Add new option flatConfigFile

[ricardogobbosouza]

Waiting #238
Simplify the use of flat config

// before
const ESLintPlugin = require('eslint-webpack-plugin');

module.exports = {
  // ...
  plugins: [new ESLintPlugin({
    configType: 'flat',
    eslintPath: 'eslint/use-at-your-own-risk',
    overrideConfigFile: 'flat-config.js',
  })],
  // ...
};

// after
const ESLintPlugin = require('eslint-webpack-plugin');

module.exports = {
  // ...
  plugins: [new ESLintPlugin({
    flatConfigFile: 'flat-config.js',
  })],
  // ...
};

1. Create a flatConfigFile option that will define:

• The eslintPath as eslint/use-at-your-own-risk
• The configType as flat
• The overrideConfigFile as flatConfigFile

2. Automatically define flatConfigFile if there is an eslint.config.js file in the project root
3. Add a section in the readme about flatConfigFile

[onigoetz]

Hi @ricardogobbosouza

I have the impression that the addition of this option will become a problem once ESLint 9 is released

My current understanding, as per these blog posts:

• https://eslint.org/blog/2023/11/whats-coming-in-eslint-9.0.0/
• https://eslint.org/blog/2023/10/flat-config-rollout-plans/

The ESLint class will now be equivalent to the FlatESLint class in v8.x. With the exception of a few options, this should mostly be a transparent change.

So that means that the import that's done right now will suddenly handle flatConfig instead of eslintrc-style config

So maybe there is something to do with imports to auto-detect ESLint's version or imports to differentiate which one we have loaded? I expect this part of the logic to become more complicated once ESLint 9 is released

[alexander-akait]

Fixed https://github.com/webpack-contrib/eslint-webpack-plugin/releases/tag/v4.1.0