github: require release notes for pull requests

.github/pull_request_template.md

@@ -1,3 +1,3 @@
 #### Pull Request Checklist
-- [ ] Update `docs/release-notes/release-notes-next.md` if your PR contains
-  major features, breaking changes or bugfixes
+- [ ] Add an entry to `docs/release-notes/release-notes-next.md` (required by
+  CI)

.github/workflows/main.yml

@@ -24,6 +24,42 @@ env:
   LITD_ITEST_BRANCH: master
 
 jobs:
+  ########################
+  # release notes
+  ########################
+  release-notes:
+    name: Release Notes
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    steps:
+      - name: git checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - name: Check for a release note
+        env:
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+          RELEASE_NOTES_FILE: docs/release-notes/release-notes-next.md
+        run: |
+          if git diff --unified=0 "$BASE_SHA...$HEAD_SHA" -- \
+              "$RELEASE_NOTES_FILE" |
+              awk '
+                /^@@/ { in_hunk = 1; next }
+                in_hunk && /^\+/ {
+                  line = substr($0, 2)
+                  if (line ~ /[^[:space:]]/) found = 1
+                }
+                END { exit found ? 0 : 1 }
+              '
+          then
+            exit 0
+          fi
+
+          echo "::error file=$RELEASE_NOTES_FILE::Add a release note for this PR."
+          exit 1
+
   ########################
   # commit message lint
   ########################

docs/release-notes/release-notes-next.md

@@ -13,4 +13,7 @@
 
 #### Maintenance
 
+* Added a CI gate requiring every pull request to include a non-empty entry in
+  the next release notes.
+
 #### Contributors (Alphabetical Order)