backport.yml

name: Backport PR to branch
on:
  issue_comment:
    types: [created]

permissions:
  contents: write
  issues: write
  pull-requests: write

jobs:
  backport:
    if: github.event.issue.pull_request != '' && contains(github.event.comment.body, '/backport to')
    runs-on: ubuntu-20.04
    steps:
    - name: Extract backport target branch
      uses: actions/github-script@v3
      id: target-branch-extractor
      with:
        result-encoding: string
        script: |
          if (context.eventName !== "issue_comment") throw "Error: This action only works on issue_comment events.";

          // extract the target branch name from the trigger phrase containing these characters: a-z, A-Z, digits, forward slash, dot, hyphen, underscore
          const regex = /^\/backport to ([a-zA-Z\d\/\.\-\_]+)/;
          target_branch = regex.exec(context.payload.comment.body);
          if (target_branch == null) throw "Error: No backport branch found in the trigger phrase.";

          return target_branch[1];
    - name: Post backport started comment to pull request
      uses: actions/github-script@v3
      with:
        script: |
          const backport_start_body = `Started backporting to ${{ steps.target-branch-extractor.outputs.result }}: https://github.com/${context.repo.owner}/${context.repo.repo}/actions/runs/${process.env.GITHUB_RUN_ID}`;
          await github.issues.createComment({
            issue_number: context.issue.number,
            owner: context.repo.owner,
            repo: context.repo.repo,
            body: backport_start_body
          });
    - name: Checkout repo
      uses: actions/checkout@v2
      with:
        fetch-depth: 0
    - name: Run backport
      uses: ./eng/actions/backport
      with:
        target_branch: ${{ steps.target-branch-extractor.outputs.result }}
        auth_token: ${{ secrets.GITHUB_TOKEN }}
        pr_description_template: |
          Backport of #%source_pr_number% to %target_branch%

          /cc %cc_users%

          ## Customer Impact

          ## Testing

          ## Risk