[stdlib] Workaround type checker ambiguity in Comparable SwiftNewtypeWrapper

Author: rintaro

stdlib/public/core/NewtypeWrapper.swift.gyb

@@ -23,7 +23,7 @@ extension _SwiftNewtypeWrapper where Self.RawValue : Hashable {
 
 % for op in ['<', '>', '<=', '>=']:
 public func ${op} <T: _SwiftNewtypeWrapper>(lhs: T, rhs: T) -> Bool
-  where T.RawValue : Comparable {
+  where T : Comparable, T.RawValue : Comparable {
   return lhs.rawValue ${op} rhs.rawValue
 }
 % end

test/ClangImporter/newtype_conformance.swift

@@ -0,0 +1,28 @@
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck -I %S/Inputs/custom-modules %s
+// REQUIRES: objc_interop
+
+// This test can't use '-verify' mode, because the potential error wouldn't
+// belong to any file.
+// e.g.:
+//   <unknown>:0: error: type 'NSNotification.Name' does not conform to protocol 'Comparable'
+
+import Foundation
+
+func acceptEquatable<T: Equatable>(_: T) {}
+func acceptHashable<T: Hashable>(_: T) {}
+func acceptComparable<T: Comparable>(_: T) {}
+
+func testNewTypeWrapperComparable(x: NSNotification.Name, y: NSNotification.Name) {
+  acceptEquatable(x)
+  acceptHashable(x)
+  acceptComparable(x)
+
+  _ = x == y
+  _ = x != y
+  _ = x.hashValue
+  _ = x < y
+  _ = x > y
+  _ = x <= y
+  _ = x >= y
+  _ = x as NSString
+}