Bump github/codeql-action/init from 4.36.2 to 4.37.9

Bumps [github/codeql-action/init](https://github.com/github/codeql-action) from 4.36.2 to 4.37.9.
- [Release notes](https://github.com/github/codeql-action/releases)
- [Changelog](https://github.com/github/codeql-action/blob/main/CHANGELOG.md)
- [Commits](https://github.com/github/codeql-action/compare/8aad20d150bbac5944a9f9d289da16a4b0d87c1e...cdf488f595d80d6e07e03d4674febd5ab45fa938)

---
updated-dependencies:
- dependency-name: github/codeql-action/init
  dependency-version: 4.37.9
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/ISSUE_TEMPLATE/issue.yml

@@ -3,8 +3,7 @@
 
 ---
 name: Report an issue
-description:
+description: Tell us about something that is not working the way we (probably) intend
-  Tell us about something that is not working the way we (probably) intend
 body:
   - type: markdown
     attributes:
@@ -13,11 +12,17 @@ body:
 
 
         Please, do not use this form for guidance, questions or support.
-        Try instead in [Elixir Forum](https://elixirforum.com),
+        Try instead in [Elixir Forum](https://elixirforum.com) or any of
-        the [IRC Chat](https://web.libera.chat/#elixir),
+        our online communities (Slack, Discord, etc).
-        [Stack Overflow](https://stackoverflow.com/questions/tagged/elixir),
+
-        [Slack](https://elixir-slackin.herokuapp.com),
+  - type: checkboxes
-        [Discord](https://discord.gg/elixir) or in other online communities.
+    id: existing-issue
+    attributes:
+      label: Existing issue
+      description: Please search [existing issues](https://github.com/elixir-lang/elixir/issues) before continuing.
+      options:
+        - label: I have searched existing issues and could not find a duplicate.
+          required: true
 
   - type: textarea
     id: elixir-and-otp-version

.github/pull_request_template.md

@@ -0,0 +1,4 @@
+* 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.

.github/workflows/ci.yml

@@ -26,33 +26,27 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - otp_version: "28.1"
+          - otp_version: "29.0"
             deterministic: true
-          - otp_version: "28.1"
+          - otp_version: "28.4"
-            erlc_opts: "warnings_as_errors"
             docs: true
             coverage: true
+          - otp_version: "28.1"
           - otp_version: "27.3"
-            erlc_opts: "warnings_as_errors"
           - otp_version: "27.0"
-            erlc_opts: "warnings_as_errors"
-          - otp_version: "26.0"
           - otp_version: master
             development: true
           - otp_version: maint
             development: true
 
-    # Earlier Erlang/OTP versions ignored compiler directives
-    # when using warnings_as_errors. So we only set ERLC_OPTS
-    # from Erlang/OTP 27+.
     env:
-      ERLC_OPTS: ${{ matrix.erlc_opts || '' }}
+      ERLC_OPTS: "warnings_as_errors"
     steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
 
-      - uses: erlef/setup-beam@e6d7c94229049569db56a7ad5a540c051a010af9 # v1.20.4
+      - uses: erlef/setup-beam@54075bcc5e249e4758d363f27d099f55d843f124 # v1.24.1
         with:
           otp-version: ${{ matrix.otp_version }}
 
@@ -98,7 +92,7 @@ jobs:
 
       - name: "Upload Coverage Artifact"
         if: ${{ matrix.coverage }}
-        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: TestCoverage
           path: cover/*
@@ -121,19 +115,19 @@ jobs:
     strategy:
       matrix:
         otp_version:
+          - "29.0"
           - "28.1"
           - "27.3"
-          - "26.2"
 
     steps:
       - name: Configure Git
         run: git config --global core.autocrlf input
 
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
 
-      - uses: erlef/setup-beam@e6d7c94229049569db56a7ad5a540c051a010af9 # v1.20.4
+      - uses: erlef/setup-beam@54075bcc5e249e4758d363f27d099f55d843f124 # v1.24.1
         with:
           otp-version: ${{ matrix.otp_version }}
 

.github/workflows/codeql.yml

@@ -28,16 +28,16 @@ jobs:
             build-mode: none
     steps:
       - name: Checkout repository
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
       - name: Initialize CodeQL
-        uses: github/codeql-action/init@89a39a4e59826350b863aa6b6252a07ad50cf83e # v4.32.4
+        uses: github/codeql-action/init@cdf488f595d80d6e07e03d4674febd5ab45fa938 # v4.37.9
         with:
           languages: ${{ matrix.language }}
           build-mode: ${{ matrix.build-mode }}
       - name: Perform CodeQL Analysis
-        uses: github/codeql-action/analyze@89a39a4e59826350b863aa6b6252a07ad50cf83e # v4.32.4
+        uses: github/codeql-action/analyze@8aad20d150bbac5944a9f9d289da16a4b0d87c1e # v4.36.2
         with:
           category: "/language:${{matrix.language}}"
 
@@ -48,8 +48,8 @@ jobs:
       security-events: write
     steps:
       - name: Checkout repository
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
       - name: Run zizmor
-        uses: zizmorcore/zizmor-action@0dce2577a4760a2749d8cfb7a84b7d5585ebcb7d # v0.5.0
+        uses: zizmorcore/zizmor-action@3dc1ecc9bcb9e94e9b2c709687979e1298497054 # v0.6.2

.github/workflows/license_compliance.yml

@@ -27,7 +27,7 @@ jobs:
 
       - name: Checkout project
         id: checkout
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
 

.github/workflows/markdown.yml

@@ -33,9 +33,9 @@ jobs:
       fail-fast: false
 
     steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
 
       - name: Run markdownlint-cli2
-        uses: DavidAnson/markdownlint-cli2-action@07035fd053f7be764496c0f8d8f9f41f98305101 # v22.0.0
+        uses: DavidAnson/markdownlint-cli2-action@21c1be1b93ad9ed58fa840aacc3f279cde2a72ff # v24.2.0

.github/workflows/notify.exs

@@ -74,6 +74,6 @@ unless System.get_env("DRYRUN") do
     "api-username" => "Elixir"
   }
 
-  resp = Req.post!("https://elixirforum.com/posts.json", {:json, post}, headers: headers)
+  resp = Req.post!("https://forum.elixirforum.com/posts.json", {:json, post}, headers: headers)
   IO.puts("#{resp.status} Elixir Forum\n#{inspect(resp.body)}")
 end

.github/workflows/ort/action.yml

@@ -89,9 +89,9 @@ runs:
 
     - name: Run OSS Review Toolkit
       id: ort
-      uses: oss-review-toolkit/ort-ci-github-action@1805edcf1f4f55f35ae6e4d2d9795ccfb29b6021 # v1.1.0
+      uses: oss-review-toolkit/ort-ci-github-action@086d928d24ef1653dc0777296b312fda5faaaf52 # v1.2.0
       with:
-        image: ghcr.io/oss-review-toolkit/ort-minimal:65.0.0
+        image: ghcr.io/oss-review-toolkit/ort:92.2.0
         run: >-
           labels,
           cache-dependencies,
@@ -107,4 +107,6 @@ 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 }}"

.github/workflows/posix_compliance.yml

@@ -32,7 +32,7 @@ jobs:
       fail-fast: false
 
     steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
 

.github/workflows/release.yml

@@ -43,7 +43,7 @@ jobs:
             --draft \
             "$GITHUB_REF_NAME"
 
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         # zizmor: ignore[artipacked]
         if: github.ref_type == 'branch'
 
@@ -71,9 +71,6 @@ jobs:
       fail-fast: true
       matrix:
         include:
-          - otp: 26
-            otp_version: "26.0"
-
           - otp: 27
             otp_version: "27.0"
 
@@ -81,8 +78,11 @@ jobs:
             otp_version: "28.0"
             build_docs: build_docs
 
+          - otp: 29
+            otp_version: "29.0"
+
     steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
 
@@ -100,19 +100,19 @@ jobs:
           shasum -a 256 Docs.zip > Docs.zip.sha256sum
 
       - name: "Upload Linux release artifacts"
-        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: build-linux-elixir-otp-${{ matrix.otp }}
           path: elixir-otp-${{ matrix.otp }}.zip
 
       - name: "Upload Windows release artifacts"
-        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: build-windows-elixir-otp-${{ matrix.otp }}
           path: elixir-otp-${{ matrix.otp }}.exe
 
       - name: "Upload doc artifacts"
-        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         if: matrix.build_docs
         with:
           name: Docs
@@ -125,7 +125,7 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        otp: [26, 27, 28]
+        otp: [27, 28, 29]
         flavor: [windows, linux]
 
     env:
@@ -139,20 +139,20 @@ jobs:
 
     steps:
       - name: "Download build"
-        uses: actions/download-artifact@37930b1c2abaa49bbe596cd826c3c89aef350131 # v7.0.0
+        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
         with:
           name: build-${{ matrix.flavor }}-elixir-otp-${{ matrix.otp }}
 
       - name: Log in to Azure
         if: ${{ matrix.flavor == 'windows' && vars.AZURE_TRUSTED_SIGNING_ACCOUNT_NAME }}
-        uses: azure/login@a457da9ea143d694b1b9c7c869ebb04ebe844ef5 # v2.3.0
+        uses: azure/login@f5d393ae46f8fde4be8b75f32e3fc50e654ad0ca # v3.0.1
         with:
           client-id: ${{ secrets.AZURE_CLIENT_ID }}
           tenant-id: ${{ secrets.AZURE_TENANT_ID }}
           subscription-id: ${{ secrets.AZURE_SUBSCRIPTION_ID }}
 
       - name: "Sign files with Trusted Signing"
-        uses: azure/trusted-signing-action@87c2e83e6868da99d3380aa309851b32ed9a8346 # v1.1.0
+        uses: azure/trusted-signing-action@c7ab2a863ab5f9a846ddb8265964877ef296ee82 # v2.0.0
         if: ${{ matrix.flavor == 'windows' && vars.AZURE_TRUSTED_SIGNING_ACCOUNT_NAME }}
         with:
           endpoint: https://eus.codesigning.azure.net/
@@ -182,7 +182,7 @@ jobs:
           shasum -a 256 "$RELEASE_FILE" > "${RELEASE_FILE}.sha256sum"
 
       - name: "Upload Linux release artifacts"
-        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: sign-${{ matrix.flavor }}-elixir-otp-${{ matrix.otp }}
           path: ${{ env.RELEASE_FILE }}*
@@ -205,13 +205,13 @@ jobs:
 
       - name: Checkout project
         id: checkout
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
 
       - name: "Download Build Artifacts"
         id: download-build-artifacts
-        uses: actions/download-artifact@37930b1c2abaa49bbe596cd826c3c89aef350131 # v7.0.0
+        uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
         with:
           pattern: "{sign-*-elixir-otp-*,Docs}"
           merge-multiple: true
@@ -226,7 +226,7 @@ jobs:
 
       - name: Attest Distribution Assets with SBoM
         id: attest-sbom
-        uses: actions/attest-sbom@4651f806c01d8637787e274ac3bdf724ef169f34 # v3.0.0
+        uses: actions/attest-sbom@c604332985a26aa8cf1bdc465b92731239ec6b9e # v4.1.0
         with:
           subject-path: |
             /tmp/build-artifacts/{elixir-otp-*.*,Docs.zip}
@@ -258,7 +258,7 @@ jobs:
           SBOM_SPDX_JSON: "${{ steps.ort.outputs.results-sbom-spdx-json-path }}"
 
       - name: "Assemble Release SBoM Artifacts"
-        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: "SBoM"
           path: |
@@ -268,7 +268,7 @@ jobs:
             ${{ steps.ort.outputs.results-sbom-spdx-json-path }}
 
       - name: "Assemble Distribution Attestations"
-        uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
           name: "Attestations"
           path: "attestations/*.sigstore"
@@ -282,7 +282,7 @@ jobs:
       contents: write
 
     steps:
-      - uses: actions/download-artifact@37930b1c2abaa49bbe596cd826c3c89aef350131 # v7.0.0
+      - uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
         with:
           pattern: "{sign-*-elixir-otp-*,Docs,SBoM,Attestations}"
           merge-multiple: true
@@ -333,7 +333,7 @@ jobs:
           echo "Required variables for uploading to hex.pm are not set up, skipping..."
           exit 1
 
-      - uses: actions/download-artifact@37930b1c2abaa49bbe596cd826c3c89aef350131 # v7.0.0
+      - uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
         with:
           pattern: "{sign-*-elixir-otp-*,Docs}"
           merge-multiple: true
@@ -356,9 +356,9 @@ jobs:
             echo "builds/elixir/${surrogate_key}" >> purge_keys.txt
 
             if [ "$zip" == "elixir-otp-${oldest_otp}.zip" ]; then
-              aws s3 cp "${zip}" "s3://${AWS_S3_BUCKET}/builds/elixir/${ref_name}.zip" \
+              aws s3 cp "${zip}" "s3://${AWS_S3_BUCKET}/builds/elixir/${GITHUB_REF_NAME}.zip" \
                 --cache-control "public,max-age=3600" \
-                --metadata "{\"surrogate-key\":\"builds builds/elixir builds/elixir/${ref_name}\",\"surrogate-control\":\"public,max-age=604800\"}"
+                --metadata "{\"surrogate-key\":\"builds builds/elixir builds/elixir/${GITHUB_REF_NAME}\",\"surrogate-control\":\"public,max-age=604800\"}"
               echo builds/elixir/${GITHUB_REF_NAME} >> purge_keys.txt
             fi
           done

.github/workflows/release_notifications.yml

@@ -17,11 +17,11 @@ jobs:
     name: Notify
 
     steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
         with:
           persist-credentials: false
 
-      - uses: erlef/setup-beam@e6d7c94229049569db56a7ad5a540c051a010af9 # v1.20.4
+      - uses: erlef/setup-beam@54075bcc5e249e4758d363f27d099f55d843f124 # v1.24.1
         with:
           otp-version: "27.3"
           elixir-version: "1.18.3"

.markdownlint-cli2.jsonc

@@ -5,7 +5,8 @@
     "**/*.md"
   ],
   "ignores": [
-    ".git/**"
+    ".git/**",
+    ".github/**"
   ],
   "gitignore": true,
   "config": {

.ort.yml

@@ -37,6 +37,11 @@ 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"

AGENTS.md

@@ -0,0 +1 @@
+CONTRIBUTING.md

CHANGELOG.md

@@ -4,268 +4,108 @@
   SPDX-FileCopyrightText: 2012 Plataformatec
 -->
 
-# Changelog for Elixir v1.20
+# Changelog for Elixir v1.21
 
-## Type system improvements
+## v1.21.0-dev
-
-This release includes type inference of all constructs.
-
-### Type inference of function definitions
-
-Elixir now performs inference of whole functions. The best way to show the new capabilities are with examples. Take the following code:
-
-```elixir
-def add_foo_and_bar(data) do
-  data.foo + data.bar
-end
-```
-
-Elixir now infers that the function expects a `map` as first argument, and the map must have the keys `.foo` and `.bar` whose values are either `integer()` or `float()`. The return type will be either `integer()` or `float()`.
-
-Here is another example:
-
-```elixir
-def sum_to_string(a, b) do
-  Integer.to_string(a + b)
-end
-```
-
-Even though the `+` operator works with both integers and floats, Elixir infers that `a` and `b` must be both integers, as the result of `+` is given to a function that expects an integer. The inferred type information is then used during type checking to find possible typing errors.
-
-### Type inference of guards
-
-This release also performs inference of guards! Let's see some examples:
-
-```elixir
-def example(x, y) when is_list(x) and is_integer(y)
-```
-
-The code above correctly infers `x` is a list and `y` is an integer.
-
-```elixir
-def example({:ok, x} = y) when is_binary(x) or is_integer(x)
-```
-
-The one above infers x is a binary or an integer, and `y` is a two element tuple with `:ok` as first element and a binary or integer as second.
-
-```elixir
-def example(x) when is_map_key(x, :foo)
-```
-
-The code above infers `x` is a map which has the `:foo` key, represented as `%{..., foo: dynamic()}`. Remember the leading `...` indicates the map may have other keys.
-
-```elixir
-def example(x) when not is_map_key(x, :foo)
-```
-
-And the code above infers `x` does not have the `:foo` key (hence `x.foo` will raise a typing violation), which has the type: `%{..., foo: not_set()}`.
-
-You can also have expressions that assert on the size of data structures:
-
-```elixir
-def example(x) when tuple_size(x) < 3
-```
-
-Elixir will correctly track the tuple has at most two elements, and therefore accessing `elem(x, 3)` will emit a typing violation. In other words, Elixir can look at complex guards, infer types, and use this information to find bugs in our code, without a need to introduce type signatures (yet).
-
-### Typing across clauses
-
-Elixir now infers the type of a given clause based on previous clauses. Let's see an example:
-
-```elixir
-case System.get_env("SOME_VAR") do
-  nil -> :not_found
-  value -> {:ok, String.upcase(value)}
-end
-```
-
-`System.get_env("SOME_VAR")` returns either `nil` or a `binary()`. Because the first clause matches on `nil`, the type system now knows `value` can no longer be `nil`, and therefore it must only be a `binary()`, which allows the second clause to also type check without violations.
-
-This type inference across clauses also helps the type system find redundant clauses and dead code in existing codebases.
-
-### Complete typing of maps keys
-
-Maps were one of the first data-structures we implemented within the Elixir type system however, up to this point, they only supported atom keys. If they had additional keys, those keys were simply marked as `dynamic()`.
-
-As of Elixir v1.20, we can track all possible domains as map keys. For example, the map:
-
-```elixir
-%{123 => "hello", 456.0 => :ok}
-```
-
-will have the type:
-
-```elixir
-%{integer() => binary(), float() => :ok}
-```
-
-It is also possible to mix domain keys, as above, with atom keys, yielding the following:
-
-```elixir
-%{integer() => integer(), root: integer()}
-```
-
-This system is an implementation of [Typing Records, Maps, and Structs, by Giuseppe Castagna (2023)](https://www.irif.fr/~gc/papers/icfp23.pdf).
-
-### Typing of map operations
-
-We have typed the majority of the functions in the `Map` module, allowing the type system to track how keys are added, updated, and removed across all possible key types.
-
-For example, imagine we are calling the following `Map` functions with a variable `map`, which we don't know the exact shape of, and an atom key:
-
-```elixir
-Map.put(map, :key, 123)
-#=> returns type %{..., key: integer()}
-
-Map.delete(map, :key)
-#=> returns type %{..., key: not_set()}
-```
-
-As you can see, we track when keys are set and also when they are removed.
-
-Some operations, like `Map.replace/3`, only replace the key if it exists, and that is also propagated by the type system:
-
-```elixir
-Map.replace(map, :key, 123)
-#=> returns type %{..., key: if_set(integer())}
-```
-
-In other words, if the key exists, it would have been replaced by an integer value. Furthermore, whenever calling a function in the `Map` module and the given key is statically proven to never exist in the map, an error is emitted.
-
-By combining full type inference with bang operations like `Map.fetch!/2`, `Map.pop!/2`, `Map.replace!/3`, and `Map.update!/3`, Elixir is able to propagate information about the desired keys. Take this module:
-
-```elixir
-defmodule User do
-  def name(map), do: Map.fetch!(map, :name)
-end
-
-defmodule CallsUser do
-  def calls_name do
-    User.name(%{})
-  end
-end
-```
-
-The code above has a type violation, which is now caught by the type system:
-
-```text
-    warning: incompatible types given to User.name/1:
-
-        User.name(%{})
-
-    given types:
-
-        %{name: not_set()}
-
-    but expected one of:
-
-        dynamic(%{..., name: term()})
-
-    type warning found at:
-    │
- 16 │     User.name(%{})
-    │         ~
-    │
-    └─ lib/calls_user.ex:7:5: CallsUser.calls_name/0
-```
-
-### Acknowledgements
-
-The type system was made possible thanks to a partnership between [CNRS](https://www.cnrs.fr/) and [Remote](https://remote.com/). The development work is currently sponsored by [Fresha](https://www.fresha.com/) and [Tidewave](https://tidewave.ai/).
-
-## v1.20.0-rc.2 (2026-03-04)
 
 ### 1. Enhancements
 
-#### Elixir
+#### EEx
 
-  * [Code] Add `module_definition: :interpreted` option to `Code` which allows module definitions to be evaluated instead of compiled. In some applications/architectures, this can lead to drastic improvements to compilation times. Note this does not affect the generated `.beam` file, which will have the same performance/behaviour as before
+  * [EEx] Support splitting middle expressions across EEx clauses
-  * [Code] Make module purging opt-in and move temporary module deletion to the background to speed up compilation times
-  * [Integer] Add `Integer.popcount/1`
-  * [Kernel] Move struct validation in patterns and updates to type checker, this means adding and remove struct fields will cause fewer files to be recompiled
-  * [Kernel] Add type inference across clauses. For example, if one clause says `x when is_integer(x)`, then the next clause may no longer be an integer
-  * [Kernel] Detect and warn on redundant clauses
-  * [List] Add `List.first!/1` and `List.last!/1`
-  * Add Software Bill of Materials guide to the Documentation
-
-#### Mix
-
-  * [mix compile] Add `module_definition: :interpreted` option to `Code` which allows module definitions to be evaluated instead of compiled. In some applications/architectures, this can lead to drastic improvements to compilation times. Note this does not affect the generated `.beam` file, which will have the same performance/behaviour as before
-  * [mix deps] Parallelize dep lock status checks during `deps.loadpaths`, improving boot times in projects with many git dependencies
-
-### 2. Potential breaking changes
 
 #### Elixir
 
-  * `map.foo()` (accessing a map field with parens) and `mod.foo` (invoking a function without parens) will now raise instead of emitting runtime warnings, aligning themselves with the type system behaviour
+  * [Access] Add support for keyword lists in `Access.key/2` and `Access.key!/1`
-
+  * [Code] Add support for the `:erlc_options` compiler option
-### 3. Bug fixes
+  * [Code.Formatter] Add a `:migrate_atom_interpolations` option
-
+  * [Kernel] Improve performance of type constructors and complex intersections
-#### IEx
+  * [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
-  * [IEx] Ensure warnings emitted during IEx parsing are properly displayed/printed
+  * [Keyword] Optimize `Keyword.pop/3`, `Keyword.pop!/2`, and `Keyword.pop_lazy/3`
-  * [IEx] Ensure pry works across remote nodes
+  * [List] Add `List.to_existing_atom/2` and `List.to_unsafe_atom/1`
-
+  * [MapSet] Optimize `MapSet.symmetric_difference/2` when set sizes differ
-#### Mix
+  * [Path] Add `Path.safe_join/2`
-
+  * [Registry] Optimize exact key matching in lookups
-  * [mix compile.erlang] Topsort Erlang modules before compilation for proper dependency resolution
+  * [String] Optimize `String.bag_distance/2`
-
+  * [String] Add `String.to_existing_atom/2` and `String.to_unsafe_atom/1`
-## v1.20.0-rc.1 (2026-01-13)
+  * [URI] Optimize percent-decoding and `URI.to_string/1`
-
-### 1. Bug fixes
-
-#### Elixir
-
-  * [Kernel] Improve the performance of the type system when working with large unions of open maps
-  * [Kernel] Do not crash on map types with struct keys when performing type operations
-  * [Kernel] Mark the outcome of bitstring types as dynamic
-  * [Kernel] `<<expr::bitstring>>` will have type `binary` instead of `bitstring` if `expr` is a binary
-  * [Kernel] Do not crash on conditional variables when calling a function on a module which is represented by a variable
-
-## v1.20.0-rc.0 (2026-01-09)
-
-### 1. Enhancements
-
-#### Elixir
-
-  * [Calendar] Optimize `date_from_iso_days` by using the Neri-Schneider algorithm
-  * [Enum] Add `Enum.min_max` sorter
-  * [Integer] Add `Integer.ceil_div/2`
-  * [IO] Add `IO.iodata_empty?/1`
-  * [File] Skip device, named pipes, etc in `File.cp_r/3` instead of erroring with reason `:eio`
-  * [Kernel] Print intermediate results of `dbg` for pipes
-  * [Kernel] Warn on unused requires
-  * [Regex] Add `Regex.import/1` to import regexes defined with `/E`
 
 #### ExUnit
 
-  * [ExUnit.CaptureLog] Add `:formatter` option for custom log formatting
+  * [ExUnit.Assertions] Add `trace/3` helper
 
-#### Mix
+### 2. Bug fixes
-
-  * [mix deps] Support filtering `mix deps` output
-  * [mix compile] Enforce `:elixirc_paths` to be a list of strings to avoid paths from being discarded (the only documented type was lists of strings)
-  * [mix test] Add `mix test --dry-run`
-
-### 2. Potential breaking changes
 
 #### Elixir
 
-  * `require SomeModule` no longer expands to the given module at compile-time, but it still returns the module at runtime. Note that while Elixir does not guarantee macros will expand to certain constructs, but since this can break code relying on the previous behaviour, such as `require(SomeMod).some_macro()`, we are adding this note to the CHANGELOG
+  * [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`
+
+#### 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
 
 #### Elixir
 
-  * [File] `File.stream!(path, modes, lines_or_bytes)` is deprecated in favor of `File.stream!(path, lines_or_bytes, modes)`
+  * [Macro.Env] `Macro.Env.fetch_alias/2` and `Macro.Env.fetch_macro_alias/2` are deprecated, use `Macro.Env.expand_alias/4` instead
-  * [Kernel] Matching on the size inside a bit pattern now requires the pin operator for consistency, such as `<<x::size(^existing_var)>>`
-  * [Kernel.ParallelCompiler] `Kernel.ParallelCompiler.async/1` is deprecated in favor of `Kernel.ParallelCompiler.pmap/2`, which is more performant and addresses known limitations
 
-#### Logger
+### 4. Soft deprecations
 
-  * [Logger] `Logger.*_backend` functions are deprecated in favor of handlers. If you really want to keep on using backends, see the `:logger_backends` package
+#### Elixir
-  * [Logger] `Logger.enable/1` and `Logger.disable/1` have been deprecated in favor of `Logger.put_process_level/2` and `Logger.delete_process_level/1`
 
-## v1.19
+  * [Kernel] Atom interpolation (`:"foo_#{bar}"`) is deprecated in favor of explicit `String.to_unsafe_atom/1`
+  * [List] `List.to_atom/1` is deprecated in favor of `List.to_unsafe_atom/1`
+  * [String] `String.to_atom/1` is deprecated in favor of `String.to_unsafe_atom/1`
 
-The CHANGELOG for v1.19 releases can be found [in the v1.19 branch](https://github.com/elixir-lang/elixir/blob/v1.19/CHANGELOG.md).
+## v1.20
+
+The CHANGELOG for v1.20 releases can be found [in the v1.20 branch](https://github.com/elixir-lang/elixir/blob/v1.20/CHANGELOG.md).

