Release process: Automatically rebuild PRs

Author: henrymercer

.github/actions/prepare-mergeback-branch/action.yml

@@ -41,7 +41,38 @@ runs:
         git add .
         git commit -m "Update changelog and version after ${VERSION}"
 
-        git push origin "${NEW_BRANCH}"
+    # Update the build artifacts with the new version number
+    - name: Rebuild the Action
+      shell: bash
+      run: |
+        set -exu
+        npm ci
+        npm run build
+
+    - name: Check for rebuild changes
+      id: rebuild_changes
+      shell: bash
+      run: |
+        set -exu
+        git add --all
+        if git diff --cached --quiet; then
+          echo "has_changes=false" >> "${GITHUB_OUTPUT}"
+        else
+          echo "has_changes=true" >> "${GITHUB_OUTPUT}"
+        fi
+
+    - name: Commit rebuild
+      if: steps.rebuild_changes.outputs.has_changes == 'true'
+      shell: bash
+      run: |
+        set -exu
+        git commit -m "Rebuild"
+
+    - name: Push mergeback branch
+      shell: bash
+      env:
+        NEW_BRANCH: "${{ inputs.branch }}"
+      run: git push origin "${NEW_BRANCH}"
 
     - name: Create PR
       shell: bash
@@ -60,8 +91,6 @@ runs:
 
           Please do the following:
 
-          - [ ] Remove and re-add the "Rebuild" label to the PR to trigger just this workflow.
-          - [ ] Wait for the "Rebuild" workflow to push a commit updating the distribution files.
           - [ ] Mark the PR as ready for review to trigger the full set of PR checks.
           - [ ] Approve and merge the PR. When merging the PR, make sure "Create a merge commit" is
                 selected rather than "Squash and merge" or "Rebase and merge".
@@ -74,7 +103,6 @@ runs:
           --head "${NEW_BRANCH}" \
           --base "${BASE_BRANCH}" \
           --title "${pr_title}" \
-          --label "Rebuild" \
           --body "${pr_body}" \
           --assignee "${GITHUB_ACTOR}" \
           --draft

.github/actions/release-initialise/action.yml

@@ -18,8 +18,8 @@ runs:
     - name: Set up Node
       uses: actions/setup-node@v6
       with:
-        node-version: 20
-        cache: 'npm'
+        node-version: 24
+        cache: 'npm' # shared with the "Rebuild Action" workflow
 
     - name: Set up Python
       uses: actions/setup-python@v6

.github/update-release-branch.py

@@ -19,6 +19,10 @@
 # Changing it requires a transition period where both old and new versions are supported.
 BACKPORT_COMMIT_MESSAGE = 'Update version and changelog for v'
 
+# Commit message used for rebuild commits, both those produced by this script and those produced
+# by the `Rebuild Action` workflow (`.github/workflows/rebuild.yml`).
+REBUILD_COMMIT_MESSAGE = 'Rebuild'
+
 # Name of the remote
 ORIGIN = 'origin'
 
@@ -43,14 +47,36 @@ def run_git(*args, allow_non_zero_exit_code=False):
     raise Exception(f'Call to {" ".join(cmd)} exited with code {p.returncode} stderr: {p.stderr.decode("ascii")}.')
   return p.stdout.decode('ascii')
 
+# Runs the given command, streaming output to the console.
+# Raises an error if the command does not exit successfully.
+def run_command(*args):
+  cmd = list(args)
+  print(f'Running `{" ".join(cmd)}`.')
+  subprocess.run(cmd, check=True)
+
+# Rebuilds the action and commits any changes.
+def rebuild_action():
+  # For backports, the only source-level change vs the source branch is the new version number,
+  # so we just need to refresh the version embedded in `lib/`.
+  run_command('npm', 'ci')
+  run_command('npm', 'run', 'build')
+
+  run_git('add', '--all')
+  # `git diff --cached --quiet` exits 0 if there are no staged changes, 1 if there are.
+  if subprocess.run(['git', 'diff', '--cached', '--quiet']).returncode == 0:
+    print('Rebuild produced no changes; skipping Rebuild commit.')
+  else:
+    run_git('commit', '-m', REBUILD_COMMIT_MESSAGE)
+    print('Created Rebuild commit.')
+
 # Returns true if the given branch exists on the origin remote
 def branch_exists_on_remote(branch_name):
   return run_git('ls-remote', '--heads', ORIGIN, branch_name).strip() != ''
 
