Allow @unsafe on enum case declarations

Author: DougGregor

include/swift/AST/DeclAttr.def

@@ -505,7 +505,7 @@ SIMPLE_DECL_ATTR(sensitive, Sensitive,
 
 SIMPLE_DECL_ATTR(unsafe, Unsafe,
   OnAbstractFunction | OnSubscript | OnVar | OnMacro | OnNominalType |
-  OnExtension | OnTypeAlias | UserInaccessible |
+  OnExtension | OnTypeAlias | OnEnumElement | UserInaccessible |
   ABIStableToAdd | ABIStableToRemove | APIBreakingToAdd | APIStableToRemove,
   160)
 

test/Unsafe/unsafe.swift

@@ -61,7 +61,7 @@ struct SuperHolder {
 // -----------------------------------------------------------------------
 // Inheritance of @unsafe
 // -----------------------------------------------------------------------
-@unsafe class UnsafeSuper { // expected-note 3{{'UnsafeSuper' declared here}}
+@unsafe class UnsafeSuper { // expected-note 5{{'UnsafeSuper' declared here}}
   func f() { } // expected-note{{unsafe instance method 'f' declared here}}
 };
 
@@ -88,3 +88,16 @@ func testMe(
 
   _ = getPointers() // expected-warning{{call to global function 'getPointers' involves unsafe type 'PointerType'}}
 }
+
+// -----------------------------------------------------------------------
+// Various declaration kinds
+// -----------------------------------------------------------------------
+typealias SuperUnsafe = UnsafeSuper // expected-warning{{reference to unsafe class 'UnsafeSuper' [Unsafe]}}
+@unsafe typealias SuperUnsafe2 = UnsafeSuper
+
+enum HasUnsafeThings {
+// expected-note@+1{{make enum case 'one' @unsafe to indicate that its use is not memory-safe}}
+case one(UnsafeSuper) // expected-warning{{reference to unsafe class 'UnsafeSuper' [Unsafe]}}
+
+@unsafe case two(UnsafeSuper)
+}