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

• I'm using eslint-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 in eslint-plugin-svelte repo and open the issue in eslint-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 of eslint-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 */  function test(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 */  function test(x) {  return x+1  } </script>

// test.js /** @param {number} x */ function test(x) { return x+1 }

npx eslint src

test.js 2:10 error 'test' is defined but never used @typescript-eslint/no-unused-vars test.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 to GitHub 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