Run rain format via pre-commit + reviewdog

This GitHub Action runs the rain-format hook from rain via pre-commit on a ref range and posts formatting suggestions to pull requests as a diff review using reviewdog.

It is intended to keep your CloudFormation YAML consistently formatted in CI, mirroring your local pre-commit setup.

Requirements

Add the rain hooks to your .pre-commit-config.yaml, for example:

repos:
  - repo: https://github.com/aws-cloudformation/rain
    rev: v1.24.1
    hooks:
      - id: rain-format
        files: ^(stacks|modules)/.*\.(yml|yaml)$
        args: ["fmt", "-w", "--node-style", "strict-booleans"]
        require_serial: true
      - id: rain-verify
        args: ["fmt", "-v", "--node-style", "strict-booleans"]
        require_serial: true
        stages: [manual]

Note: This action uses only the rain-format hook. You can still run rain-verify locally or in a separate job if you want verification without writes.

You also need:

• GitHub Actions enabled on the repository
• secrets.GITHUB_TOKEN available (default on GitHub-hosted runners)
• actions/checkout fetching enough history to include both from-ref and to-ref, for example:

- uses: actions/checkout@v4
  with:
    fetch-depth: 0

Inputs

Name	Required	Description
from-ref	✅	Base git ref (e.g. PR base SHA)
to-ref	✅	Head git ref (e.g. PR head SHA)
github-token	✅	GitHub token for reviewdog (secrets.GITHUB_TOKEN)

Outputs

Name	Description
exitcode	Exit code returned by the rain-format hook

Usage

Example workflow for pull requests:

name: Format CloudFormation with rain

on:
  pull_request:

jobs:
  rain-format:
    runs-on: ubuntu-latest

    steps:
      - name: Checkout
        uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Run rain format via pre-commit + reviewdog
        uses: leinardi/gha-pre-commit-rain-format-reviewdog@v1
        with:
          from-ref: ${{ github.event.pull_request.base.sha }}
          to-ref: ${{ github.event.pull_request.head.sha }}
          github-token: ${{ secrets.GITHUB_TOKEN }}

This will:

1. Run rain-format on CloudFormation templates changed between from-ref and to-ref.
2. Capture any formatting changes as a diff.
3. Post a review with suggested changes (rain) via reviewdog.
4. Fail the job if formatting changes are required.

Versioning

It’s recommended to pin to the major version:

uses: leinardi/gha-pre-commit-rain-format-reviewdog@v1

For fully reproducible behavior, pin to an exact tag:

uses: leinardi/gha-pre-commit-rain-format-reviewdog@v1.0.0