name: Git tree checks

on:
  pull_request:
    types: [opened, edited]
  merge_group:
permissions: read-all

jobs:
  check_base_ref:
    name: Based on `master`
    runs-on: ubuntu-latest
    steps:
      - id: not_based_on_master
        if: |
          github.event_name == 'pull_request' &&
          github.event.pull_request.base.ref != 'master'
        run: |
          echo "This PR is not based on master. Please wait until the base PR merges."
          exit 1