merge-queue-ci-skipper

GitHub Merge Queues are very useful to avoid the need for pull request authors to keep pressing "update branch" in their PR until they can merge their own PR. This happens in large, contested repositories, especially monorepos, where PRs are merged very frequently.

However, Merge Queues have one disadvantage for repositories with long-running CI checks: When a PR is enqueued into the Merge Queue, all CI checks are run again (in the merge_group context). This is because other PRs could have been ahead of them in the queue, in which case the Merge Queue automatically rebases the changes of the PR onto the changes of the higher-ranked PR. Theoretically, the changes from both PRs combined could cause tests to fail, so it is safer to run the CI checks again.

However, there is one scenario in which running the checks again is redundant. When a PR is enqueued into an empty merge queue, it immediately is the head of the queue. If the PR was already up-to-date with the target branch, the CI checks are run on identical repository content. This causes unnecessary waiting and compute times.

The merge-queue-ci-skipper GitHub Action lets you avoid this issue.

Integration

From this repository

First, add the following step in the beginning of your job:

- id: merge-queue-ci-skipper
  uses: cariad-tech/merge-queue-ci-skipper@main
  with:
      secret: ${{ secrets.GH_ACCESS_TOKEN }}

To get a stable build, please replace the version (main) with the latest released version.

From your own repository

Alternatively, you may copy the action.yml into the following path in your repository: .github/merge-queue-ci-skipper/action.yml

After that, configure the step like so:

- id: merge-queue-ci-skipper
  uses: uses: ./.github/merge-queue-ci-skipper
  with:
      secret: ${{ secrets.GH_ACCESS_TOKEN }}

Configuration

Note the secret input: GH_ACCESS_TOKEN is a token that has administration:read permissions. It needs to be issued by a user that has admin permissions for the repository. This token is used to find the list of required branch checks and confirm that they already passed. This input is optional and may be omitted as long as the repository has Require status checks to pass before merging enabled. If this setting is enabled, GitHub will not enqueue the PR into the Merge Queue until all checks have passed.

This GitHub Action seems to require read permissions for pull-requests and contents.

Next, add the following conditional to every workflow step that should be skipped if the conditions outlined in the scenario described above are true:

- name: Some build step
  if: ${{ steps.merge-queue-ci-skipper.outputs.skip-check != 'true' }}
  run: ./gradlew assemble

Legal Disclaimer

This Software / Contribution is unfinished, untested and is in particular not in a state to be used in any productive or series context. It is provided as a starting point for further development and any use requires extensive checks, improvements and testing, for which exclusively the user integrating this OSS shall be responsible.