.github/workflows/notify-revert.yml

name: Notify Reverted PR

on:
  push:
    branches: [master]

permissions:
  contents: read

jobs:
  notify-revert:
    if: github.repository == 'bazelbuild/bazel'
    runs-on: ubuntu-latest
    permissions:
      contents: read
      issues: write
    steps:
      - name: Harden Runner
        uses: step-security/harden-runner@05e31511f85b41b11d1cf0ef85d0992719546e2c # v2.21.0
        with:
          egress-policy: audit

      - name: Notify PR author on revert
        uses: actions/github-script@3a2844b7e9c422d3c10d287c895573f7108da1b3 # v9
        with:
          script: |
            const { owner, repo } = context.repo;
            for (const commit of context.payload.commits ?? []) {
              const match = commit.message.match(/^Automated rollback of commit ([0-9a-f]{40})/);
              if (!match) continue;
              const rolledBackSha = match[1];
              try {
                // Copybara closes (rather than merges) PRs, so GitHub does not associate
                // the commit with its PR. Follow the trailer and confirm this commit closed it.
                const { data: original } = await github.rest.repos.getCommit({ owner, repo, ref: rolledBackSha });
                const closes = [...original.commit.message.matchAll(/^Closes #(\d+)\.?$/gm)];
                if (!closes.length) continue;
                const issue_number = Number(closes.at(-1)[1]);
                const events = await github.paginate(github.rest.issues.listEvents, { owner, repo, issue_number, per_page: 100 });
                if (!events.some((e) => e.event === 'closed' && e.commit_id === rolledBackSha)) continue;

                const { data: pr } = await github.rest.issues.get({ owner, repo, issue_number });
                await github.rest.issues.createComment({
                  owner,
                  repo,
                  issue_number,
                  body: [
                    `⚠️ **Notice**: Commit ${rolledBackSha}, which closed this pull request, was rolled back on \`master\` in commit ${commit.id}.`,
                    '',
                    'Please check the rollback commit for details.',
                    '',
                    `cc @${pr.user.login}`,
                  ].join('\n'),
                });
              } catch (e) {
                core.warning(`Could not notify for rollback ${commit.id}: ${e.message}`);
              }
            }