's where the real fun starts.
@@ -29,7 +29,7 @@ For now, let's start by running `iex` (or `iex.bat` if you are on Windows PowerS
 Open up `iex` and type the following expressions:

 ```elixir
-Erlang/OTP 27 [64-bit] [smp:2:2] [...]
+Erlang/OTP 26 [64-bit] [smp:2:2] [...]

 Interactive Elixir - press Ctrl+C to exit
 iex(1)> 40 + 2
--- a/Show More
+++ b/Show More
Author	SHA1	Message	Date
José Valim	42fb7d2be3	Back to take 1	2026-06-25 21:31:19 +02:00
José Valim	332f2ca791	Take 2	2026-06-25 21:00:54 +02:00
José Valim	082e08664e	Take 1	2026-06-25 20:35:34 +02:00