octokit.rest.pulls.updateBranch() only when there are new commits in a PR's base branch

[thomasleplus]

Hi,

I am working on a GitHub workflow based on github-script/octokit.js. I am trying to automatically update a PR branch if there is a new commit in it's base branch. I am almost able to make it work using a scheduled workflow that regularly checks for open PRs and uses octokit.rest.pulls.updateBranch() to update the corresponding branch. But there's an issue: I expected the call to do nothing when there is no new commit but it doesn't seem to be the case. Instead it seems to always create a new merge commit in the PR branch, including an empty commit with there is nothing to update. I don't like this behavior because each empty commit triggers a bunch of workflows which is wasteful.

Since I have the SHA of the latest commit on the base branch, I am thinking one solution would be to check if the PR branch contains the last commit from the base branch. I know how to do this using the CLI:

git branch <pr-branch> --contains <latest-base-sha>

But I couldn't find the equivalent in the octokit.js API. Does it exist? Or does anyone see a better way to achieve what I am trying to do?

For reference, this is the current draft of my github-script action:

const opts = github.rest.pulls.list.endpoint.merge({
   owner: context.repo.owner,
   repo: context.repo.repo,
   state: 'open',
   base: context.ref.replace('refs/heads/', ''),
})
const prs = await github.paginate(opts)
for (const pr of prs) {
   github.rest.pulls.updateBranch({
      owner: context.repo.owner,
      repo: context.repo.repo,
      pull_number: pr.number,
   })
})

Excuse my poor node.js coding skills, I am new to this language. Also the reason why I am using a scheduled workflow to trigger this instead of doing it on each push to the base branch is that I am using various bots that push security updates via PRs that are auto-merged. Auto-merged pushes do not trigger workflows so that approach didn't work for me although it would have been much more elegant.

Cheers,

Tom