.github/workflows/check-whitespace.yml

name: check-whitespace

# Get the repo with the commits(+1) in the series.
# Process `git log --check` output to extract just the check errors.
# Add a comment to the pull request with the check errors.

on:
  pull_request:
    types: [opened, synchronize]

jobs:
  check-whitespace:
    runs-on: ubuntu-latest
    steps:
    - name: Set commit count
      shell: bash
      run: echo "COMMIT_DEPTH=$((1+$COMMITS))" >>$GITHUB_ENV
      env:
        COMMITS: ${{ github.event.pull_request.commits }}

    - uses: actions/checkout@v2
      with:
        fetch-depth: ${{ env.COMMIT_DEPTH }}

    - name: git log --check
      id: check_out
      run: |
        log=
        commit=
        while read dash etc
        do
          case "${dash}" in
          "---")
            commit="${etc}"
            ;;
          "")
            ;;
          *)
            if test -n "${commit}"
            then
              log="${log}\n${commit}"
              echo ""
              echo "--- ${commit}"
            fi
            commit=
            log="${log}\n${dash} ${etc}"
            echo "${dash} ${etc}"
            ;;
          esac
        done <<< $(git log --check --pretty=format:"---% h% s" -${{github.event.pull_request.commits}})

        if test -n "${log}"
        then
          echo "::set-output name=checkout::"${log}""
          exit 2
        fi

    - name: Add Check Output as Comment
      uses: actions/github-script@v3
      id: add-comment
      env:
        log: ${{ steps.check_out.outputs.checkout }}
      with:
        script: |
            await github.issues.createComment({
              issue_number: context.issue.number,
              owner: context.repo.owner,
              repo: context.repo.repo,
              body: `Whitespace errors found in workflow ${{ github.workflow }}:\n\n\`\`\`\n${process.env.log.replace(/\\n/g, "\n")}\n\`\`\``
            })
      if: ${{ failure() }}