CONTRIBUTING.md

@@ -55,7 +55,7 @@ To recompile all (including Erlang modules):
 make compile
 ```
 
-After your changes are done, please remember to run `make format` to guarantee
+After your changes are done, run `make format` to guarantee
 all files are properly formatted, then run the full suite with
 `make test`.
 
@@ -71,53 +71,67 @@ 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).
 
-We encourage contributors to write tests that capture both existing and newly
+## Sending a pull request
-introduced behavior, especially for bug fixes and major changes:
 
-  * **Bug Fixes:** If you are fixing a bug, please try to include a test that
+Contributions are done [via pull request](https://help.github.com/articles/using-pull-requests/)
-    *fails* before your change and *passes* afterward. This makes it easier to
+and must include tests and other relevant proof of work:
-    confirm that the fix addresses the underlying issue and helps prevent
+
-    regressions in the future.
+  * **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.
 
   * **New Features or Major Changes:** If you are adding a new feature or making
-    major changes to existing functionality, please add tests that cover the
+    major changes to existing functionality, please add assocaited tests. Aim to
-    major parts of that functionality. Aim to have the best code coverage possible.
+    have the best code coverage possible.
 
-With tests running and passing, you are ready to contribute to Elixir and
+  * **Performance improvements:** For performance improvements, please include the
-[send a pull request](https://help.github.com/articles/using-pull-requests/).
+    benchmark script, with inputs and results, in the pull request description.
-We have saved some excellent pull requests we have received in the past in
+    We recommend using [benchee](https://github.com/bencheeorg/benchee).
-case you are looking for some examples:
 
-  * [Implement Enum.member? - Pull request](https://github.com/elixir-lang/elixir/pull/992)
+Here are some pull requests we have received in the past you can use as reference:
 
-  * [Add String.valid? - Pull request](https://github.com/elixir-lang/elixir/pull/1058)
+  * [Implement Enum.member?](https://github.com/elixir-lang/elixir/pull/992)
 
-  * [Implement capture_io for ExUnit - Pull request](https://github.com/elixir-lang/elixir/pull/1059)
+  * [Add String.valid?](https://github.com/elixir-lang/elixir/pull/1058)
+
+  * [Implement capture_io for ExUnit](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.
+If changes are necessary, the team will leave appropriate comments requesting
-
+changes to the code. Unfortunately, we cannot guarantee a pull request will
-All pull requests must be approved by two committers before being merged into
+be merged, even when modifications are requested, as the Elixir team will
-the repository. If changes are necessary, the team will leave appropriate
+re-evaluate the contribution as it changes.
-comments requesting changes to the code. Unfortunately, we cannot guarantee a
-pull request will be merged, even when modifications are requested, as the Elixir
-team will re-evaluate the contribution as it changes.
-
-Committers may also push style changes directly to your branch. If you would
-rather manage all changes yourself, you can disable the "Allow edits from maintainers"
-feature when submitting your pull request.
-
-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
 a comment.
 
+## Building documentation
+
+Building the documentation requires that [ExDoc](https://github.com/elixir-lang/ex_doc)
+is cloned and compiled alongside Elixir.
+
+After cloning and compiling Elixir, run:
+
+```sh
+elixir_dir=$(pwd)
+cd .. && git clone https://github.com/elixir-lang/ex_doc.git
+cd ex_doc && "${elixir_dir}/bin/elixir" "${elixir_dir}/bin/mix" do deps.get + compile
+
+# Now we will go back to Elixir's root directory,
+cd "${elixir_dir}"
+
+# and generate HTML and EPUB documents:
+make docs
+```
+
+This will produce documentation sets for `elixir`, `eex`, `ex_unit`, `iex`, `logger`,
+and `mix` under the `doc` directory. If you are planning to contribute documentation,
+[please check our best practices for writing documentation](https://elixir.hexdocs.pm/writing-documentation.html).
+
 ## Licensing and Compliance Requirements
 
 Please review our [Open Source Policy](OPEN_SOURCE_POLICY.md) for complete
@@ -181,25 +195,50 @@ affecting **all external contributors**:
     See <https://developercertificate.org/> for a copy of the Developer Certificate
     of Origin license.
 
-## Building documentation
+## Using AI and coding agents
 
-Building the documentation requires that [ExDoc](https://github.com/elixir-lang/ex_doc)
+While we allow the use of AI on contributions and discussions, please be mindful
-is installed and built alongside Elixir.
+when doing so. Generally speaking, Elixir maintainers already have access to AI
+(like many other developers). Therefore, if we need the feedback or help of a
+coding agent, we can request so ourselves. For this reason, we often find
+the point of view of the human behind the agent more valuable.
 
-After cloning and compiling Elixir, run:
+That said, here are examples of how one might (or might not) use AI and coding
+agents in Elixir spaces:
 
-```sh
+  * When it comes to discussions, using AI to help express yourself is welcome,
-elixir_dir=$(pwd)
+    but avoid directly copy and pasting AI generated content. If there is a language
-cd .. && git clone https://github.com/elixir-lang/ex_doc.git
+    barrier, use AI to translate, review, and improve your text, but do not use AI
-cd ex_doc && "${elixir_dir}/bin/elixir" "${elixir_dir}/bin/mix" do deps.get + compile
+    to respond on your behalf.
 
-# Now we will go back to Elixir's root directory,
+  * Do not use coding agents to tackle existing issues unless they have the
-cd "${elixir_dir}"
+    "Contributions Welcome" label.
 
-# and generate HTML and EPUB documents:
+  * If you request a feature on the mailing list and it is accepted, you may
-make docs
+    use coding agents to implement it, as long as it follows the AI Contributions
-```
+    guidelines below.
 
-This will produce documentation sets for `elixir`, `eex`, `ex_unit`, `iex`, `logger`,
+  * When automating AI usage on the Elixir codebase for performance improvements,
-and `mix` under the `doc` directory. If you are planning to contribute documentation,
+    security fixes, or correctness changes to the compiler or type system, pair it
-[please check our best practices for writing documentation](https://hexdocs.pm/elixir/writing-documentation.html).
+    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.
+
+### AI contributions
+
+AI agents MUST NOT add Signed-off-by tags. Only humans can legally certify the Developer
+Certificate of Origin (DCO). The human submitter is responsible for:
+
+  * Reviewing all AI-generated code
+  * Ensuring compliance with licensing requirements
+  * Adding their own Signed-off-by tag to certify the DCO
+  * Taking full responsibility for the contribution
+  * Disclosing use of AI for comments and code contributions
+
+When AI tools contribute to Elixir, proper attribution helps track the evolving role of
+AI in the development process. Contributions should include an Assisted-by tag in the
+following format:
+
+    Assisted-by: AGENT_NAME:MODEL_VERSION

Makefile

@@ -32,9 +32,9 @@ SOURCE_DATE_EPOCH_FILE = $(SOURCE_DATE_EPOCH_PATH)/SOURCE_DATE_EPOCH
 #==> Functions
 
 define CHECK_ERLANG_RELEASE
-	erl -noshell -eval '{V,_} = string:to_integer(erlang:system_info(otp_release)), io:fwrite("~s", [is_integer(V) and (V >= 26)])' -s erlang halt | grep -q '^true'; \
+	erl -noshell -eval '{V,_} = string:to_integer(erlang:system_info(otp_release)), io:fwrite("~s", [is_integer(V) and (V >= 27)])' -s erlang halt | grep -q '^true'; \
 		if [ $$? != 0 ]; then \
-		  echo "At least Erlang/OTP 26.0 is required to build Elixir"; \
+		  echo "At least Erlang/OTP 27.0 is required to build Elixir"; \
 		  exit 1; \
 		fi
 endef
@@ -189,7 +189,7 @@ clean_elixir:
 #==> Documentation tasks
 
 SOURCE_REF = $(shell tag="$(call GIT_TAG)" revision="$(call GIT_REVISION)"; echo "$${tag:-$$revision}")
-DOCS_COMPILE = CANONICAL=$(CANONICAL) bin/elixir ../ex_doc/bin/ex_doc "$(1)" "$(VERSION)" "lib/$(2)/ebin" --main "$(3)" --source-url "https://github.com/elixir-lang/elixir" --source-ref "$(call SOURCE_REF)" --logo lib/elixir/pages/images/logo.png --output doc/$(2) --canonical "https://hexdocs.pm/$(2)/$(CANONICAL)" --homepage-url "https://elixir-lang.org/docs.html" $(DOCS_OPTIONS) $(4)
+DOCS_COMPILE = CANONICAL=$(CANONICAL) bin/elixir ../ex_doc/bin/ex_doc "$(1)" "$(VERSION)" "lib/$(2)/ebin" --main "$(3)" --source-url "https://github.com/elixir-lang/elixir" --source-ref "$(call SOURCE_REF)" --logo lib/elixir/pages/images/logo.png --output doc/$(2) --canonical "https://$(2).hexdocs.pm/$(CANONICAL)" --homepage-url "https://elixir-lang.org/docs.html" $(DOCS_OPTIONS) $(4)
 DOCS_CONFIG = bin/elixir lib/elixir/scripts/docs_config.exs "$(1)"
 
 docs: compile ../ex_doc/bin/ex_doc docs_elixir docs_eex docs_mix docs_iex docs_ex_unit docs_logger

README.md

@@ -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/images/logo/logo.png" width="200">
+  <img alt="Elixir logo" src="https://github.com/elixir-lang/elixir-lang.github.com/raw/main/public/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 dynamic, functional language designed for building scalable
+Elixir is a programming language designed for building scalable
 and maintainable applications.
 
 For more about Elixir, installation and documentation,
@@ -122,9 +122,10 @@ variable `ERL_COMPILER_OPTIONS=deterministic`.
 Contributions to Elixir are always welcome! Before you get started, please check
 out our [CONTRIBUTING.md](CONTRIBUTING.md) file. There you will find detailed
 guidelines on how to set up your environment, run the test suite, format your
-code, and submit pull requests. We also include information on our review
+code, and submit pull requests.
-process, licensing requirements, and helpful tips to ensure a smooth
+
-contribution experience.
+Note you must disclose the use of coding agents and AI written code in your
+contributions. See the "Using AI and coding agents" in [CONTRIBUTING.md](CONTRIBUTING.md).
 
 ## Development links
 

SECURITY.md

@@ -12,12 +12,12 @@ Elixir applies bug fixes only to the latest minor branch. Security patches are a
 
 Elixir version | Support
 :------------- | :-----------------------------
-1.20           | Development
+1.21           | Development
-1.19           | Bug fixes and security patches
+1.20           | Bug fixes and security patches
+1.19           | Security patches only
 1.18           | Security patches only
 1.17           | Security patches only
 1.16           | Security patches only
-1.15           | Security patches only
 
 ## Announcements
 

VERSION

@@ -1 +1 @@
-1.20.0-rc.2
+1.21.0-dev

bin/elixir

@@ -6,7 +6,7 @@
 
 set -e
 
-ELIXIR_VERSION=1.20.0-rc.2
+ELIXIR_VERSION=1.21.0-dev
 
 if [ $# -eq 0 ] || { [ $# -eq 1 ] && { [ "$1" = "--help" ] || [ "$1" = "-h" ]; }; }; then
   cat <<USAGE >&2

bin/elixir.bat

@@ -4,7 +4,7 @@
 :: SPDX-FileCopyrightText: 2021 The Elixir Team
 :: SPDX-FileCopyrightText: 2012 Plataformatec
 
-set ELIXIR_VERSION=1.20.0-rc.2
+set ELIXIR_VERSION=1.21.0-dev
 
 if    ""%1""==""""                if ""%2""=="""" goto documentation
 if /I ""%1""==""--help""          if ""%2""=="""" goto documentation

lib/eex/lib/eex.ex

@@ -293,7 +293,7 @@ defmodule EEx do
       "foo baz"
 
   """
-  @spec eval_string(String.t(), keyword, [compile_opt]) :: term()
+  @spec eval_string(String.t(), Code.binding(), [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(), keyword, [compile_opt]) :: String.t()
+  @spec eval_file(Path.t(), Code.binding(), [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)
@@ -344,6 +344,7 @@ 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}}`

lib/eex/lib/eex/compiler.ex

@@ -79,7 +79,7 @@ defmodule EEx.Compiler do
         {:error, message <> code_snippet(state.source, state.indentation, meta), meta}
 
       {:ok, expr, new_line, new_column, rest} ->
-        {key, expr} =
+        {key, expr, extra_meta} =
           case :elixir_tokenizer.tokenize(expr, 1, file: "eex", check_terminators: false) do
             {:ok, _line, _column, _warnings, rev_tokens, []} ->
               # We ignore warnings because the code will be tokenized
@@ -87,7 +87,7 @@ defmodule EEx.Compiler do
               token_key(rev_tokens, expr)
 
             {:error, _, _, _, _} ->
-              {:expr, expr}
+              {:expr, expr, %{}}
           end
 
         marker =
@@ -102,8 +102,8 @@ defmodule EEx.Compiler do
             marker
           end
 
-        token = {key, marker, expr, %{line: line, column: column}}
+        token = {key, marker, expr, Map.merge(%{line: line, column: column}, extra_meta)}
-        trim_and_tokenize(rest, new_line, new_column, state, buffer, acc, &[token | &1])
+        trim_and_tokenize(rest, new_line, new_column, state, buffer, acc, &merge_token(token, &1))
     end
   end
 
@@ -127,6 +127,27 @@ defmodule EEx.Compiler do
     tokenize(rest, line, column, state, [{line, column}], fun.(acc))
   end
 
+  # Merge middle expressions separated only by whitespace so the whitespace is
+  # part of the Elixir expression, not a separate EEx body.
+  defp merge_token(
+         {:middle_expr, ~c"", chars, meta},
+         [{:text, text, text_meta}, {:middle_expr, ~c"", prev_chars, prev_meta} | acc]
+       ) do
+    if only_spaces?(text) and clause_block_identifier?(prev_meta) do
+      [{:middle_expr, ~c"", prev_chars ++ text ++ chars, prev_meta} | acc]
+    else
+      [
+        {:middle_expr, ~c"", chars, meta},
+        {:text, text, text_meta},
+        {:middle_expr, ~c"", prev_chars, prev_meta} | acc
+      ]
+    end
+  end
+
+  defp merge_token(token, acc) do
+    [token | acc]
+  end
+
   # Retrieve marker for <%
 
   defp retrieve_marker([marker | t]) when marker in [?=, ?/, ?|] do
@@ -177,35 +198,37 @@ defmodule EEx.Compiler do
   defp token_key(rev_tokens, expr) do
     case {Enum.reverse(rev_tokens), drop_eol(rev_tokens)} do
       {[{:end, _} | _], [{:do, _} | _]} ->
-        {:middle_expr, expr}
+        {:middle_expr, expr, %{}}
 
       {_, [{:do, _} | _]} ->
-        {:start_expr, maybe_append_space(expr)}
+        {:start_expr, maybe_append_space(expr), %{}}
 
-      {_, [{:block_identifier, _, _} | _]} ->
+      {_, [{:block_identifier, _, identifier} | _]} ->
-        {:middle_expr, maybe_append_space(expr)}
+        {:middle_expr, maybe_append_space(expr), %{block_identifier: identifier}}
 
       {[{:end, _} | _], [{:stab_op, _, _} | _]} ->
-        {:middle_expr, expr}
+        {:middle_expr, expr, %{}}
 
-      {_, [{:stab_op, _, _} | reverse_tokens]} ->
+      {_, [{:stab_op, _, _} | rev_tokens]} ->
-        fn_index = Enum.find_index(reverse_tokens, &match?({:fn, _}, &1)) || :infinity
+        if fn_before_end?(rev_tokens) do
-        end_index = Enum.find_index(reverse_tokens, &match?({:end, _}, &1)) || :infinity
+          {:start_expr, expr, %{}}
-
-        if end_index > fn_index do
-          {:start_expr, expr}
         else
-          {:middle_expr, expr}
+          {:middle_expr, expr, %{}}
         end
 
       {tokens, _} ->
         case Enum.drop_while(tokens, &closing_bracket?/1) do
-          [{:end, _} | _] -> {:end_expr, expr}
+          [{:end, _} | _] -> {:end_expr, expr, %{}}
-          _ -> {:expr, expr}
+          _ -> {:expr, expr, %{}}
         end
     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
 
@@ -303,7 +326,7 @@ defmodule EEx.Compiler do
       file: file,
       source: source,
       line: line,
-      quoted: [],
+      quoted: %{},
       parser_options: [indentation: indentation] ++ parser_options,
       indentation: indentation
     }
@@ -347,7 +370,7 @@ defmodule EEx.Compiler do
         state.parser_options
 
     expr = Code.string_to_quoted!(chars, options)
-    buffer = state.engine.handle_expr(buffer, IO.chardata_to_string(mark), expr)
+    buffer = handle_expr(buffer, mark, expr, meta, state)
     generate_buffer(rest, buffer, scope, state)
   end
 
@@ -366,7 +389,7 @@ defmodule EEx.Compiler do
         rest,
         state.engine.handle_begin(buffer),
         [{contents, start_line, start_column} | scope],
-        %{state | quoted: [], line: line}
+        %{state | quoted: %{}, line: line}
       )
 
     if mark == ~c"" and not match?({:=, _, [_, _]}, contents) do
@@ -376,7 +399,7 @@ defmodule EEx.Compiler do
       IO.warn(message, file: state.file, line: meta.line, column: meta.column)
     end
 
-    buffer = state.engine.handle_expr(buffer, IO.chardata_to_string(mark), contents)
+    buffer = handle_expr(buffer, mark, contents, meta, state)
     generate_buffer(rest, buffer, scope, state)
   end
 
@@ -410,7 +433,7 @@ defmodule EEx.Compiler do
        ) do
     {wrapped, state} = wrap_expr(current, meta.line, buffer, chars, state)
     options = [file: state.file, line: line, column: column] ++ state.parser_options
-    tuples = Code.string_to_quoted!(wrapped, options)
+    tuples = Code.string_to_quoted!(:lists.flatten(wrapped), options)
     buffer = insert_quoted(tuples, state.quoted)
     {buffer, rest}
   end
@@ -426,7 +449,7 @@ defmodule EEx.Compiler do
 
   defp generate_buffer([{:eof, _meta}], _buffer, [{content, line, column} | _scope], state) do
     message = "expected a closing '<% end %>' for block expression in EEx"
-    expr_meta = non_whitespace_meta(content, line, column, state)
+    expr_meta = non_whitespace_meta(:lists.flatten(content), line, column, state)
     syntax_error!(message, expr_meta, state)
   end
 
@@ -443,10 +466,10 @@ defmodule EEx.Compiler do
 
   defp wrap_expr(current, line, buffer, chars, state) do
     new_lines = List.duplicate(?\n, line - state.line)
-    key = length(state.quoted)
+    key = map_size(state.quoted)
-    placeholder = ~c"__EEX__(" ++ Integer.to_charlist(key) ++ ~c");"
+    placeholder = [~c"__EEX__(", Integer.to_charlist(key), ~c");"]
-    count = current ++ placeholder ++ new_lines ++ chars
+    count = [current, placeholder, new_lines, chars]
-    new_state = %{state | quoted: [{key, state.engine.handle_end(buffer)} | state.quoted]}
+    new_state = %{state | quoted: Map.put(state.quoted, key, state.engine.handle_end(buffer))}
 
     {count, new_state}
   end
@@ -476,11 +499,16 @@ defmodule EEx.Compiler do
     Enum.all?(chars, &(&1 in @all_spaces))
   end
 
+  defp clause_block_identifier?(%{block_identifier: identifier}) do
+    identifier in [:else, :rescue, :catch]
+  end
+
+  defp clause_block_identifier?(_meta), do: false
+
   # Changes placeholder to real expression
 
   defp insert_quoted({:__EEX__, _, [key]}, quoted) do
-    {^key, value} = List.keyfind(quoted, key, 0)
+    Map.fetch!(quoted, key)
-    value
   end
 
   defp insert_quoted({left, line, right}, quoted) do
@@ -513,6 +541,20 @@ defmodule EEx.Compiler do
       column: meta.column
   end
 
+  defp handle_expr(buffer, mark, expr, meta, state) do
+    state.engine.handle_expr(buffer, IO.chardata_to_string(mark), expr)
+  rescue
+    e in EEx.SyntaxError ->
+      reraise %{
+                e
+                | file: e.file || state.file,
+                  line: e.line || meta.line,
+                  column: e.column || meta.column,
+                  snippet: e.snippet || code_snippet(state.source, state.indentation, meta)
+              },
+              __STACKTRACE__
+  end
+
   defp code_snippet(source, indentation, meta) do
     line_start = max(meta.line - 3, 1)
     line_end = meta.line

lib/eex/lib/eex/engine.ex

@@ -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(:"arg#{vars_count}", __MODULE__)
+    var = Macro.var(String.to_unsafe_atom("arg#{vars_count}"), __MODULE__)
 
     ast =
       quote do

lib/eex/test/eex/tokenizer_test.exs

@@ -270,7 +270,7 @@ defmodule EEx.TokenizerTest do
       {:text, ~c"foo ", %{column: 1, line: 1}},
       {:start_expr, ~c"", ~c" if true do ", %{column: 5, line: 1}},
       {:text, ~c"bar", %{column: 21, line: 1}},
-      {:middle_expr, ~c"", ~c" else ", %{column: 24, line: 1}},
+      {:middle_expr, ~c"", ~c" else ", %{block_identifier: :else, column: 24, line: 1}},
       {:text, ~c"baz", %{column: 34, line: 1}},
       {:end_expr, ~c"", ~c" end ", %{column: 37, line: 1}},
       {:eof, %{column: 46, line: 1}}
@@ -286,7 +286,7 @@ defmodule EEx.TokenizerTest do
     exprs = [
       {:start_expr, ~c"=", ~c" if true do ", %{column: 2, line: 1}},
       {:text, ~c"\n TRUE \n", %{column: 20, line: 1}},
-      {:middle_expr, ~c"", ~c" else ", %{column: 3, line: 3}},
+      {:middle_expr, ~c"", ~c" else ", %{block_identifier: :else, column: 3, line: 3}},
       {:text, ~c"\n FALSE \n", %{column: 13, line: 3}},
       {:end_expr, ~c"", ~c" end ", %{column: 3, line: 5}},
       {:eof, %{column: 3, line: 7}}

lib/eex/test/eex_test.exs

@@ -262,6 +262,37 @@ defmodule EExTest do
       assert_eval("foo 1,2,3", "foo <% require Enum, as: E %><%= E.join [1, 2, 3], \",\" %>")
     end
 
+    test "with expression with else clause split across tags" do
+      template = """
+      <%= with {:ok, x} <- @res do %>
+        <p><%= x %></p>
+      <% else %>
+        <% _ -> %>
+          <p>bad</p>
+      <% end %>
+      """
+
+      assert_eval("\n  <p>ok</p>\n\n", template, [assigns: [res: {:ok, "ok"}]],
+        engine: EEx.SmartEngine
+      )
+
+      assert_eval("\n    <p>bad</p>\n\n", template, [assigns: [res: :error]],
+        engine: EEx.SmartEngine
+      )
+    end
+
+    test "empty clauses separated by whitespace" do
+      template = """
+      <%= case x do %>
+        <% :foo -> %>
+        <% :bar -> %>
+      <% end %>
+      """
+
+      assert_eval("\n  \n", template, x: :foo)
+      assert_eval("\n\n", template, x: :bar)
+    end
+
     test "with end of token" do
       assert_eval("foo bar %>", "foo bar %>")
     end
@@ -522,7 +553,7 @@ defmodule EExTest do
 
       assert message |> Exception.message() |> strip_ansi() =~ """
                   │
-              514 │                   true && @some[\s
+              #{line + 2} │                   true && @some[\s
                   │                                │ └ missing closing delimiter (expected "]")
                   │                                └ unclosed delimiter
              """
@@ -575,6 +606,18 @@ defmodule EExTest do
         EEx.compile_string("foo <%= bar", file: "my_file.eex")
       end
     end
+
+    test "unsupported marker error carries template location metadata" do
+      error =
+        assert_raise EEx.SyntaxError, fn ->
+          EEx.compile_string("<%/ true %>", file: "sample.eex", line: 7)
+        end
+
+      assert error.file == "sample.eex"
+      assert error.line == 7
+      assert error.column == 1
+      assert Exception.message(error) =~ "sample.eex:7:1:"
+    end
   end
 
   describe "warnings" do

lib/elixir/lib/access.ex

@@ -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. Keywords supports only atoms keys, keys for maps can
+  of the box. Keyword lists support only atom keys, while keys for maps
-  be of any type. Both return `nil` if the key does not exist:
+  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]
@@ -226,6 +226,8 @@ defmodule Access do
     end
   end
 
+  defguardp is_probably_keyword(list) when list == [] or is_atom(elem(hd(list), 0))
+
   @doc """
   Fetches the value for the given key in a container (a map, keyword
   list, or struct that implements the `Access` behaviour).
@@ -485,7 +487,7 @@ defmodule Access do
   ## Accessors
 
   @doc """
-  Returns a function that accesses the given key in a map/struct.
+  Returns a function that accesses the given key in a map/struct/keyword list.
 
   The returned function is typically passed as an accessor to `Kernel.get_in/2`,
   `Kernel.get_and_update_in/3`, and friends.
@@ -514,30 +516,56 @@ defmodule Access do
       iex> pop_in(map, [Access.key(:user), Access.key(:name)])
       {"john", %{user: %{}}}
 
-  An error is raised if the accessed structure is not a map or a struct:
+      iex> keyword = [user: [name: "john"]]
+      iex> get_in(keyword, [Access.key(:unknown, []), Access.key(:name, "john")])
+      "john"
+      iex> get_and_update_in(keyword, [Access.key(:user), Access.key(:name)], fn prev ->
+      ...>   {prev, String.upcase(prev)}
+      ...> end)
+      {"john", [user: [name: "JOHN"]]}
+      iex> pop_in(keyword, [Access.key(:user), Access.key(:name)])
+      {"john", [user: []]}
 
-      iex> get_in([], [Access.key(:foo)])
+  An error is raised if the accessed structure is not a map, struct, or keyword list:
-      ** (BadMapError) expected a map, got:
+
-      ...
+      iex> get_in(123, [Access.key(:foo)])
+      ** (RuntimeError) Access.key/2 expected a map/struct/keyword list, got: ...
+
+      iex> put_in([1, 2, 3], [Access.key(:foo)], :bar)
+      ** (RuntimeError) Access.key/2 expected a map/struct/keyword list, got: ...
   """
-  @spec key(key, term) :: access_fun(data :: struct | map, current_value :: term)
+  @spec key(key, term) :: access_fun(data :: struct | map | keyword, current_value :: term)
   def key(key, default \\ nil) do
     fn
-      :get, data, next ->
+      :get, %{} = data, next ->
         next.(Map.get(data, key, default))
 
-      :get_and_update, data, next ->
+      :get_and_update, %{} = data, next ->
         value = Map.get(data, key, default)
 
         case next.(value) do
           {get, update} -> {get, Map.put(data, key, update)}
           :pop -> {value, Map.delete(data, key)}
         end
+
+      :get, data, next when is_probably_keyword(data) ->
+        next.(Keyword.get(data, key, default))
+
+      :get_and_update, data, next when is_probably_keyword(data) ->
+        value = Keyword.get(data, key, default)
+
+        case next.(value) do
+          {get, update} -> {get, Keyword.put(data, key, update)}
+          :pop -> {value, Keyword.delete(data, key)}
+        end
+
+      _op, data, _next ->
+        raise "Access.key/2 expected a map/struct/keyword list, got: #{inspect(data)}"
     end
   end
 
   @doc """
-  Returns a function that accesses the given key in a map/struct.
+  Returns a function that accesses the given key in a map/struct/keyword list.
 
   The returned function is typically passed as an accessor to `Kernel.get_in/2`,
   `Kernel.get_and_update_in/3`, and friends.
@@ -546,6 +574,19 @@ defmodule Access do
 
   ## Examples
 
+      iex> keyword = [user: [name: "john"]]
+      iex> get_in(keyword, [Access.key!(:user), Access.key!(:name)])
+      "john"
+      iex> get_and_update_in(keyword, [Access.key!(:user), Access.key!(:name)], fn prev ->
+      ...>   {prev, String.upcase(prev)}
+      ...> end)
+      {"john", [user: [name: "JOHN"]]}
+      iex> pop_in(keyword, [Access.key!(:user), Access.key!(:name)])
+      {"john", [user: []]}
+      iex> get_in(keyword, [Access.key!(:user), Access.key!(:unknown)])
+      ** (KeyError) key :unknown not found in:
+      ...
+
       iex> map = %{user: %{name: "john"}}
       iex> get_in(map, [Access.key!(:user), Access.key!(:name)])
       "john"
@@ -574,13 +615,15 @@ defmodule Access do
   `Access.key!/1` is useful when the key is not known in advance
   and must be accessed dynamically.
 
-  An error is raised if the accessed structure is not a map/struct:
+  An error is raised if the accessed structure is not a map/struct/keyword list:
 
-      iex> get_in([], [Access.key!(:foo)])
+      iex> get_in(123, [Access.key!(:foo)])
-      ** (RuntimeError) Access.key!/1 expected a map/struct, got: []
+      ** (RuntimeError) Access.key!/1 expected a map/struct/keyword list, got: 123
 
+      iex> put_in([1, 2, 3], [Access.key!(:foo)], :bar)
+      ** (RuntimeError) Access.key!/1 expected a map/struct/keyword list, got: ...
   """
-  @spec key!(key) :: access_fun(data :: struct | map, current_value :: term)
+  @spec key!(key) :: access_fun(data :: struct | map | keyword, current_value :: term)
   def key!(key) do
     fn
       :get, %{} = data, next ->
@@ -594,8 +637,19 @@ defmodule Access do
           :pop -> {value, Map.delete(data, key)}
         end
 
+      :get, data, next when is_probably_keyword(data) ->
+        next.(Keyword.fetch!(data, key))
+
+      :get_and_update, data, next when is_probably_keyword(data) ->
+        value = Keyword.fetch!(data, key)
+
+        case next.(value) do
+          {get, update} -> {get, Keyword.put(data, key, update)}
+          :pop -> {value, Keyword.delete(data, key)}
+        end
+
       _op, data, _next ->
-        raise "Access.key!/1 expected a map/struct, got: #{inspect(data)}"
+        raise "Access.key!/1 expected a map/struct/keyword list, got: #{inspect(data)}"
     end
   end
 
@@ -863,7 +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])
@@ -880,7 +934,7 @@ defmodule Access do
 
   """
   @doc since: "1.6.0"
-  @spec filter((term -> boolean)) :: access_fun(data :: list, current_value :: list)
+  @spec filter((term -> as_boolean(term))) :: 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
@@ -981,12 +1035,12 @@ defmodule Access do
   end
 
   defp slice(:get_and_update, data, range, next) when is_list(data) do
-    range = normalize_range(range, data)
+    %Range{first: first, last: last, step: step} = normalize_range(range, data)
 
-    if range.first > range.last do
+    if first > last do
       {[], data}
     else
-      get_and_update_slice(data, range, next, [], [], 0)
+      get_and_update_slice(data, first, last, step, next, [], [], 0)
     end
   end
 
@@ -1091,16 +1145,23 @@ defmodule Access do
 
   defp normalize_range(range, _list), do: range
 
-  defp get_and_update_slice([head | rest], range, next, updates, gets, index) do
+  defp get_and_update_slice(rest, _first, last, _step, _next, updates, gets, index)
-    if index in range do
+       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
       case next.(head) do
         :pop ->
-          get_and_update_slice(rest, range, next, updates, [head | gets], index + 1)
+          get_and_update_slice(rest, first, last, step, next, updates, [head | gets], index + 1)
 
         {get, update} ->
           get_and_update_slice(
             rest,
-            range,
+            first,
+            last,
+            step,
             next,
             [update | updates],
             [get | gets],
@@ -1108,11 +1169,11 @@ defmodule Access do
           )
       end
     else
-      get_and_update_slice(rest, range, next, [head | updates], gets, index + 1)
+      get_and_update_slice(rest, first, last, step, next, [head | updates], gets, index + 1)
     end
   end
 
-  defp get_and_update_slice([], _range, _next, updates, gets, _index) do
+  defp get_and_update_slice([], _first, _last, _step, _next, updates, gets, _index) do
     {:lists.reverse(gets), :lists.reverse(updates)}
   end
 
@@ -1139,7 +1200,7 @@ 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])

lib/elixir/lib/agent.ex

@@ -327,7 +327,7 @@ defmodule Agent do
   passing the agent state. The result of the function invocation is
   returned from this function.
 
-  `timeout` is an integer greater than zero which specifies how many
+  `timeout` is a non-negative integer 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 an integer greater than zero which specifies how many
+  `timeout` is a non-negative integer 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 an integer greater than zero which specifies how many
+  `timeout` is a non-negative integer 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

lib/elixir/lib/application.ex

@@ -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`,
-  returns a string.
+  and returns a string.
   """
   @spec format_error(any) :: String.t()
   def format_error(reason) do

lib/elixir/lib/base.ex

@@ -155,6 +155,255 @@ defmodule Base do
     for <<char::8 <- string>>, char not in ~c"\s\t\r\n", into: <<>>, do: <<char::8>>
   end
 
+  # SWAR (SIMD Within A Register) fast paths for valid16?/2 and valid32?/2
+  # (non-hex). Each chunk of 8 bytes is validated in one guard: 7 bytes via
+  # bitwise arithmetic on a single 56-bit integer, plus a per-byte range
+  # check for the 8th byte. 56 bits is the largest width that fits in a BEAM
+  # small int on 64-bit (fixnum range is 59-bit signed); at 64 bits every
+  # `w + 0x80..` would allocate a bignum on the heap and the optimisation
+  # would collapse. See https://github.com/erlang/otp/pull/10938 for the
+  # corresponding pattern in OTP.
+  @swar_mask80 0x80808080808080
+
+  # Per-range SWAR constants, broadcast across 7 lanes. Naming convention:
+  #   @swar_ge_X = 0x80 - X  → high bit of `(w + @swar_ge_X)` lane is set
+  #                            iff that byte is ≥ X
+  #   @swar_gt_X = 0x7F - X  → high bit of `(w + @swar_gt_X)` lane is set
+  #                            iff that byte is > X
+  # A byte is in range [lo, hi] iff
+  #   `bxor(w + @swar_ge_lo, w + @swar_gt_hi)` has its high bit set.
+  @swar_ge_0 0x50505050505050
+  @swar_gt_9 0x46464646464646
+  @swar_ge_2 0x4E4E4E4E4E4E4E
+  @swar_gt_7 0x48484848484848
+  @swar_ge_A 0x3F3F3F3F3F3F3F
+  @swar_gt_F 0x39393939393939
+  @swar_gt_V 0x29292929292929
+  @swar_gt_Z 0x25252525252525
+  @swar_ge_a 0x1F1F1F1F1F1F1F
+  @swar_gt_f 0x19191919191919
+  @swar_gt_v 0x09090909090909
+  @swar_gt_z 0x05050505050505
+
+  # 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
+  # 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
+
+  # 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).
+  @compile {:inline,
+            valid_char16upper?: 1,
+            valid_char16lower?: 1,
+            valid_char16mixed?: 1,
+            valid_char32upper?: 1,
+            valid_char32lower?: 1,
+            valid_char32mixed?: 1,
+            valid_char32hexupper?: 1,
+            valid_char32hexlower?: 1,
+            valid_char32hexmixed?: 1,
+            valid_char64base?: 1,
+            valid_char64url?: 1,
+            valid_word16upper?: 1,
+            valid_word16lower?: 1,
+            valid_word16mixed?: 1,
+            valid_word32upper?: 1,
+            valid_word32lower?: 1,
+            valid_word32mixed?: 1,
+            valid_word32hexupper?: 1,
+            valid_word32hexlower?: 1,
+            valid_word32hexmixed?: 1,
+            valid_word64base?: 1,
+            valid_word64url?: 1}
+
+  defp valid_char16upper?(c), do: c in ?0..?9 or c in ?A..?F
+  defp valid_char16lower?(c), do: c in ?0..?9 or c in ?a..?f
+  defp valid_char16mixed?(c), do: c in ?0..?9 or c in ?A..?F or c in ?a..?f
+
+  defp valid_char32upper?(c), do: c in ?A..?Z or c in ?2..?7
+  defp valid_char32lower?(c), do: c in ?a..?z or c in ?2..?7
+  defp valid_char32mixed?(c), do: c in ?A..?Z or c in ?a..?z or c in ?2..?7
+
+  # Most common range first — letters dominate (22/32) over digits (10/32)
+  # in hex base32, so letters go first in the OR short-circuit.
+  defp valid_char32hexupper?(c), do: c in ?A..?V or c in ?0..?9
+  defp valid_char32hexlower?(c), do: c in ?a..?v or c in ?0..?9
+  defp valid_char32hexmixed?(c), do: c in ?A..?V or c in ?a..?v or c in ?0..?9
+
+  defp valid_char64base?(c),
+    do: c in ?A..?Z or c in ?a..?z or c in ?0..?9 or c == ?+ or c == ?/
+
+  defp valid_char64url?(c),
+    do: c in ?A..?Z or c in ?a..?z or c in ?0..?9 or c == ?- or c == ?_
+
+  # SWAR 7-byte word validity. Structure for each function:
+  #   1. ASCII gate `band(w, MASK80) == 0` — every byte < 0x80 so the
+  #      additions below cannot carry across lanes.
+  #   2. "Each byte is in range A OR range B (OR range C)" gate — OR per-
+  #      range XOR masks (high bit set in lane iff byte in that range), AND
+  #      with MASK80, demand all 7 high bits set.
+  defp valid_word16upper?(w) do
+    band(w, @swar_mask80) == 0 and
+      band(
+        bor(
+          bxor(w + @swar_ge_0, w + @swar_gt_9),
+          bxor(w + @swar_ge_A, w + @swar_gt_F)
+        ),
+        @swar_mask80
+      ) == @swar_mask80
+  end
+
+  defp valid_word16lower?(w) do
+    band(w, @swar_mask80) == 0 and
+      band(
+        bor(
+          bxor(w + @swar_ge_0, w + @swar_gt_9),
+          bxor(w + @swar_ge_a, w + @swar_gt_f)
+        ),
+        @swar_mask80
+      ) == @swar_mask80
+  end
+
+  defp valid_word16mixed?(w) do
+    band(w, @swar_mask80) == 0 and
+      band(
+        bor(
+          bor(
+            bxor(w + @swar_ge_0, w + @swar_gt_9),
+            bxor(w + @swar_ge_A, w + @swar_gt_F)
+          ),
+          bxor(w + @swar_ge_a, w + @swar_gt_f)
+        ),
+        @swar_mask80
+      ) == @swar_mask80
+  end
+
+  defp valid_word32upper?(w) do
+    band(w, @swar_mask80) == 0 and
+      band(
+        bor(
+          bxor(w + @swar_ge_A, w + @swar_gt_Z),
+          bxor(w + @swar_ge_2, w + @swar_gt_7)
+        ),
+        @swar_mask80
+      ) == @swar_mask80
+  end
+
+  defp valid_word32lower?(w) do
+    band(w, @swar_mask80) == 0 and
+      band(
+        bor(
+          bxor(w + @swar_ge_a, w + @swar_gt_z),
+          bxor(w + @swar_ge_2, w + @swar_gt_7)
+        ),
+        @swar_mask80
+      ) == @swar_mask80
+  end
+
+  defp valid_word32mixed?(w) do
+    band(w, @swar_mask80) == 0 and
+      band(
+        bor(
+          bor(
+            bxor(w + @swar_ge_A, w + @swar_gt_Z),
+            bxor(w + @swar_ge_a, w + @swar_gt_z)
+          ),
+          bxor(w + @swar_ge_2, w + @swar_gt_7)
+        ),
+        @swar_mask80
+      ) == @swar_mask80
+  end
+
+  defp valid_word32hexupper?(w) do
+    band(w, @swar_mask80) == 0 and
+      band(
+        bor(
+          bxor(w + @swar_ge_0, w + @swar_gt_9),
+          bxor(w + @swar_ge_A, w + @swar_gt_V)
+        ),
+        @swar_mask80
+      ) == @swar_mask80
+  end
+
+  defp valid_word32hexlower?(w) do
+    band(w, @swar_mask80) == 0 and
+      band(
+        bor(
+          bxor(w + @swar_ge_0, w + @swar_gt_9),
+          bxor(w + @swar_ge_a, w + @swar_gt_v)
+        ),
+        @swar_mask80
+      ) == @swar_mask80
+  end
+
+  defp valid_word32hexmixed?(w) do
+    band(w, @swar_mask80) == 0 and
+      band(
+        bor(
+          bor(
+            bxor(w + @swar_ge_0, w + @swar_gt_9),
+            bxor(w + @swar_ge_A, w + @swar_gt_V)
+          ),
+          bxor(w + @swar_ge_a, w + @swar_gt_v)
+        ),
+        @swar_mask80
+      ) == @swar_mask80
+  end
+
+  # 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.
+  defp valid_word64base?(w) do
+    band(w, @swar_mask80) == 0 and
+      band(
+        bor(
+          bor(
+            bor(
+              bxor(w + @swar_ge_A, w + @swar_gt_Z),
+              bxor(w + @swar_ge_a, w + @swar_gt_z)
+            ),
+            bxor(w + @swar_ge_slash, w + @swar_gt_9)
+          ),
+          bxor(w + @swar_ge_plus, w + @swar_gt_plus)
+        ),
+        @swar_mask80
+      ) == @swar_mask80
+  end
+
+  defp valid_word64url?(w) do
+    band(w, @swar_mask80) == 0 and
+      band(
+        bor(
+          bor(
+            bor(
+              bxor(w + @swar_ge_A, w + @swar_gt_Z),
+              bxor(w + @swar_ge_a, w + @swar_gt_z)
+            ),
+            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)
+          )
+        ),
+        @swar_mask80
+      ) == @swar_mask80
+  end
+
   @doc """
   Encodes a binary string into a base 16 encoded string.
 
@@ -187,7 +436,7 @@ defmodule Base do
   end
 
   for {base, alphabet} <- [upper: b16_alphabet, lower: to_lower_enc.(b16_alphabet)] do
-    name = :"encode16#{base}"
+    name = String.to_unsafe_atom("encode16#{base}")
     encoded = to_encode_list.(alphabet)
 
     @compile {:inline, [{name, 1}]}
@@ -287,7 +536,7 @@ defmodule Base do
     * `:lower` - only allows lower case characters
     * `:mixed` - allows mixed case characters
 
-  An `ArgumentError` exception is raised if the padding is incorrect or
+  An `ArgumentError` exception is raised if the string has an odd length or
   a non-alphabet character is present in the string.
 
   ## Examples
@@ -368,28 +617,24 @@ 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 = :"decode16#{base}!"
+    decode_name = String.to_unsafe_atom("decode16#{base}!")
-    validate_name = :"validate16#{base}?"
+    validate_name = String.to_unsafe_atom("validate16#{base}?")
-    valid_char_name = :"valid_char16#{base}?"
+    valid_char_name = String.to_unsafe_atom("valid_char16#{base}?")
+    valid_word_name = String.to_unsafe_atom("valid_word16#{base}?")
 
     {min, decoded} = to_decode_list.(alphabet)
 
+    # SWAR fast path: 7 bytes per stride, validated entirely via
+    # `valid_word16<base>?` in the body. The `and` short-circuits when SWAR
+    # fails on any byte. Tail bytes (1-6 leftover) recurse through the
+    # single-byte clause below.
+    defp unquote(validate_name)(<<w::56, rest::binary>>),
+      do: unquote(valid_word_name)(w) and unquote(validate_name)(rest)
+
     defp unquote(validate_name)(<<>>), do: true
 
-    defp unquote(validate_name)(<<c1, c2, rest::binary>>) do
+    defp unquote(validate_name)(<<char, rest::binary>>),
-      unquote(valid_char_name)(c1) and
+      do: unquote(valid_char_name)(char) and unquote(validate_name)(rest)
-        unquote(valid_char_name)(c2) and
-        unquote(validate_name)(rest)
