action.yml

name: GHerrit – Rebase Stack
description: 'Automatically rebase the next PR in a GHerrit stack.'
inputs:
  token:
    description: '`GITHUB_TOKEN` to allow rebase and push'
    required: true
  pr_body:
    description: 'The body/description of the PR that was just merged. Used to extract the child PR ID from the GHerrit metadata.'
    required: true

runs:
  using: "composite"
  steps:
    - shell: bash
      env:
        GH_TOKEN: ${{ inputs.token }}
        MERGED_PR_BODY: ${{ inputs.pr_body }}
      run: |
        # Extract the Child ID from the merged PR's metadata by parsing the
        # JSON inside the HTML comment.
        CHILD_ID=$(echo "$MERGED_PR_BODY" | grep -oP '(?<=gherrit-meta: ).*?(?= -->)' | jq -r .child)

        if [ -z "$CHILD_ID" ] || [ "$CHILD_ID" == "null" ]; then
          echo "Merged PR has no child defined in metadata. Reached top of stack."
          exit 0
        fi

        echo "Merged PR indicates next child is ID: $CHILD_ID"

        # Find the PR associated with that ID. Since GHerrit branches are
        # named exactly after the ID (e.g. refs/heads/G...), we can lookup
        # the PR by branch name (--head).
        CHILD_PR=$(gh pr list --head "$CHILD_ID" --json number --jq '.[0].number')

        if [ -z "$CHILD_PR" ]; then
          echo "Error: Metadata says child is $CHILD_ID, but no open PR exists for branch '$CHILD_ID'."
          echo "The chain might be broken or the child was deleted."
          exit 1
        fi

        echo "Identified Child PR: #$CHILD_PR"

        git config user.name "github-actions[bot]"
        git config user.email "41898282+github-actions[bot]@users.noreply.github.com"

        gh pr checkout "$CHILD_PR"
        
        gh pr edit "$CHILD_PR" --base main
        
        if ! git rebase origin/main; then
            echo "::error::Rebase conflict for PR #$CHILD_PR. Manual intervention required."
            exit 1
        fi
        
        git push --force-with-lease