Fast-forward merge for pull requests

This action adds the ability to fast-forward merge pull requests by commenting a predefined comment on the pull request.

Example:

name: Fast-forward

on:
  issue_comment:
    types:
      - created
      - edited

jobs:
  fast-forward:

    name: Fast-forward
    runs-on: ubuntu-latest

    permissions:
      contents: write  # Allows merging the PR.
      pull-requests: write  # Writing comments on PRs.
      issues: write  # Also required for posting comments on PRs.

    # Only run if the comment is one of the defined keywords.
    if: >-
      ${{
        github.event.issue.pull_request
        && contains(fromJSON('["/fast-forward", "/ff"]'), github.event.comment.body)
      }}

    steps:
      - name: Fast-forward
        uses: MrThearMan/prff@v1

With this, by commenting either /ff or /fast-forward on the pull request, the action will run to check if the fast forward merge is possible, and that the commenter has the requird permissions to make that merge, and then make the merge if those checks pass.

If this operation is unsuccessful, a comment will be added to the pull request with the error. A detailed report is also written to the actions summary.

Note about triggering other workflows

Due to the way GitHub works, pushed created using github actions bots do not trigger additional workflows, even if the the workflow would otherwise be triggered. This applies to this fast-forward action as well.

To trigger additional workflows, you can use the repository_dispatch event. Add the following step to your workflow after uses: MrThearMan/prff@v1:

- name: Trigger tests
  run: |
    curl -L \
      -X POST \
      -H "Accept: application/vnd.github+json" \
      -H "Authorization: Bearer ${{ secrets.GITHUB_TOKEN }}" \
      -H "X-GitHub-Api-Version: 2022-11-28" \
      -H "User-Agent: ${{ github.repository }}" \
      https://api.github.com/repos/${{ github.repository }}/dispatches \
      -d '{"event_type":"fast-forward"}'

You also need to add the following trigger to the workflow(s) you want to trigger:

on:
  repository_dispatch:
    types:
      - fast-forward

Note: The event_type in the curl command matches the types in the workflow trigger.

Note: If fast-forwarding a pull request fails, the additional workflow will not be triggered, since its part of the same job. If desired, you can use the continue-on-error option on the fast-forward action to run the additional workflow even if the fast-forwarding fails.