Setup and run prettier --check with any plugin

Prettier Check is a github action that provides a way to setup and run prettier --check on your code, using your defined prettier version and prettier plugins without custom hacks.

Why?

I run prettier --check in our CI but I use non-official prettier plugins. This means I can't use actions/prettier-action to check the code, because that seems to only support bundled prettier plugins (ie. @prettier/plugin-*)

So what I was doing was just running prettier directly after installing before the rest of the code actions. But I like to run prettier as a separate job, but when doing that you need to basically install everything, and re-use any caches etc and it just requires a bunch of setup and hassle.

So this is an attempt at basically setting up only prettier and the related plugins in a relatively light-weight fashion and running it only against changed files in the current PR or commit.

Usage examples

To use this action in your github workflows:

1. Simple usage

On event push it will attempt to use the main branch as the reference for changed files. So if your main branch is a different name, you need to set it with the main-branch option.

name: CI
on: push

jobs:
  check_formatting:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v4
        with:
          fetch-depth: 0
      - name: Run prettier action
        uses: arnorhs/prettier-check@v1.0.6
        with:
          main-branch: main

2. Only changed files in a pull request

In this case, we already have the comparison sha, so you don't have to specify your main-branch.

name: CI
on: pull_request

jobs:
  check_formatting:
    runs-on: ubuntu-latest
    steps:
      - name: Checkout
        uses: actions/checkout@v4
        with:
          fetch-depth: 0
      - name: Run prettier action
        uses: arnorhs/prettier-check@v1.0.6

Options

• main-branch: This is the main reference branch that gets used to only check the formatting of changed files.

Limitations and opinions

This action only supports checking prettier for formatting, not running it and committing.

As of now, this action is pretty opinionated:

• This action doesn't format and commit the code.
• It assumes you haven't installed npm packages yet in node_modules - it will node_modules after running, so if you've already done an npm install, you shouldn't really be using this action anyways.
• If run in a pull_request action, it only checks changed files compared to the base branch (GITHUB_BASE_REF), but if its run in another context, it will check all files that have changed compared to the main-branch
• Assumes your repo has a root package.json
• Assumes you have your prettier plugins in the root package.json
• Doesn't have any options, and doesn't allow you to customize the prettier invocation.

TODO:

Make it work on other platforms