# Styler

Styler is an AST-rewriting tool. Think of it as a combination of `mix format` and `mix credo`, except instead of telling
you what's wrong, it just rewrites the code for you to fit our style rules. Hence, `mix style`!

Styler is configuration-free. Like `mix format`, it runs based on the `inputs` from `.formatter.exs` and has opinions rather than configuration.

## `mix style`

`mix style` is a 1-1 stand-in for `mix format` in all the normal use-cases. Run `mix help style` for help using it.

### Styler and Comments...

Styler is currently unaware of comments, so you may find that it puts them in really odd spots after a rewrite.

If you find that a comment was put somewhere weird after using Styler, you'll just have to manually put it back where you want it after.
Feel free to grumble about it in an Issue so that we can properly prioritize making this work better in the future.

## Current Styles

You can find the currently-enabled styles in the `Mix.Tasks.Style` module, inside of its `@styles` module attribute. Each Style's moduledoc will tell you more about what it rewrites.

## Credo Rules Styler Replaces

| credo rule                            | style that rewrites to suit          |
|---------------------------------------|--------------------------------------|
| `Credo.Check.Readability.AliasOrder`  | `Styler.Style.Aliases`               |
| `Credo.Check.Readability.MultiAlias`  | `Styler.Style.Aliases`               |
| `Credo.Check.Readability.UnnecessaryAliasExpansion` | `Styler.Style.Aliases` |
| `Credo.Check.Readability.SinglePipe`  | `Styler.Style.Pipes`                 |
| `Credo.Check.Refactor.PipeChainStart` | `Styler.Style.Pipes`                 |

## Writing Styles

Write a new Style by implementing the `Styler.Style` behaviour. See its moduledoc for more.

## Where is Sourceror?

This work was inspired by earlier large-scale rewrites of our codebase that used the fantastic tool called [`Sourceror`](https://github.com/doorgan/sourceror/).

The initial implementation of Styler used Sourceror, but Sourceror's AST-embedding comment algorithm causes Styler to be
too slow to use as a normal formatter. Still, we're grateful for the inspiration Sourceror provided and the changes to the
Elixir AST APIs that it drove.

The AST-Zipper implementation in this project was derived mostly from Sourceror's implementation.