Describe the bug

Use case

I'm building a Svelte 5 wrapper library for SAP UI5 Web Components (@ui5/webcomponents).
Each custom element (e.g. <ui5-button>) gets a generated Svelte wrapper so users get autocompletion and type safety.

<ui5-button> has a named slot badge that expects a <ui5-button-badge> element.
I also wrap <ui5-button-badge> in a Svelte component ButtonBadge.svelte.

The problem

When using <ButtonBadge slot="badge"> inside a {#snippet badge()} block, svelte-check reports a type error:

Error: '$$_nottuB0.$$slot_def' is of type 'unknown'. (js)
    {#snippet badge()}
        <ButtonBadge slot="badge"></ButtonBadge>
    {/snippet}

====================================
svelte-check found 1 error and 0 warnings in 1 file

The code works correctly at runtime — this seems to be purely a type-checking issue.
Or maybe I am doing something wrong?

Analysis

svelte-check generates $$ComponentProps = Props & Record<string, unknown> for every component.
This causes $$ComponentProps['$$slot_def'] to resolve as unknown (because Record<string, unknown> maps all unknown keys to unknown).

When the LS sees , it checks $$slot_def on the component type and gets unknown → type error.

Note: slot is explicitly declared in Props as slot?: string — the error persists regardless.

Question

In this Web Component integration pattern, slot="badge" is a native HTML attribute for browser slot assignment — not a Svelte slot directive.
The intended DOM output is:

  <ui5-button>
    <ui5-button-badge slot="badge" text="3"></ui5-button-badge>
  </ui5-button>

Is it expected that slot="..." on a Svelte 5 component triggers $$slot_def checking?
Or should slot declared as a typed prop (slot?: string) be treated as a regular prop — without triggering slot-directive type checking?

Reproduction

Minimal reproduction: https://github.com/ybbus/my-app

The .d.ts files in src/lib/ represent what svelte-package generates when building a Svelte component library for distribution.

Expected behaviour

Should work without any type errors when running svelte-check.

System Info

Environment

• Windows 11
• Svelte: 5.54.0
• svelte-check: 4.4.2
• @sveltejs/kit: 2.50.2
• Svelte VS Code extension: 109.14.2
• TypeScript: 5.9.3

Which package is the issue about?

svelte-check

Additional Information, eg. Screenshots

No response