-    end
-
-    defp unquote(validate_name)(<<_char, _rest::binary>>), do: false
-
-    @compile {:inline, [{valid_char_name, 1}]}
-    defp unquote(valid_char_name)(char)
-         when elem({unquote_splicing(decoded)}, char - unquote(min)) != nil,
-         do: true
-
-    defp unquote(valid_char_name)(_char), do: false
 
     defp unquote(decode_name)(char) do
       index = char - unquote(min)
@@ -490,7 +735,7 @@ defmodule Base do
   end
 
   for {base, alphabet} <- [base: b64_alphabet, url: b64url_alphabet] do
-    name = :"encode64#{base}"
+    name = String.to_unsafe_atom("encode64#{base}")
     encoded = to_encode_list.(alphabet)
 
     @compile {:inline, [{name, 1}]}
@@ -756,28 +1001,24 @@ defmodule Base do
   end
 
   for {base, alphabet} <- [base: b64_alphabet, url: b64url_alphabet] do
-    decode_name = :"decode64#{base}!"
+    decode_name = String.to_unsafe_atom("decode64#{base}!")
 
-    validate_name = :"validate64#{base}?"
+    validate_name = String.to_unsafe_atom("validate64#{base}?")
-    validate_main_name = :"validate_main64#{validate_name}?"
+    validate_main_name = String.to_unsafe_atom("validate_main64#{validate_name}?")
-    valid_char_name = :"valid_char64#{base}?"
+    valid_char_name = String.to_unsafe_atom("valid_char64#{base}?")
+    valid_word_name = String.to_unsafe_atom("valid_word64#{base}?")
     {min, decoded} = alphabet |> Enum.with_index() |> to_decode_list.()
 
+    # SWAR fast path: 7 bytes per stride, validated via `valid_word64<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.
+    defp unquote(validate_main_name)(<<w::56, rest::binary>>),
+      do: unquote(valid_word_name)(w) and unquote(validate_main_name)(rest)
+
     defp unquote(validate_main_name)(<<>>), do: true
 
-    defp unquote(validate_main_name)(
+    defp unquote(validate_main_name)(<<char, rest::binary>>),
-           <<c1::8, c2::8, c3::8, c4::8, c5::8, c6::8, c7::8, c8::8, rest::binary>>
+      do: unquote(valid_char_name)(char) and unquote(validate_main_name)(rest)
-         ) do
-      unquote(valid_char_name)(c1) and
-        unquote(valid_char_name)(c2) and
-        unquote(valid_char_name)(c3) and
-        unquote(valid_char_name)(c4) and
-        unquote(valid_char_name)(c5) and
-        unquote(valid_char_name)(c6) and
-        unquote(valid_char_name)(c7) and
-        unquote(valid_char_name)(c8) and
-        unquote(validate_main_name)(rest)
-    end
 
     defp unquote(validate_name)(<<>>, _pad?), do: true
 
@@ -863,13 +1104,6 @@ defmodule Base do
       end
     end
 
-    @compile {:inline, [{valid_char_name, 1}]}
-    defp unquote(valid_char_name)(char)
-         when elem({unquote_splicing(decoded)}, char - unquote(min)) != nil,
-         do: true
-
-    defp unquote(valid_char_name)(_char), do: false
-
     defp unquote(decode_name)(char) do
       index = char - unquote(min)
 
@@ -1080,7 +1314,7 @@ defmodule Base do
         hexupper: b32hex_alphabet,
         hexlower: to_lower_enc.(b32hex_alphabet)
       ] do
-    name = :"encode32#{base}"
+    name = String.to_unsafe_atom("encode32#{base}")
     encoded = to_encode_list.(alphabet)
 
     @compile {:inline, [{name, 1}]}
@@ -1154,7 +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
 
@@ -1419,27 +1653,24 @@ defmodule Base do
         hexlower: to_lower_dec.(hexupper),
         hexmixed: to_mixed_dec.(hexupper)
       ] do
-    decode_name = :"decode32#{base}!"
+    decode_name = String.to_unsafe_atom("decode32#{base}!")
-    validate_name = :"validate32#{base}?"
+    validate_name = String.to_unsafe_atom("validate32#{base}?")
-    validate_main_name = :"validate_main32#{validate_name}?"
+    validate_main_name = String.to_unsafe_atom("validate_main32#{validate_name}?")
-    valid_char_name = :"valid_char32#{base}?"
+    valid_char_name = String.to_unsafe_atom("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}?")
+
+    defp unquote(validate_main_name)(<<w::56, rest::binary>>),
+      do: unquote(valid_word_name)(w) and unquote(validate_main_name)(rest)
+
     defp unquote(validate_main_name)(<<>>), do: true
 
-    defp unquote(validate_main_name)(
+    defp unquote(validate_main_name)(<<char, rest::binary>>),
-           <<c1::8, c2::8, c3::8, c4::8, c5::8, c6::8, c7::8, c8::8, rest::binary>>
+      do: unquote(valid_char_name)(char) and unquote(validate_main_name)(rest)
-         ) do
-      unquote(valid_char_name)(c1) and
-        unquote(valid_char_name)(c2) and
-        unquote(valid_char_name)(c3) and
-        unquote(valid_char_name)(c4) and
-        unquote(valid_char_name)(c5) and
-        unquote(valid_char_name)(c6) and
-        unquote(valid_char_name)(c7) and
-        unquote(valid_char_name)(c8) and
-        unquote(validate_main_name)(rest)
-    end
 
     defp unquote(validate_name)(<<>>, _pad?), do: true
 
@@ -1519,13 +1750,6 @@ defmodule Base do
       end
     end
 
-    @compile {:inline, [{valid_char_name, 1}]}
-    defp unquote(valid_char_name)(char)
-         when elem({unquote_splicing(decoded)}, char - unquote(min)) != nil,
-         do: true
-
-    defp unquote(valid_char_name)(_char), do: false
-
     defp unquote(decode_name)(char) do
       index = char - unquote(min)
 

lib/elixir/lib/calendar.ex

@@ -3,6 +3,8 @@
 # SPDX-FileCopyrightText: 2012 Plataformatec
 
 defmodule Calendar do
+  @strftime_max_width 1024
+
   @moduledoc """
   This module defines the responsibilities for working with
   calendars, dates, times and datetimes in Elixir.
@@ -104,6 +106,7 @@ 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,
@@ -293,7 +296,7 @@ defmodule Calendar do
   @callback time_from_day_fraction(day_fraction) :: {hour, minute, second, microsecond}
 
   @doc """
-  Define the rollover moment for the calendar.
+  Defines the rollover moment for the calendar.
 
   This is the moment, in your calendar, when the current day ends
   and the next day starts.
@@ -379,13 +382,13 @@ defmodule Calendar do
   @callback iso_days_to_end_of_day(iso_days) :: iso_days
 
   @doc """
-  Shifts date by given duration according to its calendar.
+  Shifts date by the 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 given duration according to its calendar.
+  Shifts naive datetime by the given duration according to its calendar.
   """
   @doc since: "1.17.0"
   @callback shift_naive_datetime(
@@ -400,7 +403,7 @@ defmodule Calendar do
             ) :: {year, month, day, hour, minute, second, microsecond}
 
   @doc """
-  Shifts time by given duration according to its calendar.
+  Shifts time by the given duration according to its calendar.
   """
   @doc since: "1.17.0"
   @callback shift_time(hour, minute, second, microsecond, Duration.t()) ::
@@ -529,6 +532,7 @@ defmodule Calendar do
     * `%`: indicates the start of a formatted section
     * `<padding>`: set the padding (see below)
     * `<width>`: a number indicating the minimum size of the formatted section
+      (maximum #{@strftime_max_width})
     * `<format>`: the format itself (see below)
 
   ### Accepted padding options
@@ -559,11 +563,11 @@ 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, 60
+  S      | Second                                                                  | 00, 59
   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
@@ -620,7 +624,7 @@ 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"
@@ -667,9 +671,13 @@ defmodule Calendar do
   end
 
   defp parse_modifiers(<<digit, rest::binary>>, width, pad, parser_data) when digit in ?0..?9 do
-    new_width = (width || 0) * 10 + (digit - ?0)
+    width = (width || 0) * 10 + (digit - ?0)
 
-    parse_modifiers(rest, new_width, pad, parser_data)
+    if width > @strftime_max_width do
+      raise ArgumentError, "invalid strftime format: width must be at most #{@strftime_max_width}"
+    end
+
+    parse_modifiers(rest, width, pad, parser_data)
   end
 
   # set default padding if none was specified
@@ -704,7 +712,7 @@ defmodule Calendar do
 
   # Literally just %
   defp format_modifiers("%" <> rest, width, pad, datetime, format_options, acc) do
-    parse(rest, datetime, format_options, [pad_leading("%", width, pad) | acc])
+    parse(rest, datetime, format_options, [pad_leading_ascii("%", width, pad) | acc])
   end
 
   # Abbreviated name of day
@@ -773,7 +781,7 @@ 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(width, pad)
+    result = datetime.day |> Integer.to_string() |> pad_leading_ascii(width, pad)
     parse(rest, datetime, format_options, [result | acc])
   end
 
@@ -792,31 +800,35 @@ 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(width, pad)
+    result = datetime.hour |> Integer.to_string() |> pad_leading_ascii(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(width, pad)
+    result =
+      (rem(datetime.hour + 23, 12) + 1) |> Integer.to_string() |> pad_leading_ascii(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(width, pad)
+    result =
+      datetime |> Date.day_of_year() |> Integer.to_string() |> pad_leading_ascii(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(width, pad)
+    result = datetime.month |> Integer.to_string() |> pad_leading_ascii(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(width, pad)
+    result = datetime.minute |> Integer.to_string() |> pad_leading_ascii(width, pad)
     parse(rest, datetime, format_options, [result | acc])
   end
 
@@ -844,19 +856,23 @@ 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(width, pad)
+    result =
+      datetime |> Date.quarter_of_year() |> Integer.to_string() |> pad_leading_ascii(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(width, pad)
+    result = datetime.second |> Integer.to_string() |> pad_leading_ascii(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(width, pad)
+    result =
+      datetime |> Date.day_of_week() |> Integer.to_string() |> pad_leading_ascii(width, pad)
+
     parse(rest, datetime, format_options, [result | acc])
   end
 
@@ -906,20 +922,25 @@ defmodule Calendar do
 
   # Year as 2-digits
   defp format_modifiers("y" <> rest, width, pad, datetime, format_options, acc) do
-    result = datetime.year |> rem(100) |> Integer.to_string() |> pad_leading(width, pad)
+    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
+
     parse(rest, datetime, format_options, [result | acc])
   end
 
   # Year
   defp format_modifiers("Y" <> rest, width, pad, datetime, format_options, acc) do
-    {sign, year} =
+    result =
       if datetime.year < 0 do
-        {?-, -datetime.year}
+        [?- | -datetime.year |> Integer.to_string() |> pad_leading_ascii(width, pad)]
       else
-        {[], datetime.year}
+        datetime.year |> Integer.to_string() |> pad_leading_ascii(width, pad)
       end
 
-    result = [sign | year |> Integer.to_string() |> pad_leading(width, pad)]
     parse(rest, datetime, format_options, [result | acc])
   end
 
@@ -966,7 +987,7 @@ 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(offset_number, width, pad)}"
+    result = "#{sign}#{pad_leading_ascii(offset_number, width, pad)}"
     parse(rest, datetime, format_options, [result | acc])
   end
 
@@ -985,13 +1006,19 @@ defmodule Calendar do
     raise ArgumentError, "invalid strftime format: %#{next}"
   end
 
-  defp pad_preferred(result, width, pad) when length(result) < width do
+  defp pad_preferred(result, width, pad) do
-    pad_preferred([pad | result], width, pad)
+    result
+    |> IO.iodata_to_binary()
+    |> pad_leading(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

lib/elixir/lib/calendar/date.ex

@@ -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 first argument.
+  a step of -1 as third 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)}, #{step}"
+            "non-zero integer, got: #{inspect(first)}, #{inspect(last)}, #{inspect(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()
+    |> to_iso8601(format)
   end
 
   @doc """
@@ -556,14 +556,18 @@ defmodule Date do
   """
   @doc since: "1.4.0"
   @spec compare(Calendar.date(), Calendar.date()) :: :lt | :eq | :gt
-  def compare(%{calendar: calendar} = date1, %{calendar: calendar} = date2) do
+  def compare(
-    %{year: year1, month: month1, day: day1} = date1
+        %{year: year1, month: month1, day: day1, calendar: calendar},
-    %{year: year2, month: month2, day: day2} = date2
+        %{year: year2, month: month2, day: day2, calendar: calendar}
-
+      ) do
-    case {{year1, month1, day1}, {year2, month2, day2}} do
+    cond do
-      {first, second} when first > second -> :gt
+      year1 > year2 -> :gt
-      {first, second} when first < second -> :lt
+      year1 < year2 -> :lt
-      _ -> :eq
+      month1 > month2 -> :gt
+      month1 < month2 -> :lt
+      day1 > day2 -> :gt
+      day1 < day2 -> :lt
+      true -> :eq
     end
   end
 
@@ -1047,7 +1051,7 @@ defmodule Date do
   @doc """
   Calculates the quarter of the year of a given `date`.
 
-  Returns the day of the year as an integer. For the ISO 8601
+  Returns the quarter of the year as an integer. For the ISO 8601
   calendar (the default), it is an integer from 1 to 4.
 
   ## Examples

lib/elixir/lib/calendar/date_range.ex

@@ -37,21 +37,19 @@ 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)
 
-      cond do
+      in_range? =
-        empty?(range) ->
+        if step > 0 do
-          {:ok, false}
+          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
 
-        first_days <= last_days ->
+      {:ok, in_range?}
-          {: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
@@ -88,7 +86,7 @@ defmodule Date.Range do
             step: step
           } = range
         ) do
-      {:ok, size(range), &slice(first + &1 * step, step + &3 - 1, &2, calendar)}
+      {:ok, size(range), &slice(first + &1 * step, step * &3, &2, calendar)}
     end
 
     # TODO: Remove me on v2.0
@@ -185,7 +183,7 @@ defmodule Date.Range do
            last_in_iso_days: last_days,
            step: step
          }),
-         do: abs(div(last_days - first_days, step)) + 1
+         do: div(last_days - first_days, step) + 1
 
     # TODO: Remove me on v2.0
     defp size(
@@ -195,33 +193,6 @@ 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

lib/elixir/lib/calendar/datetime.ex

@@ -180,7 +180,7 @@ defmodule DateTime do
   since v1.15.0.
 
   The default unit if none gets passed is `:native`,
-  which results on a default resolution of microseconds.
+  which results in a default resolution of microseconds.
 
   ## Examples
 
@@ -720,6 +720,9 @@ 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)
@@ -753,6 +756,28 @@ 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}} ->
@@ -1177,7 +1202,7 @@ defmodule DateTime do
     datetime
     |> to_iso_days()
     # Subtract total original offset in order to get UTC and add the new offset
-    |> Calendar.ISO.add_day_fraction_to_iso_days(offset - total_offset, 86400)
+    |> Calendar.ISO.add_time_unit_to_iso_days(offset - total_offset, :second)
     |> calendar.naive_datetime_from_iso_days()
   end
 
@@ -1296,9 +1321,9 @@ 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 other timezone, please use
+  The returned `DateTime` will have `UTC` timezone, if you want another timezone, please use
   `DateTime.shift_zone/3`.
 
   ## Examples
@@ -1341,7 +1366,7 @@ 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
 
@@ -1576,15 +1601,15 @@ defmodule DateTime do
   def diff(datetime1, datetime2, unit \\ :second)
 
   def diff(datetime1, datetime2, :day) do
-    diff(datetime1, datetime2, :second) |> div(86400)
+    diff(datetime1, datetime2, :microsecond) |> div(86_400_000_000)
   end
 
   def diff(datetime1, datetime2, :hour) do
-    diff(datetime1, datetime2, :second) |> div(3600)
+    diff(datetime1, datetime2, :microsecond) |> div(3_600_000_000)
   end
 
   def diff(datetime1, datetime2, :minute) do
-    diff(datetime1, datetime2, :second) |> div(60)
+    diff(datetime1, datetime2, :microsecond) |> div(60_000_000)
   end
 
   def diff(
@@ -1626,6 +1651,9 @@ 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
@@ -1744,6 +1772,9 @@ 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
@@ -1812,44 +1843,6 @@ 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,
@@ -2060,11 +2053,12 @@ defmodule DateTime do
   end
 
   defp apply_tz_offset(iso_days, offset) do
-    Calendar.ISO.add_day_fraction_to_iso_days(iso_days, -offset, 86400)
+    Calendar.ISO.add_time_unit_to_iso_days(iso_days, -offset, :second)
   end
 
   defp from_map(%{} = datetime_map) do
     %DateTime{
+      calendar: datetime_map.calendar,
       year: datetime_map.year,
       month: datetime_map.month,
       day: datetime_map.day,

lib/elixir/lib/calendar/duration.ex

@@ -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 to achieve. Compare the results of both examples below:
+  you want to achieve. Compare the results of both examples below:
 
       # Adding one month after the other
       iex> date = ~D[2016-01-31]
@@ -129,6 +129,16 @@ 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.
   """
@@ -140,7 +150,7 @@ defmodule Duration do
           hour: integer,
           minute: integer,
           second: integer,
-          microsecond: Calendar.microsecond()
+          microsecond: microsecond()
         }
 
   @typedoc """
@@ -154,7 +164,7 @@ defmodule Duration do
           | {:hour, integer}
           | {:minute, integer}
           | {:second, integer}
-          | {:microsecond, Calendar.microsecond()}
+          | {:microsecond, microsecond()}
 
   @typedoc """
   The duration type specifies a `%Duration{}` struct or a keyword list of valid duration unit pairs.
@@ -243,19 +253,19 @@ defmodule Duration do
 
   """
   @spec add(t, t) :: t
-  def add(%Duration{} = d1, %Duration{} = d2) do
+  def add(%Duration{microsecond: {ms1, p1}} = d1, %Duration{microsecond: {ms2, p2}} = d2) do
-    {m1, p1} = d1.microsecond
+    %{year: y1, month: mo1, week: w1, day: day1, hour: h1, minute: mi1, second: s1} = d1
-    {m2, p2} = d2.microsecond
+    %{year: y2, month: mo2, week: w2, day: day2, hour: h2, minute: mi2, second: s2} = d2
 
     %Duration{
-      year: d1.year + d2.year,
+      year: y1 + y2,
-      month: d1.month + d2.month,
+      month: mo1 + mo2,
-      week: d1.week + d2.week,
+      week: w1 + w2,
-      day: d1.day + d2.day,
+      day: day1 + day2,
-      hour: d1.hour + d2.hour,
+      hour: h1 + h2,
-      minute: d1.minute + d2.minute,
+      minute: mi1 + mi2,
-      second: d1.second + d2.second,
+      second: s1 + s2,
-      microsecond: {m1 + m2, max(p1, p2)}
+      microsecond: {ms1 + ms2, max(p1, p2)}
     }
   end
 
@@ -273,19 +283,19 @@ defmodule Duration do
 
   """
   @spec subtract(t, t) :: t
-  def subtract(%Duration{} = d1, %Duration{} = d2) do
+  def subtract(%Duration{microsecond: {ms1, p1}} = d1, %Duration{microsecond: {ms2, p2}} = d2) do
-    {m1, p1} = d1.microsecond
+    %{year: y1, month: mo1, week: w1, day: day1, hour: h1, minute: mi1, second: s1} = d1
-    {m2, p2} = d2.microsecond
+    %{year: y2, month: mo2, week: w2, day: day2, hour: h2, minute: mi2, second: s2} = d2
 
     %Duration{
-      year: d1.year - d2.year,
+      year: y1 - y2,
-      month: d1.month - d2.month,
+      month: mo1 - mo2,
-      week: d1.week - d2.week,
+      week: w1 - w2,
-      day: d1.day - d2.day,
+      day: day1 - day2,
-      hour: d1.hour - d2.hour,
+      hour: h1 - h2,
-      minute: d1.minute - d2.minute,
+      minute: mi1 - mi2,
-      second: d1.second - d2.second,
+      second: s1 - s2,
-      microsecond: {m1 - m2, max(p1, p2)}
+      microsecond: {ms1 - ms2, max(p1, p2)}
     }
   end
 
@@ -302,14 +312,16 @@ defmodule Duration do
   """
   @spec multiply(t, integer) :: t
   def multiply(%Duration{microsecond: {ms, p}} = duration, integer) when is_integer(integer) do
+    %{year: y, month: mo, week: w, day: d, hour: h, minute: mi, second: s} = duration
+
     %Duration{
-      year: duration.year * integer,
+      year: y * integer,
-      month: duration.month * integer,
+      month: mo * integer,
-      week: duration.week * integer,
+      week: w * integer,
-      day: duration.day * integer,
+      day: d * integer,
-      hour: duration.hour * integer,
+      hour: h * integer,
-      minute: duration.minute * integer,
+      minute: mi * integer,
-      second: duration.second * integer,
+      second: s * integer,
       microsecond: {ms * integer, p}
     }
   end
@@ -327,14 +339,16 @@ defmodule Duration do
   """
   @spec negate(t) :: t
   def negate(%Duration{microsecond: {ms, p}} = duration) do
+    %{year: y, month: mo, week: w, day: d, hour: h, minute: mi, second: s} = duration
+
     %Duration{
-      year: -duration.year,
+      year: -y,
-      month: -duration.month,
+      month: -mo,
-      week: -duration.week,
+      week: -w,
-      day: -duration.day,
+      day: -d,
-      hour: -duration.hour,
+      hour: -h,
-      minute: -duration.minute,
+      minute: -mi,
-      second: -duration.second,
+      second: -s,
       microsecond: {-ms, p}
     }
   end

lib/elixir/lib/calendar/iso.ex

@@ -33,8 +33,9 @@ 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 the lowest component (such as
+  the day component) nor decimal precisions in components other than seconds
-  `10:01:25,5`).
+  (such as `10:01,5`). Fractional seconds are supported and truncated to
+  microsecond precision.
 
   #### Examples
 
@@ -81,6 +82,11 @@ 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.
@@ -417,16 +423,13 @@ defmodule Calendar.ISO do
   @spec parse_date(String.t(), format) ::
           {:ok, {year, month, day}}
           | {:error, atom}
-  def parse_date(string, format) when is_binary(string) and is_format(format),
+  def parse_date("-" <> string, format) when is_format(format),
-    do: parse_date_guarded(string, format)
-
-  defp parse_date_guarded("-" <> string, format),
     do: do_parse_date(string, -1, format)
 
-  defp parse_date_guarded("+" <> string, format),
+  def parse_date("+" <> string, format) when is_format(format),
     do: do_parse_date(string, 1, format)
 
-  defp parse_date_guarded(string, format),
+  def parse_date(string, format) when is_binary(string) and is_format(format),
     do: do_parse_date(string, 1, format)
 
   defp do_parse_date(unquote(match_basic_date), multiplier, :basic) when unquote(guard_date) do
@@ -502,16 +505,13 @@ 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_binary(string) and is_format(format),
+  def parse_naive_datetime("-" <> string, format) when 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)
 
-  defp parse_naive_datetime_guarded("+" <> string, format),
+  def parse_naive_datetime("+" <> string, format) when is_format(format),
     do: do_parse_naive_datetime(string, 1, format)
 
-  defp parse_naive_datetime_guarded(string, format),
+  def parse_naive_datetime(string, format) when is_binary(string) and is_format(format),
     do: do_parse_naive_datetime(string, 1, format)
 
   defp do_parse_naive_datetime(
@@ -606,16 +606,13 @@ 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_binary(string) and is_format(format),
+  def parse_utc_datetime("-" <> string, format) when 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)
 
-  defp parse_utc_datetime_guarded("+" <> string, format),
+  def parse_utc_datetime("+" <> string, format) when is_format(format),
     do: do_parse_utc_datetime(string, 1, format)
 
-  defp parse_utc_datetime_guarded(string, format),
+  def parse_utc_datetime(string, format) when is_binary(string) and is_format(format),
     do: do_parse_utc_datetime(string, 1, format)
 
   defp do_parse_utc_datetime(
@@ -666,12 +663,12 @@ defmodule Calendar.ISO do
           day_fraction = time_to_day_fraction(hour, minute, second, {0, 0})
 
           {{year, month, day}, {hour, minute, second, _}} =
-            case add_day_fraction_to_iso_days({0, day_fraction}, -offset, 86_400) do
+            case add_time_unit_to_iso_days({0, day_fraction}, -offset, :second) do
               {0, day_fraction} ->
                 {{year, month, day}, time_from_day_fraction(day_fraction)}
 
               {extra_days, day_fraction} ->
-                base_days = date_to_iso_days(year, month, day)
+                base_days = valid_date_to_iso_days(year, month, day)
                 {date_from_iso_days(base_days + extra_days), time_from_day_fraction(day_fraction)}
             end
 
@@ -683,75 +680,73 @@ defmodule Calendar.ISO do
   end
 
   @doc """
-  Parses an ISO 8601 formatted duration string to a list of `Duration` compabitble unit pairs.
+  Parses an ISO 8601 formatted duration string to a list of `Duration` compatible 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, [], year: ?Y, month: ?M, week: ?W, day: ?D)
+    parse_duration_date(string, 1, [], 0)
   end
 
   def parse_duration("+P" <> string) when byte_size(string) > 0 do
-    parse_duration_date(string, [], year: ?Y, month: ?M, week: ?W, day: ?D)
+    parse_duration_date(string, 1, [], 0)
   end
 
   def parse_duration("-P" <> string) when byte_size(string) > 0 do
-    with {:ok, fields} <- parse_duration_date(string, [], year: ?Y, month: ?M, week: ?W, day: ?D) do
+    parse_duration_date(string, -1, [], 0)
-      {: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("", acc, _allowed), do: {:ok, acc}
+  defp parse_duration_date("", _sign, acc, _min_position), do: {:ok, acc}
 
-  defp parse_duration_date("T" <> string, acc, _allowed) when byte_size(string) > 0 do
+  defp parse_duration_date("T" <> string, sign, acc, _min_position)
-    parse_duration_time(string, acc, hour: ?H, minute: ?M, second: ?S)
+       when byte_size(string) > 0 do
+    parse_duration_time(string, sign, acc, 0)
   end
 
-  defp parse_duration_date(string, acc, allowed) do
+  defp parse_duration_date(string, sign, acc, min_position) do
-    with {integer, <<next, rest::binary>>} <- Integer.parse(string),
+    with {integer, <<unit, rest::binary>>} <- Integer.parse(string),
-         {key, allowed} <- find_unit(allowed, next) do
+         {key, next_min_position} <- find_date_unit(min_position, unit) do
-      parse_duration_date(rest, [{key, integer} | acc], allowed)
+      parse_duration_date(rest, sign, [{key, integer * sign} | acc], next_min_position)
     else
       _ -> {:error, :invalid_date_component}
     end
   end
 
-  defp parse_duration_time("", acc, _allowed), do: {:ok, acc}
+  defp parse_duration_time("", _sign, acc, _min_position), do: {:ok, acc}
 
-  defp parse_duration_time(string, acc, allowed) do
+  defp parse_duration_time(string, sign, acc, min_position) do
     case Integer.parse(string) do
       {second, <<delimiter, _::binary>> = rest} when delimiter in [?., ?,] ->
-        case parse_microsecond(rest) do
+        with {:second, _next_min_position} <- find_time_unit(min_position, ?S),
-          {{ms, precision}, "S"} ->
+             {{ms, precision}, "S"} <- parse_microsecond(rest) do
-            ms =
+          ms =
-              case string do
+            case string do
-                "-" <> _ ->
+              "-" <> _ ->
-                  -ms
+                -ms
 
-                _ ->
+              _ ->
-                  ms
+                ms
-              end
+            end
-
-            {:ok, [second: second, microsecond: {ms, precision}] ++ acc}
 
+          {:ok, [second: second * sign, microsecond: {ms * sign, precision}] ++ acc}
+        else
           _ ->
             {:error, :invalid_time_component}
         end
 
-      {integer, <<next, rest::binary>>} ->
+      {integer, <<unit, rest::binary>>} ->
-        case find_unit(allowed, next) do
+        case find_time_unit(min_position, unit) do
-          {key, allowed} -> parse_duration_time(rest, [{key, integer} | acc], allowed)
+          {key, next_min_position} ->
-          false -> {:error, :invalid_time_component}
+            parse_duration_time(rest, sign, [{key, integer * sign} | acc], next_min_position)
+
+          false ->
+            {:error, :invalid_time_component}
         end
 
       _ ->
@@ -759,9 +754,17 @@ defmodule Calendar.ISO do
     end
   end
 
-  defp find_unit([{key, unit} | rest], unit), do: {key, rest}
+  # The minimum position is the earliest unit still allowed, or one past the end.
-  defp find_unit([_ | rest], unit), do: find_unit(rest, unit)
+  defp find_date_unit(min_position, ?Y) when min_position <= 0, do: {:year, 1}
-  defp find_unit([], _unit), do: false
+  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
 
   @doc """
   Returns the `t:Calendar.iso_days/0` format of the specified date.
@@ -892,12 +895,15 @@ defmodule Calendar.ISO do
 
   # Converts year, month, day to count of days since 0000-01-01.
   @doc false
-  def date_to_iso_days(0, 1, 1), do: 0
-  def date_to_iso_days(1970, 1, 1), do: @unix_epoch_days
-
   def date_to_iso_days(year, month, day) do
     ensure_day_in_month!(year, month, day)
+    valid_date_to_iso_days(year, month, day)
+  end
 
+  defp valid_date_to_iso_days(0, 1, 1), do: 0
+  defp valid_date_to_iso_days(1970, 1, 1), do: @unix_epoch_days
+
+  defp valid_date_to_iso_days(year, month, day) do
     y = if month <= 2, do: year - 1, else: year
     era = if y >= 0, do: div(y, @years_per_era), else: div(y - 399, @years_per_era)
     year_of_era = y - era * @years_per_era
@@ -1131,6 +1137,11 @@ 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)
@@ -1173,7 +1184,7 @@ 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: {abs(year) + 1, 0}
+  def year_of_era(year) when is_year_BCE(year), do: {1 - year, 0}
 
   @doc """
   Calendar callback to compute the year and era from the
@@ -1226,7 +1237,7 @@ defmodule Calendar.ISO do
   end
 
   def day_of_era(year, month, day) when is_year_BCE(year) do
-    day = abs(date_to_iso_days(year, month, day) - @iso_epoch)
+    day = @iso_epoch - date_to_iso_days(year, month, day)
     {day, 0}
   end
 
@@ -1453,7 +1464,7 @@ defmodule Calendar.ISO do
   @doc """
   Converts the given naive_datetime into a iodata.
 
-  See `naive_datetime_to_iodata/8` for more information.
+  See `naive_datetime_to_string/8` for more information.
 
   ## Examples
 
@@ -1578,7 +1589,7 @@ defmodule Calendar.ISO do
   @doc """
   Converts the given datetime into a iodata.
 
-  See `datetime_to_iodata/12` for more information.
+  See `datetime_to_string/12` for more information.
 
   ## Examples
 
@@ -1682,7 +1693,7 @@ defmodule Calendar.ISO do
   end
 
   @doc """
-  Determines if the date given is valid according to the proleptic Gregorian calendar.
+  Determines if the time given is valid.
 
   Leap seconds are not supported by the built-in Calendar.ISO.
 
@@ -1702,7 +1713,7 @@ 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_value) do
+             is_integer(ms_precision) do
     is_hour(hour) and is_minute(minute) and is_second(second) and
       is_microsecond(ms_value, ms_precision)
   end
@@ -1835,6 +1846,9 @@ 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
 
@@ -1864,6 +1878,9 @@ 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
 
@@ -1875,7 +1892,7 @@ defmodule Calendar.ISO do
   @doc false
   def shift_days({year, month, day}, days) do
     {year, month, day} =
-      date_to_iso_days(year, month, day)
+      valid_date_to_iso_days(year, month, day)
       |> Kernel.+(days)
       |> date_from_iso_days()
 
@@ -1926,8 +1943,7 @@ 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
-    ppd = System.convert_time_unit(86_400, :second, unit)
+    add_time_unit_to_iso_days(iso_days, value, unit)
-    add_day_fraction_to_iso_days(iso_days, value, ppd)
   end
 
   defp shift_time_unit_values({0, _}, {_, original_precision}) do
@@ -2008,8 +2024,8 @@ defmodule Calendar.ISO do
     total = System.convert_time_unit(integer, unit, :microsecond)
 
     if total in @unix_range_microseconds do
-      microseconds = Integer.mod(total, @microseconds_per_second)
+      {seconds, microseconds} = div_rem(total, @microseconds_per_second)
-      seconds = @unix_epoch + floor_div_positive_divisor(total, @microseconds_per_second)
+      seconds = @unix_epoch + seconds
       precision = precision_for_unit(unit)
       {date, time} = iso_seconds_to_datetime(seconds)
       {:ok, date, time, {microseconds, precision}}
@@ -2030,38 +2046,27 @@ defmodule Calendar.ISO do
     end
   end
 
-  defp parse_microsecond("." <> rest) do
+  defp parse_microsecond("." <> rest), do: parse_microsecond(rest, rest, 0)
-    case parse_microsecond(rest, 0, []) do
+  defp parse_microsecond("," <> rest), do: parse_microsecond(rest, rest, 0)
-      {[], 0, _} ->
+  defp parse_microsecond(rest), do: {{0, 0}, rest}
-        :error
 
-      {microsecond, precision, rest} ->
+  # Digits past the sixth are consumed but do not contribute to the value.
-        scale = scale_factor(precision)
+  defp parse_microsecond(<<head, tail::binary>>, digits, 6) when head in ?0..?9,
-        {{:erlang.list_to_integer(microsecond) * scale, precision}, rest}
+    do: parse_microsecond(tail, digits, 6)
-    end
-  end
 
-  defp parse_microsecond("," <> rest) do
+  defp parse_microsecond(<<head, tail::binary>>, digits, precision) when head in ?0..?9,
-    parse_microsecond("." <> rest)
+    do: parse_microsecond(tail, digits, precision + 1)
-  end
 
-  defp parse_microsecond(rest) do
+  defp parse_microsecond(_rest, _digits, 0), do: :error
-    {{0, 0}, rest}
-  end
 
-  defp parse_microsecond(<<head, tail::binary>>, 6, acc) when head in ?0..?9,
+  defp parse_microsecond(rest, digits, precision) do
-    do: parse_microsecond(tail, 6, acc)
+    scale = scale_factor(precision)
-
+    microsecond = :erlang.binary_to_integer(:binary.part(digits, 0, precision)) * scale
-  defp parse_microsecond(<<head, tail::binary>>, precision, acc) when head in ?0..?9,
+    {{microsecond, precision}, rest}
-    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)
@@ -2084,7 +2089,8 @@ 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 do
+         true <- hour < 24,
+         true <- sign == 1 or hour != 0 or min != 0 do
       {(hour * 60 + min) * 60 * sign, rest}
     else
       _ -> :error
@@ -2100,10 +2106,43 @@ defmodule Calendar.ISO do
   end
 
   @doc false
-  def iso_days_to_unit({days, {parts, ppd}}, unit) do
+  def iso_days_to_unit(iso_days, :second) do
-    day_microseconds = days * @parts_per_day
+    floor_div_positive_divisor(iso_days_to_microseconds(iso_days), @microseconds_per_second)
-    microseconds = divide_by_parts_per_day(parts, ppd)
+  end
-    System.convert_time_unit(day_microseconds + microseconds, :microsecond, unit)
+
+  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)
   end
 
   @doc false

lib/elixir/lib/calendar/naive_datetime.ex

@@ -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 changed and be set to a time zone that has
+  configuration at run time. This can change 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, :second) |> div(86400)
+    diff(naive_datetime1, naive_datetime2, :microsecond) |> div(86_400_000_000)
   end
 
   def diff(naive_datetime1, naive_datetime2, :hour) do
-    diff(naive_datetime1, naive_datetime2, :second) |> div(3600)
+    diff(naive_datetime1, naive_datetime2, :microsecond) |> div(3_600_000_000)
   end
 
   def diff(naive_datetime1, naive_datetime2, :minute) do
-    diff(naive_datetime1, naive_datetime2, :second) |> div(60)
+    diff(naive_datetime1, naive_datetime2, :microsecond) |> div(60_000_000)
   end
 
   def diff(
@@ -570,9 +570,11 @@ defmodule NaiveDateTime do
             "unsupported time unit. Expected :day, :hour, :minute, :second, :millisecond, :microsecond, :nanosecond, or a positive integer, got #{inspect(unit)}"
     end
 
-    units1 = naive_datetime1 |> to_iso_days() |> Calendar.ISO.iso_days_to_unit(unit)
+    diff_microsecond =
-    units2 = naive_datetime2 |> to_iso_days() |> Calendar.ISO.iso_days_to_unit(unit)
+      (naive_datetime1 |> to_iso_days() |> Calendar.ISO.iso_days_to_unit(:microsecond)) -
-    units1 - units2
+        (naive_datetime2 |> to_iso_days() |> Calendar.ISO.iso_days_to_unit(:microsecond))
+
+    System.convert_time_unit(diff_microsecond, :microsecond, unit)
   end
 
   @doc """
@@ -672,7 +674,7 @@ defmodule NaiveDateTime do
 
   """
   @doc since: "1.6.0"
-  @spec truncate(t(), :microsecond | :millisecond | :second) :: t()
+  @spec truncate(Calendar.naive_datetime(), :microsecond | :millisecond | :second) :: t()
   def truncate(%NaiveDateTime{microsecond: microsecond} = naive_datetime, precision) do
     %{naive_datetime | microsecond: Calendar.truncate(microsecond, precision)}
   end
@@ -715,16 +717,18 @@ defmodule NaiveDateTime do
 
   """
   @spec to_date(Calendar.naive_datetime()) :: Date.t()
-  def to_date(%{
+  def to_date(
-        year: year,
+        %{
-        month: month,
+          year: year,
-        day: day,
+          month: month,
-        calendar: calendar,
+          day: day,
-        hour: _,
+          calendar: calendar,
-        minute: _,
+          hour: _,
-        second: _,
+          minute: _,
-        microsecond: _
+          second: _,
-      }) do
+          microsecond: _
+        } = _naive_datetime
+      ) do
     %Date{year: year, month: month, day: day, calendar: calendar}
   end
 
@@ -741,16 +745,18 @@ defmodule NaiveDateTime do
 
   """
   @spec to_time(Calendar.naive_datetime()) :: Time.t()
-  def to_time(%{
+  def to_time(
-        year: _,
+        %{
-        month: _,
+          year: _,
-        day: _,
+          month: _,
-        calendar: calendar,
+          day: _,
-        hour: hour,
+          calendar: calendar,
-        minute: minute,
+          hour: hour,
-        second: second,
+          minute: minute,
-        microsecond: microsecond
+          second: second,
-      }) do
+          microsecond: microsecond
+        } = _naive_datetime
+      ) do
     %Time{
       hour: hour,
       minute: minute,
@@ -1146,16 +1152,18 @@ defmodule NaiveDateTime do
   """
   @doc since: "1.11.0"
   @spec to_gregorian_seconds(Calendar.naive_datetime()) :: {integer(), non_neg_integer()}
-  def to_gregorian_seconds(%{
+  def to_gregorian_seconds(
-        calendar: calendar,
+        %{
-        year: year,
+          calendar: calendar,
-        month: month,
+          year: year,
-        day: day,
+          month: month,
-        hour: hour,
+          day: day,
-        minute: minute,
+          hour: hour,
-        second: second,
+          minute: minute,
-        microsecond: {microsecond, precision}
+          second: second,
-      }) do
+          microsecond: {microsecond, precision}
+        } = _naive_datetime
+      ) do
     {days, day_fraction} =
       calendar.naive_datetime_to_iso_days(
         year,

lib/elixir/lib/calendar/time.ex

@@ -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 on a default resolution of microseconds.
+  The default unit if none gets passed is `:native` which results in a default resolution of microseconds.
 
   ## Examples
 
@@ -146,8 +146,9 @@ defmodule Time do
       iex> Time.new(23, 59, 59, 1_000_000)
       {:error, :invalid_time}
 
-      # Invalid precision
+  Invalid precision:
-      Time.new(23, 59, 59, {999_999, 10})
+
+      iex> Time.new(23, 59, 59, {999_999, 10})
       {:error, :invalid_time}
 
   """
@@ -466,8 +467,12 @@ defmodule Time do
           Calendar.microsecond(),
           Calendar.calendar()
         ) :: t
-  def from_seconds_after_midnight(seconds, microsecond \\ {0, 0}, calendar \\ Calendar.ISO)
+  def from_seconds_after_midnight(
-      when is_integer(seconds) do
+        seconds,
+        {microsecond, precision} \\ {0, 0},
+        calendar \\ Calendar.ISO
+      )
+      when is_integer(seconds) and microsecond in 0..999_999 and precision in 0..6 do
     seconds_in_day = Integer.mod(seconds, @seconds_per_day)
 
     {hour, minute, second, {_, _}} =
@@ -478,7 +483,7 @@ defmodule Time do
       hour: hour,
       minute: minute,
       second: second,
-      microsecond: microsecond
+      microsecond: {microsecond, precision}
     }
   end
 
@@ -496,7 +501,7 @@ defmodule Time do
 
   """
   @doc since: "1.11.0"
-  @spec to_seconds_after_midnight(Calendar.time()) :: {integer(), non_neg_integer()}
+  @spec to_seconds_after_midnight(Calendar.time()) :: {non_neg_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}
@@ -689,7 +694,7 @@ defmodule Time do
   @doc """
   Compares two time structs.
 
-  Returns `:gt` if first time is later than the second
+  Returns `:gt` if the first time is later than the second
   and `:lt` for vice versa. If the two times are equal
   `:eq` is returned.
 
@@ -715,14 +720,32 @@ defmodule Time do
   """
   @doc since: "1.4.0"
   @spec compare(Calendar.time(), Calendar.time()) :: :lt | :eq | :gt
-  def compare(%{calendar: calendar} = time1, %{calendar: calendar} = time2) do
+  def compare(
-    %{hour: hour1, minute: minute1, second: second1, microsecond: {microsecond1, _}} = time1
+        %{
-    %{hour: hour2, minute: minute2, second: second2, microsecond: {microsecond2, _}} = time2
+          hour: hour1,
-
+          minute: minute1,
-    case {{hour1, minute1, second1, microsecond1}, {hour2, minute2, second2, microsecond2}} do
+          second: second1,
-      {first, second} when first > second -> :gt
+          microsecond: {microsecond1, _},
-      {first, second} when first < second -> :lt
+          calendar: calendar
-      _ -> :eq
+        },
+        %{
+          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
     end
   end
 
