Weird behavior with Generics + SvelteHTMLElement

[paoloricciuti]

Describe the bug

I was creating an "isomorphic component" (basically where you pass as and it render the correct html element) and i started experimenting with the typings to get autocompletion. I come up with this which works fine

<script lang="ts" generics="T extends keyof HTMLElementTagNameMap">
    import type { SvelteHTMLElements } from 'svelte/elements';
    export let as: T;

    type $$Props = SvelteHTMLElements[T] & {
        as: T;
    };
</script>

the typecheck per se works fine but what is a bit iffy it's the autocompletion. You get autocomplete for every prop even the one that are not associated with the type T (for example you get autocomplete for type if you use spam for as). I tried the same generic function in the typescript playground and it works correctly.

https://github.com/sveltejs/language-tools/assets/26281609/1bfdc057-5cb0-42f2-b3b1-d1a0a9886dc8

https://github.com/sveltejs/language-tools/assets/26281609/403a5a65-8d27-4200-b28d-9d76d895fb9d

Reproduction

1. go to this TS playground https://tsplay.dev/NB1Gpw
2. verify that autocomplete works correctly
3. paste the above code in a svelte component in vscode
4. try to import it and get autocompletion

Expected behaviour

You should only get autocompletion for the correct element

System Info

• OS: Mac
• IDE: VSCode

Which package is the issue about?

No response

Additional Information, eg. Screenshots

No response

[jasonlyu123]

The generic function isn't the same. The component type is more complex than a simple function. Because of the extra complexity, the completion probably got wrong. Anyway, this will have to be fixed in TypeScript. There is probably not much we can do.

https://www.typescriptlang.org/play?#code/JYWwDg9gTgLgBDAnmApnA3nAygNxQGxhQAkAVAWQBkBRfFEFAOxgGc4BfOAMyghDgBELPIRQB6AvSasBAbgBQoSLAzYRRAMJ9IjaR269+Q9Sjnz5AExQBjfAEMoaLgFdG1mMAiM4W8AB5SOBQADyJGCzYAaxRECC44MipaKWZSOwBzADk7BnI7MAA+AAowXjAWAC4MO0q4Uk4AMjUCIkSaOgZmFgBtUgBdAEoqu0ZEBXlbGrZfMAAmAKDQpgi4aNj4tuTOmDSsnJQ8wsWwldwWlBmvaT95OAwAchr7qvq4JrPRTY7pHv75Aow7HMMyK6FucBqVQEdgEABpwQALRxcKECeTsAbjXQAdx82lmoPBpQg5SqYLud0hcHuLDAI3u8IpCGQKCq93u4PYjIQDnSKBgVQsEGszm2ADoAEYQCyIdEDIA

Edit:

I can also see type in your simple version, just not the string literal types completion for the button. You probably hit a state where Monaco returns a cached version of the completion. A level nested is also enough to make the string literals completion for type appear. So, it is probably unrelated to the SvelteComponent but the nested object.

[paoloricciuti]

The generic function isn't the same. The component type is more complex than a simple function. Because of the extra complexity, the completion probably got wrong. Anyway, this will have to be fixed in TypeScript. There is probably not much we can do.

https://www.typescriptlang.org/play?#code/JYWwDg9gTgLgBDAnmApnA3nAygNxQGxhQAkAVAWQBkBRfFEFAOxgGc4BfOAMyghDgBELPIRQB6AvSasBAbgBQoSLAzYRRAMJ9IjaR269+Q9Sjnz5AExQBjfAEMoaLgFdG1mMAiM4W8AB5SOBQADyJGCzYAaxRECC44MipaKWZSOwBzADk7BnI7MAA+AAowXjAWAC4MO0q4Uk4AMjUCIkSaOgZmFgBtUgBdAEoqu0ZEBXlbGrZfMAAmAKDQpgi4aNj4tuTOmDSsnJQ8wsWwldwWlBmvaT95OAwAchr7qvq4JrPRTY7pHv75Aow7HMMyK6FucBqVQEdgEABpwQALRxcKECeTsAbjXQAdx82lmoPBpQg5SqYLud0hcHuLDAI3u8IpCGQKCq93u4PYjIQDnSKBgVQsEGszm2ADoAEYQCyIdEDIA

Edit:

I can also see type in your simple version, just not the string literal types completion for the button. You probably hit a state where Monaco returns a cached version of the completion. A level nested is also enough to make the string literals completion for type appear. So, it is probably unrelated to the SvelteComponent but the nested object.

Oh yeah i tought that could've been the case but didn't think of ways to test it...thanks for the playground