duplicates:

• SR-2176 Add warning for ambiguous enum value assignment

Issue Description:

In the following code snippet, foo is actually nil because the compiler decides to pick Optional.none instead of MyTest.none. I spent a long time tracking this down!

enum MyTest: UInt8 {
   case none, one, two, three
}
let foo: MyTest? = .none

Another case where this occurs is in code like this:

if foo == .none { \* stuff *\ }

There are no warnings when this happens. I think there should probably at least be a fixit warning that says something about there being an ambiguity here and offering the user fix it with either `Optional.none` or `MyTest.none`.