fast-forward.yml

name: fast-forward
on:
  issue_comment:
    types: [created, edited]
jobs:
  fast-forward:
    # Only run if the comment contains the /fast-forward command.
    if: ${{ github.event.issue.pull_request && contains(github.event.comment.body, '/fast-forward') }}
    runs-on: ubuntu-latest
    concurrency:
      group: fast-forward-${{ github.event.issue.number }}
      cancel-in-progress: true

    # https://docs.github.com/ko/actions/writing-workflows/workflow-syntax-for-github-actions#permissions
    permissions:
      contents: write
      pull-requests: write
      issues: write

    steps:
      - name: Check comment
        id: check_comment
        env:
          COMMENT_BODY: ${{ github.event.comment.body }}
        run: |
          if [[ "$COMMENT_BODY" =~ (^|[[:space:]])/fast-forward($|[[:space:]]) ]]; then
            echo "MATCH=true" >> $GITHUB_OUTPUT
          else
            echo "MATCH=false" >> $GITHUB_OUTPUT
          fi

      - name: Fast forwarding
        if: ${{ steps.check_comment.outputs.MATCH == 'true' }}
        uses: sequoia-pgp/fast-forward@v1
        with:
          merge: true
          # To reduce the workflow's verbosity, use 'on-error'
          # to only post a comment when an error occurs, or 'never' to
          # never post a comment.  (In all cases the information is
          # still available in the step's summary.)
          comment: always

      - name: Check target branch
        if: ${{ steps.check_comment.outputs.MATCH == 'true' }}
        id: check_branch
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
        run: |
          # From https://github.com/sequoia-pgp/fast-forward/blob/main/src/fast-forward.sh
          PR_URL="${{ github.event.issue.pull_request.url }}"
          if test "x$PR_URL" = x
          then
            echo "Unable to find pull request's context."
            exit 1
          fi

          GITHUB_PR=$(mktemp)
          function get_pr_info {
            # https://docs.github.com/en/rest/pulls/pulls?apiVersion=2022-11-28#get-a-pull-request
            curl --silent --show-error --location \
                 -X GET \
                 -H "Accept: application/vnd.github+json" \
                 -H "Authorization: Bearer $GITHUB_TOKEN" \
                 -H "X-GitHub-Api-Version: 2022-11-28" \
                 "$PR_URL" >$GITHUB_PR
          }

          function check_pr_merged {
            local merged_status="false"
            local attempt=1
            local max_attempts=30
            local sleep_duration=1

            while [ "$merged_status" != "true" ] && [ $attempt -le $max_attempts ]; do
              get_pr_info
              merged_status=$(jq -r ".merged" <$GITHUB_PR)

              if [ "$merged_status" = "true" ]; then
                break
              else
                sleep $sleep_duration
                ((attempt++))
              fi
            done

            if [ $attempt -gt $max_attempts ]; then
              echo "The maximum number of attempts has been reached. The pull request was not merged."
              exit 1
            fi
          }

          get_pr_info
          BASE_REF=$(jq -r ".base.ref" <$GITHUB_PR)
          if [ "$BASE_REF" = "main" ]; then
            check_pr_merged
          fi