@@ -901,11 +924,11 @@ defmodule Time do
   def diff(time1, time2, unit \\ :second)
 
   def diff(time1, time2, :hour) do
-    diff(time1, time2, :second) |> div(3600)
+    diff(time1, time2, :microsecond) |> div(3_600_000_000)
   end
 
   def diff(time1, time2, :minute) do
-    diff(time1, time2, :second) |> div(60)
+    diff(time1, time2, :microsecond) |> div(60_000_000)
   end
 
   def diff(

lib/elixir/lib/code.ex

@@ -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.
+  act accordingly.
 
   ## `ensure_compiled/1` and `ensure_compiled!/1`
 
@@ -258,6 +258,7 @@ 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()}
@@ -272,6 +273,7 @@ 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.
@@ -285,20 +287,26 @@ defmodule Code do
           unescape: boolean(),
           existing_atoms_only: boolean(),
           token_metadata: boolean(),
-          literal_encoder: (term(), Macro.metadata() -> term()),
+          literal_encoder: (term(), Macro.metadata() -> {:ok, Macro.t()} | {:error, binary()}),
-          static_atoms_encoder: (atom() -> term()),
+          static_atoms_encoder: (binary(), Macro.metadata() -> {:ok, term()} | {:error, binary()}),
           emit_warnings: boolean()
         ]
 
   @typedoc """
-  Options for environment evaluation functions like eval_string/3 and eval_quoted/3.
+  Options for evaluation environment, accepted by `env_for_eval/1`.
   """
-  @type env_eval_opts :: [
+  @type env_eval_opt ::
-          file: binary(),
+          {:file, binary()}
-          line: pos_integer(),
+          | {:line, pos_integer()}
-          module: module(),
+          | {:module, module()}
-          prune_binding: boolean()
+
-        ]
+  @typedoc """
+  Options for evaluation functions like `eval_string/3`, `eval_quoted/3`
+  and `eval_quoted_with_env/4`.
+  """
+  @type eval_opt ::
+          {:prune_binding, boolean()}
+          | {:dbg_callback, {module(), atom(), list()}}
 
   @boolean_compiler_options [
     :docs,
@@ -308,7 +316,7 @@ defmodule Code do
     :relative_paths
   ]
 
-  @list_compiler_options [:tracers, :parser_options]
+  @list_compiler_options [:tracers, :parser_options, :erlc_options]
 
   @available_compiler_options @boolean_compiler_options ++
                                 @list_compiler_options ++
@@ -407,7 +415,7 @@ defmodule Code do
       operations.
 
   """
-  @spec append_path(Path.t(), cache: boolean()) :: true | false
+  @spec append_path(Path.t(), cache: boolean()) :: boolean()
   def append_path(path, opts \\ []) do
     apply(:code, :add_pathz, [to_charlist(Path.expand(path)) | cache(opts)]) == true
   end
@@ -546,8 +554,7 @@ 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.
 
-  The path is expanded with `Path.expand/1` before being deleted. If the
+  All paths are expanded with `Path.expand/1` before being deleted.
-  path does not exist, this function returns `false`.
   """
   @doc since: "1.15.0"
   @spec delete_paths([Path.t()]) :: :ok
@@ -573,9 +580,11 @@ defmodule Code do
 
   ## Options
 
-  It accepts the same options as `env_for_eval/1`. Additionally, you may
+  It accepts the same options as both `env_for_eval/1` and
-  also pass an environment as second argument, so the evaluation happens
+  `eval_quoted_with_env/4`. Additionally, you may also pass an environment
-  within that environment.
+  as third argument, so the evaluation happens within that environment.
+
+  ## Return
 
   Returns a tuple of the form `{value, binding}`, where `value` is the value
   returned from evaluating `string`. If an error occurs while evaluating
@@ -605,7 +614,7 @@ defmodule Code do
       iex> Enum.sort(binding)
       [a: 3, b: 2]
 
-  For convenience, you can pass `__ENV__/0` as the `opts` argument and
+  For convenience, you can pass `__ENV__/0` as the `opts_or_env` argument and
   all imports, requires and aliases defined in the current environment
   will be automatically carried over:
 
@@ -617,21 +626,28 @@ defmodule Code do
       [a: 1, b: 2]
 
   """
-  @spec eval_string(List.Chars.t(), binding, Macro.Env.t() | env_eval_opts) :: {term, binding}
+  @spec eval_string(List.Chars.t(), binding, Macro.Env.t() | [eval_opt | env_eval_opt]) ::
-  def eval_string(string, binding \\ [], opts \\ [])
+          {term, binding}
+  def eval_string(string, binding \\ [], opts_or_env \\ [])
 
   def eval_string(string, binding, %Macro.Env{} = env) do
-    validated_eval_string(string, binding, env)
+    validated_eval_string(string, validate_binding(binding), env_for_eval(env), [])
   end
 
   def eval_string(string, binding, opts) when is_list(opts) do
-    validated_eval_string(string, binding, opts)
+    validated_eval_string(string, validate_binding(binding), env_for_eval(opts), opts)
   end
 
-  defp validated_eval_string(string, binding, opts_or_env) do
+  defp validate_binding(binding) when is_list(binding), do: binding
-    %{line: line, file: file} = env = env_for_eval(opts_or_env)
+
+  defp validate_binding(binding) do
+    raise ArgumentError, "binding must be a list, got: #{inspect(binding)}"
+  end
+
+  defp validated_eval_string(string, binding, env, opts) do
+    %{line: line, file: file} = env
     forms = :elixir.string_to_quoted!(to_charlist(string), line, 1, file, [])
-    {value, binding, _env} = eval_verify(:eval_forms, [forms, binding, env])
+    {value, binding, _env} = eval_verify(:eval_forms, [forms, binding, env, opts])
     {value, binding}
   end
 
@@ -752,6 +768,12 @@ 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()>>`
@@ -1134,7 +1156,8 @@ defmodule Code do
   returned quoted expressions (instead of evaluated).
 
   See `eval_string/3` for a description of arguments and return types.
-  The options are described under `env_for_eval/1`.
+  It accepts the same options as both `env_for_eval/1` and
+  `eval_quoted_with_env/4`.
 
   ## Examples
 
@@ -1156,11 +1179,20 @@ defmodule Code do
       [a: 1, b: 2]
 
   """
-  @spec eval_quoted(Macro.t(), binding, Macro.Env.t() | env_eval_opts) :: {term, binding}
+  @spec eval_quoted(Macro.t(), binding, Macro.Env.t() | [eval_opt | env_eval_opt]) ::
-  def eval_quoted(quoted, binding \\ [], env_or_opts \\ []) do
+          {term, binding}
-    {value, binding, _env} =
+  def eval_quoted(quoted, binding \\ [], env_or_opts \\ [])
-      eval_verify(:eval_quoted, [quoted, binding, env_for_eval(env_or_opts)])
 
+  def eval_quoted(quoted, binding, %Macro.Env{} = env) do
+    eval_quoted(quoted, validate_binding(binding), env_for_eval(env), [])
+  end
+
+  def eval_quoted(quoted, binding, opts) when is_list(opts) do
+    eval_quoted(quoted, validate_binding(binding), env_for_eval(opts), opts)
+  end
+
+  defp eval_quoted(quoted, binding, env, opts) do
+    {value, binding, _env} = eval_verify(:eval_quoted, [quoted, binding, env, opts])
     {value, binding}
   end
 
@@ -1188,14 +1220,9 @@ defmodule Code do
 
     * `:module` - the module to run the environment on
 
-    * `:prune_binding` - (since v1.14.2) prune binding to keep only
-      variables read or written by the evaluated code. Note that
-      variables used by modules are always pruned, even if later used
-      by the modules. You can submit to the `:on_module` tracer event
-      and access the variables used by the module from its environment.
   """
   @doc since: "1.14.0"
-  @spec env_for_eval(Macro.Env.t() | env_eval_opts) :: Macro.Env.t()
+  @spec env_for_eval(Macro.Env.t() | [env_eval_opt]) :: Macro.Env.t()
   def env_for_eval(env_or_opts), do: :elixir.env_for_eval(env_or_opts)
 
   @doc """
@@ -1209,11 +1236,19 @@ defmodule Code do
 
   ## Options
 
-  It accepts the same options as `env_for_eval/1`.
+    * `:prune_binding` - (since v1.14.2) prune binding to keep only
+      variables read or written by the evaluated code. Note that
+      variables used by modules are always pruned, even if later used
+      by the modules. You can submit to the `:on_module` tracer event
+      and access the variables used by the module from its environment.
+
+    * `:dbg_callback` - (since v1.20.0) overrides the behaviour of `dbg/2`
+      used in the evaluated code. It must be a `{module, function, args}`
+      tuple, see `dbg/2` for more details.
 
   """
   @doc since: "1.14.0"
-  @spec eval_quoted_with_env(Macro.t(), binding, Macro.Env.t(), env_eval_opts) ::
+  @spec eval_quoted_with_env(Macro.t(), binding, Macro.Env.t(), [eval_opt]) ::
           {term, binding, Macro.Env.t()}
   def eval_quoted_with_env(quoted, binding, %Macro.Env{} = env, opts \\ [])
       when is_list(binding) do
@@ -1263,9 +1298,9 @@ 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 than the literal
+      `{:error, reason :: binary}`. If you return anything other than the literal
       itself as the `term`, then the AST is no longer valid. This option
-      may still useful for textual analysis of the source code.
+      may still be 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
@@ -1291,7 +1326,7 @@ defmodule Code do
   and keyword lists.
 
   The encoder function will receive the atom name (as a binary) and a
-  keyword list with the current file, line and column. It must return
+  keyword list with the current line and column. It must return
   `{:ok, token :: term} | {:error, reason :: binary}`.
 
   The encoder function is supposed to create an atom from the given
@@ -1359,12 +1394,15 @@ defmodule Code do
   while preserving information like comments and literals position.
 
   Returns `{:ok, quoted_form, comments}` if it succeeds,
-  `{:error, {line, error, token}}` otherwise.
+  `{:error, {location, error, token}}` otherwise, where `location`
+  is keyword metadata containing the line and column of the error.
 
   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
@@ -1419,7 +1457,9 @@ 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), `SyntaxError` otherwise.
+  (usually because the expression is incomplete), `MismatchedDelimiterError`
+  (in case of mismatched opening and closing delimiters) and `SyntaxError`
+  otherwise.
 
   Check `string_to_quoted/2` for options information.
   """
@@ -1522,9 +1562,13 @@ 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`, `:line_length`, `:locals_without_parens`, `:force_do_end_blocks`,
+  `:file`, `:line`, `:locals_without_parens`, `:force_do_end_blocks`, and all
-  `:syntax_colors`, and all migration options like `:migrate_charlists_as_sigils`.
+  migration options like `:migrate_charlists_as_sigils`. Note `:line_length`
+  does not apply here.
   """
   @doc since: "1.13.0"
   @spec quoted_to_algebra(Macro.t(), [format_opt() | quoted_to_algebra_opt()]) ::
@@ -1606,13 +1650,19 @@ defmodule Code do
         nil
 
       :proceed ->
-        loaded =
+        try do
-          Module.ParallelChecker.verify(fn ->
+          loaded =
-            :elixir_compiler.string(charlist, file, fn _, _ -> :ok end)
+            Module.ParallelChecker.verify(fn ->
-          end)
+              :elixir_compiler.string(charlist, file, fn _, _ -> :ok end)
+            end)
 
-        :elixir_code_server.cast({:required, file})
+          :elixir_code_server.cast({:required, file})
-        loaded
+          loaded
+        catch
+          kind, reason ->
+            :elixir_code_server.call({:release, file})
+            :erlang.raise(kind, reason, __STACKTRACE__)
+        end
     end
   end
 
@@ -1638,7 +1688,7 @@ defmodule Code do
   @doc """
   Stores all given compilation options.
 
-  Changing the compilation options affect all processes
+  Changing the compilation options affects 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`.
@@ -1702,7 +1752,7 @@ defmodule Code do
   @doc """
   Stores a compilation option.
 
-  Changing the compilation options affect all processes running in a
+  Changing the compilation options affects all processes running in a
   given Erlang VM node.
 
   Available options are:
@@ -1718,13 +1768,17 @@ 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 disables this
+      Other environments, such as `mix test`, automatically disable this
       via the `:test_elixirc_options` project configuration, as there is
       typically no need to store debug chunks for test files.
 
     * `:docs` - when `true`, retains documentation in the compiled module.
       Defaults to `true`.
 
+    * `:erlc_options` (since v1.21.0) - a list of Erlang compiler options. For example,
+      `erlc_options: [:beam_debug_info, :beam_debug_stack]` emits Erlang/OTP
+      debug metadata for BEAM debuggers. Defaults to `[]`.
+
     * `:ignore_already_consolidated` (since v1.10.0) - when `true`, does not warn
       when a protocol has already been consolidated and a new implementation is added.
       Defaults to `false`.
@@ -1732,16 +1786,13 @@ 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 of which modules
+    * `:infer_signatures` (since v1.18.0) - a list of applications whose modules
-      should be using during type inference. When `false`, it disables module-local
+      should be used 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.
-      Defaults to `true`, which is equivalent to setting it to `[:elixir]` only.
+      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
-      When setting this option, we recommend running `mix clean` so the modules can be
+      signatures for test files). Outside of Mix projects, it defaults to `[:elixir]`.
-      recompiled with the new behaviour. `mix test` automatically disables this option
-      via the `:test_elixirc_options` project configuration, as there is typically no
-      need to infer signatures for test files.
 
     * `:module_definition` (since v1.20.0) - stores if the module definition should
       be `:compiled` (the default) or `:interpreted`. Note this does not affect the
@@ -1764,7 +1815,7 @@ 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 be set it to `:warn` if you want undefined variables to
+      error. You may 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
@@ -2099,7 +2150,7 @@ 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 (or may not) become available in the future.
+  available, but it may (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:

lib/elixir/lib/code/formatter.ex

@@ -195,6 +195,7 @@ 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)
@@ -223,6 +224,7 @@ 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,
@@ -334,14 +336,20 @@ defmodule Code.Formatter do
   end
 
   defp quoted_to_algebra(
-         {{:., _, [:erlang, :binary_to_atom]}, _, [{:<<>>, _, entries}, :utf8]} = quoted,
+         {{:., _, [:erlang, :binary_to_atom]}, _, [{:<<>>, _, entries} = bitstring, :utf8]} =
+           quoted,
          context,
          state
        ) do
-    if interpolated?(entries) do
+    cond do
-      interpolation_to_algebra(entries, @double_quote, state, ":\"", @double_quote)
+      not interpolated?(entries) ->
-    else
+        remote_to_algebra(quoted, context, state)
-      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)
     end
   end
 
@@ -1457,7 +1465,7 @@ defmodule Code.Formatter do
             metadata = [
               file: state.file,
               line: meta[:line],
-              sigil: String.to_atom(name),
+              sigil: String.to_unsafe_atom(name),
               modifiers: modifiers,
               opening_delimiter: opening_delimiter
             ]
@@ -1696,7 +1704,7 @@ defmodule Code.Formatter do
     iodata |> IO.iodata_to_binary() |> string() |> color_doc(:atom, inspect_opts)
   end
 
-  defp integer_to_algebra(text, inspect_otps) do
+  defp integer_to_algebra(text, inspect_opts) do
     case text do
       <<?0, ?x, rest::binary>> ->
         "0x" <> String.upcase(rest)
@@ -1710,15 +1718,15 @@ defmodule Code.Formatter do
       decimal ->
         insert_underscores(decimal)
     end
-    |> color_doc(:number, inspect_otps)
+    |> color_doc(:number, inspect_opts)
   end
 
-  defp float_to_algebra(text, inspect_otps) do
+  defp float_to_algebra(text, inspect_opts) 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_otps)
+    color_doc(string, :number, inspect_opts)
   end
 
   defp insert_underscores("-" <> digits) do

lib/elixir/lib/code/fragment.ex

@@ -27,7 +27,8 @@ defmodule Code.Fragment do
           column: pos_integer(),
           columns: boolean(),
           token_metadata: boolean(),
-          literal_encoder: (term(), Macro.metadata() -> term()),
+          literal_encoder: (term(), Macro.metadata() -> {:ok, Macro.t()} | {:error, binary()}),
+          preserve_sigils: boolean(),
           trailing_fragment: String.t()
         ]
 
@@ -35,7 +36,7 @@ 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 the retrieve
+  considered, namely `\r\n` and `\n`. If you would like to retrieve
   lines without their line endings, use `String.split(string, ["\r\n", "\n"])`.
 
   ## Examples
@@ -51,6 +52,7 @@ defmodule Code.Fragment do
 
   """
   @doc since: "1.19.0"
+  @spec lines(String.t()) :: [String.t()]
   def lines(string) do
     lines(string, <<>>)
   end
@@ -140,6 +142,9 @@ 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`
 
@@ -157,8 +162,8 @@ 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`, or an operator starting with `~`, such as
+      of a sigil, such as `~` or `~s`. Operators starting with `~`, such as
-      `~>` and `~>>`
+      `~>` and `~>>`, are returned as :operator contexts
 
     * `{: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
@@ -204,6 +209,7 @@ defmodule Code.Fragment do
           | {:local_arity, charlist}
           | {:local_call, charlist}
           | {:anonymous_call, inside_caller}
+          | {:capture_arg, charlist}
           | {:module_attribute, charlist}
           | {:operator, charlist}
           | {:operator_arity, charlist}
@@ -656,7 +662,7 @@ 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 to `cursor_context/2`
+  ## Differences from `cursor_context/2`
 
   Because `surround_context/3` attempts to capture complex expressions,
   it has some differences to `cursor_context/2`:
@@ -670,7 +676,7 @@ 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
@@ -1234,14 +1240,43 @@ defmodule Code.Fragment do
       the cursor. This is necessary to correctly complete anonymous functions
       and the left-hand side of `->`
 
+    * `:preserve_sigils` (since v1.20.0) - preserve sigil cursor location
+      (see "Tracking sigils" section below)
+
+  ## Tracking sigils
+
+  The `:preserve_sigils` option can be used to track cursor positions inside
+  a sigil.
+
+  If the sigil is terminated abruptly, the `sigil_*` call will have the cursor
+  as the second argument:
+
+      iex> Code.Fragment.container_cursor_to_quoted("~r/foo", preserve_sigils: true)
+      {:ok,
+      {:sigil_r, [delimiter: "/", line: 1],
+        [{:<<>>, [line: 1], ["foo"]}, {:__cursor__, [line: 1, column: 7], []}]}}
+
+  In case the sigil is completed and has zero or more modifiers, the cursor will
+  be nested in the list, with all previous delimiters specified:
+
+      iex> Code.Fragment.container_cursor_to_quoted("~r/foo/i", preserve_sigils: true)
+      {:ok,
+       {:sigil_r, [delimiter: "/", line: 1],
+        [{:<<>>, [line: 1], ["foo"]}, [105, {:__cursor__, [line: 1, column: 9], []}]]}}
+
+  If the cursor is after the sigil, then it is discarded as everything else:
+
+      iex> Code.Fragment.container_cursor_to_quoted("~r/foo/i ", preserve_sigils: true)
+      {:ok, {:__cursor__, [line: 1], []}}
   """
   @doc since: "1.13.0"
   @spec container_cursor_to_quoted(List.Chars.t(), container_cursor_to_quoted_opts()) ::
           {:ok, Macro.t()} | {:error, {location :: keyword, binary | {binary, binary}, binary}}
   def container_cursor_to_quoted(fragment, opts \\ []) do
     {trailing_fragment, opts} = Keyword.pop(opts, :trailing_fragment)
+    {preserve_sigils?, opts} = Keyword.pop(opts, :preserve_sigils, false)
     opts = Keyword.take(opts, [:columns, :token_metadata, :literal_encoder])
-    opts = [check_terminators: {:cursor, []}] ++ opts
+    opts = [check_terminators: {:cursor, preserve_sigils?, []}] ++ opts
 
     file = Keyword.get(opts, :file, "nofile")
     line = Keyword.get(opts, :line, 1)
@@ -1272,7 +1307,7 @@ defmodule Code.Fragment do
                  Enum.split_while(rev_terminators, &(elem(&1, 0) not in [:do, :fn])),
                true <- maybe_missing_stab?(rev_tokens, true),
                opts =
-                 Keyword.put(opts, :check_terminators, {:cursor, before_start}),
+                 Keyword.put(opts, :check_terminators, {:cursor, false, before_start}),
                {:error, {meta, _, ~c"end"}, _rest, _warnings, trailing_rev_tokens} <-
                  :elixir_tokenizer.tokenize(to_charlist(trailing_fragment), line, column, opts) do
             trailing_tokens =

lib/elixir/lib/code/identifier.ex

@@ -65,7 +65,7 @@ defmodule Code.Identifier do
     with "-" <> rest <- Atom.to_string(atom),
          [trailing | reversed] = rest |> String.split("/") |> Enum.reverse(),
          [arity, _inner, _count, ""] <- String.split(trailing, "-") do
-      {reversed |> Enum.reverse() |> Enum.join("/") |> String.to_atom(), arity}
+      {reversed |> Enum.reverse() |> Enum.join("/") |> String.to_unsafe_atom(), arity}
     else
       _ -> :error
     end
@@ -150,20 +150,20 @@ defmodule Code.Identifier do
     <<acc::binary, char::utf8>>
   end
 
-  defp escape_char(char, acc) when char < 0x100 do
+  defp escape_char(char, acc) when char < 0x80 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, ?\\, ?x, ?{, to_hex(a), to_hex(b), to_hex(c), to_hex(d), ?}>>
+    <<acc::binary, ?\\, ?u, 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, ?\\, ?x, ?{, to_hex(a), to_hex(b), to_hex(c), to_hex(d), to_hex(e), to_hex(f),
+    <<acc::binary, ?\\, ?u, ?{, to_hex(a), to_hex(b), to_hex(c), to_hex(d), to_hex(e), to_hex(f),
       ?}>>
   end
 

lib/elixir/lib/code/normalizer.ex

@@ -4,6 +4,8 @@
 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
@@ -68,7 +70,7 @@ defmodule Code.Normalizer do
 
   # Bit containers
   defp do_normalize({:<<>>, _, args} = quoted, state) when is_list(args) do
-    normalize_bitstring(quoted, state)
+    normalize_bitstring(quoted, state, state.escape)
   end
 
   # Atoms with interpolations
@@ -89,13 +91,7 @@ defmodule Code.Normalizer do
         normalize_literal(:utf8, [], state)
       end
 
-    string =
+    string = normalize_bitstring(string, state, state.escape)
-      if state.escape do
-        normalize_bitstring(string, state, true)
-      else
-        normalize_bitstring(string, state)
-      end
-
     {{:., dot_meta, [:erlang, :binary_to_atom]}, call_meta, [string, utf8]}
   end
 
@@ -118,6 +114,7 @@ defmodule Code.Normalizer do
             end
         end)
 
+      parts = maybe_add_trailing_newline(call_meta, parts, state)
       {{:., dot_meta, [List, :to_charlist]}, call_meta, [parts]}
     else
       normalize_call(quoted, state)
@@ -187,7 +184,8 @@ defmodule Code.Normalizer do
         |> patch_meta_line(state.parent_meta)
         |> Keyword.put_new(:delimiter, "\"")
 
-      {sigil, meta, [do_normalize(string, %{state | parent_meta: meta}), modifiers]}
+      string = normalize_bitstring(string, %{state | parent_meta: meta}, false)
+      {sigil, meta, [string, modifiers]}
     else
       _ ->
         normalize_call(quoted, state)
@@ -269,7 +267,7 @@ defmodule Code.Normalizer do
           "Elixir." <> segments ->
             segments
             |> String.split(".")
-            |> Enum.map(&String.to_atom/1)
+            |> Enum.map(&String.to_unsafe_atom/1)
         end
 
       {:__aliases__, meta, segments}
@@ -351,18 +349,20 @@ defmodule Code.Normalizer do
         args = normalize_args(args, %{state | parent_meta: meta})
         {form, meta, args}
 
-      Keyword.has_key?(meta, :do) ->
+      Keyword.has_key?(meta, :do) and kw_blocks?(last) ->
         # def foo do :ok end
         # def foo, do: :ok
         normalize_kw_blocks(form, meta, args, state)
 
-      match?([{:do, _} | _], last) and Keyword.keyword?(last) ->
+      match?([{:do, _} | _], last) and kw_blocks?(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, [])
 
@@ -401,11 +401,22 @@ 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 \\ false) do
+  defp normalize_bitstring({:<<>>, meta, parts}, state, escape_interpolation) do
     meta = patch_meta_line(meta, state.parent_meta)
 
     parts =
@@ -424,9 +435,21 @@ defmodule Code.Normalizer do
         end)
       end
 
+    parts = maybe_add_trailing_newline(meta, parts, state)
     {:<<>>, meta, parts}
   end
 
+  defp maybe_add_trailing_newline(meta, parts, state) do
+    with true <- state.escape and Keyword.get(meta, :delimiter) in ["\"\"\"", "'''"],
+         last = List.last(parts),
+         true <- is_binary(last) and not String.ends_with?(last, "\n") do
+      [_last | rest] = Enum.reverse(parts)
+      Enum.reverse([last <> "\n" | rest])
+    else
+      _ -> parts
+    end
+  end
+
   defp normalize_interpolation_parts(parts, state, escape_interpolation) do
     Enum.map(parts, fn
       {:"::", interpolation_meta,
@@ -552,7 +575,7 @@ defmodule Code.Normalizer do
     atom
     |> Atom.to_string()
     |> maybe_escape_literal(state)
-    |> String.to_atom()
+    |> String.to_unsafe_atom()
   end
 
   defp maybe_escape_literal(term, _) do

lib/elixir/lib/code/typespec.ex

@@ -80,7 +80,8 @@ 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` and `:opaque`).
+  element is the type (`:typep`, `:type`, `:opaque` and, on Erlang/OTP 28+,
+  `:nominal`).
 
   The module must have a corresponding BEAM file which can be
   located by the runtime system. The types will be in the Erlang
@@ -95,9 +96,10 @@ defmodule Code.Typespec do
 
         types =
           for {:attribute, _, kind, {name, _, args} = type} <- abstract_code,
-              kind in [:opaque, :type] do
+              kind in [:opaque, :type, :nominal] do
             cond do
               kind == :opaque -> {:opaque, type}
+              kind == :nominal -> {:nominal, type}
               {name, length(args)} in exported_types -> {:type, type}
               true -> {:typep, type}
             end
@@ -117,7 +119,7 @@ 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 types will be in the Erlang
+  located by the runtime system. The specs will be in the Erlang
   Abstract Format.
   """
   @spec fetch_specs(module | binary) :: {:ok, [tuple]} | :error
@@ -135,10 +137,10 @@ 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 spec name and arity and the second is the spec.
+  element is the callback name and arity and the second is the callback.
 
   The module must have a corresponding BEAM file
-  which can be located by the runtime system. The types will be
+  which can be located by the runtime system. The callbacks will be
   in the Erlang Abstract Format.
   """
   @spec fetch_callbacks(module | binary) :: {:ok, [tuple]} | :error
@@ -191,8 +193,8 @@ defmodule Code.Typespec do
 
   ## To AST conversion
 
-  defp collect_vars({:ann_type, _anno, args}) when is_list(args) do
+  defp collect_vars({:ann_type, _anno, [_var, type]}) do
-    []
+    collect_vars(type)
   end
 
   defp collect_vars({:type, _anno, _kind, args}) when is_list(args) do
@@ -399,10 +401,10 @@ defmodule Code.Typespec do
   defp erl_to_ex_var(var) do
     case Atom.to_string(var) do
       <<"_", c::utf8, rest::binary>> ->
-        String.to_atom("_#{String.downcase(<<c::utf8>>)}#{rest}")
+        String.to_unsafe_atom("_#{String.downcase(<<c::utf8>>)}#{rest}")
 
       <<c::utf8, rest::binary>> ->
-        String.to_atom("#{String.downcase(<<c::utf8>>)}#{rest}")
+        String.to_unsafe_atom("#{String.downcase(<<c::utf8>>)}#{rest}")
     end
   end
 

lib/elixir/lib/collectable.ex

@@ -69,6 +69,22 @@ defprotocol Collectable do
       iex> Enum.into([1, 2, 3], MapSet.new())
       MapSet.new([1, 2, 3])
 
+  ## Halting
+
+  The `:halt` flag will be given whenever the collection won't
+  terminate correctly and must be used to clean up existing resources
+  (such as sockets, file handles, etc).
+
+  Note it is not guaranteed that the accumulator given to halt will
+  be the latest version of the accumulator returned by a previous call
+  with `{:cont, elem}`. Therefore, you must track the collected results
+  within the resource you intend to halt.
+
+  This is by design: ensuring halt is always called with the latest
+  accumulator would make pure collectables (the ones that do not implement
+  halt) expensive. However, given the collectables that must implement halt
+  already need to track state, the burden of tracking the accumulator
+  across invocations is put on them.
   """
 
   @type command :: {:cont, term} | :done | :halt

lib/elixir/lib/config.ex

@@ -152,6 +152,7 @@ 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)}"
@@ -198,6 +199,7 @@ 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}]}])
@@ -225,6 +227,7 @@ 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
@@ -233,7 +236,7 @@ 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:
@@ -284,8 +287,8 @@ defmodule Config do
 
   In case the file doesn't exist, an error is raised.
 
-  If file is a relative, it will be expanded relatively to the
+  If the file is relative, it will be expanded relative to the
-  directory the current configuration file is in.
+  directory of the current configuration file.
 
   ## Examples
 
@@ -377,21 +380,27 @@ defmodule Config do
     end
   end
 
-  defp validate!(config, file) do
+  defp validate!(config, file) when is_list(config) do
-    Enum.all?(config, fn
+    Enum.each(config, fn
       {app, value} when is_atom(app) ->
-        if Keyword.keyword?(value) do
+        if not Keyword.keyword?(value) do
-          true
-        else
           raise ArgumentError,
                 "expected config for app #{inspect(app)} in #{Path.relative_to_cwd(file)} " <>
                   "to return keyword list, got: #{inspect(value)}"
         end
 
-      _ ->
+      other ->
-        false
+        raise ArgumentError,
+              "expected config in #{Path.relative_to_cwd(file)} to be a keyword list " <>
+                "of {atom, keyword} pairs, got entry: #{inspect(other)}"
     end)
 
     config
   end
+
+  defp validate!(config, file) do
+    raise ArgumentError,
+          "expected config in #{Path.relative_to_cwd(file)} to be a keyword list " <>
+            "of {atom, keyword} pairs, got: #{inspect(config)}"
+  end
 end

lib/elixir/lib/config/provider.ex

@@ -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: [

lib/elixir/lib/config/reader.ex

@@ -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: [

lib/elixir/lib/enum.ex

@@ -618,7 +618,7 @@ defmodule Enum do
           acc,
           (element, acc -> {:cont, chunk, acc} | {:cont, acc} | {:halt, acc}),
           (acc -> {:cont, chunk, acc} | {:cont, acc})
-        ) :: Enumerable.t()
+        ) :: [chunk]
         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(t) :: t
+  @spec concat(Enumerable.t(Enumerable.t(elem))) :: [elem] when elem: term
   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 produces the same result as the `++/2` operator
+  This function behaves similarly to the `++/2` operator with proper
-  for lists.
+  lists, but applied to enumerables.
 
   ## Examples
 
@@ -693,7 +693,7 @@ defmodule Enum do
       [1, 2, 3, 4, 5, 6]
 
   """
-  @spec concat(t, t) :: t
+  @spec concat(Enumerable.t(elem), Enumerable.t(elem)) :: [elem] when elem: term
   def concat(left, right) when is_list(left) and is_list(right) do
     left ++ right
   end
@@ -829,7 +829,7 @@ defmodule Enum do
   """
   @spec dedup(t) :: list
   def dedup(enumerable) when is_list(enumerable) do
-    dedup_list(enumerable, []) |> :lists.reverse()
+    dedup_list(enumerable)
   end
 
   def dedup(enumerable) do
@@ -859,6 +859,10 @@ 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)
@@ -903,7 +907,7 @@ defmodule Enum do
 
   def drop(enumerable, amount) when is_integer(amount) and amount < 0 do
     {count, fun} = slice_count_and_fun(enumerable, 1)
-    amount = Kernel.min(amount + count, count)
+    amount = amount + count
 
     if amount > 0 do
       fun.(0, amount, 1)
@@ -1442,7 +1446,7 @@ defmodule Enum do
     )
 
     # Avoid warnings about Dict
-    dict_module = String.to_atom("Dict")
+    dict_module = String.to_unsafe_atom("Dict")
 
     reduce(reverse(enumerable), dict, fn entry, categories ->
       dict_module.update(categories, fun.(entry), [entry], &[entry | &1])
@@ -2023,11 +2027,16 @@ defmodule Enum do
   operators work by using this function.
   """
   @spec member?(t, element) :: boolean
-  def member?(enumerable, element) when is_list(enumerable) do
+  def member?(enumerable, element) do
+    __in__(element, enumerable)
+  end
+
+  @doc false
+  def __in__(element, enumerable) when is_list(enumerable) do
     :lists.member(element, enumerable)
   end
 
-  def member?(enumerable, element) do
+  def __in__(element, enumerable) do
     case Enumerable.member?(enumerable, element) do
       {:ok, element} when is_boolean(element) ->
         element
@@ -2224,14 +2233,19 @@ defmodule Enum do
       nil
 
   """
-  @spec min_max(t, (element, element -> boolean) | module()) :: {element, element}
+  @spec min_max(t, (element, element -> boolean) | module()) :: {min :: element, max :: element}
-  @spec min_max(t, (-> empty_result)) :: {element, element} | empty_result when empty_result: any
+  @spec min_max(t, (-> empty_result)) :: {min :: element, max :: element} | empty_result
+        when empty_result: any
   @spec min_max(t, (element, element -> boolean) | module(), (-> empty_result)) ::
-          {element, element} | empty_result
+          {min :: element, max :: 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
@@ -2338,14 +2352,14 @@ defmodule Enum do
 
   """
   @spec min_max_by(t, (element -> any), (element, element -> boolean) | module()) ::
-          {element, element} | empty_result
+          {min :: element, max :: element} | empty_result
         when empty_result: any
   @spec min_max_by(
           t,
           (element -> any),
           (element, element -> boolean) | module(),
           (-> empty_result)
-        ) :: {element, element} | empty_result
+        ) :: {min :: element, max :: element} | empty_result
         when empty_result: any
   def min_max_by(
         enumerable,
@@ -2389,6 +2403,18 @@ 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`.
 
@@ -2666,7 +2692,7 @@ defmodule Enum do
       5050
 
   """
-  @spec reduce_while(t, any, (element, any -> {:cont, any} | {:halt, any})) :: any
+  @spec reduce_while(t, acc, (element, acc -> {:cont, acc} | {:halt, acc})) :: acc
   def reduce_while(enumerable, acc, fun) do
     Enumerable.reduce(enumerable, {:cont, acc}, fun) |> elem(1)
   end
@@ -2909,8 +2935,7 @@ defmodule Enum do
   end
 
   defp slide_list_middle(list, 0, last, start_to_middle) do
-    {slid_range, tail} = slide_list_last(list, last + 1, [])
+    slide_list_last(list, last + 1, [], start_to_middle)
-    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
@@ -2918,16 +2943,16 @@ defmodule Enum do
     :lists.reverse(acc)
   end
 
-  defp slide_list_last([h | t], last, acc) when last > 0 do
+  defp slide_list_last([h | t], last, acc, start_to_middle) when last > 0 do
-    slide_list_last(t, last - 1, [h | acc])
+    slide_list_last(t, last - 1, [h | acc], start_to_middle)
   end
 
-  defp slide_list_last(rest, 0, acc) do
+  defp slide_list_last(rest, 0, acc, start_to_middle) do
-    {:lists.reverse(acc), rest}
+    :lists.reverse(acc, :lists.reverse(start_to_middle, rest))
   end
 
-  defp slide_list_last([], _, acc) do
+  defp slide_list_last([], _, acc, start_to_middle) do
-    {:lists.reverse(acc), []}
+    :lists.reverse(acc, :lists.reverse(start_to_middle))
   end
 
   @doc """
@@ -4193,7 +4218,7 @@ 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]]
 
   """
@@ -4304,11 +4329,24 @@ defmodule Enum do
         empty.()
 
       _ ->
-        last = last - rem(last - first, step)
+        # 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)
 
-        case fun.(first, last) do
+          case fun.(first, last) do
-          true -> first
+            true -> first
-          false -> last
+            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)
         end
     end
   end
@@ -4411,10 +4449,9 @@ defmodule Enum do
   ## any?/2 all?/2
 
   defp predicate_list([h | t], initial, fun) do
-    if !!fun.(h) == initial do
+    case !!fun.(h) do
-      predicate_list(t, initial, fun)
+      ^initial -> predicate_list(t, initial, fun)
-    else
+      _ -> not initial
-      not initial
     end
   end
 
@@ -4425,10 +4462,9 @@ defmodule Enum do
   defp predicate_range(first, last, step, initial, fun)
        when step > 0 and first <= last
        when step < 0 and first >= last do
-    if !!fun.(first) == initial do
+    case !!fun.(first) do
-      predicate_range(first + step, last, step, initial, fun)
+      ^initial -> predicate_range(first + step, last, step, initial, fun)
-    else
+      _ -> not initial
-      not initial
     end
   end
 
@@ -4507,19 +4543,20 @@ defmodule Enum do
 
   # dedup
 
-  defp dedup_list([value | tail], acc) do
+  defp dedup_list([value | [value | _] = tail]), do: dedup_list(tail)
-    acc =
+  defp dedup_list([value | tail]), do: [value | dedup_list(tail)]
-      case acc do
+  defp dedup_list([]), do: []
-        [^value | _] -> acc
-        _ -> [value | acc]
-      end
 
-    dedup_list(tail, acc)
+  ## 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_list([], acc) do
+  defp dedup_by_list([], _fun, _prev, acc), do: :lists.reverse(acc)
-    acc
-  end
 
   ## drop
 
@@ -5224,7 +5261,7 @@ defimpl Enumerable, for: Range do
   end
 
   def slice(first.._//step = range) do
-    {:ok, Range.size(range), &slice(first + &1 * step, step + &3 - 1, &2)}
+    {:ok, Range.size(range), &slice(first + &1 * step, step * &3, &2)}
   end
 
   # TODO: Remove me on v2.0

lib/elixir/lib/exception.ex

@@ -26,7 +26,7 @@ defmodule Exception do
   @typedoc "The exception type"
   @type t :: %{
           required(:__struct__) => module,
-          required(:__exception__) => true,
+          required(:__exception__) => term,
           optional(atom) => any
         }
 
@@ -77,7 +77,7 @@ defmodule Exception do
   @doc false
   @deprecated "Use Kernel.is_exception/1 instead"
   def exception?(term)
-  def exception?(%_{__exception__: true}), do: true
+  def exception?(%_{__exception__: _}), do: true
   def exception?(_), do: false
 
   @doc """
@@ -89,7 +89,7 @@ defmodule Exception do
   return a descriptive error message instead.
   """
   @spec message(t) :: String.t()
-  def message(%module{__exception__: true} = exception) do
+  def message(%module{__exception__: _} = exception) do
     try do
       module.message(exception)
     rescue
@@ -123,7 +123,7 @@ defmodule Exception do
   @spec normalize(:error, any, stacktrace) :: t
   @spec normalize(non_error_kind, payload, stacktrace) :: payload when payload: var
   def normalize(kind, payload, stacktrace \\ [])
-  def normalize(:error, %_{__exception__: true} = payload, _stacktrace), do: payload
+  def normalize(:error, %_{__exception__: _} = payload, _stacktrace), do: payload
   def normalize(:error, payload, stacktrace), do: ErlangError.normalize(payload, stacktrace)
   def normalize(_kind, payload, _stacktrace), do: payload
 
@@ -1046,7 +1046,7 @@ defmodule RuntimeError do
       iex> raise "oops!"
       ** (RuntimeError) oops!
 
-  You should use this exceptions sparingly, since most of the time it might be
+  You should use this exception sparingly, since most of the time it might be
   better to define your own exceptions specific to your application or library.
   Sometimes, however, there are situations in which you don't expect a condition to
   happen, but you want to give a meaningful error message if it does. In those cases,
@@ -1137,7 +1137,7 @@ defmodule SystemLimitError do
 
   For example, this can happen if you try to create an atom that is too large:
 
-      iex> String.to_atom(String.duplicate("a", 100_000))
+      iex> String.to_unsafe_atom(String.duplicate("a", 100_000))
       ** (SystemLimitError) a system limit has been reached
   """
 
@@ -1807,7 +1807,7 @@ defmodule UndefinedFunctionError do
 
   defp load_module({name, _path, _loaded?}) do
     name
-    |> List.to_atom()
+    |> List.to_unsafe_atom()
     |> Code.ensure_loaded()
   end
 
@@ -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 non existent file:
+  For example, this exception is raised, when trying to read a nonexistent 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 file or directory that isn't present:
+  For example, this exception is raised when trying to copy to a 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 file that isn't present:
+  For example, this exception is raised when trying to link to a 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

lib/elixir/lib/file.ex

@@ -400,6 +400,13 @@ defmodule File do
 
   You can use `:file.format_error/1` to get a descriptive string of the error.
 
+  ## Options (since v1.20)
+
+  The supported options are:
+
+    * `:raw` - a single atom to bypass the file server and only check
+      for the file locally
+
   ## Examples
 
       File.read("hello.txt")
@@ -408,15 +415,24 @@ defmodule File do
