struct S {
  subscript(x: Int) -> Int { x }
}

func foo(_ fn: @escaping () -> Int) {
  var i: Int?
  _ = \S.[i] // error: '(@lvalue Int?) -> Int' is not convertible to '(Int) -> Int'

  _ = \S.[nil] // error: Type of expression is ambiguous without more context
  _ = \S.[fn] // error: '(@escaping () -> Int) -> Int' is not convertible to '(Int) -> Int'
}

@propertyWrapper
struct Wrapper<T> {
  var wrappedValue: T
}

struct R {
  @Wrapper
  var i: Int

  subscript(takesWrapper x: Wrapper<Int>) -> Int { x.wrappedValue }
  func bar() {
    _ = \Self.[takesWrapper: i] // error: Type of expression is ambiguous without more context
  }
}