Incorrectly detects that PR branch is no longer needed

[antifuchs]

I initially reported the same underlying issue in #3496, but I wasn't exactly clear in describing it (and I didn't have a good reproducer case). I think I have a clearer understanding of what's going on now, and have made a repository with a self-contained workflow for reproducing the issue:

• The repo is at https://github.com/antifuchs/pull-request-event-repro
• There is a workflow, https://github.com/antifuchs/pull-request-event-repro/blob/b4cf2eb32d89936cbce80072dd1f6b7ee5336ae6/.github/workflows/pr_close_repro.yml, which can be triggered two ways:
  • Using the workflow_dispatch trigger, where it makes a small commit on top of main and then files a PR - this works.
  • Using the pull_request / edited trigger, where it takes the head of the PR, makes yet another commit on top of it and then updates the PR - and this behaves unexpectedly.

What I'd expect to see

In the "pull_request/edited" case, I'd expect that the create-pull-request action takes the current branch, force-pushes the existing pull request branch and updates the PR to reflect what's in the working tree inside which it's operating - just like the workflow_dispatch triggered action does.

What happens instead

The create-pull-request action erroneously detects that the say-hi branch no longer differs from main, which is incorrect - there is one existing commit that isn't on main, and one new commit that isn't even on the pull request head yet: https://github.com/antifuchs/pull-request-event-repro/actions/runs/13501344759/job/37720294582#step:6:8

[peter-evans]

Hi @antifuchs

I suspect that the pull_request trigger isn't working because it checks out a merge commit. You might need to checkout the head_ref in the case of pull_request events. See this section for more detail.

      - uses: actions/checkout@v4
        with:
          ref: ${{ github.head_ref }}

In the "pull_request/edited" case, I'd expect that the create-pull-request action takes the current branch, force-pushes the existing pull request branch and updates the PR to reflect what's in the working tree inside which it's operating - just like the workflow_dispatch triggered action does.

Except that's not what the workflow_dispatch event does. It creates a new PR to merge into the base, main. If you get the pull_request event working, what will happen is that a second new PR is created to merge into the first PR. The first PR won't be updated in-place, that's not how the action works.

[antifuchs]

You're right, I'm pretty sure this is related to, but not singularly caused by, the pull_request trigger vs. the pull_request_target trigger. I have played around with that a little bit and while that behaves a bit better (c-p-r doesn't try to close the PR because it can't tell there are changes), the create-pull-request action still shows weird behavior:

It looks like the logic it contains to determine what changes are "ahead" of the target branch loses commits.

This can be observed in a single run of the action with workflow_dispatch, on a feature branch where I tried to get pull_request_target to work in the repro repo, no pull_request trigger necessary: https://github.com/antifuchs/pull-request-event-repro/actions/runs/13505647183/job/37734461799 is that run. Stepping through:

1. The workflow is triggered from a feature branch, use-pr-target, which is 1 commit ahead of main.
2. The workflow starts, creates a dummy commit, and the worktree is now two commits ahead of main: that one commit plus the "Say hi there" commit.
3. create-pull-request runs and tries to determine the ahead/evenness of the worktree. It determines that the worktree is one commit ahead of main: https://github.com/antifuchs/pull-request-event-repro/actions/runs/13505647183/job/37734461799#step:8:134 - and this is where I scratch my head.

I think from the log messages it almost looks like the action is modifying the main head in the worktree and then makes determinations off the moved head, does that sound right?

[peter-evans]

The problem is that you are setting base: main. This is incorrect, the base is use-pr-target. Just remove base: main altogether because you don't need it.