Elm-format - Detailed Review

Here are some frequently asked questions about `elm-format` along with detailed responses:

Q: What is elm-format and what are its benefits?

`elm-format` is a tool that formats Elm source code according to a standard set of rules, inspired by the popular `gofmt`. The benefits include making code easier to write, read, and maintain. It saves time by avoiding debates over formatting and reduces diffs related only to formatting changes.

Q: How do I install elm-format?

To install `elm-format`, you can run the following command in your terminal:

npm install elm-format -g

This installs the package globally, allowing you to use the `elm-format` command from anywhere.

Q: How do I use elm-format to format my Elm files?

You can format Elm files using the `elm-format` command. For example, to format all Elm files in the current directory, you can use:

elm-format .

This command will format all `*.elm` files in the current directory and its subdirectories, ignoring directories like `elm-stuff` and `node_modules`.

Q: How can I integrate elm-format into my continuous integration (CI) builds?

To ensure that changes to your project are properly formatted in your CI builds, you can use the `–validate` option with `elm-format`. Here’s an example:

elm-format --validate .

This command checks if all specified files are properly formatted without changing any files on disk. It exits with an exit code of 0 if all files are formatted correctly and 1 otherwise, providing a JSON list of errors if any.

Q: Can I automate the formatting process using git hooks?

Yes, you can automate the formatting process using git hooks with tools like Husky and Lint-staged. Here’s how you can set it up:

{
  "scripts": {
    "precommit": "lint-staged"
  },
  "lint-staged": {
    "*.elm": [],
    "*.js": []
  }
}

This configuration runs `elm-format` on all staged Elm files before the commit, ensuring they are properly formatted.

Q: How does elm-format handle errors and output?

When using the `–validate` option, `elm-format` outputs a JSON list of `FormattingError` objects. Each error object contains a `path` field with the relative path of the file and a `message` field describing the error. If all files are properly formatted, the output will be an empty list.

Q: Can I use elm-format with my source code editor?

Yes, most source code editors offer plugins for `elm-format` that can automatically format your Elm files every time you save them. You need to install the plugin for your editor and possibly enable the “format on save” option according to the plugin’s instructions.

Q: What are the constraints and rules followed by elm-format?

`elm-format` formats Elm code without requiring any information outside of the code being formatted. It ensures that the same code always formats in the same way with a given version of `elm-format`, and it avoids configuration options to make code easier to read and maintain.

Q: Is elm-format stable, or is it still in development?

While `elm-format` is still considered to be in beta, it is widely used in the Elm community and is stable enough for practical use. However, the format produced by future versions (e.g., 1.0.0) might differ slightly from the current version.