What is a predictable commit sha to use when merging pull request to a master using GitHub actions?

Question

I am using [github-actions]. I have two worksflows:

• triggered on pull_request
• triggered on push

on:
  workflow_dispatch:
  pull_request:
    branches:
      - master

on:
  workflow_dispatch:
  push:
    branches:
      - master

The pull_request workflow generates assets that need be used in push workflow. I need some sort of an identifier that would allow me to connect the two workflows, ideally SHA of git merge commit. However, I was not able to identify a reliable reference to use.

At the moment I am using ${{ github.event.pull_request.head.sha }} in pull_request workflow, and in push workflow I am using:

- name: Setup repository
  uses: actions/checkout@v2
  with:
    fetch-depth: 2
- name: Set CI_COMMIT_SHORT_SHA env property
  shell: bash
  run: echo "CI_COMMIT_SHORT_SHA=$(git rev-parse --short=8 HEAD^2)" >> $GITHUB_ENV

This works most of the time but breaks when commits are force pushed to the PR branch before it is merged.

What is a reliable git reference to associate pull_request with push workflows?

Answer 1

If you're looking to trigger the second workflow only on a PR merge to master, you could use the pull_request.closed event. From within that workflow, $GITHUB_REF should get you the reference to the PR merge branch (refs/pull/:prNumber/merge). Would that work for you to tie the two workflows together?

on:
  pull_request:
    branches:
      - master
    types: [closed]

Also, note that to ignore closed PRs that weren't merged, you'll need to add a condition in your job to skip it in that case: if: github.event.pull_request.merged == true