"Object is of type 'unknown'" when using event handler on non-ts svelte component

[dominic-simplan]

Describe the bug
After upgrading to the latest (101.7.0) VSCode plugin, I get an error when using an event handler on a svelte component, which is written in plain js.

Usage:

import { PlainJsComponent } from "otherLibrary";

<div>
    <PlainJsComponent on:someEvent={onSomeEvent}/>
</div>

Manual typings (which worked previously):
declare module 'otherLibrary';

Error message: Object is of type 'unknown'

If I remove the event handler, no error is display.
Don't know if this is a bug or if I just need to adjust my type definitions. If it is the latter, in which way do I need to adjust the type definitions?

Expected behavior
It should be possible to use a non-ts svelte component from a ts svelte component.

System (please complete the following information):

• OS: Windows 10
• IDE: VSCode 1.47.2
• Plugin/Package: "Svelte for VSCode 101.7.0"

"svelte": "^3.24.0",
"svelte-check": "^0.1.55",
"svelte-loader": "^2.13.6",
"svelte-preprocess": "^4.0.8",
"@tsconfig/svelte": "^1.0.3",
"typescript": "^3.9.7",

tsconfig:

{
    "extends": "@tsconfig/svelte/tsconfig.json",
    "include": [
        "src/**/*",
        "src/node_modules"
    ],
    "exclude": [
        "node_modules/*",
        "dist/*"
    ],
    "compilerOptions": {
        "strict": true,
        "noImplicitAny": true,
        "resolveJsonModule": true,
        "sourceMap": true,
        "importsNotUsedAsValues": "remove"
    }
}

Additional context
Add any other context about the problem here.

[jasonlyu123]

Can you post your definition here? we change the component type check mechanism in #303.

[dominic-simplan]

I just had this single line in my typings.d.ts:
declare module 'otherLibrary';

Just figured out I can do this to make the error disappear:

declare module 'otherLibrary' {
    export class PlainJsComponent {
        $$prop_def: any;
        $on: any;
    }
}

Would this be an appropriate solution in my case or is there a better way?

[dummdidumm]

This solution is appropriate. We changed the internals so that a component event handler like your on:someEvent is converted to __sveltets_instanceOf(PlainJsComponent ).$on('someEvent', .... At this point the type of PlainJsComponent has to be known explicitely, which is why you need to define the class.

We should definitely provide some docs/guidance on this once we have decided on how to properly define typings.

[dominic-simplan]

I see, thanks for the explanation!