fix(types): keep optional props when a runtime prop uses a generic PropType - #15523

close #9546

Inside <script setup lang="ts" generic="T">, a runtime props object that uses Object as PropType<T> lost every prop that was not required: true (even unrelated ones like qux: String), and the ones that survived never resolved to T.

Cause. PropMethod<T> is a conditional type on T. When T is a type parameter that conditional is deferred, which makes the whole PropType<T> union a generic type. RequiredKeys / OptionalKeys then defer for the entire options object, so ExtractPropTypes yields a generic mapped type and property access fails for everything on the optional side. InferPropType's [T] extends [Prop<infer V, infer D>] was deferred for the same reason.

Fix.

• Make PropMethod a plain object type. It only exists so Function as PropType<() => void> type-checks; the conditional never changed what a cast accepts, since (): T still has to be comparable with the constructor's call signature.
• In InferPropType, fall back to V when no default type was inferred (unknown extends D). For concrete types the result is unchanged; for a type parameter it keeps the deferred type's constraint at V, so props.bar is assignable to T.

The added test is the case @pikax asked for in #9652, plus a bare Object as PropType<T> prop, an unrelated String prop, and passing props where { bar: T } is expected (#9277). It fails on main with 5 errors and passes with this change; the rest of dts-test and pnpm check are unaffected.

Summary by CodeRabbit

• Bug Fixes

  • Improved TypeScript inference for component props declared with generic PropType values.
  • Optional, required, defaulted, and untyped props now receive more accurate inferred types, including appropriate null and undefined handling.
  • Generic prop definitions remain correctly assignable to expected prop structures.

• Tests

  • Added coverage validating inferred prop names and types across common runtime declaration patterns.