backport.yml

name: Backport merged PR

on:
  pull_request_target:
    types:
      - closed
      - labeled

permissions:
  contents: write
  pull-requests: write

jobs:
  backport:
    name: Backport merged PR
    runs-on: ubuntu-latest
    # closed: when PR is merged with label `backport *`
    # labeled: when `backport *` label is added to a merged PR
    if: >
      (github.event.action == 'closed' &&
       github.event.pull_request.merged == true &&
       contains(join(github.event.pull_request.labels.*.name, ' '), 'backport '))
      ||
      (github.event.action == 'labeled' &&
       github.event.pull_request.merged == true &&
       startsWith(github.event.label.name, 'backport '))
    steps:
      - name: Checkout repository
        uses: actions/checkout@v6

      - name: Expand backport label into target branches
        id: targets
        uses: actions/github-script@v8
        with:
          script: |
            // definitions
            const labelPattern = /^backport (.+)$/
            const esBranches = ["es-9", "es-8.18-plus", "es-8.10-8.17"]
            const osBranches = ["os-3", "os-2.6-plus"]
            const groups = {
              "es": esBranches,
              "os": osBranches,
              "all": [...esBranches, ...osBranches],
            }

            const labels = new Set(
              (context.payload.pull_request.labels || []).map(l => l.name)
            )
            const targets = new Set()
            for (const label of labels) {
              const m = labelPattern.exec(label)
              if (!m) continue
              const key = m[1]

              if (groups[key]) {
                for (const branch of groups[key]) {
                  targets.add(branch)
                }
              } else {
                targets.add(key)
              }
            }
            core.setOutput("target_branches", Array.from(targets).join(" "))

      - name: Create backport PRs
        id: backport
        # Keep third-party actions pinned to a commit SHA for supply-chain safety.
        # https://github.com/korthout/backport-action/releases/tag/v4.5.2
        uses: korthout/backport-action@4aaf0e03a94ff0a619c9a511b61aeb42adea5b02
        with:
          github_token: ${{ secrets.GITHUB_TOKEN }}
          # Target branches are resolved by the github-script step above.
          # Disable the action's own label parsing so shorthand keys such as
          # "all" are not treated as literal branch names.
          label_pattern: '^$'
          target_branches: ${{ steps.targets.outputs.target_branches }}
          branch_name: 'backport/${target_branch}/${pull_number}'
          pull_title: '[Backport ${target_branch}] #${pull_number} ${pull_title}'
          experimental: >-
            { "conflict_resolution": "draft_commit_conflicts" }