Before You File a Bug Report Please Confirm You Have Done The Following...

• I'm usingeslint-plugin-svelte. (*.svelte file linting does not work with the parser alone. You should also use eslint-plugin-svelte with it.)
• I'm sure the problem is a parser problem. (If you are not sure, search for the issue ineslint-plugin-svelte repo and open the issue ineslint-plugin-svelte repo if there is no solution.
• I have tried restarting my IDE and the issue persists.
• I have updated to the latest version of the packages.

What version of ESLint are you using?

9.3.0

What version ofeslint-plugin-svelte and svelte-eslint-parser are you using?

• svelte-eslint-parser@0.36.0
• eslint-plugin-svelte@2.39.0

What did you do?

import tsEslint from 'typescript-eslint'import epSvelte from 'eslint-plugin-svelte'import svelteParser from 'svelte-eslint-parser'export default [  ...tsEslint.configs.strictTypeChecked,  ...epSvelte.configs['flat/recommended'],  {    languageOptions: {      parser: tsEslint.parser,      parserOptions: {        project: true,        programs: false,        extraFileExtensions: ['.svelte']      },    },  },  {    files: ['**/*.svelte'],    languageOptions: {      parser: svelteParser,      parserOptions: {        parser: tsEslint.parser,      }    },  },]

<script>/**@param{number}x*/functiontest(x) {return x+1  }</script>

While both .svelte and .js files are scanned by ESLint the same function yields different results:

// test.svelte<script>/**@param{number}x*/functiontest(x) {return x+1  }</script>

// test.js/**@param {number} x */functiontest(x){returnx+1}

npx eslint src

test.js   2:10  error  'test' is defined but never used     @typescript-eslint/no-unused-varstest.svelte    3:12  error  'test' is defined but never used  @typescript-eslint/no-unused-vars    4:5   error  Unsafe return of an `any` typed value  @typescript-eslint/no-unsafe-return    5:12  error  Invalid operand for a '+' operation. Operands must each be a number or string. Got `any`  @typescript-eslint/restrict-plus-operands

What did you expect to happen?

I expected the same code to produce the same warnings, irrespective of appearing in a .svelte or .js file.

What actually happened?

It seems like the typescript-eslint parser cannot parse type information from the code in the .svelte files. Maybe the svelte-parser strips JSDoc comments from the code before forwarding it to the typescript parser?

Link toGitHub Repo with Minimal Reproducible Example

https://github.com/falco467/svelte-jsdoc-typescript-example

Additional comments

Migrated from eslint-plugin-svelte since it is a parser problem:sveltejs/eslint-plugin-svelte#767