# 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 its 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.

## Installation

Add `:styler` as a dependency to your project's `mix.exs`:

```elixir
def deps do
  [
    {:styler, "~> 0.3", only: [:dev, :test], runtime: false},
  ]
end
```

## Usage

```bash
$ mix style
```

This will rewrite your code according to the Styles of `Styler` and format it.

Run `mix help style` for more details on arguments and flags.

### Replacing `mix format`

As stated above, `Styler` takes a cue from Elixir's Formatter and offers no configuration. Instead, it harnesses the same `.formatter.exs` file as Formatter to know which files within your project it should style.

`Styler` wraps up its work by running its rewrites through the Formatter - in fact, it's meant to be a complete stand-in for  `mix format`. You can alias it as `format` to quickly standardize its use across your project and save yourself the work of having to update existing formatter-related CI scripts and documentation.

```elixir
def aliases do
  [
    # `mix format` will now actually run `mix style` behind the scenes
    # saving you from updating your existing CI scripts etc!
    format: "style"
  ]
end
```

## 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.Check`                                        | `Styler.Style`                       | Style notes              |
|------------------------------------------------------|--------------------------------------|--------------------------|
| `Credo.Check.Consistency.MultiAliasImportRequireUse` | `Styler.Style.ModuleDirectives`      | always expands `A.{B, C}`
| `Credo.Check.Readability.AliasOrder`                 | `Styler.Style.ModuleDirectives`      |
| `Credo.Check.Readability.BlockPipe`                  | `Styler.Style.Pipes`                 |
| `Credo.Check.Readability.LargeNumbers`               | `Styler.Style.Simple`                | fixes bad underscores, ie: `100_00`
| `Credo.Check.Readability.ModuleDoc`                  | `Styler.Style.ModuleDirectives`      | adds `@moduledoc false`
| `Credo.Check.Readability.MultiAlias`                 | `Styler.Style.ModuleDirectives`      |
| `Credo.Check.Readability.SinglePipe`                 | `Styler.Style.Pipes`                 |
| `Credo.Check.Readability.StrictModuleLayout`         | `Styler.Style.ModuleDirectives`      | potentially destructive! (see moduledoc)
| `Credo.Check.Readability.UnnecessaryAliasExpansion`  | `Styler.Style.ModuleDirectives`      |
| `Credo.Check.Refactor.PipeChainStart`                | `Styler.Style.Pipes`                 |

If you're using Credo and Styler, we recommend disabling these rules in Credo to save on unnecessary checks in CI.

## Thanks & Inspiration

### [Sourceror](https://github.com/doorgan/sourceror/)

This work was inspired by earlier large-scale rewrites of an internal codebase that used the fantastic tool `Sourceror`.

The initial implementation of Styler used Sourceror, but Sourceror's AST-embedding comment algorithm slows Styler down to
the point that it's no longer an appropriate drop-in for `mix format`.

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 forked from Sourceror's implementation.

### [Credo](https://github.com/rrrene/credo/)

Similarly, this project originated from one-off scripts doing large scale rewrites of an enormous codebase as part of an
effort to enable particular Credo rules for that codebase. Credo's tests and implementations were referenced for implementing
Styles that took the work the rest of the way. Thanks to Credo & the Elixir community at large for coalescing around
many of these Elixir style credos.

### Elixir's Formatter

The low-hassle, (almost) no-config design of `mix format` greatly influenced the implementation of `mix style`.