Flat eslint config: can't understand a way how it is intended to used, it's design is wrong and it is not documented as expected

[andrew-aladjev]

Body

I am trying to migrate to Eslint 9.0.0. I want to prepare a flat eslint configuration based on the old .eslintrc.json. I've read the flat config documentation and found that the new config consists of objects that will be applied to each source file. Let's go deeper:

import typescriptEslint from 'typescript-eslint';
console.log(typescriptEslint.configs.all);

[
  {
    languageOptions: { parser: ..., sourceType: 'module' },
    plugins: { '@typescript-eslint': ... }
  },
  {
    files: [ '**/*.ts', '**/*.tsx', '**/*.mts', '**/*.cts' ],
    rules: {
      'constructor-super': 'off',
      ...
    }
  },
  {
    rules: { ... },
  }
]

We can see that default configuration consists of objects:

1. The first object includes just language options, parser, parser options, and plugin.
2. The second object includes rule exceptions that should be applied to special files only and should not be applied to any other files.
3. The third object includes rules that should be applied to all files.

I've read several pages of documentation and found a recommended "way" to prepare the configuration:

console.log(typescriptEslint.config({
  files: ['src/**/*'],
  languageOptions: { sourceType: 'other', parserOptions: { sourceType: 'other' } },
  plugins: { 'my-plugin': 'my-plugin' },
  extends: typescriptEslint.configs.all,
}));

[
  {
    languageOptions: { parser: [Object], sourceType: 'module' },
    plugins: { '@typescript-eslint': [Object] },
    files: [ 'src/**/*' ]
  },
  {
    files: [ 'src/**/*' ],
    rules: {
      'constructor-super': 'off',
      ...
    }
  },
  {
    rules: { ... },
    files: [ 'src/**/*' ]
  },
  {
    files: [ 'src/**/*' ],
    languageOptions: { sourceType: 'other', parserOptions: [Object] },
    plugins: { 'my-plugin': 'my-plugin' }
  }
]

1. First object has just limited the set of source files where parser should be applied. I am not able to change language or parser options for typescript-eslint parser. I am not able to add plugin toward typescript-eslint plugin.
2. Second rule is broken completely: we have wider range of files where exceptions should be applied.
3. Third rules is valid, we have just limited the set of files for all rules.
4. 4-th object has no sense: it applies my-plugin together with some options for all files.

I am pretty sure that typescript-eslint should not recommend typescriptEslint.config function in current form.

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