Is it expected for github.base_ref and github.event.pull_request.base.ref to differ in stacked PRs?

[lucetre]

Hi team,

I have a question about the expected behavior of gh-stack.

We have a GitHub Actions workflow that relies on the PR base branch. While investigating a workflow failure on a stacked PR, we noticed two behaviors that we didn’t expect.

First, a workflow configured as:

on:
  pull_request:
    types: [opened, synchronize, reopened]
    branches:
      - master

was triggered for a stacked PR in the preview stage. Is this the expected behavior?

Additionally, our workflow failed because these two values were different:

github.event.pull_request.base.ref != github.base_ref
github.base_ref == main

We expected github.event.pull_request.base.ref and github.base_ref to refer to the same base branch, but they appear to differ for stacked PRs.

Is this the intended behavior? If so, which value should GitHub Actions workflows rely on?

Thanks!