JSDoc types are lost in svelte files (typescript-eslint)

[falco467]

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

• 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 are you using?

2.39.0

What did you do?

Configuration

import eslint from '@eslint/js'
import globals from 'globals'
import tsEslint from 'typescript-eslint'
import epSvelte from 'eslint-plugin-svelte'
import svelteParser from 'svelte-eslint-parser'

export default [
  eslint.configs.recommended,
  ...tsEslint.configs.strictTypeChecked,
  ...tsEslint.configs.stylisticTypeChecked,
  ...epSvelte.configs['flat/recommended'],
  {
    languageOptions: {
      parser: tsEslint.parser,
      parserOptions: {
        project: true,
        programs: false,
        extraFileExtensions: ['.astro','.svelte']
      },
      globals: {
        ...globals.browser
      }
    },
  },
  {
    files: ['**/*.svelte'],
    languageOptions: {
      parser: svelteParser,
      parserOptions: {
        parser: tsEslint.parser,
      }
    },
  },
]

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

No response

[ota-meshi]

Thank you for posting this issue.
Hmm... The parser used by this plugin is not designed to handle JSDoc type information well.
If that doesn't work, I recommend using TypeScript in your .svelte scripts too.

[falco467]

@ota-meshi
If I understand it right when I use parserOptions: parser: typescript-eslint-parser,
should the svelte-parser not forward all JavaScript code to the typescript-eslint parser? Because it handles JSDoc Type Information perfectly well. So svelte-parser would not have to parse type information - it just needs to forward the comment-tokens as they are in the source code to typescript-eslint-parser, their parser will interpret the Type information from the comment-tokens.

I'm working with a big code-base which opted for JS with JSDoc Typing (like the svelte team did for the whole svelte code base and many other projects are too) - a rewrite to typescript is not a viable option for our an many other code bases.

[ota-meshi]

Pull requests are welcome.

[falco467]

@ota-meshi after trying to solve it, it seems this needs to be solved upstream in the svelte-eslint-parser. I migrated the issue to their repo.