Fourmolu action

This Fourmolu Action helps to ensure that your Haskell project is formatted with Fourmolu. The action tries to find all Haskell source code files in your repository and fails if any of them are not formatted. In case of failure it prints the diff between the actual contents of the file and its formatted version.

Example usage

In the simple case all you need to do is to add this step to your job:

- uses: fourmolu/fourmolu-action@v1

The @v1 after fourmolu-action should be replaced with the version of the Fourmolu Action you want to use. See Releases for all versions available. Each version of the Fourmolu Action generally has a corresponding version of fourmolu. Make sure you pick a Fourmolu Action version that uses the version of fourmolu you use locally.

Full Example

Here's a full YAML file you can copy and paste into your repo that runs fourmolu-action. Add this as a file like .github/workflows/fourmolu.yaml. This Workflow will run everytime you push to a branch.

name: fourmolu
on: push
jobs:
  format:
    runs-on: ubuntu-latest
    steps:
      # Note that you must checkout your code before running fourmolu/fourmolu-action
      - uses: actions/checkout@v2
      - uses: fourmolu/fourmolu-action@v1

Example with more Options

Here's a more complicated example that shows more options being used:

- uses: fourmolu/fourmolu-action@v1
  with:
    # Only check the format of .hs in the src/ directory.
    pattern: |
      src/**/*.hs

    # Don't follow symbolic links to .hs files.
    follow-symbolic-links: false

    # Extra args to pass to fourmolu on the command line.
    extra-args: "--indent-wheres true"

Example Usage with Build Matrix

If you are using a build matrix, then it is more efficient to have a separate job for checking of formatting:

jobs:
  fourmolu:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: fourmolu/fourmolu-action@v1
  build:
    runs-on: ubuntu-latest
    needs: fourmolu
    ...

Here, the build job depends on fourmolu and will not run unless fourmolu passes.

Options

The available options are defined in ./action.yml. See that file for more explanation.

Hacking on this repo

In order to do development on this repo, you first need to install NodeJS and npm to your system. This has been confirmed to work with the following versions, but newer (or slightly older) versions may work as well:

NodeJS: 14.19.1
npm: 6.14.16

Next, clone this repo:

$ git clone git@github.com:fourmolu/fourmolu-action.git

Then, within this repo, install all dependencies defined in package.json:

$ npm install

Now, you should be setup to start development. Development consists of hacking on the ./index.js file. After making changes to this file, you'll need to regenerate the files in ./dist/. You can do that with the following command:

$ npm run prepare

When sending a PR, make sure to run npm run prepare and commit the changes to ./dist whenever you make a change in ./index.js.