Perform a fastforward merge to avoid rebuilding same commit on master

[blindpirate]

Hi thanks for the great feature mergify provides!

We're a team where many people work on personal branches and merges to master when the work finishes. We want to leverage strict merge to implement our pre-test commit, especially avoid rebuilding same commit on master. We would like to have a workflow:

• People work on PR branches, aka. head branch.
• When everything is ok, mergify merges master (aka. base branch) to PR branch because of strict merge. Let's call this merge commit MergeCommitA.
• Wait CI to pass.
• Now merge PR branch to master. Mergify will generate a new merge commit (let's call it MergeCommitB).

We want to avoid MergeCommitB, i.e. run git merge --ff instead of mergify default git merge --no-ff because:

• It makes no sense to create MergeCommitB. MergeCommitA is up-to-date.
• Even with identical contents, MergeCommitA/MergeCommitB is recognized as different commits by CI thus requires rebuilding everything, this adds unnecessary pressure to CI.

Is there anything I can do to avoid this problem?

Reference: https://docs.mergify.io/actions/merge.html#git-merge-workflow-and-mergify-equivalent-configuration

[jd]

👋 @blindpirate!
Happy to have you on board.

I understand what you want, which is basically re-using the "update" commit as the merge commit. That makes sense to us.

Unfortunately, GitHub API does not allow this, which means Mergify would have to do git push itself. Doable, but we don't support this case for now. I've added this to our backlog in case that'd interest other people.

Another question would also be: why are you testing master with your CI? Since you have strict mode enabled, there's really no point in testing the master branch anymore in theory.

[blindpirate]

Thanks @jd for the detailed explanation!

We use master's status as an indicator of CI health. Plus, we occasionally push to master directly when the change is tiny or urgent, so we'd like to enable testing on master. Anyway, thanks a lot for the answer!

[sileht]

Mergify now provides two ways to do this fast-forward of pull request commits to master branch:

• the queue/merge option merge_method: fast-forward for simple queue.
• the queue rules option queue_branch_merge_method: fast-forward for advanced queues with speculative checks and batches.