name: No PRs on main

on:
  pull_request:
    types: [opened, synchronize, reopened, edited]

permissions:
  contents: read

jobs:
  reject-main-prs:
    runs-on: ubuntu-latest
    steps:
      - name: Check base branch
        env:
          # Explicitly fallback to an empty string if it doesn't exist
          TARGET_BRANCH: ${{ github.base_ref || ''}}
        run: |
          if [ "$TARGET_BRANCH" = "main" ]; then
            echo "::error::Do not open PRs on `main`. The primary branch is `master`. You can change the base branch of this PR to `master`. See: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/changing-the-base-branch-of-a-pull-request"
            exit 1
          fi