async-auto-label.yml

---
name: Apply requested async label

'on':
  workflow_call:

permissions:
  pull-requests: write   # to update labels

jobs:
  apply-label:
    name: Apply label
    runs-on: ubuntu-latest
    if: ${{ github.event.issue.pull_request &&
            startsWith(github.event.comment.body, '+async-label') }}

    steps:
      - name: Install prerequisites
        run: python3 -m pip install --user pygithub

      - name: Parse comment to find label name
        shell: python
        env:
          comment: ${{ github.event.comment.body }}
          requester: ${{ github.event.comment.user.login }}
          repo: ${{ github.event.repository.full_name }}
          pr: ${{ github.event.issue.number }}
          token: ${{ github.token }}
          association: ${{ github.event.comment.author_association }}
        run: |
          import re
          import os
          import github

          accepted_associations = ['COLLABORATOR', 'CONTRIBUTOR', 'MEMBER', 'OWNER']
          repo = github.Github(os.environ['token']).get_repo(os.environ['repo'])
          pr = repo.get_pull(int(os.environ['pr']))
          requester = os.environ['requester']

          def modify_labels():
            match = re.match(r'\+async-label\s+(.+)', os.environ['comment'])
            assert match, f'could not parse comment: {os.environ["comment"]!r}'
            labels = [label.strip() for label in match.group(1).split(',')]

            # Since changing the labels may change which branches this PR is
            # merged into, stay on the safe side and dismiss any approvals.
            for review in pr.get_reviews():
                if review.state == 'APPROVED':
                    review.dismiss('Labels updated; please review again.')

            possible_labels = {label.name: label for label in repo.get_labels() if label.name.startswith('async-')}
            add_labels, invalid_labels = [], []
            for label_name in labels:
                delete = label_name.startswith('!')
                label_name = label_name.lstrip('!')
                try:
                    label = possible_labels[label_name]
                except KeyError:
                    print(f'::warning::Ignoring unknown label {label_name!r}')
                    invalid_labels.append(label_name)
                    continue
                if delete:
                    pr.remove_from_labels(label)
                else:
                    add_labels.append(label)

            pr.add_to_labels(*add_labels)

            if invalid_labels:
                pr.create_issue_comment(
                    f'Hi @{requester}, the following label names '
                    f'could not be recognised: {", ".join(invalid_labels)}'
                )

          if os.environ['association'] in accepted_associations:
            modify_labels()

          else:
            pr.create_issue_comment(
                f'Hi @{requester}, due to your association, '
                 'labels are not added automatically. '
                 'Probably, this is your first contribution. '
                 'Please contact one of the reviewers or '
                 'code owners.'
            )