       File.read("non_existing.txt")
       #=> {:error, :enoent}
   """
-  @spec read(Path.t()) :: {:ok, binary} | {:error, posix | :badarg | :terminated | :system_limit}
+  @spec read(Path.t(), [exists_option]) ::
-  def read(path) do
+          {:ok, binary} | {:error, posix | :badarg | :terminated | :system_limit}
-    :file.read_file(IO.chardata_to_string(path))
+        when exists_option: :raw
+  def read(path, opts \\ []) do
+    :file.read_file(IO.chardata_to_string(path), opts)
   end
 
   @doc """
   Returns a binary with the contents of the given filename,
   or raises a `File.Error` exception if an error occurs.
 
+  ## Options (since v1.20)
+
+  The supported options are:
+
+    * `:raw` - a single atom to bypass the file server and only check
+      for the file locally
+
   ## Examples
 
       File.read!("hello.txt")
@@ -425,9 +441,9 @@ defmodule File do
       File.read!("non_existing.txt")
       ** (File.Error) could not read file "non_existing.txt": no such file or directory
   """
-  @spec read!(Path.t()) :: binary
+  @spec read!(Path.t(), [exists_option]) :: binary when exists_option: :raw
-  def read!(path) do
+  def read!(path, opts \\ []) do
-    case read(path) do
+    case read(path, opts) do
       {:ok, binary} ->
         binary
 
@@ -881,7 +897,7 @@ defmodule File do
       File.copy("non_existing.txt", "copy.txt")
       #=> {:error, :enoent}
   """
-  @spec copy(Path.t() | io_device, Path.t() | io_device, pos_integer | :infinity) ::
+  @spec copy(Path.t() | io_device, Path.t() | io_device, non_neg_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)
@@ -902,7 +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, pos_integer | :infinity) ::
+  @spec copy!(Path.t() | io_device, Path.t() | io_device, non_neg_integer | :infinity) ::
           non_neg_integer
   def copy!(source, destination, bytes_count \\ :infinity) do
     case copy(source, destination, bytes_count) do
@@ -1087,7 +1103,7 @@ defmodule File do
 
   @doc ~S"""
   Copies the contents in `source` to `destination` recursively, maintaining the
-  source directory structure and modes.
+  source directory structure and regular file modes.
 
   If `source` is a file or a symbolic link to it, `destination` must be a path
   to an existent file, a symbolic link to one, or a path to a non-existent file.
@@ -1098,7 +1114,9 @@ defmodule File do
   If the source is a file, it copies `source` to `destination`. If the `source`
   is a directory, it copies the contents inside source into the `destination` directory.
 
-  If a file already exists in the destination, it invokes the optional `on_conflict`
+  For regular files, their respective file modes are preserved in the destination.
+  Directory modes are preserved only when `:preserve_directory_permissions` is `true`.
+  If a file already exists in the destination, it invokes the optional `:on_conflict`
   callback given as an option. See "Options" for more information.
 
   This function may fail while copying files, in such cases, it will leave the
@@ -1116,6 +1134,12 @@ defmodule File do
 
   Special files such as device files, sockets, and named pipes are not copied.
 
+  Typical error reasons are:
+
+    * `:enoent`  - `source` does not exist
+    * `:eisdir`  - `source` is a file and `destination` is a directory
+    * `:einval`  - `destination` is the same as or a subdirectory of `source`
+
   ## Options
 
     * `:on_conflict` - (since v1.14.0) Invoked when a file already exists in the destination.
@@ -1129,6 +1153,11 @@ defmodule File do
       dereferenced and have their contents copied instead when set to `true`. If the dereferenced
       files do not exist, than the operation fails. The default is `false`.
 
+    * `:preserve_directory_permissions` - (since v1.20.0) when `true`, the permissions of
+      source directories are copied to the destination directories after their contents are
+      written. This is useful when source directories are read-only or have restricted
+      permissions that must be preserved. The default is `false`.
+
   ## Examples
 
       # Copies file "a.txt" to "b.txt"
@@ -1146,11 +1175,16 @@ defmodule File do
       #=> {:ok, ["z.txt", "y.txt", "x.txt]}
 
       File.cp_r("non_existing.txt", "copy.txt")
-      #=> {:error, :enoent}
+      #=> {:error, :enoent, "non_existing.txt"}
+
+      # Copying into a subdirectory of source is not allowed
+      File.cp_r("src", "src/dest")
+      #=> {:error, :einval, "src/dest"}
   """
   @spec cp_r(Path.t(), Path.t(),
           on_conflict: on_conflict_callback,
-          dereference_symlinks: boolean()
+          dereference_symlinks: boolean(),
+          preserve_directory_permissions: boolean()
         ) ::
           {:ok, [binary]} | {:error, posix | :badarg | :terminated, binary}
 
@@ -1172,6 +1206,7 @@ defmodule File do
   def cp_r(source, destination, options) when is_list(options) do
     on_conflict = Keyword.get(options, :on_conflict, fn _, _ -> true end)
     dereference? = Keyword.get(options, :dereference_symlinks, false)
+    preserve_directory_permissions? = Keyword.get(options, :preserve_directory_permissions, false)
 
     source =
       source
@@ -1183,9 +1218,25 @@ defmodule File do
       |> IO.chardata_to_string()
       |> assert_no_null_byte!("File.cp_r/3")
 
-    case do_cp_r(source, destination, on_conflict, dereference?, []) do
+    source_parts = source |> Path.expand() |> Path.split()
-      {:error, _, _} = error -> error
+    dest_parts = destination |> Path.expand() |> Path.split()
-      res -> {:ok, res}
+
+    if source_parts != dest_parts and List.starts_with?(dest_parts, source_parts) do
+      {:error, :einval, destination}
+    else
+      dereference = if dereference?, do: MapSet.new(), else: nil
+
+      case do_cp_r(
+             source,
+             destination,
+             on_conflict,
+             dereference,
+             preserve_directory_permissions?,
+             []
+           ) do
+        {:error, _, _} = error -> error
+        res -> {:ok, res}
+      end
     end
   end
 
@@ -1206,7 +1257,8 @@ defmodule File do
   """
   @spec cp_r!(Path.t(), Path.t(),
           on_conflict: on_conflict_callback,
-          dereference_symlinks: boolean()
+          dereference_symlinks: boolean(),
+          preserve_directory_permissions: boolean()
         ) :: [binary]
   def cp_r!(source, destination, options \\ []) do
     case cp_r(source, destination, options) do
@@ -1223,7 +1275,7 @@ defmodule File do
     end
   end
 
-  defp do_cp_r(src, dest, on_conflict, dereference?, acc) when is_list(acc) do
+  defp do_cp_r(src, dest, on_conflict, dereference, preserve_dir_perms?, acc) when is_list(acc) do
     case :elixir_utils.read_link_type(src) do
       {:ok, :regular} ->
         case do_cp_file(src, dest, on_conflict, acc) do
@@ -1236,8 +1288,15 @@ defmodule File do
 
       {:ok, :symlink} ->
         case :file.read_link(src) do
-          {:ok, link} when dereference? ->
+          {:ok, link} when dereference != nil ->
-            do_cp_r(Path.expand(link, Path.dirname(src)), dest, on_conflict, dereference?, acc)
+            resolved = Path.expand(link, Path.dirname(src))
+
+            if MapSet.member?(dereference, resolved) do
+              {:error, :eloop, src}
+            else
+              dereference = MapSet.put(dereference, resolved)
+              do_cp_r(resolved, dest, on_conflict, dereference, preserve_dir_perms?, acc)
+            end
 
           {:ok, link} ->
             do_cp_link(link, src, dest, on_conflict, acc)
@@ -1251,9 +1310,35 @@ defmodule File do
           {:ok, files} ->
             case mkdir(dest) do
               success when success in [:ok, {:error, :eexist}] ->
-                Enum.reduce(files, [dest | acc], fn x, acc ->
+                files
-                  do_cp_r(Path.join(src, x), Path.join(dest, x), on_conflict, dereference?, acc)
+                |> Enum.reduce_while([dest | acc], fn x, acc ->
+                  case do_cp_r(
+                         Path.join(src, x),
+                         Path.join(dest, x),
+                         on_conflict,
+                         dereference,
+                         preserve_dir_perms?,
+                         acc
+                       ) do
+                    {:error, _, _} = error -> {:halt, error}
+                    acc -> {:cont, acc}
+                  end
                 end)
+                |> case do
+                  {:error, _, _} = error ->
+                    error
+
+                  files when preserve_dir_perms? ->
+                    # Change the directory after writing files in case
+                    # it was originally read only
+                    case copy_file_mode(src, dest) do
+                      :ok -> files
+                      {:error, reason} -> {:error, reason, src}
+                    end
+
+                  files ->
+                    files
+                end
 
               {:error, reason} ->
                 {:error, reason, dest}
@@ -1272,14 +1357,13 @@ defmodule File do
   end
 
   # If we reach this clause, there was an error while processing a file.
-  defp do_cp_r(_, _, _, _, acc) do
+  defp do_cp_r(_, _, _, _, _, acc) do
     acc
   end
 
   defp copy_file_mode(src, dest) do
-    with {:ok, dest_fileinfo} <- stat(dest),
+    with {:ok, src_fileinfo} <- stat(src) do
-         {:ok, src_fileinfo} <- stat(src) do
+      chmod(dest, src_fileinfo.mode)
-      write_stat(dest, %{dest_fileinfo | mode: src_fileinfo.mode})
     end
   end
 
@@ -2136,7 +2220,7 @@ 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.

lib/elixir/lib/file/stream.ex

@@ -18,7 +18,13 @@ defmodule File.Stream do
 
   defstruct path: nil, modes: [], line_or_bytes: :line, raw: true, node: nil
 
-  @type t :: %__MODULE__{}
+  @type t :: %__MODULE__{
+          path: Path.t(),
+          modes: [term()],
+          line_or_bytes: :line | pos_integer(),
+          raw: boolean(),
+          node: node()
+        }
 
   @doc false
   def __build__(path, line_or_bytes, modes) do
@@ -119,7 +125,7 @@ defmodule File.Stream do
 
       counter = fn device ->
         device = skip_bom_and_offset(device, raw, modes)
-        count_lines(device, path, pattern, read_function(stream), 0)
+        count_lines(device, path, pattern, read_function(stream), 0, :empty)
       end
 
       {:ok, open!(stream, modes, counter)}
@@ -229,21 +235,28 @@ defmodule File.Stream do
       for mode <- modes, mode not in [:write, :append, :trim_bom], do: mode
     end
 
-    defp count_lines(device, path, pattern, read, count) do
+    defp count_lines(device, path, pattern, read, count, last_byte) do
       case read.(device) do
+        data when is_binary(data) and byte_size(data) > 0 ->
+          newlines = length(:binary.matches(data, pattern))
+          last = :binary.last(data)
+          count_lines(device, path, pattern, read, count + newlines, last)
+
         data when is_binary(data) ->
-          count_lines(device, path, pattern, read, count + count_lines(data, pattern))
+          count_lines(device, path, pattern, read, count, last_byte)
 
         :eof ->
-          count
+          case last_byte do
+            :empty -> 0
+            ?\n -> count
+            _ -> count + 1
+          end
 
         {:error, reason} ->
           raise File.Error, reason: reason, action: "stream", path: path
       end
     end
 
-    defp count_lines(data, pattern), do: length(:binary.matches(data, pattern))
-
     defp read_function(%{raw: true}), do: &IO.binread(&1, @read_ahead_size)
     defp read_function(%{raw: false}), do: &IO.read(&1, @read_ahead_size)
   end

lib/elixir/lib/float.ex

@@ -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
@@ -167,51 +167,73 @@ defmodule Float do
     parse_unsigned(binary)
   end
 
-  defp parse_unsigned(<<digit, rest::binary>>) when digit in ?0..?9,
+  defp parse_unsigned(<<digit, rest::binary>> = binary) when digit in ?0..?9,
-    do: parse_unsigned(rest, false, false, [digit])
+    do: parse_mantissa(binary, rest, false)
 
   defp parse_unsigned(binary) when is_binary(binary), do: :error
 
-  defp parse_unsigned(<<digit, rest::binary>>, dot?, e?, acc) when digit in ?0..?9,
+  defp parse_mantissa(binary, <<digit, rest::binary>>, dot?) when digit in ?0..?9,
-    do: parse_unsigned(rest, dot?, e?, [digit | acc])
+    do: parse_mantissa(binary, rest, dot?)
 
-  defp parse_unsigned(<<?., digit, rest::binary>>, false, false, acc) when digit in ?0..?9,
+  defp parse_mantissa(binary, <<?., digit, rest::binary>>, false) when digit in ?0..?9,
-    do: parse_unsigned(rest, true, false, [digit, ?. | acc])
+    do: parse_mantissa(binary, rest, true)
 
-  defp parse_unsigned(<<exp_marker, digit, rest::binary>>, dot?, false, acc)
+  defp parse_mantissa(binary, <<exp_marker, digit, rest::binary>> = tail, dot?)
        when exp_marker in ~c"eE" and digit in ?0..?9,
-       do: parse_unsigned(rest, true, true, [digit, ?e | add_dot(acc, dot?)])
+       do: parse_exponent(binary, byte_size(binary) - byte_size(tail), rest, dot?)
 
-  defp parse_unsigned(<<exp_marker, sign, digit, rest::binary>>, dot?, false, acc)
+  defp parse_mantissa(binary, <<exp_marker, sign, digit, rest::binary>> = tail, dot?)
        when exp_marker in ~c"eE" and sign in ~c"-+" and digit in ?0..?9,
-       do: parse_unsigned(rest, true, true, [digit, sign, ?e | add_dot(acc, dot?)])
+       do: parse_exponent(binary, byte_size(binary) - byte_size(tail), rest, dot?)
 
-  # When floats are expressed in scientific notation, :erlang.binary_to_float/1 can raise an
+  defp parse_mantissa(binary, rest, dot?), do: finish_mantissa(binary, rest, dot?)
-  # 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_exponent(binary, exp_pos, <<digit, rest::binary>>, dot?) when digit in ?0..?9,
-  defp parse_unsigned(rest, dot?, true = _e?, acc) do
+    do: parse_exponent(binary, exp_pos, rest, dot?)
-    acc
+
-    |> add_dot(dot?)
+  defp parse_exponent(binary, exp_pos, rest, dot?),
-    |> :lists.reverse()
+    do: finish_exponent(binary, exp_pos, rest, dot?)
-    |> :erlang.list_to_float()
+
+  defp finish_mantissa(binary, rest, _dot? = true) do
+    {:erlang.binary_to_float(consumed(binary, rest)), rest}
   rescue
     ArgumentError -> :error
-  else
-    float -> {float, rest}
   end
 
-  defp parse_unsigned(rest, dot?, false = _e?, acc) do
+  # Bare integer: * 1.0 casts to the nearest float without building a new binary,
-    float =
+  # and raises ArithmeticError on overflow (for example a 400-digit integer).
-      acc
+  defp finish_mantissa(binary, rest, _dot? = false) do
-      |> add_dot(dot?)
+    {:erlang.binary_to_integer(consumed(binary, rest)) * 1.0, rest}
-      |> :lists.reverse()
+  rescue
-      |> :erlang.list_to_float()
+    ArithmeticError -> :error
-
-    {float, rest}
   end
 
-  defp add_dot(acc, true), do: acc
+  # binary_to_float/1 raises ArgumentError when the exponent is too big, e.g. "1.0e400".
-  defp add_dot(acc, false), do: [?0, ?. | acc]
+  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))
 
   @doc """
   Rounds a float to the largest float less than or equal to `number`.
@@ -264,7 +286,7 @@ 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 down
+  `ceil/2` also accepts a precision to round a floating-point value up
   to an arbitrary number of fractional digits (between 0 and 15).
 
   The operation is performed on the binary floating point, without a
@@ -333,7 +355,7 @@ 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
-  to reference implementations, such as "Correctly Rounded Binary-Decimal and
+  with reference implementations, such as "Correctly Rounded Binary-Decimal and
   Decimal-Binary Conversions" by David M. Gay.
 
   ## Examples
@@ -355,15 +377,12 @@ defmodule Float do
 
   """
   @spec round(float, precision_range) :: float
-  # This implementation is slow since it relies on big integers.
-  # Faster implementations are available on more recent papers
-  # and could be implemented in the future.
   def round(float, precision \\ 0)
 
-  def round(float, 0) when float == 0.0, do: float
+  def round(float, 0) when float === 0.0 or float === -0.0, do: float
 
   def round(float, 0) when is_float(float) do
-    case float |> :erlang.round() |> :erlang.float() do
+    case :erlang.round(float) * 1.0 do
       zero when zero == 0.0 and float < 0.0 -> -0.0
       rounded -> rounded
     end
@@ -377,140 +396,170 @@ defmodule Float do
     raise ArgumentError, invalid_precision_message(precision)
   end
 
+  # Decimal-place rounding via exact rational scaling. This is the bignum
+  # core used by reference implementations like David M. Gay's "Correctly
+  # Rounded Binary-Decimal and Decimal-Binary Conversions" (cited in the
+  # @doc above), Python's round(), and Java's BigDecimal.setScale.
+  #
+  # 1. Decompose float exactly: |float| = mantissa / 2^shift.
+  # 2. Scale exactly: |float| * 10^precision = mantissa * 10^precision / 2^shift.
+  #    Because precision is bounded to 0..15, the product fits in ~103 bits
+  #    (53-bit mantissa + ~50-bit power of ten) and BEAM bignums handle it
+  #    directly without approximation.
+  # 3. Round the exact rational to an integer per the requested mode
+  #    (half_up / floor / ceil) using quotient and remainder.
+  # 4. Emit the float closest to rounded_int / 10^precision:
+  #    - fast path: when rounded_int < 2^53, both operands are exactly
+  #      representable as floats and IEEE division is correctly rounded.
+  #    - slow path: bignum alignment + manual mantissa extraction with
+  #      round-to-nearest-even for the trailing bit.
+  #
+  # The integer-rounding decision (step 3) and the binary-emission decision
+  # (step 4) are deliberately independent: step 3 picks the exact rational
+  # the user asked for, step 4 picks the closest float to that rational.
+  # Conflating them is the classic source of double-rounding bugs.
+  #
+  # Faster algorithms exist (Cox 2026's table-based uscale; Ryū / Schubfach
+  # for round-trip printing) but target different problems or assume
+  # fixed-width machine arithmetic that BEAM doesn't expose efficiently.
+  # At precision <= 15, the exact path is small, easy to audit, and fast
+  # enough that a more complex algorithm has not been justified by benchmarks.
   defp round(num, _precision, _rounding) when is_float(num) and num == 0.0, do: num
 
-  defp round(float, precision, rounding) do
+  defp round(float, precision, mode) do
-    <<sign::1, exp::11, significant::52-bitstring>> = <<float::float>>
+    <<sign::1, exp::11, mantissa::52>> = <<float::float>>
-    {num, count} = decompose(significant, 1)
-    count = count - exp + 1023
 
     cond do
-      # Precision beyond 15 digits
+      # Subnormal — tiny but non-zero; treat per-mode (ceil(+) and floor(-) bump
-      count >= 104 ->
+      # to 10^-precision; everything else rounds to signed zero).
-        case rounding do
+      exp == 0 ->
-          :ceil when sign === 0 -> 1 / power_of_10(precision)
+        tiny_round(sign, precision, mode)
-          :floor when sign === 1 -> -1 / power_of_10(precision)
-          :ceil when sign === 1 -> minus_zero()
-          :half_up when sign === 1 -> minus_zero()
-          _ -> 0.0
-        end
 
-      # We are asking more precision than we have
+      # |float| >= 2^52 — has no fractional bits, return unchanged.
-      count <= precision ->
+      exp - 1075 >= 0 ->
         float
 
       true ->
-        # Difference in precision between float and asked precision
+        mantissa = @power_of_2_to_52 ||| mantissa
-        # We subtract 1 because we need to calculate the remainder too
+        shift = 1075 - exp
-        diff = count - precision - 1
+        do_round(sign, mantissa, shift, precision, mode)
-
-        # Get up to latest so we calculate the remainder
-        power_of_10 = power_of_10(diff)
-
-        # Convert the numerand to decimal base
-        num = num * power_of_5(count)
-
-        # Move to the given precision - 1
-        num = div(num, power_of_10)
-        div = div(num, 10)
-        num = rounding(rounding, sign, num, div)
-
-        # Convert back to float without loss
-        # https://www.exploringbinary.com/correct-decimal-to-floating-point-using-big-integers/
-        den = power_of_10(precision)
-        boundary = den <<< 52
-
-        cond do
-          num == 0 and sign == 1 ->
-            minus_zero()
-
-          num == 0 ->
-            0.0
-
-          num >= boundary ->
-            {den, exp} = scale_down(num, boundary, 52)
-            decimal_to_float(sign, num, den, exp)
-
-          true ->
-            {num, exp} = scale_up(num, boundary, 52)
-            decimal_to_float(sign, num, den, exp)
-        end
     end
   end
 
-  # TODO remove once we require Erlang/OTP 27+
+  # |float * 10^precision| < 0.5 — integer round is 0; ceil/floor still bump per sign.
-  # This function tricks the compiler to avoid this bug in previous versions:
+  defp do_round(sign, _mantissa, shift, precision, mode) when shift >= 104 do
-  # https://github.com/elixir-lang/elixir/blob/main/lib/elixir/lib/float.ex#L408-L412
+    tiny_round(sign, precision, mode)
-  defp minus_zero, do: -0.0
-
-  defp decompose(significant, initial) do
-    decompose(significant, 1, 0, initial)
   end
 
-  defp decompose(<<1::1, bits::bitstring>>, count, last_count, acc) do
+  defp do_round(sign, mantissa, shift, precision, mode) do
-    decompose(bits, count + 1, count, (acc <<< (count - last_count)) + 1)
+    power = power_of_10(precision)
-  end
+    product = mantissa * power
+    half = 1 <<< (shift - 1)
+    quotient = product >>> shift
+    remainder = product - (quotient <<< shift)
+    rounded_int = round_step(mode, sign, quotient, remainder, half)
 
-  defp decompose(<<0::1, bits::bitstring>>, count, last_count, acc) do
+    cond do
-    decompose(bits, count + 1, last_count, acc)
+      rounded_int == 0 ->
-  end
+        signed_zero(sign)
 
-  defp decompose(<<>>, _count, last_count, acc) do
+      rounded_int < @power_of_2_to_52 <<< 1 ->
-    {acc, last_count}
+        # Both rounded_int and power fit in 53 bits, so IEEE float division
-  end
+        # is correctly rounded.
+        result = rounded_int / power
+        if sign == 1, do: -result, else: result
 
-  defp scale_up(num, boundary, exp) when num >= boundary, do: {num, exp}
+      true ->
-  defp scale_up(num, boundary, exp), do: scale_up(num <<< 1, boundary, exp - 1)
+        bignum_to_float(sign, rounded_int, power)
-
-  defp scale_down(num, den, exp) do
-    new_den = den <<< 1
-
-    if num < new_den do
-      {den >>> 52, exp}
-    else
-      scale_down(num, new_den, exp + 1)
     end
   end
 
-  defp decimal_to_float(sign, num, den, exp) do
+  defp round_step(:half_up, _sign, quotient, remainder, half) do
-    quo = div(num, den)
+    if remainder >= half, do: quotient + 1, else: quotient
-    rem = num - quo * den
+  end
 
-    tmp =
+  defp round_step(:floor, 0, quotient, _remainder, _half), do: quotient
-      case den >>> 1 do
+  defp round_step(:floor, 1, quotient, remainder, _half) when remainder > 0, do: quotient + 1
-        den when rem > den -> quo + 1
+  defp round_step(:floor, 1, quotient, _remainder, _half), do: quotient
-        den when rem < den -> quo
+
-        _ when (quo &&& 1) === 1 -> quo + 1
+  defp round_step(:ceil, 0, quotient, remainder, _half) when remainder > 0, do: quotient + 1
-        _ -> quo
+  defp round_step(:ceil, 0, quotient, _remainder, _half), do: quotient
+  defp round_step(:ceil, 1, quotient, _remainder, _half), do: quotient
+
+  defp signed_zero(0), do: 0.0
+  defp signed_zero(1), do: -0.0
+
+  # Result of rounding a non-zero float whose |float * 10^precision| < 0.5.
+  # ceil(+) → +10^-precision, floor(-) → -10^-precision, others → signed 0.
+  defp tiny_round(0, precision, :ceil), do: 1.0 / power_of_10(precision)
+  defp tiny_round(1, precision, :floor), do: -1.0 / power_of_10(precision)
+  defp tiny_round(sign, _precision, _mode), do: signed_zero(sign)
+
+  # Slow path: emit float closest to `sign * rounded_int / power` when
+  # rounded_int >= 2^53. The binary emission step is always IEEE
+  # round-to-nearest-even, regardless of the integer-rounding mode.
+  defp bignum_to_float(sign, rounded_int, power) do
+    shift_adjust = bit_length(rounded_int) - bit_length(power) - 53
+    {numerator, denominator, exp} = align(rounded_int, power, shift_adjust)
+
+    quotient = div(numerator, denominator)
+    remainder = numerator - quotient * denominator
+    half = denominator >>> 1
+
+    mantissa =
+      cond do
+        remainder > half -> quotient + 1
+        remainder < half -> quotient
+        (quotient &&& 1) === 1 -> quotient + 1
+        true -> quotient
       end
 
-    tmp = tmp - @power_of_2_to_52
+    # Carry-bit normalization: `mantissa` lives in [2^52, 2^53]. The upper
-    <<tmp::float>> = <<sign::1, exp + 1023::11, tmp::52>>
+    # bound `2^53` is reachable when `align/3` returns an upper-bound quotient
-    tmp
+    # or when rounding carries. Rebalance into the canonical [2^52, 2^53)
+    # range so the 52-bit packing below doesn't silently truncate.
+    {mantissa, exp} =
+      if mantissa == @power_of_2_to_52 <<< 1,
+        do: {@power_of_2_to_52, exp + 1},
+        else: {mantissa, exp}
+
+    <<result::float>> = <<sign::1, exp + 1023::11, mantissa - @power_of_2_to_52::52>>
+    result
   end
 
-  defp rounding(:floor, 1, _num, div), do: div + 1
+  # Pick (numerator, denominator, exp) so that numerator/denominator ∈ [2^52, 2^53)
-  defp rounding(:ceil, 0, _num, div), do: div + 1
+  # and the resulting float = numerator/denominator * 2^(exp-52).
+  defp align(rounded_int, power, shift_adjust) when shift_adjust >= 0 do
+    new_power = power <<< shift_adjust
 
-  defp rounding(:half_up, _sign, num, div) do
+    if rounded_int < new_power <<< 53,
-    case rem(num, 10) do
+      do: {rounded_int, new_power, 52 + shift_adjust},
-      rem when rem < 5 -> div
+      else: {rounded_int, new_power <<< 1, 53 + shift_adjust}
-      rem when rem >= 5 -> div + 1
+  end
+
+  defp align(rounded_int, power, shift_adjust) do
+    shifted = rounded_int <<< -shift_adjust
+
+    cond do
+      shifted >= power <<< 53 -> {shifted, power <<< 1, 53 + shift_adjust}
+      shifted >= power <<< 52 -> {shifted, power, 52 + shift_adjust}
+      true -> {shifted <<< 1, power, 51 + shift_adjust}
     end
   end
 
-  defp rounding(_, _, _, div), do: div
+  defp bit_length(0), do: 0
+  defp bit_length(integer) when integer > 0, do: bit_length(integer, 0)
+  defp bit_length(integer, acc) when integer >= 1 <<< 64, do: bit_length(integer >>> 64, acc + 64)
+  defp bit_length(integer, acc) when integer >= 1 <<< 16, do: bit_length(integer >>> 16, acc + 16)
+  defp bit_length(integer, acc) when integer >= 1 <<< 4, do: bit_length(integer >>> 4, acc + 4)
+  defp bit_length(integer, acc) when integer >= 1, do: bit_length(integer >>> 1, acc + 1)
+  defp bit_length(_integer, acc), do: acc
 
-  Enum.reduce(0..104, 1, fn x, acc ->
+  Enum.reduce(0..15, 1, fn exponent, acc ->
-    defp power_of_10(unquote(x)), do: unquote(acc)
+    defp power_of_10(unquote(exponent)), do: unquote(acc)
     acc * 10
   end)
 
-  Enum.reduce(0..104, 1, fn x, acc ->
-    defp power_of_5(unquote(x)), do: unquote(acc)
-    acc * 5
-  end)
-
   @doc """
   Returns a pair of integers whose ratio is exactly equal
   to the original float and with a positive denominator.
@@ -656,7 +705,7 @@ defmodule Float do
   end
 
   defp invalid_precision_message(precision) do
-    "precision #{precision} is out of valid range of #{inspect(@precision_range)}"
+    "precision #{inspect(precision)} is out of valid range of #{inspect(@precision_range)}"
   end
 
   defp expand_compact([{:compact, false} | t]), do: expand_compact(t)

lib/elixir/lib/function.ex

@@ -69,7 +69,6 @@ defmodule Function do
           | :name
           | :new_index
           | :new_uniq
-          | :pid
           | :type
           | :uniq
 
@@ -112,8 +111,6 @@ 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.
@@ -159,7 +156,7 @@ 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`, `:uniq`, and `:pid`.
+  atoms `:index`, `:new_index`, `:new_uniq`, and `:uniq`.
   For a named function, the value of any of these items is always the
   atom `:undefined`.
 
@@ -179,8 +176,6 @@ 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"

lib/elixir/lib/gen_event.ex

@@ -36,7 +36,7 @@ defmodule GenEvent do
   alternative. GenStage is an external Elixir library maintained by the Elixir
   team; it provides a tool to implement systems that exchange events in a
   demand-driven way with built-in support for back-pressure. See the [GenStage
-  documentation](https://hexdocs.pm/gen_stage) for more information.
+  documentation](https://gen-stage.hexdocs.pm) for more information.
 
   ### `:gen_event`
 

lib/elixir/lib/gen_server.ex

@@ -232,6 +232,8 @@ defmodule GenServer do
   a name on start via the `:name` option. Registered names are also
   automatically cleaned up on termination. The supported values are:
 
+    * `nil` (default) - the GenServer is not registered with a name.
+
     * an atom - the GenServer is registered locally (to the current node)
       with the given name using `Process.register/2`.
 
@@ -565,9 +567,12 @@ defmodule GenServer do
      `Supervisor`. Likely this approach involves calling `Supervisor.restart_child/2`
       after a delay to attempt a restart.
 
-  Returning `{:stop, reason}` will cause `start_link/3` to return
+  Returning `{:error, reason}` will cause `start_link/3` to return
-  `{:error, reason}` and the process to exit with reason `reason` without
+  `{:error, reason}`.
-  entering the loop or calling `c:terminate/2`.
+
+  Returning `{:stop, reason}` will the process to exit with reason `reason`,
+  without entering the loop or calling `c:terminate/2`. `start_link/3` will
+  return `{:error, reason}`, but only if the caller is trapping exits.
   """
   @callback init(init_arg :: term) ::
               {:ok, state}
@@ -858,7 +863,7 @@ defmodule GenServer do
   @type on_start :: {:ok, pid} | :ignore | {:error, {:already_started, pid} | term}
 
   @typedoc "The GenServer name"
-  @type name :: atom | {:global, term} | {:via, module, term}
+  @type name :: nil | atom | {:global, term} | {:via, module, term}
 
   @typedoc "Options used by the `start*` functions"
   @type options :: [option]
@@ -1153,7 +1158,7 @@ defmodule GenServer do
 
   ## Timeouts
 
-  `timeout` is an integer greater than zero which specifies how many
+  `timeout` is a non-negative integer 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

lib/elixir/lib/hash_dict.ex

@@ -265,13 +265,13 @@ defimpl Enumerable, for: HashDict do
 
   def reduce(dict, acc, fun) do
     # Avoid warnings about HashDict being deprecated.
-    module = String.to_atom("HashDict")
+    module = String.to_unsafe_atom("HashDict")
     module.reduce(dict, acc, fun)
   end
 
   def member?(dict, {key, value}) do
     # Avoid warnings about HashDict being deprecated.
-    module = String.to_atom("HashDict")
+    module = String.to_unsafe_atom("HashDict")
     {:ok, match?({:ok, ^value}, module.fetch(dict, key))}
   end
 
@@ -281,7 +281,7 @@ defimpl Enumerable, for: HashDict do
 
   def count(dict) do
     # Avoid warnings about HashDict being deprecated.
-    module = String.to_atom("HashDict")
+    module = String.to_unsafe_atom("HashDict")
     {:ok, module.size(dict)}
   end
 
@@ -296,7 +296,7 @@ defimpl Collectable, for: HashDict do
 
   def into(original) do
     # Avoid warnings about HashDict being deprecated.
-    module = String.to_atom("HashDict")
+    module = String.to_unsafe_atom("HashDict")
 
     collector_fun = fn
       dict, {:cont, {key, value}} -> module.put(dict, key, value)
@@ -315,7 +315,7 @@ defimpl Inspect, for: HashDict do
 
   def inspect(dict, opts) do
     # Avoid warnings about HashDict being deprecated.
-    module = String.to_atom("HashDict")
+    module = String.to_unsafe_atom("HashDict")
     concat(["#HashDict<", Inspect.List.inspect(module.to_list(dict), opts), ">"])
   end
 end

lib/elixir/lib/hash_set.ex

@@ -279,19 +279,19 @@ defimpl Enumerable, for: HashSet do
 
   def reduce(set, acc, fun) do
     # Avoid warnings about HashSet being deprecated.
-    module = String.to_atom("HashSet")
+    module = String.to_unsafe_atom("HashSet")
     module.reduce(set, acc, fun)
   end
 
   def member?(set, term) do
     # Avoid warnings about HashSet being deprecated.
-    module = String.to_atom("HashSet")
+    module = String.to_unsafe_atom("HashSet")
     {:ok, module.member?(set, term)}
   end
 
   def count(set) do
     # Avoid warnings about HashSet being deprecated.
-    module = String.to_atom("HashSet")
+    module = String.to_unsafe_atom("HashSet")
     {:ok, module.size(set)}
   end
 
@@ -306,7 +306,7 @@ defimpl Collectable, for: HashSet do
 
   def into(original) do
     # Avoid warnings about HashSet being deprecated.
-    module = String.to_atom("HashSet")
+    module = String.to_unsafe_atom("HashSet")
 
     collector_fun = fn
       set, {:cont, term} -> module.put(set, term)
@@ -325,7 +325,7 @@ defimpl Inspect, for: HashSet do
 
   def inspect(set, opts) do
     # Avoid warnings about HashSet being deprecated.
-    module = String.to_atom("HashSet")
+    module = String.to_unsafe_atom("HashSet")
     concat(["#HashSet<", Inspect.List.inspect(module.to_list(set), opts), ">"])
   end
 end

lib/elixir/lib/inspect.ex

@@ -92,7 +92,7 @@ defprotocol Inspect do
       end
 
       inspect(%Point{x: 1})
-      %Point{x: 1, y: 0}
+      #=> %Point{x: 1, y: 0}
 
   ## Custom implementation
 
@@ -387,13 +387,20 @@ defimpl Inspect, for: List do
     close = color_doc("]", :list, opts)
 
     cond do
-      lists == :as_charlists or (lists == :infer and List.ascii_printable?(term, printable_limit)) ->
+      (lists == :as_charlists and unicode_list?(term, printable_limit)) or
-        inspected =
+          (lists == :infer and List.ascii_printable?(term, printable_limit)) ->
-          case Identifier.escape(IO.chardata_to_string(term), ?", printable_limit) do
+        {split, tail} =
-            {escaped, ""} -> [?~, ?c, ?", escaped, ?"]
+          if is_integer(printable_limit) do
-            {escaped, _} -> [?~, ?c, ?", escaped, ?", " ++ ..."]
+            case Enum.split(term, printable_limit) do
+              {split, []} -> {split, []}
+              {split, _} -> {split, " ++ ..."}
+            end
+          else
+            {term, []}
           end
 
+        {escaped, _} = Identifier.escape(IO.chardata_to_string(split), ?")
+        inspected = [?~, ?c, ?", escaped, ?" | tail]
         color_doc(IO.iodata_to_binary(inspected), :charlist, opts)
 
       keyword?(term) ->
@@ -407,6 +414,19 @@ 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)
@@ -416,8 +436,8 @@ defimpl Inspect, for: List do
 
   @doc false
   def keyword?([{key, _value} | rest]) when is_atom(key) do
-    case Atom.to_charlist(key) do
+    case Atom.to_string(key) do
-      [?E, ?l, ?i, ?x, ?i, ?r, ?.] ++ _ -> false
+      "Elixir." <> _ -> false
       _ -> keyword?(rest)
     end
   end
@@ -669,6 +689,11 @@ defimpl Inspect, for: Any do
     Inspect.Map.inspect_as_struct(struct, Macro.inspect_atom(:literal, module), info, opts)
   end
 
+  # A temporary clause to deal with native records until they are officially supported
+  def inspect(native_record, _opts) do
+    :io_lib.format("~p", [native_record]) |> IO.iodata_to_binary()
+  end
+
   def inspect_as_struct(map, name, infos, opts) do
     open = color_doc("#" <> name <> "<", :map, opts)
     sep = color_doc(",", :map, opts)

lib/elixir/lib/inspect/algebra.ex

@@ -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 lists will be printed as charlists,
+    * `:charlists` - when `:as_charlists` all charlists will be printed as charlists,
-      non-printable elements will be escaped.
+      non-printable code points will be escaped. Other lists will be printed as lists.
 
       When `:as_lists` all lists will be printed as lists.
 
@@ -46,8 +46,8 @@ defmodule Inspect.Opts do
     * `:limit` - limits the number of items that are inspected for tuples,
       bitstrings, maps, lists and any other collection of items, with the exception of
       printable strings and printable charlists which use the `:printable_limit` option.
-      It accepts a positive integer or `:infinity`. It defaults to `100` since
+      It accepts a positive integer or `:infinity`. It defaults to `200` since
-      `Elixir v1.19.0`, as it has better defaults to deal with nested collections.
+      `Elixir v1.20.0`, as it has better defaults to deal with nested collections.
 
     * `:pretty` - if set to `true` enables pretty printing. Defaults to `false`.
 
@@ -90,7 +90,7 @@ defmodule Inspect.Opts do
             charlists: :infer,
             custom_options: [],
             inspect_fun: &Inspect.inspect/2,
-            limit: 100,
+            limit: 200,
             pretty: false,
             printable_limit: 4096,
             safe: true,

lib/elixir/lib/integer.ex

@@ -108,7 +108,7 @@ defmodule Integer do
   defguard is_even(integer) when is_integer(integer) and (integer &&& 1) == 0
 
   @doc """
-  Computes `base` raised to power of `exponent`.
+  Computes `base` raised to the power of `exponent`.
 
   Both `base` and `exponent` must be integers.
   The exponent must be zero or positive.
@@ -297,8 +297,9 @@ defmodule Integer do
 
   defp undigits([], _base, acc), do: acc
 
-  defp undigits([digit | _], base, _) when is_integer(digit) and digit >= base,
+  defp undigits([digit | _], base, _)
-    do: raise(ArgumentError, "invalid digit #{digit} in base #{base}")
+       when is_integer(digit) and (digit >= base or digit <= -base),
+       do: raise(ArgumentError, "invalid digit #{digit} in base #{base}")
 
   defp undigits([digit | tail], base, acc) when is_integer(digit),
     do: undigits(tail, base, acc * base + digit)
@@ -531,8 +532,12 @@ defmodule Integer do
 
       iex> Integer.extended_gcd(10, 0)
       {10, 1, 0}
+      iex> Integer.extended_gcd(-10, 0)
+      {10, -1, 0}
       iex> Integer.extended_gcd(0, 10)
       {10, 0, 1}
+      iex> Integer.extended_gcd(0, -10)
+      {10, 0, -1}
       iex> Integer.extended_gcd(0, 0)
       {0, 0, 0}
 
@@ -540,8 +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), 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), do: {a, 1, 0}
+  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(integer1, integer2) when is_integer(integer1) and is_integer(integer2) do
     extended_gcd(integer2, integer1, 0, 1, 1, 0)

lib/elixir/lib/io.ex

@@ -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, term}]
+  @type inspect_opts :: [Inspect.Opts.new_opt() | {:label, String.Chars.t()}]
 
   @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 represents a number of bytes. The device is
+    * if `line_or_chars` is an integer, it is the number of Unicode
-      iterated by that number of bytes. This should be the preferred mode for reading
+      code points to be retrieved for devices open in Unicode/utf8 mode.
-      non-textual inputs.
+      Otherwise, it is the number of raw bytes to be retrieved.
 
     * 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 bytes from IO device `:stdio`.
+  Gets a number of characters 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 bytes from the IO `device`.
+  Gets a number of characters from the IO `device`.
 
   If the IO `device` is a Unicode device, `count` implies
   the number of Unicode code points to be retrieved.

lib/elixir/lib/io/ansi.ex

@@ -111,13 +111,15 @@ defmodule IO.ANSI do
   end
 
   defsequence = fn name, code, terminator ->
+    sequence = "\e[#{code}#{terminator}"
+
     @spec unquote(name)() :: String.t()
     def unquote(name)() do
-      "\e[#{unquote(code)}#{unquote(terminator)}"
+      unquote(sequence)
     end
 
     defp format_sequence(unquote(name)) do
-      unquote(name)()
+      unquote(sequence)
     end
   end
 
@@ -159,7 +161,7 @@ defmodule IO.ANSI do
 
   for font_n <- [1, 2, 3, 4, 5, 6, 7, 8, 9] do
     @doc "Sets alternative font #{font_n}."
-    defsequence.(:"font_#{font_n}", font_n + 10, "m")
+    defsequence.(String.to_unsafe_atom("font_#{font_n}"), font_n + 10, "m")
   end
 
   @doc "Normal color or intensity."
@@ -193,13 +195,13 @@ defmodule IO.ANSI do
     defsequence.(color, code + 30, "m")
 
     @doc "Sets foreground color to light #{color}."
-    defsequence.(:"light_#{color}", code + 90, "m")
+    defsequence.(String.to_unsafe_atom("light_#{color}"), code + 90, "m")
 
     @doc "Sets background color to #{color}."
-    defsequence.(:"#{color}_background", code + 40, "m")
+    defsequence.(String.to_unsafe_atom("#{color}_background"), code + 40, "m")
 
     @doc "Sets background color to light #{color}."
-    defsequence.(:"light_#{color}_background", code + 100, "m")
+    defsequence.(String.to_unsafe_atom("light_#{color}_background"), code + 100, "m")
   end
 
   @doc "Default text color."
@@ -332,7 +334,7 @@ defmodule IO.ANSI do
   end
 
   defp do_format([], [], acc, true, true) do
-    [acc | IO.ANSI.reset()]
+    [acc | reset()]
   end
 
   defp do_format([], [], acc, _emit?, _append_reset) do

lib/elixir/lib/io/ansi/docs.ex

