`project: './tsconfig.json'` in config for .svelte files

[malininss]

I have a big Svelte project with a lot of heavy ESLint rules. This is my original .eslintrc.cjs config:

module.exports = {
  root: true,
  parser: '@typescript-eslint/parser',
  extends: [
    'eslint:recommended',
    'plugin:@typescript-eslint/recommended',
    'plugin:svelte/recommended',
  ],
  plugins: ['@typescript-eslint'],
  parserOptions: {
    ecmaVersion: 2022,
    sourceType: 'module',
    project: './tsconfig.json',
    extraFileExtensions: ['.svelte'],
  },
  overrides: [
    {
      files: ['*.svelte'],
      parser: 'svelte-eslint-parser',
      parserOptions: {
        parser: '@typescript-eslint/parser',
      },
    },
  ],
  rules: {
    ...complex rules
  },
}

With this setup, linting the whole project takes a LONG time (about 4 minutes on a MacBook Pro M2).
I checked the latest Svelte demo project and saw this ESLint config:

export default tseslint.config(
  eslint.configs.recommended,
  ...tseslint.configs.recommended,
  ...svelte.configs['flat/recommended'],
  prettier,
  ...svelte.configs['flat/prettier'],
  {
    languageOptions: {
      globals: {
        ...globals.browser,
        ...globals.node,
      },
    },
  },
  {
    files: ['**/*.svelte'],
    languageOptions: {
      parserOptions: {
        parser: tseslint.parser,
      },
    },
  },
  {
    ignores: ['build/', '.svelte-kit/', 'dist/'],
  }
);

I noticed that it doesn’t include project: './tsconfig.json'. I removed project: './tsconfig.json' from my config for .svelte files (but kept it for .ts files), and now linting only takes 50 seconds.

And everything still works in .svelte files — all the rules and checks are applied, as if it still knows about tsconfig.json.

My Questions:

• Why does ESLint still work in .svelte files without project: './tsconfig.json'?
• Did I do the right thing by removing it? If yes, should the documentation mention this?

[baseballyama]

I think it’s probably related to the project service.
https://typescript-eslint.io/troubleshooting/typed-linting/performance/#project-service-issues

Why does ESLint still work in .svelte files without project: './tsconfig.json'?

Because typescript-eslint will find tsconfig automatically.
https://typescript-eslint.io/troubleshooting/typed-linting/monorepos/#one-root-tsconfigjson

Did I do the right thing by removing it? If yes, should the documentation mention this?

It’s ok to update the README to suggest using tseslint.config for TypeScript users.