name: Check PR source branch

on:
  pull_request_target:
    types: [opened, synchronize]

jobs:
  check-source-branch-is-not-main-or-master:
    runs-on: ubuntu-latest
    if:  contains(fromJSON('["main", "master"]'), github.head_ref)
    # or github.event.pull_request.head.ref
    steps:
      - run: |
          echo "Error: Pull requests should not be from your 'main' or 'master' branch. :("
          exit 1