Does not respect default language in svelte.config.js

Describe the bug My svelte.config.js file looks like this:

import sveltePreprocess from "svelte-preprocess";

module.exports = {
  preprocess: sveltePreprocess({
    defaults: {
      script: "typescript",
      style: "scss",
    },
    postcss: {
      plugins: [require("autoprefixer")()],
    },
  }),
};

Expected behavior It is showing me that you have to add lang='ts' to svelte file that looks something like this:

<script>
  export let segment: string;
</script>

{segment}

Screenshots

System (please complete the following information):

• OS: Windows
• IDE: VSCode
• Plugin/Package: Svelte for VSCode

[dummdidumm]

See #509 for more info on this. Also you are allowed to import CommonJS modules from ES modules, you just need to change your file ending to become svelte.config.cjs.

[nathanblair]

svelte.config.js doesn’t support ES6 import syntax, AFAIK. Try changing the import to

const sveltePreprocess = require('svelte-preprocess');

I tried to reproduce it using your config and it immediately complains with

The part I was missing was that the svelte language-tools doesn’t read the defaults from the rollup.config.js. I had to add a svelte.config.js file to the root of my project that includes the same config options for sveltePreprocess as in the rollup config.

This is documented in the documentation for svelte-preprocess: https://github.com/sveltejs/svelte-preprocess/blob/master/docs/usage.md#with-svelte-vs-code

Would reading the defaults from the rollup.config.js file be out of the question for the svelte language-tools? Because the onboarding experience for me on this one was a bit painful.

Importing svelte.config.js as an ES6 module should be something that is possible. Not being able to use svelte.config.js so we can have LSP support due to being limited to by CJS is a real pain point in adopting svelte, particularly when the rest of the ecosystem is moving forward with adopting ES6 so everything can stop being so fragmented.

Node recognizes type: "module" from package.json so CJS and module loading at that point become irreconcilable.

What would the blocker be? Is this a LSP issue? Or is it a rollup plugin issue (with the svelte rollup plugin or the svelte-preprocess rollup plugin)?