Issue Description:

Error Description

Class that conforms to protocol with associated type and has as function with generic requirement doesn't compile, altough the compiler knows the exact type but doesn't use it to automatically infer the associated type.

The code to reproduce the error is:

protocol GenericPAT {
    associatedtype T
    func f<U>(u: U) -> T
}

// error: type 'NotWorking' does not conform to protocol 'GenericPAT'
// struct NotWorking: GenericPAT {
//        ^
// note: do you want to add protocol stubs?
// struct NotWorking: GenericPAT {
//        ^
struct NotWorking: GenericPAT {
    func f<U>(u: U) -> some Collection { [0] }
}

Next code compiles as expected because type is explicit:

struct Working1: GenericPAT {
    func f<U>(u: U) -> [Int] { [0] }
}

On the forums I discuss this topic and @groue verified it but with a different error note that I don't see in my Xcode 13 (different version maybe?). And just at the beginning there is a simplified implementation where I got the error and to reproduce it too.
‎

Working code

This is some code to verify that the compiler infers the type in other similar cases:

struct Working2 {
    func f<U>(u: U) -> some Collection { [0] }
}

protocol NonGenericPAT {
    associatedtype T
    func f() -> T
}

extension Working2: NonGenericPAT {
    func f() -> some Collection { [0] }
}