 # Opens a PR from the given branch to the target branch
 def open_pr(
   repo, all_commits, source_branch_short_sha, new_branch_name, source_branch, target_branch,
-  conductor, is_primary_release, conflicted_files):
+  conductor, is_primary_release, conflicted_files, needs_rebuild):
   # Sort the commits into the pull requests that introduced them,
   # and any commits that don't have a pull request
   pull_requests = []
@@ -108,10 +134,6 @@ def open_pr(
   body.append(f' - [ ] Check that there are not any unexpected commits being merged into the `{target_branch}` branch.')
   body.append(' - [ ] Ensure the docs team is aware of any documentation changes that need to be released.')
 
-  if not is_primary_release:
-    body.append(' - [ ] Remove and re-add the "Rebuild" label to the PR to trigger just this workflow.')
-    body.append(' - [ ] Wait for the "Rebuild" workflow to push a commit updating the distribution files.')
-
   body.append(' - [ ] Mark the PR as ready for review to trigger the full set of PR checks.')
   body.append(' - [ ] Approve and merge this PR. Make sure `Create a merge commit` is selected rather than `Squash and merge` or `Rebase and merge`.')
 
@@ -120,13 +142,11 @@ def open_pr(
     body.append(' - [ ] Merge all backport PRs to older release branches, that will automatically be created once this PR is merged.')
 
   title = f'Merge {source_branch} into {target_branch}'
-  labels = ['Rebuild'] if not is_primary_release else []
 
   # Create the pull request
   # PR checks won't be triggered on PRs created by Actions. Therefore mark the PR as draft so that
   # a maintainer can take the PR out of draft, thereby triggering the PR checks.
   pr = repo.create_pull(title=title, body='\n'.join(body), head=new_branch_name, base=target_branch, draft=True)
-  pr.add_to_labels(*labels)
   print(f'Created PR #{str(pr.number)}')
 
   # Assign the conductor
@@ -385,8 +405,9 @@ def main():
       # releases.
       run_git('revert', vOlder_update_commits[0], '--no-edit')
 
-      # Also revert the "Rebuild" commit created by Actions.
-      rebuild_commit = run_git('log', '--grep', '^Rebuild$', '--format=%H').split()[0]
+      # Also revert the "Rebuild" commit, whether created by this script or by the
+      # `Rebuild Action` workflow.
+      rebuild_commit = run_git('log', '--grep', f'^{REBUILD_COMMIT_MESSAGE}$', '--format=%H').split()[0]
       print(f'  Reverting {rebuild_commit}')
       run_git('revert', rebuild_commit, '--no-edit')
 
@@ -401,9 +422,10 @@ def main():
       run_git('add', '.')
       run_git('commit', '--no-edit')
 
-    # Migrate the package version number from a vLatest version number to a vOlder version number
+    # Migrate the package version number from a vLatest version number to a vOlder version number.
+    # `package-lock.json` is updated as part of the subsequent rebuild step (see `rebuild_action`).
     print(f'Setting version number to {version} in package.json')
-    replace_version_package_json(get_current_version(), version) # We rely on the `Rebuild` workflow to update package-lock.json
+    replace_version_package_json(get_current_version(), version)
     run_git('add', 'package.json')
 
     # Migrate the changelog notes from vLatest version numbers to vOlder version numbers
@@ -426,6 +448,13 @@ def main():
     run_git('add', 'CHANGELOG.md')
     run_git('commit', '-m', f'Update changelog for v{version}')
 
+  if not is_primary_release:
+    if len(conflicted_files) == 0:
+      print('Rebuilding the Action.')
+      rebuild_action()
+    else:
+      print(f'Skipping automatic rebuild because the merge produced conflicts in {conflicted_files}.')
+
   run_git('push', ORIGIN, new_branch_name)
 
   # Open a PR to update the branch

.github/workflows/post-release-mergeback.yml

@@ -48,6 +48,9 @@ jobs:
         with:
           fetch-depth: 0  # ensure we have all tags and can push commits
       - uses: actions/setup-node@v6
+        with:
+          node-version: 24
+          cache: 'npm' # shared with the "Rebuild Action" workflow
       - uses: actions/setup-python@v6
         with:
           python-version: '3.12'