Open Radar

 
Summary:
In Xcode 8.2, an enum inheriting from OSStatus can also be conformed to RawRepresentable in an extension. In Xcode 8.3 beta 2, this throws a compiler error.

Steps to Reproduce:
1. Paste this code into a macOS or iOS playground:

enum Status: OSStatus {
    case myStatus
}

extension Status: RawRepresentable {

    var description: String {
        switch self {
        case .myStatus: return "foo"
        }
    }

}

Status.myStatus.description

// END CODE SAMPLE

Expected Results:
The code builds and runs, outputting “foo”.

Actual Results:
The code fails to compile with the error:
Playground execution failed: error: 8.playground:1:14: error: use of undeclared type 'OSStatus'
enum Status: OSStatus {
             ^~~~~~~~

error: 8.playground:1:6: error: type 'Status' does not conform to protocol 'RawRepresentable'
enum Status: OSStatus {
     ^

Swift.RawRepresentable:96:20: note: protocol requires nested type 'RawValue'; do you want to add it?
    associatedtype RawValue
                   ^

error: 8.playground:5:19: error: redundant conformance of 'Status' to protocol 'RawRepresentable'
extension Status: RawRepresentable {
                  ^

8.playground:1:6: note: 'Status' declares conformance to protocol 'RawRepresentable' here
enum Status: OSStatus {
     ^
// END COMPILATION ERROR SAMPLE

Regression:
The code compiles and runs correctly in Xcode 8.2.1

Notes:
I encountered this when trying to build a project in Xcode 8.3 beta 2. The project has a dependency on the KeychainAccess library, which has an enum that inherits from OSStatus and then conforms to RawRepresentable in an extension. I filed a bug on that library to track this bug there as well: https://github.com/kishikawakatsumi/KeychainAccess/issues/306