action.yml

name: Trigger CI with empty commit
description: Push an empty commit to a PR branch to trigger CI, or explain why push is not possible.
author: Shamrock-code

branding:
  icon: refresh-cw
  color: green

inputs:
  github_token:
    description: PAT used for label removal and pushing to the PR head branch.
    required: true
  label:
    description: Label to remove and mention in the fork PR comment.
    required: false
    default: trigger-ci

runs:
  using: composite
  steps:

    - name: Remove label
      uses: actions-ecosystem/action-remove-labels@v1
      with:
        labels: ${{ inputs.label }}
        github_token: ${{ inputs.github_token }}

    - name: Determine if we can push to the PR branch
      id: can_push
      shell: bash
      run: |
        IS_FORK="${{ github.event.pull_request.head.repo.full_name != github.repository }}"
        MAINTAINER_CAN_MODIFY="${{ github.event.pull_request.maintainer_can_modify }}"

        if [ "$IS_FORK" = "true" ] && [ "$MAINTAINER_CAN_MODIFY" != "true" ]; then
          echo "can_push=false" >> "$GITHUB_OUTPUT"
          echo "Cannot push: PR is from a fork and 'Allow edits from maintainers' is disabled."
          exit 0
        fi

        echo "can_push=true" >> "$GITHUB_OUTPUT"

    - name: Checkout PR branch
      if: steps.can_push.outputs.can_push == 'true'
      uses: actions/checkout@v7
      with:
        fetch-depth: 0
        repository: ${{ github.event.pull_request.head.repo.full_name }}
        ref: ${{ github.event.pull_request.head.ref }}
        token: ${{ inputs.github_token }}
        allow-unsafe-pr-checkout: true

    - name: Create and push empty commit
      if: steps.can_push.outputs.can_push == 'true'
      shell: bash
      env:
        HEAD_REF: ${{ github.event.pull_request.head.ref }}
      run: |
        git config --global --add safe.directory '*'
        git config user.name "github-actions[bot]"
        git config user.email "41898282+github-actions[bot]@users.noreply.github.com"

        git commit --allow-empty -m "[gh-action] trigger CI with empty commit"
        git push origin "HEAD:${HEAD_REF}"

    - name: Explain why we could not push (fork PRs without maintainer edits)
      if: steps.can_push.outputs.can_push != 'true'
      uses: actions/github-script@v6
      with:
        github-token: ${{ inputs.github_token }}
        script: |
          const label = '${{ inputs.label }}';
          const owner = context.repo.owner;
          const repo = context.repo.repo;
          const issue_number = context.payload.pull_request.number;

          const msg = [
            "I can't push the empty commit to this PR branch because it comes from a fork and **'Allow edits from maintainers'** is disabled.",
            "",
            "To trigger CI, either:",
            `- enable **Allow edits from maintainers** on the PR, then re-add the \`${label}\` label, or`,
            "- push an empty commit yourself with message `[gh-action] trigger CI with empty commit`."
          ].join("\n");

          await github.rest.issues.createComment({ owner, repo, issue_number, body: msg });