@@ -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

lib/elixir/lib/io/stream.ex

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

lib/elixir/lib/json.ex

@@ -24,7 +24,7 @@ defprotocol JSON.Encoder do
   > #### Leaking Private Information {: .error}
   >
   > Prefer using `:only` to avoid accidentally leaking private information when
-  > new fields are added. Other approaches should be used with auction.
+  > new fields are added. Other approaches should be used with caution.
 
   You can also use `Protocol.derive/3` if you don't own the struct that you want
   to encode to JSON:
@@ -67,7 +67,7 @@ defprotocol JSON.Encoder do
 
     {io, _prefix} =
       Enum.flat_map_reduce(kv, ?{, fn {field, value}, prefix ->
-        key = IO.iodata_to_binary([prefix, :elixir_json.encode_binary(Atom.to_string(field)), ?:])
+        key = IO.iodata_to_binary([prefix, :json.encode_binary(Atom.to_string(field)), ?:])
         {[key, quote(do: encoder.(unquote(value), encoder))], ?,}
       end)
 
@@ -130,25 +130,25 @@ end
 
 defimpl JSON.Encoder, for: BitString do
   def encode(value, _encoder) do
-    :elixir_json.encode_binary(value)
+    :json.encode_binary(value)
   end
 end
 
 defimpl JSON.Encoder, for: List do
   def encode(value, encoder) do
-    :elixir_json.encode_list(value, encoder)
+    :json.encode_list(value, encoder)
   end
 end
 
 defimpl JSON.Encoder, for: Integer do
   def encode(value, _encoder) do
-    :elixir_json.encode_integer(value)
+    :json.encode_integer(value)
   end
 end
 
 defimpl JSON.Encoder, for: Float do
   def encode(value, _encoder) do
-    :elixir_json.encode_float(value)
+    :json.encode_float(value)
   end
 end
 
@@ -175,6 +175,7 @@ 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)
@@ -408,7 +409,7 @@ defmodule JSON do
     decoders = Keyword.put_new(decoders, :null, nil)
 
     try do
-      :elixir_json.decode(binary, acc, Map.new(decoders))
+      :json.decode(binary, acc, Map.new(decoders))
     catch
       :error, :unexpected_end ->
         {:error, {:unexpected_end, byte_size(binary)}}
@@ -528,16 +529,16 @@ defmodule JSON do
   end
 
   def protocol_encode(value, _encoder) when is_binary(value),
-    do: :elixir_json.encode_binary(value)
+    do: :json.encode_binary(value)
 
   def protocol_encode(value, _encoder) when is_integer(value),
-    do: :elixir_json.encode_integer(value)
+    do: :json.encode_integer(value)
 
   def protocol_encode(value, _encoder) when is_float(value),
-    do: :elixir_json.encode_float(value)
+    do: :json.encode_float(value)
 
   def protocol_encode(value, encoder) when is_list(value),
-    do: :elixir_json.encode_list(value, encoder)
+    do: :json.encode_list(value, encoder)
 
   def protocol_encode(%{} = value, encoder) when not is_map_key(value, :__struct__),
     do: JSON.Encoder.Map.encode(value, encoder)

lib/elixir/lib/kernel.ex

@@ -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
@@ -2109,7 +2109,7 @@ defmodule Kernel do
     assert_no_match_or_guard_scope(__CALLER__.context, "!")
 
     annotate_case(
-      [optimize_boolean: true, type_check: {:case, :!}],
+      [optimize_boolean: true, type_check: {:case, :"!!"}],
       quote do
         case unquote(value) do
           x when unquote(x_is_false_or_nil()) -> false
@@ -2752,7 +2752,7 @@ defmodule Kernel do
       nil ->
         quote do
           case unquote(term) do
-            %_{__exception__: true} -> true
+            %_{__exception__: _} -> true
             _ -> false
           end
         end
@@ -2764,8 +2764,7 @@ defmodule Kernel do
         quote do
           is_map(unquote(term)) and :erlang.is_map_key(:__struct__, unquote(term)) and
             is_atom(:erlang.map_get(:__struct__, unquote(term))) and
-            :erlang.is_map_key(:__exception__, unquote(term)) and
+            :erlang.is_map_key(:__exception__, unquote(term))
-            :erlang.map_get(:__exception__, unquote(term)) == true
         end
     end
   end
@@ -2792,7 +2791,7 @@ defmodule Kernel do
           case unquote(name) do
             name when is_atom(name) ->
               case unquote(term) do
-                %{__struct__: ^name, __exception__: true} -> true
+                %{__struct__: ^name, __exception__: _} -> true
                 _ -> false
               end
 
@@ -2810,8 +2809,7 @@ defmodule Kernel do
             (is_atom(unquote(name)) or :fail) and
             :erlang.is_map_key(:__struct__, unquote(term)) and
             :erlang.map_get(:__struct__, unquote(term)) == unquote(name) and
-            :erlang.is_map_key(:__exception__, unquote(term)) and
+            :erlang.is_map_key(:__exception__, unquote(term))
-            :erlang.map_get(:__exception__, unquote(term)) == true
         end
     end
   end
@@ -3090,7 +3088,7 @@ defmodule Kernel do
   @doc """
   Pops a key from the given nested structure.
 
-  Uses the `Access` protocol to traverse the structures
+  Uses the `Access` behaviour 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`.
@@ -4705,14 +4703,10 @@ defmodule Kernel do
         false
 
       [] ->
-        quote do
+        # inlined as false in erlang pass
-          _ = unquote(left)
+        quote(do: :lists.member(unquote(left), []))
-          false
-        end
 
       [head | tail] = list ->
-        # We only expand lists in the body if they are relatively
-        # short and it is made only of literal expressions.
         case in_body? do
           false -> in_list(left, head, tail, expand, list)
           true -> quote(do: :lists.member(unquote(left), unquote(right)))
@@ -4727,7 +4721,7 @@ defmodule Kernel do
             in_var(in_body?, left, &in_range(&1, expand.(first), expand.(last), expand.(step)))
 
           _ when in_body? ->
-            quote(do: Elixir.Enum.member?(unquote(right), unquote(left)))
+            quote(do: Elixir.Enum.__in__(unquote(left), unquote(right)))
 
           _ ->
             raise_on_invalid_args_in_2(right)
@@ -4966,6 +4960,7 @@ 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)
@@ -5039,6 +5034,7 @@ 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)
@@ -5153,7 +5149,7 @@ defmodule Kernel do
   warning saying that a module has been redefined.
 
   There are some modules that Elixir does not currently implement but it
-  may be implement in the future. Those modules are reserved and defining
+  may implement in the future. Those modules are reserved and defining
   them will result in a compilation error:
 
       defmodule Any do
@@ -5254,12 +5250,12 @@ defmodule Kernel do
   # defmodule Alias nested
   defp alias_defmodule({:__aliases__, _, [h | t]}, _module, env) when is_atom(h) do
     module = :elixir_aliases.concat([env.module, h])
-    alias = String.to_atom("Elixir." <> Atom.to_string(h))
+    alias = String.to_unsafe_atom("Elixir." <> Atom.to_string(h))
     opts = [as: alias, warn: false]
 
     case t do
       [] -> {module, module, opts}
-      _ -> {String.to_atom(Enum.join([module | t], ".")), module, opts}
+      _ -> {String.to_unsafe_atom(Enum.join([module | t], ".")), module, opts}
     end
   end
 
@@ -5566,7 +5562,7 @@ 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
 
@@ -5593,6 +5589,9 @@ 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}
@@ -5877,11 +5876,15 @@ defmodule Kernel do
   end
 
   @doc """
-  Defines a macro suitable for use in guard expressions.
+  Defines a custom guard with the given name.
 
-  It raises at compile time if the `guard` uses expressions that aren't
+  Once defined, custom guards can be invoked within regular code or in
-  allowed in [guard clauses](patterns-and-guards.html#guards),
+  guards. The module that contains the custom guard must be required before usage.
-  and otherwise creates a macro that can be used both inside or outside guards.
+
+  Custom guards are defined by providing a valid guard expression to
+  the right-hand side of `when`. `defguard` will then expand and validate
+  the expressions as guards. `defguard` will raise at compile time if the
+  guard uses expressions that aren't allowed in [guard clauses](patterns-and-guards.html#guards).
 
   When defining your own guards, consider the
   [naming conventions](naming-conventions.html#is_-prefix-is_foo)
@@ -5889,31 +5892,30 @@ defmodule Kernel do
 
   ## Example
 
+  For example, to define a guard similar to `Integer.is_even/1`, you can write:
+
       defmodule Integer.Guards do
         defguard is_even(value) when is_integer(value) and rem(value, 2) == 0
       end
 
-      defmodule Collatz do
+  which can then be used as:
-        @moduledoc "Tools for working with the Collatz sequence."
-        import Integer.Guards
 
-        @doc "Determines the number of steps `n` takes to reach `1`."
+      require Integer.Guards
-        # If this function never converges, please let me know what `n` you used.
+      Integer.Guards.is_even(3)
-        def converge(n) when n > 0, do: step(n, 0)
+      #=> false
 
-        defp step(1, step_count) do
+  ## Implementation details
-          step_count
-        end
 
-        defp step(n, step_count) when is_even(n) do
+  Behind the scenes, `defguard` will generate a macro which can be used
-          step(div(n, 2), step_count + 1)
+  inside and outside of guards, preserving their respective semantics.
-        end
 
-        defp step(n, step_count) do
+  When invoked inside a guard, it behaves as if the right-hand side of
-          step(3 * n + 1, step_count + 1)
+  `when` is injected as part of the guard, replacing the custom guard
-        end
+  arguments by the expressions given as inputs.
-      end
 
+  When invoked outside of a guard, it preserves regular function calling
+  semantics with one caveat: all arguments are evaluated before invocation,
+  except arguments which are unused, which are then never evaluated.
   """
   @doc since: "1.6.0"
   @spec defguard(Macro.t()) :: Macro.t()
@@ -6281,7 +6283,7 @@ defmodule Kernel do
   step through the code it sees). For general stepping, you can set breakpoints
   using `IEx.break!/4`.
 
-  For more information, [see IEx documentation](https://hexdocs.pm/iex/IEx.html#module-dbg-and-breakpoints).
+  For more information, [see IEx documentation](https://iex.hexdocs.pm/IEx.html#module-dbg-and-breakpoints).
 
   ## Configuring the debug function
 
@@ -6328,7 +6330,15 @@ defmodule Kernel do
   """
   @doc since: "1.14.0"
   defmacro dbg(code \\ quote(do: binding()), options \\ []) do
-    {mod, fun, args} = Application.compile_env!(__CALLER__, :elixir, :dbg_callback)
+    # The compiling process may override the callback by putting it in
+    # the process dictionary.
+    dbg_callback =
+      case :erlang.get({:elixir, :dbg_callback}) do
+        :undefined -> Application.compile_env!(__CALLER__, :elixir, :dbg_callback)
+        value -> value
+      end
+
+    {mod, fun, args} = dbg_callback
     Macro.compile_apply(mod, fun, [code, options, __CALLER__ | args], __CALLER__)
   end
 
@@ -6372,7 +6382,7 @@ defmodule Kernel do
 
   ### Passing timeouts
 
-  You can also pass timeouts directly to this functions, that is, milliseconds or
+  You can also pass timeouts directly to this function, that is, milliseconds or
   the atom `:infinity`. In this case, this function just returns the given argument.
 
   ## Examples
@@ -6417,12 +6427,20 @@ defmodule Kernel do
         {microsecond, _precision} = duration.microsecond
         millisecond = :erlang.convert_time_unit(microsecond, :microsecond, :millisecond)
 
-        duration.week * unquote(week_in_ms) +
+        total =
-          duration.day * unquote(day_in_ms) +
+          duration.week * unquote(week_in_ms) +
-          duration.hour * unquote(hour_in_ms) +
+            duration.day * unquote(day_in_ms) +
-          duration.minute * 60_000 +
+            duration.hour * unquote(hour_in_ms) +
-          duration.second * 1000 +
+            duration.minute * 60_000 +
-          millisecond
+            duration.second * 1000 +
+            millisecond
+
+        if total < 0 do
+          raise ArgumentError,
+                "duration must be positive, got: #{inspect(duration)}"
+        end
+
+        total
     end
   end
 
@@ -6884,7 +6902,7 @@ defmodule Kernel do
   defp maybe_atomize_calendar(<<alias, _::binary>> = last_part, string)
        when alias >= ?A and alias <= ?Z do
     string = binary_part(string, 0, byte_size(string) - byte_size(last_part) - 1)
-    {String.to_atom("Elixir." <> last_part), string}
+    {String.to_unsafe_atom("Elixir." <> last_part), string}
   end
 
   defp maybe_atomize_calendar(_last_part, string) do
@@ -6995,7 +7013,7 @@ defmodule Kernel do
 
         case mod do
           ?s -> parts
-          ?a -> :lists.map(&String.to_atom/1, parts)
+          ?a -> :lists.map(&String.to_unsafe_atom/1, parts)
           ?c -> :lists.map(&String.to_charlist/1, parts)
         end
 
@@ -7004,7 +7022,7 @@ defmodule Kernel do
 
         case mod do
           ?s -> parts
-          ?a -> quote(do: :lists.map(&String.to_atom/1, unquote(parts)))
+          ?a -> quote(do: :lists.map(&String.to_unsafe_atom/1, unquote(parts)))
           ?c -> quote(do: :lists.map(&String.to_charlist/1, unquote(parts)))
         end
     end
@@ -7038,7 +7056,7 @@ defmodule Kernel do
       :guard ->
         raise ArgumentError,
               "invalid expression in guard, #{exp} is not allowed in guards. " <>
-                "To learn more about guards, visit: https://hexdocs.pm/elixir/patterns-and-guards.html"
+                "To learn more about guards, visit: https://elixir.hexdocs.pm/patterns-and-guards.html"
 
       _ ->
         :ok

lib/elixir/lib/kernel/cli.ex

@@ -49,7 +49,7 @@ defmodule Kernel.CLI do
 
   @doc """
   Runs the given function by catching any failure
-  and printing them to stdout. `at_exit` hooks are
+  and printing them to stderr. `at_exit` hooks are
   also invoked before exiting.
 
   This function is used by Elixir's CLI and also
@@ -99,9 +99,14 @@ defmodule Kernel.CLI do
   Shared helper for error formatting on CLI tools.
   """
   def format_error(kind, reason, stacktrace) do
+    {banner, rest} = format_error_parts(kind, reason, stacktrace)
+    [banner, rest]
+  end
+
+  defp format_error_parts(kind, reason, stacktrace) do
     {blamed, stacktrace} = Exception.blame(kind, reason, stacktrace)
 
-    iodata =
+    banner =
       case blamed do
         %FunctionClauseError{} ->
           formatted = Exception.format_banner(kind, reason, stacktrace)
@@ -112,7 +117,7 @@ defmodule Kernel.CLI do
           Exception.format_banner(kind, blamed, stacktrace)
       end
 
-    [iodata, ?\n, Exception.format_stacktrace(prune_stacktrace(stacktrace))]
+    {banner, [?\n, Exception.format_stacktrace(prune_stacktrace(stacktrace))]}
   end
 
   @doc """
@@ -179,7 +184,8 @@ defmodule Kernel.CLI do
   ## Error handling
 
   defp print_error(kind, reason, stacktrace) do
-    IO.write(:stderr, format_error(kind, reason, stacktrace))
+    {banner, rest} = format_error_parts(kind, reason, stacktrace)
+    IO.write(:stderr, [IO.ANSI.format([:red, banner]), rest])
   end
 
   defp blame_match(%{match?: true, node: node}), do: blame_ansi(:normal, "+", node)
@@ -200,7 +206,7 @@ defmodule Kernel.CLI do
   end
 
   @elixir_internals [:elixir, :elixir_aliases, :elixir_clauses, :elixir_compiler, :elixir_def] ++
-                      [:elixir_def, :elixir_dispatch, :elixir_expand, :elixir_lexical] ++
+                      [: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]
@@ -338,7 +344,7 @@ defmodule Kernel.CLI do
     parse_argv(t, %{config | verbose_compile: true})
   end
 
-  defp parse_argv([~c"--profile", "time" | t], %{mode: :elixirc} = config) do
+  defp parse_argv([~c"--profile", ~c"time" | t], %{mode: :elixirc} = config) do
     parse_argv(t, %{config | profile: :time})
   end
 
@@ -427,7 +433,7 @@ defmodule Kernel.CLI do
   end
 
   defp process_command({:rpc_eval, node, expr}, _config) when is_list(expr) do
-    node = List.to_atom(node)
+    node = List.to_unsafe_atom(node)
 
     # Explicitly connect the node in case the rpc node was started with --sname/--name undefined.
     _ = :net_kernel.connect_node(node)

lib/elixir/lib/kernel/lexical_tracker.ex

@@ -23,7 +23,7 @@ defmodule Kernel.LexicalTracker do
 
   @doc """
   Invoked during module expansion to annotate a require
-  must be warned if unused.
+  that 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
-  must be warned if unused.
+  that 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
-  must be warned if unused.
+  that must be warned if unused.
   """
   def warn_import(pid, module) do
     :gen_server.cast(pid, {:warn_import, module})

lib/elixir/lib/kernel/parallel_compiler.ex

@@ -25,9 +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: ([module()], [Code.diagnostic(:warning)] ->
+          each_cycle: (-> {:compile, [Path.t()], [Code.diagnostic(:warning)]}
-                         {:compile, [module()], [Code.diagnostic(:warning)]}
+                          | {:runtime, [{module(), Path.t()}], [Code.diagnostic(:warning)]}),
-                         | {:runtime, [module()], [Code.diagnostic(:warning)]}),
           long_compilation_threshold: pos_integer(),
           long_verification_threshold: pos_integer(),
           verification: boolean(),
@@ -101,6 +100,8 @@ 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()
 
@@ -172,25 +173,25 @@ 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
-      compile, invoke this callback passing the module as its argument (and
+      verify, 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` - after the given files are compiled, invokes this function
+    * `:each_cycle` - invoked after each compilation cycle and should return one
-      that should return the following values:
+      of the following values:
       * `{:compile, modules, warnings}` - to continue compilation with a list of
-        further modules to compile
+        further module files to compile
       * `{:runtime, modules, warnings}` - to stop compilation and verify the list
-        of modules because dependent modules have changed
+        of `{module, path}` pairs 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 compile. For each module that exceeds the
+      check for modules taking too long to verify. For each module that exceeds the
       threshold, the `:each_long_verification` callback is invoked. Defaults to
       `10` seconds.
 
@@ -198,8 +199,8 @@ defmodule Kernel.ParallelCompiler do
       deprecation warnings, and type checking should run. Defaults to `true`.
       We recommend disabling it only for debugging purposes.
 
-    * `:profile` - if set to `:time` measure the compilation time of each compilation cycle
+    * `:profile` - if set to `:time`, measure the compilation time of each compilation cycle,
-       and group pass checker
+      each module type check, and group pass checker
 
     * `:purge_compiler_modules` - if set to `true`, automatically purge compilation modules
       after compilation (see `Code.purge_compiler_modules/0`)
@@ -213,7 +214,7 @@ 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 backwards compatibibility reasons.
+      This option must be set to true, except for backward compatibility reasons.
 
     * `:max_concurrency` - the maximum number of files to compile in parallel.
       Setting this option to 1 will compile files sequentially.
@@ -270,7 +271,7 @@ 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 backwards compatibibility reasons.
+      This option must be set to true, except for backward compatibility reasons.
 
   """
   @doc since: "1.6.0"
@@ -340,7 +341,7 @@ defmodule Kernel.ParallelCompiler do
 
   defp spawn_workers(schedulers, checker, files, output, options) do
     threshold = Keyword.get(options, :long_compilation_threshold, 10) * 1000
-    timer_ref = Process.send_after(self(), :threshold_check, threshold)
+    timer_ref = :erlang.send_after(threshold, self(), :threshold_check)
 
     purge_compiler_modules =
       if Keyword.get(options, :purge_compiler_modules, false) do
@@ -841,7 +842,7 @@ defmodule Kernel.ParallelCompiler do
             end
           end
 
-        timer_ref = Process.send_after(self(), :threshold_check, state.long_compilation_threshold)
+        timer_ref = :erlang.send_after(state.long_compilation_threshold, self(), :threshold_check)
         state = %{state | timer_ref: timer_ref}
         spawn_workers(queue, spawned, waiting, files, result, warnings, errors, state)
 

lib/elixir/lib/kernel/special_forms.ex

@@ -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 number :: integer | float
+      @type num :: integer | float
-      @spec add(number, number) :: number
+      @spec add(num, num) :: num
 
   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
-  Which the argument for the `:sum` function call is not the
+  injects the representation of the `value` variable,
-  expected result:
+  not its contents:
 
       {:sum, [], [1, {:value, [], Elixir}, 3]}
 
@@ -2077,9 +2077,9 @@ defmodule Kernel.SpecialForms do
       iex> try do
       ...>   1 / 0
       ...> rescue
-      ...>   x in [ArithmeticError] -> [:rescued, is_exception(x)]
+      ...>   x in [ArithmeticError] -> {:rescued, Exception.message(x)}
       ...> end
-      [:rescued, true]
+      {:rescued, "bad argument in arithmetic expression"}
 
   Rescue different errors with separate clauses:
 

lib/elixir/lib/kernel/typespec.ex

@@ -255,9 +255,20 @@ defmodule Kernel.Typespec do
 
       case type_to_signature(expr) do
         {name, arity} = type_pair ->
-          if built_in_type?(name, arity) do
+          cond do
-            message = "type #{name}/#{arity} is a built-in type and it cannot be redefined"
+            # This is a built-in type since OTP 29 but it just generates a warning for now
-            compile_error(env, message)
+            {name, arity} == {:record, 0} ->
+              IO.warn("type #{name}/#{arity} is overriding a built-in type",
+                file: file,
+                line: line
+              )
+
+            built_in_type?(name, arity) ->
+              message = "type #{name}/#{arity} is a built-in type and it cannot be redefined"
+              compile_error(env, message)
+
+            true ->
+              :ok
           end
 
           if Map.has_key?(type_pairs, type_pair) do
@@ -599,8 +610,7 @@ defmodule Kernel.Typespec do
         types =
           :lists.map(
             fn %{field: field} ->
-              default_type = if field == :__exception__, do: true, else: quote(do: term())
+              {field, Keyword.get(fields, field, quote(do: term()))}
-              {field, Keyword.get(fields, field, default_type)}
             end,
             struct_info
           )
@@ -676,6 +686,13 @@ 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)
@@ -850,29 +867,29 @@ defmodule Kernel.Typespec do
     {{:type, location(meta), :nonempty_string, args}, state}
   end
 
-  defp typespec({type, _meta, []}, vars, caller, state) when type in [:charlist, :char_list] do
+  defp typespec({type, meta, []}, vars, caller, state) when type in [:charlist, :char_list] do
     if type == :char_list do
       warning = "the char_list() type is deprecated, use charlist()"
       IO.warn(warning, caller)
     end
 
-    typespec(quote(do: :elixir.charlist()), vars, caller, state)
+    remote_typespec(:charlist, meta, [], vars, caller, state)
   end
 
-  defp typespec({:nonempty_charlist, _meta, []}, vars, caller, state) do
+  defp typespec({:nonempty_charlist, meta, []}, vars, caller, state) do
-    typespec(quote(do: :elixir.nonempty_charlist()), vars, caller, state)
+    remote_typespec(:nonempty_charlist, meta, [], vars, caller, state)
   end
 
-  defp typespec({:struct, _meta, []}, vars, caller, state) do
+  defp typespec({:struct, meta, []}, vars, caller, state) do
-    typespec(quote(do: :elixir.struct()), vars, caller, state)
+    remote_typespec(:struct, meta, [], vars, caller, state)
   end
 
-  defp typespec({:as_boolean, _meta, [arg]}, vars, caller, state) do
+  defp typespec({:as_boolean, meta, [arg]}, vars, caller, state) do
-    typespec(quote(do: :elixir.as_boolean(unquote(arg))), vars, caller, state)
+    remote_typespec(:as_boolean, meta, [arg], vars, caller, state)
   end
 
-  defp typespec({:keyword, _meta, args}, vars, caller, state) when length(args) <= 1 do
+  defp typespec({:keyword, meta, args}, vars, caller, state) when length(args) <= 1 do
-    typespec(quote(do: :elixir.keyword(unquote_splicing(args))), vars, caller, state)
+    remote_typespec(:keyword, meta, args, vars, caller, state)
   end
 
   defp typespec({:fun, meta, args}, vars, caller, state) do
@@ -997,6 +1014,10 @@ defmodule Kernel.Typespec do
     {{:remote_type, location(meta), [remote, name, args]}, state}
   end
 
+  defp remote_typespec(name, meta, args, vars, caller, state) do
+    typespec({{:., meta, [:elixir, name]}, meta, args}, vars, caller, state)
+  end
+
   defp collect_union({:|, _, [a, b]}), do: [a | collect_union(b)]
   defp collect_union(v), do: [v]
 

lib/elixir/lib/kernel/utils.ex

@@ -162,16 +162,8 @@ defmodule Kernel.Utils do
     # TODO: Make it raise on v2.0
     warn_on_duplicate_struct_key(:lists.keysort(1, fields), env)
 
-    foreach = fn
+    field_map = :maps.from_list(fields)
-      key when is_atom(key) ->
+    struct = :maps.put(:__struct__, module, field_map)
-        :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 =
@@ -215,7 +207,7 @@ defmodule Kernel.Utils do
           end
       end
 
-    case enforce_keys -- :maps.keys(struct) do
+    case enforce_keys -- :maps.keys(field_map) do
       [] ->
         mapper = fn {key, val} ->
           %{field: key, default: val, required: :lists.member(key, enforce_keys)}
@@ -225,10 +217,9 @@ 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}
 
-      error_keys ->
+      invalid_keys ->
         raise ArgumentError,
-              "@enforce_keys required keys (#{inspect(error_keys)}) that are not defined in defstruct: " <>
+              "unknown or duplicate keys given to @enforce_keys, got: #{inspect(invalid_keys)}"
-                "#{inspect(fields)}"
     end
   end
 
@@ -266,7 +257,7 @@ defmodule Kernel.Utils do
     module.exception([])
   end
 
-  def raise(%_{__exception__: true} = exception) do
+  def raise(%_{__exception__: _} = exception) do
     exception
   end
 
@@ -329,21 +320,27 @@ defmodule Kernel.Utils do
 
   @spec defguard([Macro.t()], Macro.t(), Macro.Env.t()) :: Macro.t()
   def defguard(args, expr, env) do
-    {^args, vars} = extract_refs_from_args(args)
+    {_, vars} = extract_refs_from_args(args)
-    env = :elixir_env.with_vars(%{env | context: :guard}, vars)
+    guard_expr = expand_defguard(expr, %{env | context: :guard}, vars)
-    {expr, _, _} = :elixir_expand.expand(expr, :elixir_env.env_to_ex(env), env)
+    body_expr = expand_defguard(expr, %{env | context: nil}, vars)
 
     quote do
       case Macro.Env.in_guard?(__CALLER__) do
         true ->
-          unquote(literal_quote(unquote_every_ref(expr, vars), []))
+          unquote(literal_quote(unquote_every_ref(guard_expr, vars), []))
 
         false ->
-          unquote(literal_quote(unquote_refs_once(expr, vars, env.module), generated: true))
+          unquote(literal_quote(unquote_refs_once(body_expr, vars, env), generated: true))
       end
     end
   end
 
+  defp expand_defguard(expr, env, vars) do
+    env = :elixir_env.with_vars(env, vars)
+    {expr, _, _} = :elixir_expand.expand(expr, :elixir_env.env_to_ex(env), env)
+    expr
+  end
+
   defp extract_refs_from_args(args) do
     Macro.postwalk(args, [], fn
       {ref, meta, context} = var, acc when is_atom(ref) and is_atom(context) ->
@@ -369,7 +366,7 @@ defmodule Kernel.Utils do
   end
 
   # Prefaces `guard` with unquoted versions of `refs`.
-  defp unquote_refs_once(guard, refs, module) do
+  defp unquote_refs_once(guard, refs, %{module: module}) do
     {guard, used_refs} =
       Macro.postwalk(guard, %{}, fn
         {ref, meta, context} = var, acc when is_atom(ref) and is_atom(context) ->
@@ -382,7 +379,7 @@ defmodule Kernel.Utils do
                   {new_var, acc}
 
                 %{} ->
-                  generated = String.to_atom("arg" <> Integer.to_string(map_size(acc) + 1))
+                  generated = String.to_unsafe_atom("arg" <> Integer.to_string(map_size(acc) + 1))
                   new_var = Macro.unique_var(generated, module)
                   {new_var, Map.put(acc, pair, {new_var, var})}
               end

lib/elixir/lib/keyword.ex

@@ -38,7 +38,7 @@ defmodule Keyword do
 
   ## Duplicate keys and ordering
 
-  A keyword may have duplicate keys so it is not strictly a key-value
+  A keyword list 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
@@ -119,14 +119,23 @@ defmodule Keyword do
 
       iex> Keyword.from_keys([:foo, :bar, :baz], :atom)
       [foo: :atom, bar: :atom, baz: :atom]
+
       iex> Keyword.from_keys([], :atom)
       []
 
+      iex> Keyword.from_keys(["foo"], :bar)
+      ** (ArgumentError) expected a list of atoms as keys, got: "foo"
   """
   @doc since: "1.14.0"
   @spec from_keys([key], value) :: t(value)
   def from_keys(keys, value) when is_list(keys) do
-    :lists.map(&{&1, value}, keys)
+    :lists.map(
+      fn
+        key when is_atom(key) -> {key, value}
+        other -> raise ArgumentError, "expected a list of atoms as keys, got: #{inspect(other)}"
+      end,
+      keys
+    )
   end
 
   @doc """
@@ -260,38 +269,60 @@ defmodule Keyword do
   @doc since: "1.13.0"
   @spec validate(keyword(), values :: [atom() | {atom(), term()}]) ::
           {:ok, keyword()} | {:error, [atom]}
+  def validate([], values) when is_list(values), do: {:ok, move_pairs!(values, [])}
+
   def validate(keyword, values) when is_list(keyword) and is_list(values) do
-    validate(keyword, values, [], [], [])
+    validate_merge(keyword, values, [], keyword)
   end
 
-  defp validate([{key, _} = pair | keyword], values1, values2, acc, bad_keys) when is_atom(key) do
+  defp validate_merge([], values, values_pre, original),
-    case find_key!(key, values1, values2) do
+    do: {:ok, move_pairs!(values, move_pairs!(values_pre, original))}
-      {values1, values2} ->
-        validate(keyword, values1, values2, [pair | acc], bad_keys)
 
-      :error ->
+  defp validate_merge([{key, _} = pair | keyword], [head | tail], values_pre, original)
-        case find_key!(key, values2, values1) do
+       when is_atom(key) do
-          {values1, values2} ->
+    case head do
-            validate(keyword, values1, values2, [pair | acc], bad_keys)
+      ^key -> validate_merge(keyword, tail, values_pre, original)
-
+      {^key, _} -> validate_merge(keyword, tail, values_pre, original)
-          :error ->
+      _ -> validate_merge([pair | keyword], tail, [head | values_pre], original)
-            validate(keyword, values1, values2, acc, [key | bad_keys])
-        end
     end
   end
 
-  defp validate([], values1, values2, acc, []) do
+  defp validate_merge([{key, _} | keyword], [], values_pre, original) when is_atom(key) do
-    {:ok, move_pairs!(values1, move_pairs!(values2, acc))}
+    case find_key!(key, values_pre, []) do
+      {new_values, new_values_pre} ->
+        validate_merge(keyword, new_values, new_values_pre, original)
+
+      :error ->
+        validate_fallback(keyword, values_pre, [key])
+    end
   end
 
-  defp validate([], _values1, _values2, _acc, bad_keys) do
+  defp validate_merge([pair | _], _, _, _),
-    {:error, bad_keys}
+    do:
+      raise(
+        ArgumentError,
+        "expected a keyword list as first argument, got invalid entry: #{inspect(pair)}"
+      )
+
+  defp validate_fallback([{key, _} | keyword], values, bad_keys)
+       when is_atom(key) do
+    case find_key!(key, values, []) do
+      {rest, acc} ->
+        validate_fallback(keyword, rest ++ acc, bad_keys)
+
+      :error ->
+        validate_fallback(keyword, values, [key | bad_keys])
+    end
   end
 
-  defp validate([pair | _], _values1, _values2, _acc, []) do
+  defp validate_fallback([], _, bad), do: {:error, bad}
-    raise ArgumentError,
+
-          "expected a keyword list as first argument, got invalid entry: #{inspect(pair)}"
+  defp validate_fallback([p | _], _, _),
-  end
+    do:
+      raise(
+        ArgumentError,
+        "expected a keyword list as first argument, got invalid entry: #{inspect(p)}"
+      )
 
   defp find_key!(key, [key | rest], acc), do: {rest, acc}
   defp find_key!(key, [{key, _} | rest], acc), do: {rest, acc}
@@ -486,7 +517,7 @@ defmodule Keyword do
         {get, :lists.reverse(acc, [{key, value} | delete(t, key)])}
 
       :pop ->
-        {current, :lists.reverse(acc, t)}
+        {current, :lists.reverse(acc, delete(t, key))}
 
       other ->
         raise "the given function must return a two-element tuple or :pop, got: #{inspect(other)}"
@@ -552,7 +583,7 @@ defmodule Keyword do
         {get, :lists.reverse(acc, [{key, value} | delete(t, key)])}
 
       :pop ->
-        {value, :lists.reverse(acc, t)}
+        {value, :lists.reverse(acc, delete(t, key))}
 
       other ->
         raise "the given function must return a two-element tuple or :pop, got: #{inspect(other)}"
@@ -956,7 +987,7 @@ defmodule Keyword do
       iex> Keyword.equal?([a: 1, b: 2, a: 3], [b: 2, a: 3, a: 1])
       true
 
-  Comparison between values is done with `===/3`,
+  Comparison between values is done with `===/2`,
   which means integers are not equivalent to floats:
 
       iex> Keyword.equal?([a: 1.0], [a: 1])
@@ -1292,7 +1323,8 @@ defmodule Keyword do
   @doc """
   Drops the given `keys` from the keyword list.
 
-  Removes duplicate keys from the new keyword list.
+  If a key occurs multiple times, all of its entries are removed when that key
+  is included in `keys`.
 
   ## Examples
 
@@ -1333,9 +1365,9 @@ defmodule Keyword do
   """
   @spec pop(t, key, default) :: {value | default, t}
   def pop(keywords, key, default \\ nil) when is_list(keywords) and is_atom(key) do
-    case fetch(keywords, key) do
+    case :lists.keyfind(key, 1, keywords) do
-      {:ok, value} -> {value, delete(keywords, key)}
+      {^key, value} -> {value, delete_key(keywords, key)}
-      :error -> {default, keywords}
+      false -> {default, keywords}
     end
   end
 
@@ -1360,9 +1392,9 @@ defmodule Keyword do
   @doc since: "1.10.0"
   @spec pop!(t, key) :: {value, t}
   def pop!(keywords, key) when is_list(keywords) and is_atom(key) do
-    case fetch(keywords, key) do
+    case :lists.keyfind(key, 1, keywords) do
-      {:ok, value} -> {value, delete(keywords, key)}
+      {^key, value} -> {value, delete_key(keywords, key)}
-      :error -> raise KeyError, key: key, term: keywords
+      false -> raise KeyError, key: key, term: keywords
     end
   end
 
@@ -1402,7 +1434,7 @@ defmodule Keyword do
     do: {values, acc}
 
   @doc """
-  Lazily returns and removes all values associated with `key` in the keyword list.
+  Lazily returns the first value for `key` and removes all associated entries 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.
@@ -1425,9 +1457,9 @@ defmodule Keyword do
   @spec pop_lazy(t, key, (-> value)) :: {value, t}
   def pop_lazy(keywords, key, fun)
       when is_list(keywords) and is_atom(key) and is_function(fun, 0) do
-    case fetch(keywords, key) do
+    case :lists.keyfind(key, 1, keywords) do
-      {:ok, value} -> {value, delete(keywords, key)}
+      {^key, value} -> {value, delete_key(keywords, key)}
-      :error -> {fun.(), keywords}
+      false -> {fun.(), keywords}
     end
   end
 

lib/elixir/lib/list.ex

@@ -102,7 +102,7 @@ defmodule List do
   Even though the representation changed, the raw data does remain a list of
   integers, which can be handled as such:
 
-      iex> inspect(~c"abc", charlists: :as_list)
+      iex> inspect(~c"abc", charlists: :as_lists)
       "[97, 98, 99]"
       iex> Enum.map(~c"abc", fn num -> 1000 + num end)
       [1097, 1098, 1099]
@@ -311,9 +311,6 @@ 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
@@ -366,9 +363,6 @@ 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
@@ -435,7 +429,7 @@ defmodule List do
 
   """
   @doc since: "1.13.0"
-  @spec keyfind!([tuple], any, non_neg_integer) :: any
+  @spec keyfind!([tuple], any, non_neg_integer) :: tuple
   def keyfind!(list, key, position) when is_integer(position) do
     :lists.keyfind(key, position + 1, list) ||
       raise KeyError,
@@ -520,8 +514,8 @@ 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 third
+  semantic one. In such cases, you shall pass a sorting function as the third
-  element or any module that implements a `compare/2` function. For example,
+  argument 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:
@@ -661,7 +655,7 @@ defmodule List do
   end
 
   @doc """
-  Wraps `term` in a list if this is not list.
+  Wraps `term` in a list if it is not a list.
 
   If `term` is already a list, it returns the list.
   If `term` is `nil`, it returns an empty list.
@@ -960,9 +954,12 @@ 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
-      do_pop_at(list, length(list) + index, default, [])
+      case length(list) + index do
+        index when index < 0 -> {default, list}
+        index -> do_pop_at(list, index, default, [], list)
+      end
     else
-      do_pop_at(list, index, default, [])
+      do_pop_at(list, index, default, [], list)
     end
   end
 
@@ -1024,31 +1021,51 @@ defmodule List do
     :lists.suffix(suffix, list)
   end
 
-  @doc """
+  @doc deprecated: "Use to_existing_atom/1 or to_unsafe_atom/1 instead"
-  Converts a charlist to an atom.
-
-  Elixir supports conversions from charlists which contain any Unicode
-  code point.
-
-  Inlined by the compiler.
-
-  ## Examples
-
-      iex> List.to_atom(~c"Elixir")
-      :Elixir
-
-      iex> List.to_atom(~c"🌢 Elixir")
-      :"🌢 Elixir"
-
-  """
-  @spec to_atom(charlist) :: atom
   def to_atom(charlist) do
     :erlang.list_to_atom(charlist)
   end
 
+  @doc """
+  Converts a charlist to an existing atom or creates a new one.
+
+  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
+
+      iex> List.to_unsafe_atom(~c"Elixir")
+      :Elixir
+
+      iex> List.to_unsafe_atom(~c"🌢 Elixir")
+      :"🌢 Elixir"
+
+  """
+  @doc since: "1.21.0"
+  @spec to_unsafe_atom(charlist) :: atom
+  def to_unsafe_atom(charlist) do
+    :erlang.list_to_atom(charlist)
+  end
+
   @doc """
   Converts a charlist to an existing atom.
 
+  If the list of expected atoms is known upfront, prefer `to_existing_atom/2`.
+
   Elixir supports conversions from charlists which contain any Unicode
   code point. Raises an `ArgumentError` if the atom does not exist.
 
@@ -1079,6 +1096,47 @@ defmodule List do
     :erlang.list_to_existing_atom(charlist)
   end
 
+  @doc """
+  Converts a charlist to one of the `allowed_atoms` or raises.
+
+  Raises an `ArgumentError` if the atom either does not exist or is not within
+  the existing list.
+
+  This should be preferred to `to_existing_atom/1` if the list is known upfront,
+  since there is no risk that the atom has not been loaded.
+
+  ## Examples
+
+      iex> List.to_existing_atom(~c"foo", [:foo, :bar])
+      :foo
+
+      iex> List.to_existing_atom(~c"unknown", [:foo, :bar])
+      ** (ArgumentError) unexpected value: ~c\"unknown\", the allowed atoms are: [:foo, :bar]
+
+  """
+  @doc since: "1.21.0"
+  @spec to_existing_atom(charlist, nonempty_list(a)) :: a when a: atom()
+  def to_existing_atom(charlist, [_ | _] = allowed_atoms) when is_list(charlist) do
+    atom = :erlang.list_to_existing_atom(charlist)
+
+    if atom not in allowed_atoms do
+      to_existing_atom_unexpected(charlist, allowed_atoms)
+    end
+
+    atom
+  end
+
+  # used just to have a less cryptic stacktrace and consistent error
+  @doc false
+  def __to_existing_atom__(charlist, allowed_atoms) do
+    to_existing_atom_unexpected(charlist, allowed_atoms)
+  end
+
+  defp to_existing_atom_unexpected(charlist, allowed_atoms) do
+    raise ArgumentError,
+          "unexpected value: #{inspect(charlist)}, the allowed atoms are: #{inspect(allowed_atoms)}"
+  end
+
   @doc """
   Returns the float whose text representation is `charlist`.
 
@@ -1090,7 +1148,7 @@ defmodule List do
       2.2017764
 
   """
-  @spec to_float(charlist) :: float
+  @spec to_float(nonempty_charlist) :: float
   def to_float(charlist) do
     :erlang.list_to_float(charlist)
   end
@@ -1106,7 +1164,7 @@ defmodule List do
       123
 
   """
-  @spec to_integer(charlist) :: integer
+  @spec to_integer(nonempty_charlist) :: integer
   def to_integer(charlist) do
     :erlang.list_to_integer(charlist)
   end
@@ -1124,7 +1182,7 @@ defmodule List do
       1023
 
   """
-  @spec to_integer(charlist, 2..36) :: integer
+  @spec to_integer(nonempty_charlist, 2..36) :: integer
   def to_integer(charlist, base) do
     :erlang.list_to_integer(charlist, base)
   end
@@ -1193,7 +1251,7 @@ defmodule List do
 
         Please check the given list or call inspect/1 to get the list representation, got:
 
-        #{inspect(list)}
+        #{inspect(list, charlists: :as_lists)}
         """
     else
       result when is_binary(result) ->
@@ -1245,7 +1303,7 @@ defmodule List do
 
         Please check the given list or call inspect/1 to get the list representation, got:
 
