Generics don't work properly when passing down slot props

[aradalvand]

Consider the following components:
Form.svelte:

<script lang="ts">
    type TValues = $$Generic;

    export let values: TValues;

    type Errors<T> = {
        [K in keyof T]: string;
    };

    let errors: Errors<TValues>;
</script>

<form>
    <slot {errors} />
</form>

SpecialForm.svelte:

<script lang="ts">
    import Form from './Form.svelte';

    type TValues = $$Generic;

    export let values: TValues;
</script>

<Form
    {values}
    let:errors
>
    <slot {errors} />
</Form>

App.svelte:

<script lang="ts">
    import SpecialForm from './SpecialForm.svelte';

    let values: {
        firstName: string;
        lastName: string;
    };
</script>

<SpecialForm
    {values}
    let:errors
>
    {errors.firstName}
</SpecialForm>

In the last component (App.svelte), the slot prop errors doesn't have the right type, it's of type Errors<unknown> even though the generic type is properly detected for values.

I have quite a few components that have this kind of relationship, and generics are not working as expected currently, so I'd appreciate it if you fix this. Thank you.

[dummdidumm]

Every issue you open is the most pressing you currently have. It's not like maintainers are idle and jump on every post you create. We will eventually get to answering these, and adding passive aggressive posts that are essentialy just elaborate "bump"s isn't helping. Locking and limiting the conversation on this issue, other people who have the same problem and could post actual helpful context but can't now, please thank @AradAral for that.

[dummdidumm]

Problem is that our transformation of the render return is not specific enough. Component instances are instanciated with instanceOf in this case, not with the new keyword and the specific props:

// is currently this
return { ..., slots: {'default': {errors:__sveltets_1_instanceOf(Form).$$slot_def['default'].errors}}, ... }}
// would need to be something like this
return { ..., slots: {'default': {errors:new Form({ target: __sveltets_2_any(), props: {  values,}}).$$slot_def['default'].errors}}, ... }}
// or this:
declare function createComponent<Props, Events, Slots, T extends Svelte2TsxComponent<Props, Events, Slots>>(t: new (args: {target: any, props?: Props}) => T, p: Props) : T;
// ..
return { ..., slots: {'default': {errors:createComponent(Form, { values,}).$$slot_def['default'].errors}}, ... }}

Fixing this is hard because we need to apply the same logic we apply in the context of each/await (unwrapping stuff) and additionally instantiate the component.

[dummdidumm]

Closing since Svelte 5 replaces slots with snippets and render tags, which don't have this problem (because you're required to type it properly)