Style (pull_request) always fails on Git detached HEAD error

[nanxstats]

Describe the bug
When creating a pull request, two workflow runs will be created for the {styler} workflow. The Style (push) run is successful but Style (pull_request) always fails at the "Commit and push changes" step on a Git detached HEAD error.

To Reproduce
Example pull request: https://github.com/nanxstats/stylertest/pull/1
Full log for failed run: https://github.com/nanxstats/stylertest/actions/runs/3875928032/jobs/6609199407

Expected behavior
Both runs of the workflow should be successful.

Additional context
The error message often looks like this:

Run git config --local user.name "$GITHUB_ACTOR"
HEAD detached at pull/1/merge
nothing to commit, working tree clean
No changes to commit
You are not currently on a branch.
Please specify which branch you want to merge with.
See git-pull(1) for details.

    git pull <remote> <branch>

Error: Process completed with exit code 1.

[dpprdan]

Confirmed and I see the same on the document (pull_request) workflow.

Are the on: pull_request workflows even necessary, with on: push in place without a branch filter? I.e. the latter are executed on all branches anyway (also on forked repos), including PR branches?! 🤔

@arisp99 (who authored the workflows) any idea, what's going on here?

[arisp99]

Based on actions/checkout#124, it seems that when the code is checked out during the pull_request trigger, the code is checked out in the detached HEAD state, so we can't pull and push to the branch. This doesn't happen for the push trigger. It is possible to work around this, but @dpprdan is correct that the push trigger also catches pull requests so the easiest solution would likely be to remove the pull_request trigger.

[github-actions]

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