Automatically delete branches of unmerged pull requests

delete-branch.yaml

# .github/workflows/delete-branch.yaml
name: Delete unmerged branch

on:
  pull_request:
    branches: [ main ]
    types: [ closed ]

jobs:
  worker:
    runs-on: ubuntu-latest
    steps:
      - name: delete-branch
        uses: actions/github-script@v4.1
        with:
          github-token: ${{ secrets.GITHUB_TOKEN }}
          script: |
            const { repo, owner } = context.repo;
            const pull_number = context.payload.pull_request.number;
            const ref = `heads/${context.payload.pull_request.head.ref}`;
            const checkParams = { owner, repo, pull_number };
            const deleteParams = { owner, repo, ref };

            const isMerged = await (async () => {
              try {
                await github.pulls.checkIfMerged(checkParams);
                return true;
              } catch (e) {
                if (e.status && e.status === 404) { return false; }
                // escalate all unexpected errors
                throw e;
              }
            })();

            if (!isMerged) {
              console.log(`Deleting branch: "${ref}"`);
              try {
                github.git.deleteRef(deleteParams);
              } catch(e) {
                console.log("Cannot delete branch; error:", e);
              }
            }