Incorrect parameter type checking for omitted parameters

[Jojoshua]

Describe the bug

I'm not exactly sure how to phrase the title of this bug report so please update if it doesn't make sense. While trying to workaround/create a concept so that a set of components could follow a strict pattern and enforce an abstract class (sveltejs/svelte#15552), I found this issue.

The doSomething method requires a data parameter of type number. The type checker got it right when the parameter was passed in (S1.svelte and S3.svelte) but not when it was simply left out (S2.svelte)

Reproduction

See https://github.com/Jojoshua/svelte5-issue1/tree/master/src/Specialty

Expected behaviour

I expect an error to be shown for S2.svelte where it requires a parameter of type number to be passed into the component prop

System Info

• OS: [e.g. Windows]
• IDE: [e.g. VSCode, Atom]

Which package is the issue about?

No response

Additional Information, eg. Screenshots

No response

[jasonlyu123]

This is controlled by TypeScript and is considered as "working as intended" https://github.com/microsoft/TypeScript/wiki/FAQ#parameter-arity-variance-is-correct. I don't know any workaround to force TypeScript to error on this either, unfortunately.

[Jojoshua]

This is controlled by TypeScript and is considered as "working as intended" https://github.com/microsoft/TypeScript/wiki/FAQ#parameter-arity-variance-is-correct. I don't know any workaround to force TypeScript to error on this either, unfortunately.

Thanks for finding the reference...I've never heard of that. I will close this since it appears to be a TS design decision.