Re TypeScript declarations:
https://github.com/micha-lmxt/svelte-types-writer
And
https://github.com/firefish5000/svelte2dts
Both implement something like this for Svelte files. Basically they transform Svelte (with unpreprocessed TypeScript) to tsx using svelte2tsx (part of language tools) and run tsc on it to emit declaration files. (You can ignore the part in their readme about not placing DTS next to the Svelte file, this is now possible)
I think something like this (generating this DTS files) would make sense to extract into a separate official package once we are happy with the results.

Oh, that's good to know. svelte2dts looks particularly promising, especially if it can be coaxed into generating declaration files for Svelte components with JSDoc types. May take a stab at integrating that later if I get time, though I suppose an alternative could be to just support vanilla JS for now and worry about types in a follow-up

We'll have to add some docs for this as well

I had a crack at integrating svelte2dts but got nowhere, so in the interests of shipping the MVP version of this command I think it probably makes sense to tackle types in a follow-up.

@dummdidumm @halfnelson I did notice that svelte2tsx returns an object with exportedNames and events properties. I didn't study it too closely but it almost feels like we could generate .d.ts files from that information? I'm glossing over slots and inferred types here, and probably many other things, but is there a future in which we can generate declarations directly from svelte2tsx or have I grossly underestimated the problem?

I don't see a near future where this is happening, precisely because of inferred types. I also think that it's better to just let TypeScript handle this stuff, especially since the wrapper to get this working is that small (the svelte2dts code is only a couple of hundred lines).
Happy to take a crack at this after this is merged.

For generating Svelte type definitions there's also https://github.com/IBM/sveld (no lang="ts" support yet if ever) and svelte-type-generator https://github.com/material-svelte/material-svelte/tree/main/tools/svelte-type-generator (uses svelte2tsx)

Two things that come to my mind:

• what about css files that are referenced?
• when writing a package I often want to define the public API myself. That means I have some index.js/ts from which I re-export the public stuff. This makes for both better imports (only one location) and I can also freely reorganize my files internally without risking breaking changes. Is that possible with the current solution?

what about css files that are referenced?

any non .svelte files are copied across as-is, so a module can do import './foo.css' and it will continue to work. they will also have exports generated for them by default, so a consumer can do import 'some-lib/base.css' or whatever

when writing a package I often want to define the public API myself

yes, any src/lib/index.js or src/lib/index.svelte becomes the main entry point. you can disable all other entry points by doing this...

// svelte.config.js
export default {
  kit: {
    package: {
      exports: ['index.js']
    }
  }
};

...and defining the API in src/lib/index.js. Consumers can then do this:

import { X, Y, Z } from 'your-lib';

For generating Svelte type definitions there's also https://github.com/IBM/sveld (no lang="ts" support yet if ever) and svelte-type-generator https://github.com/material-svelte/material-svelte/tree/main/tools/svelte-type-generator (uses svelte2tsx)

Just a warning, pls try to not use sveld as it cannot parse custom css such as sass and cannot detect props which are exported as export {localName as name}. If you need jsdoc-like syntax for generating declaration files, please check out what I made. But I think it is better to provide an official way to generate types instead of looking into third part ones.

Any chance we can get a new kit release for this? #1543
That would create the possibility to easily test it out.

How is this supposed to work for single-component packages? If I add an index file that simply reexports the Svelte component,

// src/lib/index.js
export { default } from './MyComponent.svelte'

and then install the package and try

import MyComponent from 'my-package'

I get

Must use import to load ES Module: my-package/index.js
require() of ES modules is not supported.
require() of my-package/index.js from repo/node_modules/vite/dist/node/chunks/dep-0ed4fbc0.js is an ES module file as it is a .js file whose nearest parent package.json contains "type": "module" which defines all .js files in that package scope as ES modules.
Instead rename index.js to end in .cjs, change the requiring code to use import(), or remove "type": "module" from my-package/package.json.

The easiest solution to this in the past was to use the "svelte" field in package.json but sveltekit package does not copy that field into its output...

I'm not super familiar with svelte-kit package, but I think you can just have Index.svelte and don't need an index.js if all you're doing is exporting a single component

I don't think using a Index.svelte would allow me to import as

import MyComponent from 'my-package'

Would't I have to do this?

import MyComponent from 'my-package/Index.svelte'

If so, I'd say it's better to keep MyComponent.svelte and import it as

import MyComponent from 'my-package/MyComponent.svelte'

• expose compiled components for consumption as regular modules

Is there any workaround to do it until it's possible with svelte-kit package ?

• expose compiled components for consumption as regular modules

Is there any workaround to do it until it's possible with svelte-kit package ?

Finally I did it with rollup, in addition to vite in my svelte-kit project.