protocol P {
    static var theThing: Self { get }
}
extension Never : P {
    static var theThing: Never { return fatalError() }
}
func test<T: P>(_ type: T.Type) -> T {
    return type.theThing
}
func f(i: Int?) {
    guard i != nil else { Never.theThing } // ok
    guard i != nil else { test(Never.self) } // nope!
}