pr-labels.yaml

---
name: PR Labels

# Each PR must carry exactly one of the labels release-drafter knows
# how to slot into a release-notes section. We derive that label from
# the "Types of changes" checkbox in the PR template and apply it
# automatically — most external contributors can't label their own
# PRs. The job only fails when no checkbox is ticked.
#
# Bot-authored PRs (dependabot, pre-commit-ci, …) don't fill in the
# PR template; they tag themselves with the appropriate label
# directly, so the job skips them.

# yamllint disable-line rule:truthy
on:
  pull_request_target:
    types:
      - opened
      - edited
      - synchronize
      - labeled
      - unlabeled
    branches:
      - main

permissions:
  pull-requests: write

jobs:
  apply_label:
    name: Apply
    runs-on: ubuntu-latest
    if: >-
      github.event.pull_request.state == 'open'
      && 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', 'refactor',
              'new-feature', 'enhancement', 'maintenance',
              'ci', 'dependencies', 'docs',
            ];

            // Match `- [x] ... `<label>`` lines in the PR body. The
            // PR template puts the canonical label name in backticks
            // at the end of each "Types of changes" bullet.
            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];
              if (known.includes(name) && !ticked.includes(name)) {
                ticked.push(name);
              }
            }

            const { owner, repo } = context.repo;
            const issue_number = context.payload.pull_request.number;

            if (ticked.length === 0) {
              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;
            }
            if (ticked.length > 1) {
              core.setFailed(
                `Multiple "Types of changes" checkboxes are ticked ` +
                `(${ticked.join(', ')}). Tick exactly one.`
              );
              return;
            }

            const desired = ticked[0];
            const current = (context.payload.pull_request.labels || [])
              .map(l => l.name);

            // Strip any stale labels from the known set so a
            // contributor changing their mind in the description
            // doesn't leave the previous label behind.
            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],
              });
            }