duplicates:

• SR-2176 Add warning for ambiguous enum value assignment

relates to:

• SR-2176 Add warning for ambiguous enum value assignment

Issue Description:

https://twitter.com/pilky/status/823942988665589760

If you have a static Self-typed member some or none in your own type, attempting to use the contextual lookup in Optional context will favor Optional's members:

enum PiggyState {
  case market, home, roastBeef, none
}

func setState(to state: PiggyState?) {}

setState(to: .none) // passes `Optional.none`, not `.some(.none)`

Instead of quietly treating this as Optional.none, we should raise an error (or warning for source compatibility) that the lookup is ambiguous.