Auto-label PRs and sort all labels into release notes

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,24 @@
+# What does this implement/fix?
+
+<!-- Quick description and explanation of changes. -->
+
+**Related issue (if applicable):**
+
+- <link>
+
+## Types of changes
+
+<!--
+Tick exactly one box. CI (.github/workflows/pr-labels.yaml) applies the
+matching label, and the release notes use it to sort this change.
+-->
+
+- [ ] Bugfix (non-breaking change which fixes an issue): `bugfix`
+- [ ] New feature (non-breaking change which adds functionality): `new-feature`
+- [ ] Enhancement to an existing feature: `enhancement`
+- [ ] Breaking change (changes CLI options, settings, hooks or the protocol in a way that is not backwards compatible): `breaking-change`
+- [ ] Refactor (no behavior change): `refactor`
+- [ ] Documentation only: `documentation`
+- [ ] Maintenance / chore: `maintenance`
+- [ ] CI / workflow change: `ci`
+- [ ] Dependencies bump: `dependencies`

.github/release-drafter.yml

@@ -12,19 +12,20 @@ categories:
 
   - title: "🚀 Features"
     labels:
-      - "feature"
+      - "new-feature"
       - "enhancement"
 
   - title: "🧰 Maintenance"
     labels:
+      - "refactor"
+      - "documentation"
       - "ci"
       - "maintenance"
 
-  - title: "⬆️ Dependencies and CI"
+  - title: "⬆️ Dependencies"
     collapse-after: 1
     labels:
       - "dependencies"
-      - "ci"
 template: |
   ## What’s Changed
 

.github/workflows/pr-labels.yaml

@@ -0,0 +1,95 @@
+---
+name: PR Labels
+
+# Each PR must carry exactly one of the labels the release notes sort by.
+# The label comes from the ticked "Types of changes" checkbox in the PR
+# template, since external contributors can't label their own PRs.
+
+# yamllint disable-line rule:truthy
+on:
+  pull_request_target:
+    types:
+      - opened
+      - edited
+      - synchronize
+      - labeled
+      - unlabeled
+      - reopened
+      - ready_for_review
+    branches:
+      - main
+
+permissions:
+  pull-requests: write
+
+jobs:
+  pr_labels:
+    name: Verify
+    runs-on: ubuntu-latest
+    # Bots like Dependabot don't use the template and label their own PRs.
+    if: github.event.pull_request.user.type != 'Bot'
+    steps:
+      - name: 🏷 Apply label from PR description checkbox
+        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3  # v9.0.0
+        with:
+          script: |
+            const known = [
+              'breaking-change', 'bugfix', 'new-feature', 'enhancement',
+              'refactor', 'documentation', 'maintenance', 'ci', 'dependencies',
+            ];
+
+            const { owner, repo } = context.repo;
+            const issue_number = context.payload.pull_request.number;
+            const current = (context.payload.pull_request.labels || [])
+              .map(l => l.name);
+
+            // Match a ticked bullet whose first backticked word is a label,
+            // e.g.  - [x] CI / workflow change: `ci`
+            const body = context.payload.pull_request.body || '';
+            const re = /^\s*-\s*\[x\][^`\n]*`([^`]+)`/gim;
+            const ticked = [];
+            for (const m of body.matchAll(re)) {
+              const name = m[1].trim();
+              if (known.includes(name) && !ticked.includes(name)) {
+                ticked.push(name);
+              }
+            }
+
+            if (ticked.length > 1) {
+              core.setFailed(
+                `Multiple "Types of changes" checkboxes are ticked ` +
+                `(${ticked.join(', ')}). Tick exactly one.`
+              );
+              return;
+            }
+
+            // A ticked box wins. Without one, accept a single known label
+            // already on the PR, for PRs opened without the template.
+            if (ticked.length === 0) {
+              const existing = current.filter(n => known.includes(n));
+              if (existing.length === 1) {
+                core.info(`Skipping: PR already labelled '${existing[0]}'.`);
+                return;
+              }
+              core.setFailed(
+                'No "Types of changes" checkbox is ticked in the PR ' +
+                'description. Edit the description and tick exactly ' +
+                'one box so this PR can be release-noted.'
+              );
+              return;
+            }
+
+            const desired = ticked[0];
+
+            for (const name of current) {
+              if (known.includes(name) && name !== desired) {
+                await github.rest.issues.removeLabel({
+                  owner, repo, issue_number, name,
+                }).catch(() => {});
+              }
+            }
+            if (!current.includes(desired)) {
+              await github.rest.issues.addLabels({
+                owner, repo, issue_number, labels: [desired],
+              });
+            }