-        #{inspect(list)}
+        #{inspect(list, charlists: :as_lists)}
         """
     else
       result when is_list(result) ->
@@ -1310,13 +1368,13 @@ defmodule List do
 
   defp myers_difference_with_diff_script(list1, list2, diff_script) do
     path = {0, list1, list2, []}
-    find_script(0, length(list1) + length(list2), [path], diff_script)
+    find_script(0, [path], diff_script)
   end
 
-  defp find_script(envelope, max, paths, diff_script) do
+  defp find_script(envelope, paths, diff_script) do
     case each_diagonal(-envelope, envelope, paths, [], diff_script) do
       {:done, edits} -> compact_reverse(edits, [])
-      {:next, paths} -> find_script(envelope + 1, max, paths, diff_script)
+      {:next, paths} -> find_script(envelope + 1, paths, diff_script)
     end
   end
 
@@ -1461,15 +1519,16 @@ defmodule List do
 
   # pop_at
 
-  defp do_pop_at([], _index, default, acc) do
+  # The original list is returned when the index is out of bounds
-    {default, :lists.reverse(acc)}
+  defp do_pop_at([], _index, default, _acc, original) do
+    {default, original}
   end
 
-  defp do_pop_at([head | tail], 0, _default, acc) do
+  defp do_pop_at([head | tail], 0, _default, acc, _original) do
     {head, :lists.reverse(acc, tail)}
   end
 
-  defp do_pop_at([head | tail], index, default, acc) do
+  defp do_pop_at([head | tail], index, default, acc, original) do
-    do_pop_at(tail, index - 1, default, [head | acc])
+    do_pop_at(tail, index - 1, default, [head | acc], original)
   end
 end

lib/elixir/lib/macro.ex

@@ -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 surround by parens
+      in the same metadata if the expression is surrounded 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()]
+  @spec unpipe(t()) :: [{t(), non_neg_integer}]
   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, [counter: integer], context}, ...]
+          [{atom, metadata(), context}, ...]
         when context: atom
   def generate_unique_arguments(amount, context),
     do: generate_arguments(amount, context, &unique_var/2)
@@ -527,7 +527,7 @@ defmodule Macro do
 
   defp generate_arguments(amount, context, fun)
        when is_integer(amount) and amount > 0 and is_atom(context) do
-    for id <- 1..amount, do: fun.(String.to_atom("arg" <> Integer.to_string(id)), context)
+    for id <- 1..amount, do: fun.(String.to_unsafe_atom("arg" <> Integer.to_string(id)), context)
   end
 
   @doc """
@@ -576,7 +576,7 @@ defmodule Macro do
 
   """
   @doc since: "1.11.3"
-  @spec unique_var(var, context) :: {var, [counter: integer], context}
+  @spec unique_var(var, context) :: {var, metadata(), 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}
@@ -690,7 +690,39 @@ defmodule Macro do
   """
   @spec prewalk(t, (t -> t)) :: t
   def prewalk(ast, fun) when is_function(fun, 1) do
-    elem(prewalk(ast, nil, fn x, nil -> {fun.(x), nil} end), 0)
+    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)
   end
 
   @doc """
@@ -728,11 +760,41 @@ defmodule Macro do
   """
   @spec postwalk(t, (t -> t)) :: t
   def postwalk(ast, fun) when is_function(fun, 1) do
-    elem(postwalk(ast, nil, fn x, nil -> {fun.(x), nil} end), 0)
+    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)
   end
 
   @doc """
-  This functions behaves like `prewalk/3`, but performs a depth-first,
+  This function 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}
@@ -940,7 +1002,7 @@ 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 in the defined
+  not have been compiled (including structs defined
   under the module being compiled). For compiled modules,
   it will invoke `module.__info__(:struct)`.
 
@@ -973,7 +1035,7 @@ defmodule Macro do
   def struct_info!(module, env) when is_atom(module) do
     meta = [line: env.line]
 
-    case :elixir_map.maybe_load_struct_info(meta, module, env) do
+    case :elixir_map.maybe_load_struct_info(meta, module, :hard, env) do
       {:ok, info} ->
         :elixir_env.trace({:struct_expansion, meta, module, []}, env)
         info
@@ -1034,7 +1096,7 @@ 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
@@ -1092,7 +1154,7 @@ 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
@@ -1195,14 +1257,15 @@ 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 escaping respectively, and for which the mapping function must return
+  a boolean.
 
   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
@@ -1225,7 +1288,11 @@ defmodule Macro do
       Macro.unescape_string("example\\n", &unescape_map(&1))
 
   """
-  @spec unescape_string(String.t(), (non_neg_integer -> non_neg_integer | false)) :: String.t()
+  @spec unescape_string(
+          String.t(),
+          (non_neg_integer | :newline | :unicode | :hex ->
+             non_neg_integer | boolean)
+        ) :: String.t()
   def unescape_string(string, map) do
     :elixir_interpolation.unescape_string(string, map)
   end
@@ -1740,9 +1807,9 @@ defmodule Macro do
 
   defp kw_blocks_to_string(kw, fun) do
     Enum.reduce(unquote(kw_keywords), " ", fn x, acc ->
-      case Keyword.has_key?(kw, x) do
+      case Keyword.fetch(kw, x) do
-        true -> acc <> kw_block_to_string(x, Keyword.get(kw, x), fun)
+        {:ok, value} -> acc <> kw_block_to_string(x, value, fun)
-        false -> acc
+        :error -> acc
       end
     end) <> "end"
   end
@@ -1856,6 +1923,7 @@ 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)
@@ -1980,10 +2048,9 @@ 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
-    if Map.has_key?(env, field) do
+    case Map.fetch(env, field) do
-      {maybe_escape_map(Map.get(env, field)), true}
+      {:ok, value} -> {maybe_escape_map(value), true}
-    else
+      :error -> {original, false}
-      {original, false}
     end
   end
 
@@ -2121,6 +2188,9 @@ 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)
 
@@ -2196,7 +2266,7 @@ defmodule Macro do
   Please check `expand_literals/2` for use cases and pitfalls.
   """
   @doc since: "1.14.1"
-  @spec expand_literals(t(), acc, (t(), acc -> {t(), acc})) :: t() when acc: term()
+  @spec expand_literals(t(), acc, (t(), acc -> {t(), acc})) :: {t(), acc} when acc: term()
   def expand_literals(ast, acc, fun)
 
   def expand_literals({:__aliases__, meta, args}, acc, fun) do
@@ -2500,7 +2570,7 @@ defmodule Macro do
 
   ### As a remote call
 
-  Inspect an atom the function name of a remote call.
+  Inspect an atom as the function name of a remote call.
 
       iex> Macro.inspect_atom(:remote_call, :foo)
       "foo"
@@ -2621,55 +2691,77 @@ defmodule Macro do
         :unquoted_operator
 
       true ->
-        charlist = Atom.to_charlist(atom)
+        classify_binary(Atom.to_string(atom), atom)
-
-        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
-
-                # 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
-              end
-
-            _ ->
-              :other
-          end
-        end
     end
   end
 
-  defp valid_alias?([?E, ?l, ?i, ?x, ?i, ?r] ++ rest), do: valid_alias_piece?(rest)
+  # ASCII identifiers and aliases are recognized on the binary to avoid building a
-  defp valid_alias?(_other), do: false
+  # 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
 
-  defp valid_alias_piece?([?., char | rest]) when char >= ?A and char <= ?Z,
+  defp classify_binary("Elixir" <> rest, atom) do
-    do: valid_alias_piece?(trim_leading_while_valid_identifier(rest))
+    if valid_alias_piece?(rest), do: :alias, else: classify_with_tokenizer(atom)
+  end
 
-  defp valid_alias_piece?([]), do: true
+  defp classify_binary(_binary, atom), do: classify_with_tokenizer(atom)
-  defp valid_alias_piece?(_other), do: false
 
-  defp trim_leading_while_valid_identifier([char | rest])
+  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
+        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
-    trim_leading_while_valid_identifier(rest)
+    valid_identifier_rest?(rest)
   end
 
-  defp trim_leading_while_valid_identifier(other) do
+  defp valid_identifier_rest?(<<char>>) when char == ?? when char == ?!, do: true
-    other
+  defp valid_identifier_rest?(<<>>), do: true
+  defp valid_identifier_rest?(_other), do: false
+
+  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?(_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>>)
+       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)
   end
 
+  defp valid_alias_piece_rest?(other), do: valid_alias_piece?(other)
+
   @doc """
   Default backend for `Kernel.dbg/2`.
 
@@ -2699,7 +2791,7 @@ defmodule Macro do
       :guard ->
         raise ArgumentError,
               "invalid expression in guard, dbg is not allowed in guards. " <>
-                "To learn more about guards, visit: https://hexdocs.pm/elixir/patterns-and-guards.html"
+                "To learn more about guards, visit: https://elixir.hexdocs.pm/patterns-and-guards.html"
 
       _ ->
         :ok
@@ -2954,6 +3046,8 @@ 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
@@ -2961,8 +3055,6 @@ 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

lib/elixir/lib/macro/env.ex

@@ -203,23 +203,23 @@ defmodule Macro.Env do
   Returns a keyword list containing the file and line
   information as keys.
   """
-  @spec location(t) :: keyword
+  @spec location(t) :: [file: file, line: line]
   def location(env)
 
   def location(%{__struct__: Macro.Env, file: file, line: line}) do
     [file: file, line: line]
   end
 
-  # TODO: Deprecate on Elixir 1.21 in favor of expand_alias/4
   @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, :"Elixir.#{atom}")
+    do: Keyword.fetch(aliases, String.to_unsafe_atom("Elixir.#{atom}"))
 
-  # TODO: Deprecate on Elixir 1.21 in favor of expand_alias/4
   @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, :"Elixir.#{atom}")
+      do: Keyword.fetch(aliases, String.to_unsafe_atom("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 to do not use it to expand imports into qualified
+  > but 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.SpecialForm.require/2` plus:
+  It accepts the same options as `Kernel.SpecialForms.require/2` plus:
 
     * #{trace_option}
 
@@ -367,7 +367,8 @@ defmodule Macro.Env do
 
   """
   @doc since: "1.17.0"
-  @spec define_require(t, Macro.metadata(), module, define_require_opts) :: {:ok, t}
+  @spec define_require(t, Macro.metadata(), module, define_require_opts) ::
+          {:ok, t} | {:error, String.t()}
   def define_require(env, meta, module, opts \\ [])
       when is_list(meta) and is_atom(module) and is_list(opts) do
     {trace, opts} = Keyword.pop(opts, :trace, true)
@@ -385,7 +386,7 @@ defmodule Macro.Env do
 
   ## Additional options
 
-  It accepts the same options as `Kernel.SpecialForm.import/2` plus:
+  It accepts the same options as `Kernel.SpecialForms.import/2` plus:
 
     * `:emit_warnings` - emit warnings found when defining imports
 
@@ -393,7 +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
@@ -405,7 +406,7 @@ defmodule Macro.Env do
       iex> Macro.Env.lookup_import(env, {:flatten, 1})
       [{:function, List}]
 
-  It accepts the same options as `Kernel.SpecialForm.import/2`:
+  It accepts the same options as `Kernel.SpecialForms.import/2`:
 
       iex> env = __ENV__
       iex> Macro.Env.lookup_import(env, {:is_odd, 1})
@@ -447,7 +448,7 @@ defmodule Macro.Env do
 
   ## Additional options
 
-  It accepts the same options as `Kernel.SpecialForm.alias/2` plus:
+  It accepts the same options as `Kernel.SpecialForms.alias/2` plus:
 
     * #{trace_option}
 
@@ -699,7 +700,7 @@ defmodule Macro.Env do
   @doc """
   Returns the environment stacktrace.
   """
-  @spec stacktrace(t) :: list
+  @spec stacktrace(t) :: [{module, atom, arity, keyword}]
   def stacktrace(%{__struct__: Macro.Env} = env) do
     cond do
       is_nil(env.module) ->

lib/elixir/lib/map.ex

@@ -201,7 +201,7 @@ defmodule Map do
       %{}
 
   """
-  @spec new :: map
+  @spec new :: %{}
   def new, do: %{}
 
   @doc """
@@ -1109,7 +1109,7 @@ defmodule Map do
       iex> Map.equal?(%{a: 1, b: 2}, %{b: 1, a: 2})
       false
 
-  Comparison between keys and values is done with `===/3`,
+  Comparison between keys and values is done with `===/2`,
   which means integers are not equivalent to floats:
 
       iex> Map.equal?(%{a: 1.0}, %{a: 1})
@@ -1138,9 +1138,9 @@ defmodule Map do
   > #### Performance considerations {: .tip}
   >
   > If you find yourself doing multiple calls to `Map.filter/2`
-  > and `Map.reject/2` in a pipeline, it is likely more efficient
+  > and/or `Map.reject/2` in a pipeline, it is likely more efficient
-  > to use `Enum.map/2` and `Enum.filter/2` instead and convert to
+  > to use `Enum.filter/2` and `Enum.reject/2` instead and convert to
-  > a map at the end using `Map.new/1`.
+  > a map at the end using `Map.new/1` or `Map.new/2`.
 
   ## Examples
 
@@ -1172,6 +1172,13 @@ defmodule Map do
 
   See also `filter/2`.
 
+  > #### Performance considerations {: .tip}
+  >
+  > If you find yourself doing multiple calls to `Map.filter/2`
+  > and/or `Map.reject/2` in a pipeline, it is likely more efficient
+  > to use `Enum.filter/2` and `Enum.reject/2` instead and convert to
+  > a map at the end using `Map.new/1` or `Map.new/2`.
+
   ## Examples
 
       iex> Map.reject(%{one: 1, two: 2, three: 3}, fn {_key, val} -> rem(val, 2) == 1 end)

lib/elixir/lib/map_set.ex

@@ -51,13 +51,23 @@ 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
 
   # We don't use @opaque (or `:sets.set` which is opaque) because MapSets can be inlined,
   # either via module attributes or by the compiler.
-  @typep internal(value) :: %{optional(value) => term()}
+  # Defaulting to a broad `term()` type to prevent opaqueness violations.
+  @typep internal(_value) :: term()
 
   @type t(value) :: %__MODULE__{map: internal(value)}
   @type t :: t(term)
@@ -170,18 +180,14 @@ defmodule MapSet do
   @doc since: "1.14.0"
   @spec symmetric_difference(t(val1), t(val2)) :: t(val1 | val2) when val1: value, val2: value
   def symmetric_difference(%MapSet{map: set1} = map_set1, %MapSet{map: set2} = _map_set2) do
-    {small, large} = if :sets.size(set1) <= :sets.size(set2), do: {set1, set2}, else: {set2, set1}
+    map =
-
+      if :sets.is_disjoint(set1, set2) do
-    disjointer_fun = fn elem, {small, acc} ->
+        :sets.union(set1, set2)
-      if :sets.is_element(elem, small) do
-        {:sets.del_element(elem, small), acc}
       else
-        {small, [elem | acc]}
+        :sets.union(:sets.subtract(set1, set2), :sets.subtract(set2, set1))
       end
-    end
 
-    {new_small, list} = :sets.fold(disjointer_fun, {small, []}, large)
+    %{map_set1 | map: map}
-    %{map_set1 | map: :sets.union(new_small, :sets.from_list(list, version: 2))}
   end
 
   @doc """
@@ -204,7 +210,7 @@ defmodule MapSet do
   Checks if two sets are equal.
 
   The comparison between elements is done using `===/2`,
-  which a set with `1` is not equivalent to a set with
+  which means a set with `1` is not equivalent to a set with
   `1.0`.
 
   ## Examples
@@ -343,7 +349,7 @@ 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 map at the end using `MapSet.new/1`.
+  > a set at the end using `MapSet.new/1`.
 
   ## Examples
 
@@ -399,15 +405,15 @@ defmodule MapSet do
       iex> while_false
       MapSet.new([1, 3])
 
-      iex> {while_true, while_false} = MapSet.split_with(MapSet.new(), fn {_k, v} -> v > 50 end)
+      iex> {while_true, while_false} = MapSet.split_with(MapSet.new([10, 20, 60, 70]), fn v -> v > 50 end)
       iex> while_true
-      MapSet.new([])
+      MapSet.new([60, 70])
       iex> while_false
-      MapSet.new([])
+      MapSet.new([10, 20])
 
   """
   @doc since: "1.15.0"
-  @spec split_with(MapSet.t(), (term() -> as_boolean(term))) :: {MapSet.t(), MapSet.t()}
+  @spec split_with(t(a), (a -> as_boolean(term))) :: {t(a), t(a)} when a: value
   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}}

lib/elixir/lib/module.ex

@@ -190,7 +190,7 @@ defmodule Module do
 
     * a string (often a heredoc)
     * `false`, which will make the entity invisible to documentation-extraction
-      tools like [`ExDoc`](https://hexdocs.pm/ex_doc/)
+      tools like [`ExDoc`](https://ex-doc.hexdocs.pm/)
     * a keyword list, since Elixir 1.7.0
 
   For example:
@@ -216,7 +216,7 @@ defmodule Module do
 
   As can be seen in the example above, since Elixir 1.7.0 `@doc` and `@typedoc`
   also accept a keyword list that serves as a way to provide arbitrary metadata
-  about the entity. Tools like [`ExDoc`](https://hexdocs.pm/ex_doc/) and
+  about the entity. Tools like [`ExDoc`](https://ex-doc.hexdocs.pm/) and
   `IEx` may use this information to display annotations. A common use
   case is the `:since` key, which may be used to annotate in which version the
   function was introduced.
@@ -263,7 +263,7 @@ defmodule Module do
 
   Tools may use this information to ensure the module is recompiled
   in case any of the external resources change, see for example:
-  [`mix compile.elixir`](https://hexdocs.pm/mix/Mix.Tasks.Compile.Elixir.html).
+  [`mix compile.elixir`](https://mix.hexdocs.pm/Mix.Tasks.Compile.Elixir.html).
 
   The specified file path provided is interpreted as relative to
   the folder containing the project's `mix.exs`, which is the
@@ -321,7 +321,7 @@ defmodule Module do
 
   Accepts a string (often a heredoc) or `false` where `@moduledoc false`
   will make the module invisible to documentation extraction tools like
-  [`ExDoc`](https://hexdocs.pm/ex_doc/).
+  [`ExDoc`](https://ex-doc.hexdocs.pm/).
 
   Similarly to `@doc` also accepts a keyword list to provide metadata
   about the module. For more details, see the documentation of `@doc`
@@ -366,7 +366,8 @@ defmodule Module do
   Unlike other hooks, `@on_definition` will only invoke functions and
   never macros. This is to avoid `@on_definition` callbacks from
   redefining functions that have just been defined in favor of more
-  explicit approaches.
+  explicit approaches. They are also invoked in the reverse order of
+  registration.
 
   When just a module is provided, the function is assumed to be
   `__on_definition__/6`.
@@ -656,7 +657,8 @@ defmodule Module do
       @spec module_info(:attributes) :: keyword()
       @spec module_info(:compile) :: keyword()
       @spec module_info(:md5) :: binary()
-      @spec module_info(:nifs) :: module()
+      @spec module_info(:nifs) :: [function_info]
+        when function_info: {function_name :: atom(), arity :: non_neg_integer()}
       @spec module_info(:exports) :: [function_info]
         when function_info: {function_name :: atom(), arity :: non_neg_integer()}
       @spec module_info(:functions) :: [function_info]
@@ -679,7 +681,7 @@ defmodule Module do
   information. For documentation, see `c:Module.__info__/1`.
   '''
 
-  @type definition :: {atom, arity}
+  @type definition :: {function_name :: atom, arity}
   @type def_kind :: :def | :defp | :defmacro | :defmacrop
 
   @type create_opts :: [
@@ -752,7 +754,7 @@ defmodule Module do
 
   """
   @doc since: "1.12.0"
-  @spec reserved_attributes() :: map
+  @spec reserved_attributes() :: %{optional(atom()) => %{doc: binary()}}
   def reserved_attributes() do
     %{
       after_compile: %{
@@ -958,7 +960,7 @@ defmodule Module do
 
   It handles binaries and atoms.
 
-  > #### Untracked compile-time dependencies {. :warning}
+  > #### Untracked compile-time dependencies {: .warning}
   >
   > Use this function with care, as dynamically defining
   > module names at compilation time may lead to
@@ -984,7 +986,7 @@ defmodule Module do
   It handles binaries and atoms. If one of the aliases
   is nil, it is discarded.
 
-  > #### Untracked compile-time dependencies {. :warning}
+  > #### Untracked compile-time dependencies {: .warning}
   >
   > Use this function with care, as dynamically defining
   > module names at compilation time may lead to
@@ -1015,7 +1017,7 @@ defmodule Module do
   If the alias was not referenced yet, fails with `ArgumentError`.
   It handles binaries and atoms.
 
-  > #### Untracked compile-time dependencies {. :warning}
+  > #### Untracked compile-time dependencies {: .warning}
   >
   > Use this function with care, as dynamically defining
   > module names at compilation time may lead to
@@ -1039,7 +1041,7 @@ defmodule Module do
   If the alias was not referenced yet, fails with `ArgumentError`.
   It handles binaries and atoms.
 
-  > #### Untracked compile-time dependencies {. :warning}
+  > #### Untracked compile-time dependencies {: .warning}
   >
   > Use this function with care, as dynamically defining
   > module names at compilation time may lead to
@@ -1146,7 +1148,7 @@ defmodule Module do
   defp simplify_var(var, guess_priority) do
     case Atom.to_string(var) do
       "_" -> {:_, [], guess_priority}
-      "_" <> rest -> {String.to_atom(rest), [], guess_priority}
+      "_" <> rest -> {String.to_unsafe_atom(rest), [], guess_priority}
       _ -> {var, [], nil}
     end
   end
@@ -1157,7 +1159,7 @@ defmodule Module do
     rescue
       ArgumentError -> module
     else
-      module_name -> String.to_atom(Macro.underscore(List.last(module_name)))
+      module_name -> String.to_unsafe_atom(Macro.underscore(List.last(module_name)))
     end
   end
 
@@ -1190,7 +1192,7 @@ defmodule Module do
   defp expand_key(key, counters) do
     case counters do
       %{^key => count} when is_integer(count) and count >= 1 ->
-        {{:"#{key}#{count}", [], Elixir}, Map.put(counters, key, count - 1)}
+        {{String.to_unsafe_atom("#{key}#{count}"), [], Elixir}, Map.put(counters, key, count - 1)}
 
       _ ->
         {{key, [], Elixir}, counters}
@@ -1223,7 +1225,8 @@ defmodule Module do
   defp merge_signature({var, _, _} = older, {var, _, _}, _), do: older
 
   # Otherwise, returns a generic guess
-  defp merge_signature({_, meta, _}, _newer, i), do: {:"arg#{i}", meta, Elixir}
+  defp merge_signature({_, meta, _}, _newer, i),
+    do: {String.to_unsafe_atom("arg#{i}"), meta, Elixir}
 
   @doc """
   Checks if the module defines the given function or macro.
@@ -1249,17 +1252,18 @@ defmodule Module do
 
   """
   @spec defines?(module, definition) :: boolean
-  def defines?(module, {name, arity} = tuple)
+  def defines?(module, {function_name, arity} = definition)
-      when is_atom(module) and is_atom(name) and is_integer(arity) and arity >= 0 and arity <= 255 do
+      when is_atom(module) and is_atom(function_name) and is_integer(arity) and arity >= 0 and
+             arity <= 255 do
     {set, _bag} = data_tables_for!(module, __ENV__.function, @extra_error_msg_defines?)
-    :ets.member(set, {:def, tuple})
+    :ets.member(set, {:def, definition})
   end
 
   @doc """
   Checks if the module defines a function or macro of the
-  given `kind`.
+  given kind.
 
-  `kind` can be any of `:def`, `:defp`, `:defmacro`, or `:defmacrop`.
+  `def_kind` can be any of `:def`, `:defp`, `:defmacro`, or `:defmacrop`.
 
   This function can only be used on modules that have not yet been compiled.
   Use `Kernel.function_exported?/3` and `Kernel.macro_exported?/3` to check for
@@ -1275,12 +1279,13 @@ defmodule Module do
 
   """
   @spec defines?(module, definition, def_kind) :: boolean
-  def defines?(module, {name, arity} = tuple, def_kind)
+  def defines?(module, {function_name, arity} = definition, def_kind)
-      when is_atom(module) and is_atom(name) and is_integer(arity) and arity >= 0 and arity <= 255 and
+      when is_atom(module) and is_atom(function_name) and is_integer(arity) and arity >= 0 and
+             arity <= 255 and
              def_kind in [:def, :defp, :defmacro, :defmacrop] do
     {set, _bag} = data_tables_for!(module, __ENV__.function, @extra_error_msg_defines?)
 
-    case :ets.lookup(set, {:def, tuple}) do
+    case :ets.lookup(set, {:def, definition}) do
       [{_, ^def_kind, _, _, _, _}] -> true
       _ -> false
     end
@@ -1293,7 +1298,9 @@ defmodule Module do
   """
   @doc since: "1.7.0"
   @spec defines_type?(module, definition) :: boolean
-  def defines_type?(module, definition) when is_atom(module) do
+  def defines_type?(module, {function_name, arity} = definition)
+      when is_atom(module) and is_atom(function_name) and is_integer(arity) and arity >= 0 and
+             arity <= 255 do
     Kernel.Typespec.defines_type?(module, definition)
   end
 
@@ -1306,7 +1313,9 @@ defmodule Module do
   """
   @doc since: "1.7.0"
   @spec spec_to_callback(module, definition) :: boolean
-  def spec_to_callback(module, definition) do
+  def spec_to_callback(module, {function_name, arity} = definition)
+      when is_atom(module) and is_atom(function_name) and is_integer(arity) and arity >= 0 and
+             arity <= 255 do
     Kernel.Typespec.spec_to_callback(module, definition)
   end
 
@@ -1358,7 +1367,7 @@ defmodule Module do
 
   """
   @doc since: "1.13.0"
-  @spec overridables_in(module) :: [atom]
+  @spec overridables_in(module) :: [definition]
   def overridables_in(module) when is_atom(module) do
     assert_not_compiled!(__ENV__.function, module, :all)
     :elixir_overridable.overridables_for(module)
@@ -1407,10 +1416,10 @@ defmodule Module do
 
   """
   @spec definitions_in(module, def_kind) :: [definition]
-  def definitions_in(module, kind)
+  def definitions_in(module, def_kind)
-      when is_atom(module) and kind in [:def, :defp, :defmacro, :defmacrop] do
+      when is_atom(module) and def_kind in [:def, :defp, :defmacro, :defmacrop] do
     {set, _} = data_tables_for!(module, __ENV__.function, @extra_error_msg_definitions_in)
-    :ets.select(set, [{{{:def, :"$1"}, kind, :_, :_, :_, :_}, [], [:"$1"]}])
+    :ets.select(set, [{{{:def, :"$1"}, def_kind, :_, :_, :_, :_}, [], [:"$1"]}])
   end
 
   @doc """
@@ -1441,16 +1450,17 @@ defmodule Module do
            [{meta :: keyword, arguments :: [Macro.t()], guards :: [Macro.t()], Macro.t()}]}
           | nil
   @doc since: "1.12.0"
-  def get_definition(module, {name, arity}, options \\ [])
+  def get_definition(module, {function_name, arity} = _definition, options \\ [])
-      when is_atom(module) and is_atom(name) and is_integer(arity) and is_list(options) do
+      when is_atom(module) and is_atom(function_name) and is_integer(arity) and arity >= 0 and
+             arity <= 255 and is_list(options) do
     {set, bag} = data_tables_for!(module, __ENV__.function, "")
 
-    case :ets.lookup(set, {:def, {name, arity}}) do
+    case :ets.lookup(set, {:def, {function_name, arity}}) do
       [{_key, kind, meta, _, _, _}] ->
         clauses =
           if options[:skip_clauses],
             do: [],
-            else: bag_lookup_element(bag, {:clauses, {name, arity}}, 2)
+            else: bag_lookup_element(bag, {:clauses, {function_name, arity}}, 2)
 
         {:v1, kind, meta, clauses}
 
@@ -1467,10 +1477,11 @@ defmodule Module do
   """
   @doc since: "1.12.0"
   @spec delete_definition(module, definition) :: boolean()
-  def delete_definition(module, {name, arity})
+  def delete_definition(module, {function_name, arity} = _definition)
-      when is_atom(module) and is_atom(name) and is_integer(arity) do
+      when is_atom(module) and is_atom(function_name) and is_integer(arity) and arity >= 0 and
+             arity <= 255 do
     assert_not_compiled!(__ENV__.function, module, :writeable)
-    :elixir_def.take_definition(module, {name, arity}) != false
+    :elixir_def.take_definition(module, {function_name, arity}) != false
   end
 
   @doc """
@@ -1486,20 +1497,20 @@ defmodule Module do
   given.
   """
   @spec make_overridable(module, [definition]) :: :ok
-  def make_overridable(module, tuples) when is_atom(module) and is_list(tuples) do
+  def make_overridable(module, definitions) when is_atom(module) and is_list(definitions) do
     assert_not_compiled!(__ENV__.function, module, :writeable)
 
     func = fn
-      {function_name, arity} = tuple
+      {function_name, arity} = definition
       when is_atom(function_name) and is_integer(arity) and arity >= 0 and arity <= 255 ->
-        case :elixir_def.take_definition(module, tuple) do
+        case :elixir_def.take_definition(module, definition) do
           false ->
             raise ArgumentError,
                   "cannot make function #{function_name}/#{arity} " <>
                     "overridable because it was not defined"
 
           clause ->
-            :elixir_overridable.record_overridable(module, tuple, clause)
+            :elixir_overridable.record_overridable(module, definition, clause)
         end
 
       other ->
@@ -1508,7 +1519,7 @@ defmodule Module do
                 "{function_name :: atom, arity :: 0..255} tuple, got: #{inspect(other)}"
     end
 
-    :lists.foreach(func, tuples)
+    :lists.foreach(func, definitions)
   end
 
   @spec make_overridable(module, module) :: :ok
@@ -1566,9 +1577,10 @@ defmodule Module do
   exists or one is pending.
   """
   @spec overridable?(module, definition) :: boolean
-  def overridable?(module, {function_name, arity} = tuple)
+  def overridable?(module, {function_name, arity} = definition)
-      when is_atom(function_name) and is_integer(arity) and arity >= 0 and arity <= 255 do
+      when is_atom(module) and is_atom(function_name) and is_integer(arity) and arity >= 0 and
-    :elixir_overridable.overridable_for(module, tuple) != :not_overridable
+             arity <= 255 do
+    :elixir_overridable.overridable_for(module, definition) != :not_overridable
   end
 
   @doc """

lib/elixir/lib/module/behaviour.ex

@@ -228,11 +228,7 @@ defmodule Module.Behaviour do
   defp behaviour_defined?(callbacks, behaviour) do
     callbacks
     |> Map.values()
-    |> List.flatten()
+    |> Enum.any?(fn list -> :lists.keymember(behaviour, 2, list) end)
-    |> Enum.any?(fn
-      {_kind, ^behaviour, _optional?} -> true
-      {_kind, _behaviour, _optional?} -> false
-    end)
   end
 
   defp warn_missing_impls(%{callbacks: callbacks} = context, _impl_contexts, _defs)

lib/elixir/lib/module/parallel_checker.ex

@@ -20,6 +20,7 @@ defmodule Module.ParallelChecker do
           {:max_concurrency, pos_integer()}
           | {:long_verification_threshold, pos_integer()}
           | {:each_long_verification, (module() -> term()) | (module(), pid() -> term())}
+          | {:profile, :time}
           | {atom(), term()}
         ]
 
@@ -67,17 +68,37 @@ 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.
-    info =
+    if beam_location != [] and Keyword.has_key?(module_map.attributes, :__protocol__) do
-      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?)
-        List.to_string(beam_location)
+    else
-      else
+      {mode, module_tuple} = cache_from_module_map(table, module_map, signatures)
-        cache_from_module_map(table, module_map, signatures)
+      ref = make_ref()
-      end
+      spawned = spawn_checker(ref, pid, checker, table, module, module_tuple, log?)
-
+      register_cache_and_checker(checker, mode, module, spawned, ref)
-    inner_spawn(pid, checker, table, module, info, log?)
+      :ok
+    end
   end
 
-  defp inner_spawn(pid, checker, table, module, info, log?) do
+  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
+      end
+    end)
+  end
+
+  defp spawn_and_register_cache(pid, checker, table, module, info, log?) do
     ref = make_ref()
 
     spawned =
@@ -88,48 +109,28 @@ defmodule Module.ParallelChecker do
           {^ref, :cache} ->
             Process.link(pid)
 
-            {mode, module_tuple} =
+            location =
-              cond do
+              case :code.which(module) do
-                is_binary(info) ->
+                [_ | _] = path -> path
-                  location =
+                _ -> info
-                    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
-                    _ -> {:not_found, nil}
-                  end
-
-                is_tuple(info) ->
-                  info
               end
 
-            # We only make the module available now, so they are not visible during inference
+            with {:ok, binary} <- File.read(location),
-            :ets.insert(table, {module, mode})
+                 {:ok, {_, [{:debug_info, {:debug_info_v1, backend, data}}, {~c"ExCk", exck}]}} <-
-            send(checker, {ref, :cached})
+                   :beam_lib.chunks(binary, [:debug_info, ~c"ExCk"]),
-
+                 {:ok, module_map} <- backend.debug_info(:elixir_v1, module, data, []),
-            receive do
+                 {@elixir_checker_version, contents} <- :erlang.binary_to_term(exck) do
-              {^ref, :check} ->
+              mode = cache_chunk(table, module, contents)
-                # Set the compiler info so we can collect warnings
+              module_tuple = module_map_to_module_tuple(module_map)
-                :erlang.put(:elixir_compiler_info, {pid, self()})
+              spawned = spawn_checker(ref, pid, checker, table, module, module_tuple, log?)
-
+              :ets.insert(table, {module, mode})
-                {warnings, errors} =
+              send(checker, {__MODULE__, :cached, module, spawned, ref})
-                  if module_tuple do
+            else
-                    check_module(module_tuple, {checker, table}, log?)
+              _ ->
-                  else
+                # Nothing to check, so we notify everyone we are done
-                    {[], []}
+                :ets.insert(table, {module, :uncached})
-                  end
+                send(checker, {__MODULE__, :cached, module, nil, ref})
-
+                send(pid, {__MODULE__, module, [], []})
-                send(pid, {__MODULE__, module, warnings, errors})
-                send(checker, {__MODULE__, :done, module})
             end
 
           {:DOWN, ^mon_ref, _, _, _} ->
@@ -137,7 +138,7 @@ defmodule Module.ParallelChecker do
         end
       end)
 
-    register(checker, module, spawned, ref)
+    register_cache(checker, module, spawned, ref)
     :ok
   end
 
@@ -191,7 +192,7 @@ defmodule Module.ParallelChecker do
     log? = not match?({_, false}, value)
 
     for {module, file} <- runtime_files do
-      inner_spawn(self(), checker, table, module, file, log?)
+      spawn_and_register_cache(self(), checker, table, module, file, log?)
     end
 
     count = :gen_server.call(checker, :start, :infinity)
@@ -262,7 +263,7 @@ defmodule Module.ParallelChecker do
 
   ## Module checking
 
-  defp check_module(module_tuple, cache, log?) do
+  defp check_module(module_tuple, cache, log?, profile) do
     {module, file, line, definitions, no_warn_undefined, behaviours, impls, attrs, after_verify} =
       module_tuple
 
@@ -276,9 +277,13 @@ defmodule Module.ParallelChecker do
         definitions
       )
 
+    type_warnings =
+      profile(module, profile, fn ->
+        Module.Types.warnings(module, file, attrs, definitions, no_warn_undefined, cache)
+      end)
+
     {warnings, errors} =
-      module
+      type_warnings
-      |> Module.Types.warnings(file, attrs, definitions, no_warn_undefined, cache)
       |> Kernel.++(behaviour_warnings)
       |> group_diagnostics()
       |> emit_diagnostics(file, log?)
@@ -528,8 +533,12 @@ defmodule Module.ParallelChecker do
     :gen_server.call(server, {:unlock, module, mode}, :infinity)
   end
 
-  defp register(server, module, pid, ref) do
+  defp register_cache_and_checker(server, mode, module, pid, ref) do
-    :gen_server.cast(server, {:register, module, pid, ref})
+    :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})
   end
 
   ## Server callbacks
@@ -572,11 +581,13 @@ defmodule Module.ParallelChecker do
 
     state = %{
       waiting: %{},
-      modules: [],
+      caches: [],
+      checkers: [],
       spawned: %{},
       schedulers: schedulers,
       threshold: threshold,
       callback: callback,
+      profile: Keyword.get(options, :profile),
       protocols: [],
       table: table
     }
@@ -584,20 +595,9 @@ defmodule Module.ParallelChecker do
     :gen_server.enter_loop(__MODULE__, [], state)
   end
 
-  def handle_call(:start, _from, %{modules: modules, protocols: protocols, table: table} = state) do
+  def handle_call(:start, _from, %{caches: caches, 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
@@ -627,10 +627,21 @@ defmodule Module.ParallelChecker do
     {:noreply, state}
   end
 
-  def handle_info({__MODULE__, :done, module}, state) do
+  def handle_info({__MODULE__, :cached, module, pid, ref}, state) do
-    # Unfortunately we cannot assume uniqueness because the same module
+    {_nil, spawned} = Map.pop(state.spawned, ref)
-    # may be defined by mistake several times
+
-    {timer, spawned} = Map.pop(state.spawned, module)
+    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)
     timer && Process.cancel_timer(timer)
     {:noreply, run_checkers(%{state | spawned: spawned})}
   end
@@ -639,11 +650,41 @@ defmodule Module.ParallelChecker do
     {:stop, :normal, state}
   end
 
-  def handle_cast({:register, module, pid, ref}, %{modules: modules} = state) do
+  def handle_cast({:register_cache, module, pid, ref}, %{caches: caches} = state) do
-    {:noreply, %{state | modules: [{module, pid, ref} | modules]}}
+    {:noreply, %{state | caches: [{module, pid, ref} | caches]}}
   end
 
-  defp run_checkers(%{modules: []} = state) do
+  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
     state
   end
 
@@ -652,10 +693,25 @@ defmodule Module.ParallelChecker do
     state
   end
 
-  defp run_checkers(%{modules: [{module, pid, ref} | modules]} = state) do
+  defp run_checkers(%{checkers: [{module, pid, ref} | checkers]} = state) do
-    send(pid, {ref, :check})
+    send(pid, {ref, :check, state.profile})
-    timer = Process.send_after(self(), {__MODULE__, :timeout, module, pid}, state.threshold)
+    timer = :erlang.send_after(state.threshold, self(), {__MODULE__, :timeout, module, pid})
-    spawned = Map.put(state.spawned, module, timer)
+    spawned = Map.put(state.spawned, ref, timer)
-    run_checkers(%{state | modules: modules, spawned: spawned})
+    run_checkers(%{state | checkers: checkers, spawned: spawned})
+  end
+
+  defp profile(module, :time, fun) do
+    {time, result} = :timer.tc(fun)
+
+    IO.puts(
+      :stderr,
+      "[profile] Type checked #{inspect(module)} in #{div(time, 1000)}ms"
+    )
+
+    result
+  end
+
+  defp profile(_module, _profile, fun) do
+    fun.()
   end
 end

lib/elixir/lib/module/types.ex

@@ -4,7 +4,7 @@
 
 defmodule Module.Types do
   @moduledoc false
-  alias Module.Types.{Descr, Expr, Pattern, Helpers}
+  alias Module.Types.{Apply, Descr, Expr, Helpers, Pattern}
 
   # The mode controls what happens on function application when
   # there are gradual arguments. Non-gradual arguments always
@@ -86,7 +86,7 @@ defmodule Module.Types do
           {_kind, inferred, context} = local_handler(meta, fun_arity, stack, context, finder)
 
           if infer_signatures? and kind == :def and fun_arity not in @no_infer do
-            {[{fun_arity, inferred} | types], private, context}
+            {[{fun_arity, group_clauses_by_return(inferred)} | types], private, context}
           else
             {types, private, context}
           end
@@ -136,8 +136,8 @@ defmodule Module.Types do
   defp impl_for(attrs) do
     case List.keyfind(attrs, :__impl__, 0) do
       {:__impl__, [protocol: protocol, for: for]} ->
-        if Code.ensure_loaded?(protocol) and function_exported?(protocol, :behaviour_info, 1) do
+        if Code.ensure_loaded?(protocol) and function_exported?(protocol, :__protocol__, 1) do
-          {for, protocol.behaviour_info(:callbacks)}
+          {for, protocol.__protocol__(:functions)}
         else
           nil
         end
@@ -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 the definition
+        # Optimized version of finder, since we already have the definition
         finder = fn _ -> default_domain(:dynamic, def, fun_arity, impl) end
         {_kind, _inferred, context} = local_handler(meta, fun_arity, stack, context, finder)
         context
@@ -251,15 +251,21 @@ defmodule Module.Types do
       context ->
         {_kind, info, mapping} = Map.fetch!(context.local_sigs, fun_arity)
 
-        clauses_indexes =
+        {used_indexes, unused_indexes} =
-          for type_index <- pending,
+          Enum.reduce(mapping, {[], []}, fn {clause_index, type_index},
-              not skip_unused_clause?(info, type_index),
+                                            {used_indexes, unused_indexes} ->
-              {clause_index, ^type_index} <- mapping,
+            if type_index in pending and not skip_unused_clause?(info, type_index) do
-              do: clause_index
+              {used_indexes, [clause_index | unused_indexes]}
+            else
+              {[clause_index | used_indexes], unused_indexes}
+            end
+          end)
 
-        Enum.reduce(clauses_indexes, context, fn clause_index, context ->
+        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}
+          stack = %{stack | function: fun_arity} |> with_file_meta(meta)
           Helpers.warn(__MODULE__, {:unused_clause, kind, fun_arity}, meta, stack, context)
         end)
     end
@@ -289,11 +295,11 @@ defmodule Module.Types do
 
       local_sigs ->
         case finder.(fun_arity) do
-          {mode, {fun_arity, kind, meta, clauses}, expected} ->
