This is support for SE-0069: Mutability and Foundation Value Types.
In cases where someone has overridden a method that takes, e.g.
'NSURL', the override will no longer be valid, because the system
class will now use the value type 'URL' instead. If an override's
full name matches exactly, the compiler will offer fix-its for any
uses of reference types where value types are now preferred.
(This must be a direct match; subclasses, including the mutable
variants of many Foundation types, will need to be updated by hand.)
One wrinkle here is the use of generics. In Swift 2, Objective-C
generics weren't imported at all, so it's unlikely that the overriding
method will have the correct generic arguments. Simple migration
might insert the "bound" type, but it can't know what specific type
might be more appropriate. Therefore, the logic to add the fix-it
ignores generic arguments, assuming the parent's type is correct.
rdar://problem/26183575
This lets us eliminate the _getObjectiveCType() value witness, which
was working around the lack of proper type witness metadata in witness
tables. Boilerplate -= 1.
Eliminate the String/Array/Dictionary/Set special cases, using
_ObjectiveCBridgeable conformances instead.
Note: Clang update required for the test to success.
