First-class support for stacked PRs in Github Actions

[jasondamour]

Hello,

We'd like to skip triggering CI on Stacked PRs, since CI will be re-triggered when base branches are updated and we want to save cost. However, we want to keep CI enabled for other PRs targeting non-default branches.

Is there anything in the Github Actions trigger payload we can use to determine if a PR trigger is stacked? Will there be first-class triggers for stack events?

Thank you

[skarim]

Yes and yes! There is a stack object included in all pull_request webhook events. And there is a new stacked event that fires when a PR is added to a stack. More on this here: https://github.github.com/gh-stack/reference/webhooks/

jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - name: Run for the lowest unmerged PR in the stack
        if: github.event.pull_request.stack.base.ref == github.event.pull_request.base.ref
        run: echo "Lowest unmerged PR in the stack"

      - name: Run for the top PR in the stack
        if: github.event.pull_request.stack != null && github.event.pull_request.stack.position == github.event.pull_request.stack.size
        run: echo "Top PR in the stack"

[jasondamour]

I should have looked before commenting, thank you!