protocol P {}

struct S<T> {
  subscript<U : P & Hashable>(x x: U) -> U { x }
}

extension S where T : P {
  var foo: Int { 0 }
}

func foo() {
  _ = \S<Int>.foo
  _ = \S<Int>.[x: 5]
}

main.swift:477:7: error: generic class 'KeyPath' requires that 'Int' conform to 'P'
  _ = \S<Int>.foo
      ^
Swift.KeyPath:1:14: note: where 'T' = 'Int'
public class KeyPath<Root, Value> : PartialKeyPath<Root> {
             ^
main.swift:478:7: error: generic class 'KeyPath' requires that 'Int' conform to 'P'
  _ = \S<Int>.[x: 5]
      ^
Swift.KeyPath:1:14: note: where 'U' = 'Int'
public class KeyPath<Root, Value> : PartialKeyPath<Root> {
             ^