Fix PR labeling and generate nightly build notes from them. (#4077)

This configures the nightly build to generate release notes and provides
a template for organizing them. The organization is done through
labeling of PRs and categorizing them based on those labels. I've tried
to provide a rough categorization that seems reasonable for folks.

While doing this I looked at our PR labeling and found a few bugs that
were preventing many labels form being attached. I've fixed those and
significantly expanded the coverage of file-based labeling. I've also
added code to do author-based labeling for automated PRs so those can be
separated out from human PRs.

.github/release.yaml

@@ -0,0 +1,44 @@
+# Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+# Exceptions. See /LICENSE for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#
+# Provide the configuration and categorization for generated release notes.
+
+changelog:
+  exclude:
+    labels:
+      - ignore-for-release
+
+  categories:
+    - title: 'Proposals accepted and merged :scroll:'
+      labels:
+        - proposal
+      exclude.labels:
+        - bot
+    - title: 'Toolchain and implementation changes :hammer_and_wrench:'
+      labels:
+        - toolchain
+        - explorer
+      exclude.labels:
+        - bot
+    - title: 'Documentation changes :memo:'
+      labels:
+        - documentation
+      exclude.labels:
+        - bot
+    - title: 'Utilities :triangular_ruler:'
+      labels:
+        - utilities
+      exclude.labels:
+        - bot
+    - title: 'Infrastructure changes :building_construction:'
+      labels:
+        - infrastructure
+      exclude.labels:
+        - bot
+    - title: 'Automated robot PRs :robot:'
+      labels:
+        - bot
+    - title: 'Other changes'
+      labels:
+        - '*'

.github/workflows/label_prs.yaml

@@ -26,20 +26,48 @@ jobs:
             documentation:
               - '*.md'
               - 'docs/**'
+              - 'examples/**'
+              - 'third_party/examples/**'
+
             explorer:
               - 'explorer/**'
+              - 'installers/**'
+
             infrastructure:
-              - 'BUILD'
-              - 'WORKSPACE'
+              - '*.bzl'
+              - '*.cfg'
+              - '*.toml'
               - '.*'
               - '.*/**'
+              - 'BUILD'
+              - 'MODULE.*'
+              - 'WORKSPACE'
               - 'bazel/**'
+              - 'github_tools/**'
+              - 'proposal/scripts/**'
               - 'scripts/**'
+
+            # Here we only want the `proposal` label when a *new* file is added
+            # directly in this directory. We use `added` and a single level glob
+            # to achieve that.
+            proposal:
+              - added: 'proposals/*'
+
+            # We include common, shared code into the toolchain label for
+            # convenience. Essentially, this is everything we intend to ship as
+            # part of the reference implementation of the language.
             toolchain:
+              - 'common/**'
+              - 'core/**'
+              - 'language_server/**'
+              - 'testing/**'
               - 'toolchain/**'
 
+            utilities:
+              - 'utils/**'
+
       - id: documentation
-        if: steps.filter.outputs.docs == 'true'
+        if: steps.filter.outputs.documentation == 'true'
         run: |
           gh pr edit "${PR}" --add-label "documentation"
         env:
@@ -55,13 +83,21 @@ jobs:
           PR: ${{ github.event.pull_request.html_url }}
 
       - id: infrastructure
-        if: steps.filter.outputs.docs == 'true'
+        if: steps.filter.outputs.infrastructure == 'true'
         run: |
           gh pr edit "${PR}" --add-label "infrastructure"
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           PR: ${{ github.event.pull_request.html_url }}
 
+      - id: proposal
+        if: steps.filter.outputs.proposal == 'true'
+        run: |
+          gh pr edit "${PR}" --add-label "proposal"
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PR: ${{ github.event.pull_request.html_url }}
+
       - id: toolchain
         if: steps.filter.outputs.toolchain == 'true'
         run: |
@@ -69,3 +105,23 @@ jobs:
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           PR: ${{ github.event.pull_request.html_url }}
+
+      - id: utilities
+        if: steps.filter.outputs.utilities == 'true'
+        run: |
+          gh pr edit "${PR}" --add-label "utilities"
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PR: ${{ github.event.pull_request.html_url }}
+
+      # Note that this is not a path-based label, but an *author* based label,
+      # and it applies orthogonally to the others.
+      - id: automated
+        if:
+          contains(fromJSON('["CarbonInfraBot", "dependabot"]'),
+          github.event.pull_request.user.login)
+        run: |
+          gh pr edit "${PR}" --add-label "automated"
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+          PR: ${{ github.event.pull_request.html_url }}

.github/workflows/nightly-release.yaml

@@ -88,7 +88,7 @@ jobs:
         run: |
           gh release create \
             --title "Nightly build ${{ env.nightly_date }}" \
-            --notes 'A nightly development build of Carbon.' \
+            --generate-notes \
             --prerelease \
             v${{ env.release_version }} \
             "bazel-bin/toolchain/install/carbon_toolchain-${{ env.release_version }}.tar.gz"