@putout/eslint/README.md

Wrapper that simplifies ESLint API and makes it compatible with 🐊Putout

# @putout/eslint [![NPM version][NPMIMGURL]][NPMURL]

[NPMIMGURL]: https://img.shields.io/npm/v/@putout/eslint.svg?style=flat&longCache=true
[NPMURL]: https://npmjs.org/package/@putout/eslint "npm"

Wrapper that simplifies [**ESLint**](https://eslint.org/) API and makes it compatible with 🐊[**Putout**](https://github.com/coderaiser/putout).

☝️ *[FlatConfig](https://eslint.org/blog/2022/08/new-config-system-part-2/) supported from the box.*

## Install

```
npm i @putout/eslint
```

## Environment Variables

- ☝️ To set custom config file for **ESLint** use `ESLINT_CONFIG_FILE` env variable:
- ☝️ To disable **ESLint** support use `NO_ESLINT=1` env variable:
- ☝️ If you want to ignore **ESLint** warnings (which is unfixable errors in 🐊**Putout** language) use `NO_ESLINT_WARNINGS=1`:

````sh
NO_ESLINT_WARNINGS=1 putout --fix lib

## API

### `eslint(options)`

**ESLint** begins his work as a formatter when 🐊**Putout** done his transformations. That's why it used a lot in different parts of application, for testing purpose and using **API** in a simplest possible way. You can access it with:

```js
import {eslint} from '@putout/eslint';
````

To use it simply write:

```js
const [source, places] = await eslint({
    name: 'hello.js',
    code: `const t = 'hi'\n`,
    fix: false,
});
```

Isn't it looks similar to 🐊**Putout** way? It definitely is! But... It has a couple differences you should remember:

- ☝️ *[🐊**Putout** returns object with `code` and `places` properties](https://github.com/coderaiser/putout#plugins), and **ESLint* returns a tuple**
- ☝️ ***ESLint** has a `name` property that is used to calculate configuration file.*

And you can even override any of **ESLint** ⚙️ options with help of `config` property:

```js
import {safeAlign} from 'eslint-plugin-putout';

const [source, places] = await eslint({
    name: 'hello.js',
    code: `const t = 'hi'\n`,
    fix: false,
    config: [safeAlign],
});
```

If you want to apply 🐊**Putout** transformations using [`putout/putout`](https://github.com/coderaiser/putout/tree/master/packages/eslint-plugin-putout#readme) **ESLint** rule, enable 🐊**Putout** with the same called but lowercased flag:

```js
import {safeAlign} from 'eslint-plugin-putout';

const [source, places] = await eslint({
    name: 'hello.js',
    code: `const t = 'hi'\n`,
    fix: true,
    putout: true,
    config: [safeAlign],
});
```

It is disabled by default, because **ESLint** always runs after 🐊**Putout** transformations, so there is no need to traverse tree again.

### `createPlugin(options)`

You can also simplify creating of plugins for **ESLint** with help of `createPlugin`.
🐊**Putout**-based **ESLint** plugin are highly inspired by [**Putout Plugins API**](https://github.com/coderaiser/putout/tree/master/packages/engine-runner#readme) of [**Includer**](https://github.com/coderaiser/putout/tree/master/packages/engine-runner#includer).

So it must contain classic `4` methods:

```js
export const report = () => 'debugger statement should not be used';

export const fix = (path) => {
    return '';
};

export const include = () => [
    'DebuggerStatement',
];

export const filter = (path, {options}) => {
    return true;
};
```

The main difference with [Includer](https://github.com/coderaiser/putout/tree/master/packages/engine-runner#includer) is:

- `fix` works with text;
- `include` does not support 🦎[PutoutScript](https://github.com/coderaiser/putout/blob/master/docs/putout-script.md#-putoutscript);
- there is no `exclude`;

Take a look at more sophisticated example, rule [`remove-duplicate-extensions`](https://github.com/coderaiser/putout/tree/master/packages/eslint-plugin-putout/lib/remove-duplicate-extensions#readme):

```js
const getValue = ({source}) => source?.value;

export const report = () => 'Avoid duplicate extensions in relative imports';
export const include = () => [
    'ImportDeclaration',
    'ImportExpression',
    'ExportAllDeclaration',
    'ExportNamedDeclaration',
];

export const fix = ({text}) => {
    return text.replace('.js.js', '.js');
};

export const filter = ({node}) => {
    const value = getValue(node);
    return /\.js\.js/.test(value);
};
```

To use it just add couple lines to your main plugin file:

```js
import {createPlugin} from '@putout/eslint/create-plugin';

const createRule = (a) => ({
    [a]: createPlugin(require(`./${a}`)),
});

module.exports.rules = createRule('remove-duplicate-extensions');
```

Or just:

```js
import {createPlugin} from '@putout/eslint/create-plugin';

module.exports.rules = {
    'remove-duplicate-extensions': createPlugin(require('./remove-duplicate-extensions')),
};
```

### `lint(source, {fix, plugins, options, filename})`

When you need to run **ESLint** with one plugin (*rule*), just use `lint` it will do the thing.

```js
import {lint} from '@putout/eslint/lint';
import {createPlugin} from '@putout/eslint/create-plugin';
import * as removeDebugger from 'remove-debugger';

const [code, places] = lint('debugger', {
    fix: true, // default
    plugins: [
        ['remove-debugger', createPlugin(removeDebugger)],
    ],
});
```

When you want to skip plugins, and just provide `options` and `filename` you can:

```js
import {lint} from '@putout/eslint/lint';

const [code, places] = lint('debugger', {
    filename: 'index.js',
    options: [{
        rules: {
            semi: 'error',
        },
    }],
});
```

## License

MIT