[PrintAsObjC] Include a message when making +new unavailable

Another follow-up to 49c65fa. We've seen a few people run into
this and not know what changed.

rdar://problem/35942058

Author: jrose-apple

lib/PrintAsObjC/PrintAsObjC.cpp

@@ -679,7 +679,8 @@ class ObjCPrinter : private DeclVisitor<ObjCPrinter>,
 
     if (makeNewUnavailable) {
       assert(!makeNewExplicitlyAvailable);
-      os << "+ (nonnull instancetype)new SWIFT_UNAVAILABLE;\n";
+      os << "+ (nonnull instancetype)new SWIFT_UNAVAILABLE_MSG("
+              "\"-init is unavailable\");\n";
     } else if (makeNewExplicitlyAvailable) {
       os << "+ (nonnull instancetype)new;\n";
     }

test/PrintAsObjC/availability.swift

@@ -57,7 +57,7 @@
 
 // CHECK-LABEL: @interface AvailabilitySub
 // CHECK-NEXT: - (nonnull instancetype)init SWIFT_UNAVAILABLE;
-// CHECK-NEXT: + (nonnull instancetype)new SWIFT_UNAVAILABLE;
+// CHECK-NEXT: + (nonnull instancetype)new SWIFT_UNAVAILABLE_MSG("-init is unavailable");
 // CHECK-NEXT: - (nonnull instancetype)initWithX:(NSInteger)_ SWIFT_UNAVAILABLE;
 // CHECK-NEXT: @end
 

test/PrintAsObjC/classes.swift

@@ -178,7 +178,7 @@ class DiscardableResult : NSObject {
 // CHECK-LABEL: @interface InheritedInitializersRequired
 // CHECK-NEXT: - (nonnull instancetype)initWithEvenMoreFun OBJC_DESIGNATED_INITIALIZER;
 // CHECK-NEXT: - (nonnull instancetype)init SWIFT_UNAVAILABLE;
-// CHECK-NEXT: + (nonnull instancetype)new SWIFT_UNAVAILABLE;
+// CHECK-NEXT: + (nonnull instancetype)new SWIFT_UNAVAILABLE_MSG("-init is unavailable");
 // CHECK-NEXT: @end
 @objc class InheritedInitializersRequired : InheritedInitializers {
   @objc required init(evenMoreFun: ()) { super.init() }
@@ -436,7 +436,7 @@ class MyObject : NSObject {}
 // CHECK-LABEL: @interface NewBanned
 // CHECK-NEXT: - (nonnull instancetype)initWithArbitraryArgument:(NSInteger)arbitraryArgument OBJC_DESIGNATED_INITIALIZER;
 // CHECK-NEXT: - (nonnull instancetype)init SWIFT_UNAVAILABLE;
-// CHECK-NEXT: + (nonnull instancetype)new SWIFT_UNAVAILABLE;
+// CHECK-NEXT: + (nonnull instancetype)new SWIFT_UNAVAILABLE_MSG("-init is unavailable");
 // CHECK-NEXT: @end
 @objc class NewBanned : NSObject {
   init(arbitraryArgument: Int) { super.init() }

validation-test/PrintAsObjC/reintroduced-new.m

@@ -17,7 +17,7 @@ void test() {
   (void)[[Base alloc] init];
    // CHECK-NOT: error:
   (void)[[Sub alloc] init];
-  // CHECK: :[[@LINE+1]]:{{[0-9]+}}: error: 'new' is unavailable
+  // CHECK: :[[@LINE+1]]:{{[0-9]+}}: error: 'new' is unavailable: -init is unavailable
   (void)[Base new];
    // CHECK-NOT: error:
   (void)[Sub new];