Documentation update: Use `head_ref` for comments on PR commits? about commit-comment

[peter-evans]

Hi @mpdude

Does github.head_ref work for you? I've not tried it but I would be surprised if that works. The GitHub API is expecting a commit SHA, not a ref.

Even if it works, I think it might be more correct to use github.event.pull_request.head.sha instead. I know this works because I use it in my CI build. See here

Anyway, it's a good idea to add something to the readme about this. I'll add a section to explain about avoiding the merge commit.

[peter-evans]

I just checked and using head_ref does work because the API is converting the ref into the "last sha on the ref." There is a small risk that you will hit the wrong commit sha though. If another commit is pushed to the branch before the action runs it will add the comment to the latest commit SHA, not the commit SHA that the Actions run is executing on.

[peter-evans]

I don't think anyone would ever want to add a comment to the merge commit, so I'm now thinking of updating the action to detect that it is running on a pull_request event and just defaulting the SHA to the pull request branch HEAD.

[peter-evans]

Updated v1 to default sha to the branch HEAD on pull request events.