backport.yml

name: Backport

on:
  pull_request_target:
    types: [closed, labeled]

permissions:
  contents: write
  pull-requests: write

jobs:
  backport:
    name: Backport
    runs-on: ubuntu-latest
    # Fire on merge (for PRs already labeled) and on labels added after merge.
    if: |
      github.event.pull_request.merged == true && (
        (github.event.action == 'closed' && contains(github.event.pull_request.labels.*.name, 'backport')) ||
        (github.event.action == 'labeled' && github.event.label.name == 'backport')
      )
    steps:
      - uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Resolve patch-release branch from latest release tag
        id: resolve
        run: |
          # Highest release tag, including pre-releases. The maintainer decides
          # at dispatch time whether to cut a `release` or `pre-release` from
          # the resulting `patch-release/v<version>` branch.
          last_tag="$(git tag --sort=-v:refname --list 'v*' | head -1)"
          if [ -z "$last_tag" ]; then
            echo "No release tags found." >&2
            exit 1
          fi
          target="patch-release/$last_tag"
          echo "last_tag=$last_tag" >> "$GITHUB_OUTPUT"
          echo "target=$target" >> "$GITHUB_OUTPUT"

      - name: Ensure patch-release branch exists
        run: |
          target="${{ steps.resolve.outputs.target }}"
          last_tag="${{ steps.resolve.outputs.last_tag }}"
          if git ls-remote --exit-code --heads origin "$target" >/dev/null; then
            echo "Branch $target already exists."
          else
            echo "Creating $target from $last_tag."
            git push origin "refs/tags/$last_tag:refs/heads/$target"
          fi

      - name: Create backport PR
        uses: korthout/backport-action@v3
        with:
          target_branches: ${{ steps.resolve.outputs.target }}
          copy_labels_pattern: '.*'
          cherry_picking: 'auto'
          merge_commits: 'skip'
          pull_description: |-
            Backport of #${pull_number} to `${target_branch}`.

            Cherry-picked from ${source_sha} (via `git cherry-pick -x`).