api-compat-verification.yml

name: API compatibility verification

on:
  pull_request:
    types: [ opened, synchronize, reopened, labeled, unlabeled ]
    branches: [ main ]

jobs:
  api-compat-verification:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: Check for API compatibility
        if: ${{ !contains(github.event.pull_request.labels.*.name, 'acknowledge-api-break') }}
        run: |
          git fetch origin ${{ github.base_ref }} --depth 1 && \
          git diff remotes/origin/${{ github.base_ref }} --numstat "*.api" | awk '
            BEGIN { s = 0 }
            
            # git diff numstat shows lines deleted in field 2, hence sum up field 2 across all items 
            { s += $2 }
            
            # exit with the number of lines deleted as the result code so that `if failure()` works below
            END { exit s }
          '
      - name: Error message
        if: ${{ failure() }}
        run: |
          echo "::error ::This change modifies the public API in a way that may be backwards-incompatible. Carefully review this pull request and either:"
          echo "::error ::* Revert the changes which caused the API incompatibility –or–"
          echo "::error ::* Add the 'acknowledge-api-break' label to this PR (in rare cases warranting an API breakage)"
          exit 1