UnwrapPartial: Add test case for non-Partial instantiation

[porada]

Context

[sindresorhus]

I think this change is wrong because the removed guard is what preserves the documented no-op behavior for non-Partial<T> inputs. Without it, a normal object type with both required and optional properties is inferred through Partial<infer ObjectType> and the optional property becomes required.

Please add this regression test:

type MixedRequiredAndOptional = {
	required: string;
	optional?: number;
};

expectType<MixedRequiredAndOptional>({} as UnwrapPartial<MixedRequiredAndOptional>);

This fails with the simplified implementation, but passes with the previous guarded version.

[porada]

Whoa, good catch. Thanks for staying vigilant.

I think this is worth merging for the guard alone.

[som-sm]

This fails with the simplified implementation, but passes with the previous guarded version.

Yeah, the check is necessary in UnwrapPartial, but looks like it's not necessary in UnwrapRequired. Because in UnwrapRequired, non-Required objects won't match the outer conditional, so the result would come directly from the else branch, refer:

type UnwrapRequired<RequiredObjectType> =
	RequiredObjectType extends Required<infer ObjectType>
		? ObjectType
		: 'No Match';

type T1 = UnwrapRequired<{a?: number; b: string}>;
//=> 'No Match'

type T2 = UnwrapRequired<{a: number; b?: string}>;
//=> 'No Match'

type T3 = UnwrapRequired<{a?: number; b?: string}>;
//=> 'No Match'