+          {mode, {fun_arity, kind, _meta, clauses}, expected} ->
             context = put_in(context.local_sigs, Map.put(local_sigs, fun_arity, kind))
 
             {inferred, mapping, context} =
-              local_handler(mode, fun_arity, kind, meta, clauses, expected, stack, context)
+              local_handler(mode, fun_arity, kind, clauses, expected, stack, context)
 
             context =
               update_in(context.local_sigs, &Map.put(&1, fun_arity, {kind, inferred, mapping}))
@@ -306,9 +312,10 @@ defmodule Module.Types do
     end
   end
 
-  defp local_handler(:traverse, {_, arity}, _kind, _meta, clauses, _expected, stack, context) do
+  defp local_handler(:traverse, {_, arity}, _kind, clauses, _expected, stack, context) do
     context =
-      Enum.reduce(clauses, context, fn {_meta, _args, _guards, body}, context ->
+      Enum.reduce(clauses, context, fn {meta, _args, _guards, body}, context ->
+        stack = with_file_meta(stack, meta)
         Module.Types.Traverse.of_expr(body, stack, context)
       end)
 
@@ -316,59 +323,234 @@ defmodule Module.Types do
     {inferred, [{0, 0}], context}
   end
 
-  defp local_handler(mode, fun_arity, kind, meta, clauses, expected, stack, context) do
+  defp local_handler(mode, fun_arity, kind, clauses, expected, stack, context) do
     {fun, _arity} = fun_arity
-    stack = stack |> fresh_stack(mode, fun_arity) |> with_file_meta(meta)
+    stack = fresh_stack(stack, mode, fun_arity)
     base_info = {:def, kind, fun, expected}
 
-    {_, _, _, mapping, clauses_types, clauses_context} =
+    case clauses do
-      Enum.reduce(clauses, {0, 0, [], [], [], context}, fn
+      [{meta, args, [], {:super, _, [_ | _]} = body}] ->
-        {meta, args, guards, body}, {index, total, previous, mapping, inferred, acc_context} ->
+        default_local_handler(meta, args, body, base_info, kind, fun, expected, stack, context)
+
+      _ ->
+        infer_local_handler(clauses, base_info, kind, fun, expected, stack, context)
+    end
+  end
+
+  defp default_local_handler(meta, args, body, base_info, kind, fun, expected, stack, context) do
+    stack = with_file_meta(stack, meta)
+    guards = []
+    previous = Pattern.init_previous()
+    fresh_context = fresh_context(context)
+    info = {base_info, args, guards}
+
+    try do
+      {trees, _, _, _, head_context} =
+        Pattern.of_head(args, guards, expected, previous, info, meta, stack, fresh_context)
+
+      # Compute the intersected arrows from the function call
+      {:super, meta, call_args} = body
+      {_kind, call_fun} = Keyword.fetch!(meta, :super)
+      term = Descr.term()
+      of_fun = &Expr.of_expr/5
+
+      {arrows, body_context} =
+        Apply.local_arrows(call_fun, call_args, term, body, stack, head_context, of_fun)
+
+      # For each arrow, compute the default arrow
+      {_, _, mapping, inferred} =
+        Enum.reduce(arrows, {0, 0, [], []}, fn
+          {clause_domain, return_type}, {index, total, mapping, inferred} ->
+            of_fun = &Expr.of_expr(&1, &2, body, stack, &3)
+
+            {_clause_args, clause_context} =
+              Helpers.zip_map_reduce(call_args, clause_domain, head_context, of_fun)
+
+            clause_types = Pattern.of_domain(trees, stack, clause_context)
+
+            {type_index, inferred} =
+              add_inferred(inferred, clause_types, return_type, total - 1, [])
+
+            total = if type_index == -1, do: total + 1, else: total
+            {index + 1, total, [{0, index} | mapping], inferred}
+        end)
+
+      domain =
+        case inferred do
+          [_] ->
+            nil
+
+          _ ->
+            inferred
+            |> Enum.map(fn {args, _} -> args end)
+            |> Enum.zip_with(fn types -> Enum.reduce(types, &Descr.opt_union/2) end)
+        end
+
+      {{:infer, domain, Enum.reverse(inferred)}, mapping, restore_context(body_context, context)}
+    rescue
+      e ->
+        internal_error!(e, __STACKTRACE__, kind, meta, fun, args, guards, body, stack)
+    end
+  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} ->
+          stack = with_file_meta(stack, meta)
           fresh_context = fresh_context(acc_context)
           info = {base_info, args, guards}
 
           try do
-            {trees, previous, 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} =
-              Expr.of_expr(body, Descr.term(), body, stack, context)
+              Expr.of_expr(body, Descr.term(), body, stack, head_context)
 
             args_types = Pattern.of_domain(trees, stack, context)
 
-            {type_index, inferred} =
+            head_args_types =
-              add_inferred(inferred, args_types, return_type, total - 1, [])
+              case inferred do
+                [] -> nil
+                _ -> Pattern.of_domain(trees, stack, head_context)
+              end
 
-            if type_index == -1 do
+            args_triplet = {args_types, head_args_types, head_no_previous_args_types}
-              {index + 1, total + 1, previous, [{index, total} | mapping], inferred, context}
+            inferred = [{args_triplet, return_type, precise?} | inferred]
-            else
+            {previous, inferred, context}
-              {index + 1, total, previous, [{index, type_index} | 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
-          nil
+        _ -> domain
-
-        _ ->
-          clauses_types
-          |> Enum.map(fn {args, _} -> args end)
-          |> Enum.zip_with(fn types -> Enum.reduce(types, &Descr.union/2) end)
       end
 
-    inferred = {:infer, domain, Enum.reverse(clauses_types)}
+    inferred = {:infer, domain, 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],
+         [no_prev_arg | no_prev_args_types],
+         [d | domain]
+       ) do
+    [
+      # This is an optimization that broadens the domain, but it is acceptable
+      # because the domain is used for reverse arrows and not type checking.
+      #
+      # The overall idea is that, if we have a function with three clauses,
+      # the domain is computed by unioning their inferred types. However, their
+      # inferred types often have the different of the previous clauses:
+      #
+      #     opt_union(r3 ^ (c3 - c2 - c1), r2 ^ (c2 - c1), r1 ^ c1)
+      #
+      # Where `rN` represents the refinement in every function body.
+      #
+      # What this function does is, if the type of a given arg in a clause
+      # before and after the body is the same (meaning r3 is term), then
+      # we replace all of `(c3 - c2 - c1)` by just `c3`, which removes
+      # many of the differences in the node. However, keep in mind that,
+      # because `r2` may have refine `c2` in the previous clause, the domain
+      # may end-up being broader. Take this example:
+      #
+      #     % %{..., foo: integer()} -> binary()
+      #     def example(%{foo: var}), do: Integer.to_string(var)
+      #
+      #     % %{...} and not %{..., foo: term()} -> :error
+      #     def example(%{}), do: :error
+      #
+      # The actual domain is:
+      #
+      #     %{..., foo: not_set()} or %{..., foo: integer()}
+      #     #=> %{..., foo: if_set(integer())}
+      #
+      # But we will infer:
+      #
+      #     %{...} or %{..., foo: integer()}
+      #     #=> %{...}
+      #
+      # We lose precision but this is exactly what we want: to have simpler types.
+      # Furthermore, the signature used in type checking is not refined in any way,
+      # so type checking is still sound.
+      if arg == head_arg do
+        Descr.opt_union(Descr.upper_bound(no_prev_arg), d)
+      else
+        Descr.opt_union(arg, d)
+      end
+      | compute_domain(args_types, head_args_types, no_prev_args_types, domain)
+    ]
+  end
+
+  defp compute_domain([], [], [], []), do: []
+
   # We check for term equality of types as an optimization
   # to reduce the amount of check we do at runtime.
   defp add_inferred([{args, existing_return} | tail], args, return, index, acc),
-    do: {index, Enum.reverse(acc, [{args, Descr.union(existing_return, return)} | tail])}
+    do: {index, Enum.reverse(acc, [{args, Descr.opt_union(existing_return, return)} | tail])}
 
   defp add_inferred([head | tail], args, return, index, acc),
     do: add_inferred(tail, args, return, index - 1, [head | acc])
@@ -376,6 +558,58 @@ defmodule Module.Types do
   defp add_inferred([], args, return, -1, acc),
     do: {-1, [{args, return} | Enum.reverse(acc)]}
 
+  # Compact clauses that have the same return and differ in exactly one
+  # argument by unioning that argument. For example:
+  #
+  #   (integer(), atom() -> boolean()) and (float(), atom() -> boolean())
+  #
+  # becomes:
+  #
+  #   (number(), atom() -> boolean())
+  #
+  # Arity-zero clauses have no argument position to widen.
+  defp group_clauses_by_return({:infer, domain, [{[_ | _], _} | _] = clauses}) do
+    clauses =
+      Enum.reduce(clauses, [], fn {args, return}, acc ->
+        group_clause_by_return(acc, args, return)
+      end)
+
+    {:infer, domain, clauses}
+  end
+
+  defp group_clauses_by_return(info), do: info
+
+  defp group_clause_by_return([{existing_args, return} | tail], args, return) do
+    case union_args(existing_args, args, [], false) do
+      nil ->
+        [{existing_args, return} | group_clause_by_return(tail, args, return)]
+
+      new_args ->
+        [{new_args, return} | tail]
+    end
+  end
+
+  defp group_clause_by_return([head | tail], args, return) do
+    [head | group_clause_by_return(tail, args, return)]
+  end
+
+  defp group_clause_by_return([], args, return), do: [{args, return}]
+
+  defp union_args([arg | existing], [arg | args], acc, changed?) do
+    union_args(existing, args, [arg | acc], changed?)
+  end
+
+  # Allow exactly one differing argument. That one position is widened
+  # with union/2. A second difference means the clauses must stay separate.
+  defp union_args([existing_arg | existing], [arg | args], acc, false) do
+    union_args(existing, args, [Descr.opt_union(existing_arg, arg) | acc], true)
+  end
+
+  defp union_args([_ | _], [_ | _], _acc, true), do: nil
+
+  # In theory fully equal args are merged on add_inferred
+  defp union_args([], [], acc, _changed?), do: Enum.reverse(acc)
+
   defp with_file_meta(stack, meta) do
     case Keyword.fetch(meta, :file) do
       {:ok, {meta_file, _}} -> %{stack | file: meta_file}
@@ -437,7 +671,9 @@ defmodule Module.Types do
       # The mode to be used, see the @modes attribute
       mode: mode,
       # The function for handling local calls
-      local_handler: handler
+      local_handler: handler,
+      # Reverse arrow handling (nil | :cache | :except_none | :include_none)
+      reverse_arrow: nil
     }
   end
 
@@ -452,27 +688,33 @@ defmodule Module.Types do
       subpatterns: %{},
       # Variables that are specific to the current environment/conditional
       conditional_vars: nil,
-      # Track metadata specific to matches and guards
+      # Track metadata specific to patterns and guards
       pattern_info: nil,
       # If type checking has found an error/failure
       failed: false,
       # Local signatures used by local handler
       local_sigs: %{},
       # Track which clauses have been used across private local calls
-      local_used: %{}
+      local_used: %{},
+      # Cached reverse arrows
+      reverse_arrows: %{}
     }
   end
 
   defp fresh_stack(stack, mode, function) when mode in @modes do
-    %{stack | mode: mode, function: function}
+    %{stack | mode: mode, function: function, reverse_arrow: nil}
   end
 
   defp fresh_context(context) do
-    %{context | vars: %{}, failed: false}
+    %{context | vars: %{}, failed: false, reverse_arrows: %{}}
   end
 
-  defp restore_context(later_context, %{vars: vars, failed: failed}) do
+  defp restore_context(later_context, %{
-    %{later_context | vars: vars, failed: failed}
+         vars: vars,
+         failed: failed,
+         reverse_arrows: reverse_arrows
+       }) do
+    %{later_context | vars: vars, failed: failed, reverse_arrows: reverse_arrows}
   end
 
   ## Diagnostics
@@ -480,7 +722,7 @@ defmodule Module.Types do
   def format_diagnostic({:unused_clause, kind, {fun, arity}}) do
     %{
       message:
-        "this clause of #{kind} #{fun}/#{arity} is never used (or it will always fail when invoked)"
+        "this clause of #{kind} #{fun}/#{arity} is never used (or it will always fail/warn when invoked)"
     }
   end
 

lib/elixir/lib/module/types/helpers.ex

@@ -57,7 +57,7 @@ defmodule Module.Types.Helpers do
   ## Warnings
 
   @doc """
-  Converts an itneger into ordinal.
+  Converts an integer into ordinal.
   """
   def integer_to_ordinal(i) do
     case rem(i, 10) do
@@ -329,6 +329,13 @@ defmodule Module.Types.Helpers do
             end
         end
 
+      {{:., _, [:lists, :member]}, meta, [expr, args]} = call when is_list(args) ->
+        if Enum.any?(args, &match?({:|, _, [_, _]}, &1)) do
+          call
+        else
+          {:in, meta, [expr, args]}
+        end
+
       {{:., _, [Elixir.String.Chars, :to_string]}, meta, [arg]} ->
         {:to_string, meta, [arg]}
 
@@ -356,7 +363,7 @@ defmodule Module.Types.Helpers do
 
       {:case, meta, [expr, [do: clauses]]} ->
         case meta[:type_check] do
-          {:case, _} ->
+          {:case, op} ->
             case clauses do
               [
                 {:->, _,
@@ -375,7 +382,8 @@ defmodule Module.Types.Helpers do
                    true
                  ]},
                 {:->, _, [[{:_, _, Kernel}], false]}
-              ] ->
+              ]
+              when op == :! ->
                 {:!, meta, [expr]}
 
               [
@@ -395,7 +403,8 @@ defmodule Module.Types.Helpers do
                    right_side
                  ]},
                 {:->, _, [[{var, _, Kernel}], {var, _, Kernel}]}
-              ] ->
+              ]
+              when op == :|| ->
                 {:||, meta, [expr, right_side]}
 
               [
@@ -415,7 +424,8 @@ defmodule Module.Types.Helpers do
                    {var, _, Kernel}
                  ]},
                 {:->, _, [[{:_, _, Kernel}], right_side]}
-              ] ->
+              ]
+              when op == :&& ->
                 {:&&, meta, [expr, right_side]}
 
               [
@@ -435,15 +445,33 @@ defmodule Module.Types.Helpers do
                    else_block
                  ]},
                 {:->, _, [[{:_, _, Kernel}], do_block]}
-              ] ->
+              ]
+              when op == :if ->
                 {:if, meta, [expr, [do: do_block, else: else_block]]}
 
               [
                 {:->, _, [[false], else_block]},
                 {:->, _, [[true], do_block]}
-              ] ->
+              ]
+              when op == :if ->
                 {:if, meta, [expr, [do: do_block, else: else_block]]}
 
+              [
+                {:->, _, [[false], false]},
+                {:->, _, [[true], right]}
+                | _
+              ]
+              when op == :and ->
+                {:and, meta, [expr, right]}
+
+              [
+                {:->, _, [[false], right]},
+                {:->, _, [[true], true]}
+                | _
+              ]
+              when op == :or ->
+                {:or, meta, [expr, right]}
+
               _ ->
                 {:case, meta, [expr, [do: {:..., [], []}]]}
             end

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

@@ -11,7 +11,7 @@ defmodule Module.Types.Of do
   @prefix quote(do: ...)
   @suffix quote(do: ...)
 
-  @integer_or_float union(integer(), float())
+  @integer_or_float opt_union(integer(), float())
   @integer integer()
   @float float()
   @binary binary()
@@ -31,7 +31,7 @@ defmodule Module.Types.Of do
   @doc """
   Marks a variable with error.
 
-  This purposedly deletes all traces of the variable,
+  This purposely deletes all traces of the variable,
   as it is often invoked when the cause for error is elsewhere.
   """
   def error_var({_, meta, _}, context) do
@@ -48,7 +48,7 @@ defmodule Module.Types.Of do
   @doc """
   Declares a variable.
   """
-  def declare_var(var, context) do
+  def declare_var(var, type \\ term(), context) do
     {var_name, meta, var_context} = var
     version = Keyword.fetch!(meta, :version)
 
@@ -58,7 +58,7 @@ defmodule Module.Types.Of do
 
       vars ->
         data = %{
-          type: term(),
+          type: type,
           name: var_name,
           context: var_context,
           off_traces: [],
@@ -86,13 +86,14 @@ defmodule Module.Types.Of do
   or if we are doing a guard analysis or occurrence typing.
   Returns `true` if there was a refinement, `false` otherwise.
   """
-  def refine_body_var(var_or_version, type, expr, stack, context, allow_empty? \\ false)
+  @skip_refinement_for [term(), dynamic()]
+  def refine_body_var(var_or_version, type, expr, stack, context)
 
-  def refine_body_var({_, meta, _}, type, expr, stack, context, allow_empty?) do
+  def refine_body_var({_, meta, _}, type, expr, stack, context) do
-    refine_body_var(Keyword.fetch!(meta, :version), type, expr, stack, context, allow_empty?)
+    refine_body_var(Keyword.fetch!(meta, :version), type, expr, stack, context)
   end
 
-  def refine_body_var(version, type, expr, stack, context, allow_empty?)
+  def refine_body_var(version, type, expr, stack, context)
       when is_integer(version) or is_reference(version) do
     %{vars: %{^version => %{type: old_type, off_traces: off_traces} = data} = vars} = context
 
@@ -105,31 +106,50 @@ defmodule Module.Types.Of do
           context
       end
 
-    if gradual?(old_type) and type not in [term(), dynamic()] and not is_map_key(data, :errored) do
+    case stack do
-      case compatible_intersection(old_type, type) do
+      _ when type in @skip_refinement_for or is_map_key(data, :errored) ->
-        {:error, _} when allow_empty? ->
+        {old_type, context}
-          data = %{
-            data
-            | type: none(),
-              off_traces: new_trace(expr, none(), stack, off_traces)
-          }
 
-          {none(), %{context | vars: %{vars | version => data}}}
+      %{reverse_arrow: reverse_arrow} when reverse_arrow in [:except_none, :include_none] ->
+        new_type = opt_intersection(old_type, type)
 
-        {:ok, new_type} when new_type != old_type ->
+        case empty?(new_type) do
-          data = %{
+          true when reverse_arrow == :include_none ->
-            data
+            data = %{
-            | type: new_type,
+              data
-              off_traces: new_trace(expr, new_type, stack, off_traces)
+              | type: none(),
-          }
+                off_traces: new_trace(expr, none(), stack, off_traces)
+            }
 
-          {new_type, %{context | vars: %{vars | version => data}}}
+            {none(), %{context | vars: %{vars | version => data}}}
 
-        _ ->
+          false when new_type != old_type ->
-          {old_type, context}
+            data = %{
-      end
+              data
-    else
+              | type: new_type,
-      {old_type, context}
+                off_traces: new_trace(expr, new_type, stack, off_traces)
+            }
+
+            {new_type, %{context | vars: %{vars | version => data}}}
+
+          _ ->
+            {old_type, context}
+        end
+
+      _ ->
+        case gradual?(old_type) and compatible_intersection(old_type, type) do
+          {:ok, new_type} when new_type != old_type ->
+            data = %{
+              data
+              | type: new_type,
+                off_traces: new_trace(expr, new_type, stack, off_traces)
+            }
+
+            {new_type, %{context | vars: %{vars | version => data}}}
+
+          _ ->
+            {old_type, context}
+        end
     end
   end
 
@@ -151,7 +171,7 @@ defmodule Module.Types.Of do
         {:ok, error_type(), context}
 
       %{^version => %{type: old_type, off_traces: off_traces} = data} = vars ->
-        new_type = intersection(type, old_type)
+        new_type = opt_intersection(type, old_type)
 
         data = %{
           data
@@ -225,7 +245,7 @@ defmodule Module.Types.Of do
         type =
           Enum.reduce(vars_conds, type, fn {vars, _cond}, acc ->
             %{^version => %{type: type}} = vars
-            union(acc, type)
+            opt_union(acc, type)
           end)
 
         {_, context} = refine_body_var(version, type, expr, stack, context)
@@ -244,8 +264,8 @@ defmodule Module.Types.Of do
     {Float, float()},
     {Function, fun()},
     {Integer, integer()},
-    {List, union(empty_list(), non_empty_list(term(), term()))},
+    {List, opt_union(empty_list(), non_empty_list(term(), term()))},
-    {Map, open_map(__struct__: if_set(negation(atom())))},
+    {Map, open_map(__struct__: {Module.Types.Descr.opt_negation(atom()), true})},
     {Port, port()},
     {PID, pid()},
     {Reference, reference()},
@@ -274,7 +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]))
+      open_map(__struct__: {atom([struct]), false})
     end
   end
 
@@ -345,7 +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} | single], multiple}
+                  {dynamic?, domain, [{key, {value_type, false}} | single], multiple}
 
                 _ ->
                   {dynamic?, domain, single, [{pos, value_type} | multiple]}
@@ -361,37 +381,47 @@ defmodule Module.Types.Of do
           closed_map(non_multiple)
 
         [{keys, type} | tail] ->
-          for key <- keys, t <- cartesian_map(tail) do
+          products = cartesian_map(tail)
-            closed_map(non_multiple ++ [{key, type} | t])
+
+          for key <- keys, product <- products do
+            closed_map(non_multiple ++ [{key, {type, false}} | product])
           end
-          |> Enum.reduce(&union/2)
+          |> Enum.reduce(&opt_union/2)
       end
 
     {if(dynamic?, do: dynamic(map), else: map), context}
   end
 
   defp union_negated([], new_type, single, multiple) do
-    single = Enum.map(single, fn {key, old_type} -> {key, union(old_type, new_type)} end)
+    single =
-    multiple = Enum.map(multiple, fn {keys, old_type} -> {keys, union(old_type, new_type)} end)
+      Enum.map(single, fn
+        {key, {old_type, optional?}} ->
+          {key, {opt_union(old_type, new_type), optional?}}
+      end)
+
+    multiple =
+      Enum.map(multiple, fn {keys, old_type} -> {keys, opt_union(old_type, new_type)} end)
+
     {single, multiple}
   end
 
   defp union_negated(negated, new_type, single, multiple) do
     {single, matched} =
-      Enum.map_reduce(single, [], fn {key, old_type}, matched ->
+      Enum.map_reduce(single, [], fn
-        if key in negated do
+        {key, {old_type, optional?}}, matched ->
-          {{key, old_type}, [key | matched]}
+          if key in negated do
-        else
+            {{key, {old_type, optional?}}, [key | matched]}
-          {{key, union(old_type, new_type)}, matched}
+          else
-        end
+            {{key, {opt_union(old_type, new_type), optional?}}, matched}
+          end
       end)
 
     multiple =
       Enum.map(multiple, fn {keys, old_type} ->
-        {keys, union(old_type, new_type)}
+        {keys, opt_union(old_type, new_type)}
       end)
 
-    {Enum.map(negated -- matched, fn key -> {key, not_set()} end) ++ single, multiple}
+    {Enum.map(negated -- matched, fn key -> {key, {none(), true}} end) ++ single, multiple}
   end
 
   defp pairs(pairs, expected, stack, context, of_fun) do
@@ -400,7 +430,7 @@ defmodule Module.Types.Of do
 
       expected_value_type =
         with {[key], [], []} <- pos_neg_domain,
-             {_, expected_value_type} <- map_fetch_key(expected, key) do
+             {_optional?, expected_value_type} <- map_fetch_key(expected, key) do
           expected_value_type
         else
           _ -> term()
@@ -435,7 +465,8 @@ defmodule Module.Types.Of do
         [[]]
 
       [{keys, type} | tail] ->
-        for key <- keys, t <- cartesian_map(tail), do: [{key, type} | t]
+        products = cartesian_map(tail)
+        for key <- keys, product <- products, do: [{key, {type, false}} | product]
     end
   end
 
@@ -447,35 +478,35 @@ defmodule Module.Types.Of do
   # TODO: Type check the fields match the struct
   def struct_instance(struct, args, expected, meta, stack, context, of_fun)
       when is_atom(struct) do
-    {info, context} = struct_info(struct, :expr, meta, stack, context)
+    {info, context} = struct_info(struct, :expr, meta, stack, context, true)
 
     if is_nil(info) do
-      raise "expected #{inspect(struct)} to return struct metadata, but got none"
+      {dynamic(), context}
+    else
+      # The compiler has already checked the keys are atoms and which ones are required.
+      {args_types, context} =
+        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
+              _ -> term()
+            end
+
+          {type, context} = of_fun.(value, value_type, stack, context)
+          {{key, {type, false}}, context}
+        end)
+
+      {closed_map([__struct__: {atom([struct]), false}] ++ args_types), context}
     end
-
-    # The compiler has already checked the keys are atoms and which ones are required.
-    {args_types, context} =
-      Enum.map_reduce(args, context, fn {key, value}, context when is_atom(key) ->
-        value_type =
-          case map_fetch_key(expected, key) do
-            {_, expected_value_type} -> expected_value_type
-            _ -> term()
-          end
-
-        {type, context} = of_fun.(value, value_type, stack, context)
-        {{key, type}, context}
-      end)
-
-    {closed_map([{:__struct__, atom([struct])} | args_types]), context}
   end
 
   @doc """
   Returns `__info__(:struct)` information about a struct.
   """
-  def struct_info(struct, kind, meta, stack, context) do
+  def struct_info(struct, kind, meta, stack, context, must_exist? \\ false) do
     case stack.no_warn_undefined do
       %Macro.Env{} = env ->
-        case :elixir_map.maybe_load_struct_info(meta, struct, env) do
+        case :elixir_map.maybe_load_struct_info(meta, struct, :soft, env) do
           {:ok, info} -> {info, context}
           {:error, _desc} -> {nil, context}
         end
@@ -491,7 +522,7 @@ defmodule Module.Types.Of do
 
           {info, context}
         else
-          error = {:unknown_struct, kind, struct}
+          error = {:unknown_struct, kind, struct, must_exist?}
           {nil, error(error, meta, stack, context)}
         end
     end
@@ -504,9 +535,16 @@ 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}
+    pairs = for %{field: field} <- info, do: {field, {term, false}}
-    pairs = [{:__struct__, atom([struct])} | pairs]
+    pairs = [{:__struct__, {atom([struct]), false}} | pairs]
-    pairs = if args_types == [], do: pairs, else: pairs ++ args_types
+
+    pairs =
+      if args_types == [] do
+        pairs
+      else
+        pairs ++ args_types
+      end
+
     closed_map(pairs)
   end
 
@@ -828,19 +866,26 @@ defmodule Module.Types.Of do
     }
   end
 
-  def format_diagnostic({:unknown_struct, kind, module}) do
+  def format_diagnostic({:unknown_struct, kind, module, must_exist?}) do
-    message =
+    detail =
-      if Code.ensure_loaded?(module) do
+      case {Code.ensure_loaded?(module), must_exist?} do
-        "struct #{inspect(module)} is undefined (there is such module but it does not define a struct)"
+        {true, false} ->
-      else
+          "there is such module but it does not define a struct"
-        "struct #{inspect(module)} is undefined " <>
+
-          "(module #{inspect(module)} is not available or is yet to be defined)"
+        {false, false} ->
+          "module #{inspect(module)} is not available or is yet to be defined"
+
+        {true, true} ->
+          "the module may have been redefined as it no longer defines a struct"
+
+        {false, true} ->
+          "the module was also only available but may have been removed during compilation"
       end
 
     %{
-      message: message,
+      message: "struct #{inspect(module)} is undefined (#{detail})",
       group: true,
-      severity: if(kind == :pattern, do: :error, else: :warning)
+      severity: if(kind == :pattern or must_exist?, do: :error, else: :warning)
     }
   end
 

lib/elixir/lib/node.ex

@@ -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 also is the default.
+    fully qualified domain names will be used, which is also 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.
@@ -338,8 +338,6 @@ 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

lib/elixir/lib/option_parser.ex

@@ -43,7 +43,7 @@ defmodule OptionParser do
 
   defmodule ParseError do
     @moduledoc """
-    An exception raised when parsing option fails.
+    An exception raised when parsing an 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 exist but it has wrong value
+        # the option exists 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)
@@ -852,7 +852,7 @@ defmodule OptionParser do
     |> to_existing_key(allow_nonexistent_atoms?)
   end
 
-  defp to_existing_key(option, true), do: String.to_atom(option)
+  defp to_existing_key(option, true), do: String.to_unsafe_atom(option)
 
   defp to_existing_key(option, false) do
     try do
@@ -952,8 +952,14 @@ defmodule OptionParser do
 
         case types |> List.delete(:keep) |> List.first(:string) do
           :boolean ->
-            base = "#{to_switch(name)}, #{to_switch(name, "--no-")}"
+            case to_switch(name) do
-            add_aliases(base, name, reverse_aliases)
+              "--no-" <> _ = switch ->
+                add_aliases(switch, name, reverse_aliases)
+
+              switch ->
+                base = "#{switch}, #{to_switch(name, "--no-")}"
+                add_aliases(base, name, reverse_aliases)
+            end
 
           type ->
             base = "#{to_switch(name)} #{String.upcase(Atom.to_string(type))}"

lib/elixir/lib/partition_supervisor.ex

@@ -170,6 +170,8 @@ defmodule PartitionSupervisor do
           | {:max_seconds, non_neg_integer()}
           | {:with_arguments, (args :: [term()], partition() -> updated_args :: [term()])}
 
+  defguardp is_name(name) when is_atom(name) or elem(name, 0) == :via
+
   @doc false
   def child_spec(opts) when is_list(opts) do
     id =
@@ -366,7 +368,7 @@ defmodule PartitionSupervisor do
   """
   @doc since: "1.18.0"
   @spec resize!(name(), non_neg_integer()) :: non_neg_integer()
-  def resize!(name, partitions) when is_integer(partitions) do
+  def resize!(name, partitions) when is_name(name) and is_integer(partitions) do
     supervisor =
       GenServer.whereis(name) || exit({:noproc, {__MODULE__, :resize!, [name, partitions]}})
 
@@ -421,8 +423,8 @@ defmodule PartitionSupervisor do
   Returns the number of partitions for the partition supervisor.
   """
   @doc since: "1.14.0"
-  @spec partitions(name()) :: pos_integer()
+  @spec partitions(name()) :: non_neg_integer()
-  def partitions(name) do
+  def partitions(name) when is_name(name) do
     name |> table() |> partitions(name)
   end
 
@@ -470,7 +472,7 @@ defmodule PartitionSupervisor do
           # Inlining [module()] | :dynamic here because :supervisor.modules() is not exported
           {integer(), pid | :restarting, :worker | :supervisor, [module()] | :dynamic}
         ]
-  def which_children(name) when is_atom(name) or elem(name, 0) == :via do
+  def which_children(name) when is_name(name) do
     Supervisor.which_children(name)
   end
 
@@ -498,7 +500,7 @@ defmodule PartitionSupervisor do
           supervisors: non_neg_integer,
           workers: non_neg_integer
         }
-  def count_children(supervisor) when is_atom(supervisor) do
+  def count_children(supervisor) when is_name(supervisor) do
     Supervisor.count_children(supervisor)
   end
 
@@ -514,7 +516,7 @@ defmodule PartitionSupervisor do
   """
   @doc since: "1.14.0"
   @spec stop(name(), reason :: term, timeout) :: :ok
-  def stop(supervisor, reason \\ :normal, timeout \\ :infinity) when is_atom(supervisor) do
+  def stop(supervisor, reason \\ :normal, timeout \\ :infinity) when is_name(supervisor) do
     Supervisor.stop(supervisor, reason, timeout)
   end
 

lib/elixir/lib/path.ex

@@ -485,7 +485,7 @@ defmodule Path do
   def relative_to_cwd(path, opts \\ []) when is_list(opts) do
     case :file.get_cwd() do
       {:ok, base} -> relative_to(path, IO.chardata_to_string(base), opts)
-      _ -> path
+      _ -> IO.chardata_to_string(path)
     end
   end
 
@@ -699,6 +699,32 @@ 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.
 

lib/elixir/lib/port.ex

@@ -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 processes.
+      connected process. This message makes `new_pid` the new connected process.
       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` or `.com` files
+  > This is particularly troublesome when invoking `.bat`, `.cmd`, or `.com`
-  > as these run implicitly through `cmd.exe`, whose argument parsing is
+  > 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 check the program is indeed not a batch
+  > such as `.exe`, and double-checking 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

lib/elixir/lib/process.ex

@@ -79,10 +79,11 @@ defmodule Process do
   @typedoc """
   A process destination.
 
-  A remote or local PID, a local port, a locally registered name, or a tuple in
+  A remote or local PID, a local port, a process alias, a locally registered name,
-  the form of `{registered_name, node}` for a registered name at another node.
+  or a tuple in the form of `{registered_name, node}` for a registered name at
+  another node.
   """
-  @type dest :: pid | port | (registered_name :: atom) | {registered_name :: atom, node}
+  @type dest :: pid | port | alias | (registered_name :: atom) | {registered_name :: atom, node}
 
   @doc """
   Tells whether the given process is alive on the local node.
@@ -226,7 +227,7 @@ 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
@@ -339,7 +340,7 @@ defmodule Process do
   @doc """
   Sends a message to the given `dest`.
 
-  `dest` may be a remote or local PID, a local port, a locally
+  `dest` may be 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.
 
@@ -387,8 +388,6 @@ defmodule Process do
   automatically canceled when `dest` is an atom (as the atom resolution is done
   on delivery).
 
-  Inlined by the compiler.
-
   ## Options
 
     * `:abs` - (boolean) when `false`, `time` is treated as relative to the
@@ -832,12 +831,16 @@ 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
@@ -980,10 +983,34 @@ defmodule Process do
   defdelegate unalias(alias), to: :erlang
 
   @doc """
-  Add a descriptive term to the current process.
+  Returns the label set for the process `pid` as set with `set_label/1`
+  or `:proc_lib.set_label/1`.
 
-  The term does not need to be unique, and in Erlang/OTP 27+ will be shown in
+  Defaults to the current process when `pid` is not passed.
-  Observer and in crash logs.
+
+  ## Examples
+
+      Process.set_label({:any, "term"})
+      Process.get_label()
+      #=> {:any, "term"}
+
+  Returns `nil` when not set:
+
+      Process.get_label(pid)
+      #=> nil
+
+  """
+  @doc since: "1.20.0"
+  @spec get_label(pid()) :: term()
+  def get_label(pid \\ self()) do
+    nilify(:proc_lib.get_label(pid))
+  end
+
+  @doc """
+  Adds 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.
   This label may be useful for identifying a process as one of multiple in a
   given role, such as `:queue_worker` or `{:live_chat, user_id}`.
 
@@ -997,12 +1024,7 @@ defmodule Process do
   """
   @doc since: "1.17.0"
   @spec set_label(term()) :: :ok
-  def set_label(label) do
+  defdelegate set_label(label), to: :proc_lib
-    # TODO: switch to `:proc_lib.set_label/2` when we require Erlang/OTP 27+
-    Process.put(:"$process_label", label)
-    # mimic return value of `:proc_lib.set_label/2`
-    :ok
-  end
 
   @compile {:inline, nilify: 1}
   defp nilify(:undefined), do: nil

lib/elixir/lib/protocol.ex

@@ -215,7 +215,7 @@ defmodule Protocol do
         ...
       end
 
-  If you are using `Mix.install/2`, you can do by passing the `consolidate_protocols`
+  If you are using `Mix.install/2`, you can do so by passing the `consolidate_protocols`
   option:
 
       Mix.install(
@@ -282,7 +282,9 @@ defmodule Protocol do
     type_args = :lists.map(fn _ -> quote(do: term) end, :lists.seq(2, arity))
     type_args = [quote(do: t) | type_args]
 
-    to_var = fn pos -> Macro.var(String.to_atom("arg" <> Integer.to_string(pos)), __MODULE__) end
+    to_var = fn pos ->
+      Macro.var(String.to_unsafe_atom("arg" <> Integer.to_string(pos)), __MODULE__)
+    end
 
     call_args = :lists.map(to_var, :lists.seq(2, arity))
     call_args = [quote(do: term) | call_args]
@@ -689,15 +691,15 @@ defmodule Protocol do
           structs_domain =
             case structs do
               [] -> Descr.none()
-              _ -> Descr.open_map(__struct__: Descr.atom(structs))
+              _ -> Descr.open_map(__struct__: {Descr.atom(structs), false})
             end
 
           domain =
             Enum.reduce(types_minus_any -- structs, structs_domain, fn impl, acc ->
-              Descr.union(Module.Types.Of.impl(impl, :open), acc)
+              Descr.opt_union(Module.Types.Of.impl(impl, :open), acc)
             end)
 
-          not_domain = Descr.negation(domain)
+          not_domain = Descr.opt_negation(domain)
 
           if Any in types do
             clauses =
@@ -786,7 +788,7 @@ defmodule Protocol do
   end
 
   defp fallback_clause_for(value, _protocol, meta) do
-    {meta, [quote(do: _)], [], value}
+    {meta, [{:_, [version: -1], __MODULE__}], [], value}
   end
 
   # Finally compile the module and emit its bytecode.
@@ -818,11 +820,9 @@ defmodule Protocol do
         @fallback_to_any false
         @undefined_impl_description ""
 
-        # Invoke the user given block
+        res = unquote(block)
-        _ = unquote(block)
-
-        # Finalize expansion
         unquote(after_defprotocol())
+        res
       end
     end
   end
@@ -932,7 +932,7 @@ defmodule Protocol do
       quote bind_quoted: [built_in: built_in()] do
         any_impl_for =
           if @fallback_to_any do
-            __MODULE__.Any
+            Protocol.__concat__(__MODULE__, "Any")
           else
             nil
           end
@@ -1225,10 +1225,12 @@ defmodule Protocol do
   end
 
   @doc false
-  def __concat__(left, right) do
+  def __concat__(left, right) when is_atom(right) do
-    String.to_atom(
+    __concat__(left, remove_prefix(Atom.to_string(right)))
-      ensure_prefix(Atom.to_string(left)) <> "." <> remove_prefix(Atom.to_string(right))
+  end
-    )
+
+  def __concat__(left, right) when is_binary(right) do
+    String.to_unsafe_atom(ensure_prefix(Atom.to_string(left)) <> "." <> right)
   end
 
   defp ensure_prefix("Elixir." <> _ = left), do: left

lib/elixir/lib/range.ex

@@ -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: abs(div(last - first, step)) + 1
+  def size(first..last//step), do: 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 = range1, first2..last2//step2 = range2) do
+  def disjoint?(first1..last1//step1, first2..last2//step2) do
-    if size(range1) == 0 or size(range2) == 0 do
+    if empty?(first1, last1, step1) or empty?(first2, last2, step2) do
       true
     else
       {first1, last1, step1} = normalize(first1, last1, step1)
@@ -487,7 +487,7 @@ defmodule Range do
         last2 < first1 or last1 < first2 ->
           true
 
-        abs(step1) == 1 and abs(step2) == 1 ->
+        step1 == 1 and step2 == 1 ->
           false
 
         true ->
@@ -498,9 +498,9 @@ defmodule Range do
 
           if rem(first2 - first1, gcd) == 0 do
             c = first1 - first2 + step2 - step1
-            t1 = -c / step2 * u
+            t1 = Integer.floor_div(-c * u, step2)
-            t2 = -c / step1 * v
+            t2 = Integer.floor_div(-c * v, step1)
-            t = max(floor(t1) + 1, floor(t2) + 1)
+            t = max(t1 + 1, t2 + 1)
             x = div(c * u + t * step2, gcd) - 1
             y = div(c * v + t * step1, gcd) - 1
 
@@ -513,9 +513,20 @@ defmodule Range do
     end
   end
 
-  @compile inline: [normalize: 3]
+  @compile inline: [empty?: 3, normalize: 3]
+  defp empty?(first, last, step) do
+    case step > 0 do
+      true -> first > last
+      false -> first < last
+    end
+  end
+
   defp normalize(first, last, step) when first > last,
-    do: {first - abs(div(first - last, step) * step), first, -step}
+    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)}
 
   defp normalize(first, last, step), do: {first, last, step}
 

lib/elixir/lib/record.ex

@@ -340,7 +340,7 @@ defmodule Record do
     fields
   end
 
-  # Normalizes of record fields to have default values.
+  # Normalizes record fields to have default values.
   defp fields(kind, fields) do
     normalizer_fun = fn
       {key, value} when is_atom(key) ->

lib/elixir/lib/record/extractor.ex

@@ -40,7 +40,7 @@ defmodule Record.Extractor do
   defp from_lib_file(file) do
     [app | path] = :filename.split(String.to_charlist(file))
 
-    case :code.lib_dir(List.to_atom(app)) do
+    case :code.lib_dir(List.to_unsafe_atom(app)) do
       {:error, _} ->
         raise ArgumentError, "lib file #{file} could not be found"