# Styler

Styler is an Elixir formatter plugin that's 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.

## Installation

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

```elixir
def deps do
  [
    {:styler, "~> 0.7", only: [:dev, :test], runtime: false},
  ]
end
```

## Usage

We recommend using `Styler` as a formatter plugin, but it comes with a task for making it easy to try styling smaller
portions of your project or for installing without modifying your dependencies (via mix's archive.install feature)

### As a Formatter plugin

Add `Styler` as a plugin to your `.formatter.exs` file

```elixir
[
  plugins: [Styler]
]
```

And that's it! Now when you run `mix format` you'll also get the benefits of Styler's *definitely-always-right* style fixes.

### As a Mix Task

```bash
$ mix style
```

The task can helpful for slowly converting a codebase directory-by-directory. It also allows you to use `mix archive.install`
to easily test run `Styler` on a project without modifying its dependencies:

```bash
$ mix archive.install hex styler
```

`mix style` is designed to take the same basic options as `mix format`.

See `mix help style` for more.

### Configuration

There isn't any! This is intentional.

Styler's @adobe's internal Style Guide Enforcer - allowing exceptions to the styles goes against that ethos. Happily, it's open source and thus yours to do with as you will =)

### Your first Styling

**Speed**: Expect the first run to take some time as `Styler` rewrites violations of styles.

Once styled the first time, future styling formats shouldn't take noticeably more time

**Comments and compilation**: Additionally, two sad situations may happen on your first run:

* **module compilation breaks** if a reference to an alias is moved to be before the alias's declaration (part of the `StrictModuleLayout` credo rule)
    - write out aliases in full when using them before the `alias` block of a module
    - similarly, write out constant values rather than module directives
* **comments get put weird places** when module directives are moved
    - manually put them back where you want them, and they shouldn't be moved again
    - feel free to open or +1 an issue in the hopes that we get around to handling this

## Styles

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

### Credo Rules Styler Replaces

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

| `Credo` credo | notes |
|---------------|-------|
| `Credo.Check.Consistency.MultiAliasImportRequireUse` | always expands `A.{B, C}` |
| `Credo.Check.Consistency.ParameterPatternMatching` | also case statements, anon functions |
| `Credo.Check.Readability.AliasOrder` | |
| `Credo.Check.Readability.BlockPipe` | |
| `Credo.Check.Readability.LargeNumbers` | goes further than formatter - fixes bad underscores, eg: `100_00` -> `10_000` |
| `Credo.Check.Readability.ModuleDoc` | adds `@moduledoc false` |
| `Credo.Check.Readability.MultiAlias` | |
| `Credo.Check.Readability.OneArityFunctionInPipe` | |
| `Credo.Check.Readability.ParenthesesOnZeroArityDefs` | removes parens |
| `Credo.Check.Readability.PipeIntoAnonymousFunctions` | |
| `Credo.Check.Readability.PreferImplicitTry` | |
| `Credo.Check.Readability.SinglePipe` | |
| `Credo.Check.Readability.StrictModuleLayout` | **potentially breaks compilation** (see notes above) |
| `Credo.Check.Readability.UnnecessaryAliasExpansion` | |
| `Credo.Check.Refactor.CaseTrivialMatches` | |
| `Credo.Check.Refactor.FilterCount` | in pipes only |
| `Credo.Check.Refactor.MapInto` | in pipes only |
| `Credo.Check.Refactor.MapJoin` | in pipes only |
| `Credo.Check.Refactor.PipeChainStart` | allows ecto's `from`|

## 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.