Issue Description:

Given the following code:

struct S {
func f(a: Int) -> Int { return 1 }
func f(b: String) -> Int { return 2 }
{{}}}

let s = S()

let ff1 = S.f(s) as (Int) -> Int
let ff2 = S.f(s) as (String) -> Int

The compiler emits the following suspicious errors:

error: 'f' produces 'Int', not the expected contextual result type 'Int'
let ff1 = S.f(s) as (Int) -> Int
{{ ^}}

error: 'f' produces 'Int', not the expected contextual result type 'Int'
let ff2 = S.f(s) as (String) -> Int
{{ ^}}

If the argument labels are omitted (i.e. func f(_ a: Int) -> Int { return 1 }) the errors disappear.

The same error can be observed if S is a class or an enum but not if f are global functions.