duplicates:

• SR-1420 Provide compiler warning when shadowing generic type

Issue Description:

> swiftc --version
Apple Swift version 2.2 (swiftlang-703.0.18.8 clang-703.0.31)
Target: x86_64-apple-macosx10.9

> cat StrangeError.swift 
class Provider<T> {
   func strange<T>() -> Provider<T> {
       return self
   }
}

> swiftc StrangeError.swift 
StrangeError.swift:3:15: error: cannot convert return expression of type 'Provider<T>' to return type 'Provider<T>'
       return self
              ^~~~

The problem in this code is that method strange introduces a second generic type variable named T. The error message referes to two different type variables, but this is not apparent. It would be more robust if swiftc either warns if type variables are overwritten or to forbid (in a future revision of the language) to overwrite type variables.