[PrintAsObjC] Downgrade +new unavailability to deprecation in Swift 4

The general policy has been that even if something crashes at run
time, we don't make it a hard error in Swift 4 mode (or Swift 3 mode!)
if it wasn't a hard error in Swift 4.0 (3.0). In this case, we thought
we could get away with it, and then it turns out it actually caused
some problems. (And as 2bc0106 shows, we can still make mistakes.)

This change isn't perfect because the diagnostic appears in /clients/
rather than in the module that's being compiled as Swift 4 (instead of
Swift 5). But it still means that someone who hasn't changed
/anything/ from a valid Swift 4.0 project will be able to compile
without any changes, even if they were relying on being able to call
+new when -init was unavailable for some reason.

More rdar://problem/35942058

Author: jrose-apple

lib/PrintAsObjC/PrintAsObjC.cpp

@@ -679,8 +679,14 @@ class ObjCPrinter : private DeclVisitor<ObjCPrinter>,
 
     if (makeNewUnavailable) {
       assert(!makeNewExplicitlyAvailable);
-      os << "+ (nonnull instancetype)new SWIFT_UNAVAILABLE_MSG("
-              "\"-init is unavailable\");\n";
+      // Downgrade this to a warning in pre-Swift-5 mode. This isn't perfect
+      // because it's a diagnostic inflicted on /clients/, but it's close
+      // enough. It really is invalid to call +new when -init is unavailable.
+      StringRef annotationName = "SWIFT_UNAVAILABLE_MSG";
+      if (!M.getASTContext().isSwiftVersionAtLeast(5))
+        annotationName = "SWIFT_DEPRECATED_MSG";
+      os << "+ (nonnull instancetype)new " << annotationName
+         << "(\"-init is unavailable\");\n";
     } else if (makeNewExplicitlyAvailable) {
       os << "+ (nonnull instancetype)new;\n";
     }

validation-test/PrintAsObjC/Inputs/reintroduced-new.swift renamed to test/PrintAsObjC/Inputs/reintroduced-new.swift

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

test/PrintAsObjC/availability.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_MSG("-init is unavailable");
+// CHECK-NEXT: + (nonnull instancetype)new SWIFT_DEPRECATED_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_MSG("-init is unavailable");
+// CHECK-NEXT: + (nonnull instancetype)new SWIFT_DEPRECATED_MSG("-init is unavailable");
 // CHECK-NEXT: @end
 @objc class NewBanned : NSObject {
   init(arbitraryArgument: Int) { super.init() }

test/PrintAsObjC/classes.swift

@@ -55,7 +55,7 @@ protocol CustomNameType2 {}
 // CHECK-LABEL: @interface MyObject : NSObject <NSCoding, Fungible>
 // CHECK-NEXT: initWithCoder
 // CHECK-NEXT: init SWIFT_UNAVAILABLE
-// CHECK-NEXT: new SWIFT_UNAVAILABLE
+// CHECK-NEXT: new SWIFT_DEPRECATED
 // CHECK-NEXT: @end
 // NEGATIVE-NOT: @protocol NSCoding
 class MyObject : NSObject, NSCoding, Fungible {

test/PrintAsObjC/protocols.swift

@@ -6,9 +6,13 @@
 // RUN:  %target-swift-frontend(mock-sdk: -sdk %S/../../test/Inputs/clang-importer-sdk -I %t) -emit-module -o %t %S/../../test/Inputs/clang-importer-sdk/swift-modules/ObjectiveC.swift
 // FIXME: END -enable-source-import hackaround
 
-// RUN: %target-swift-frontend(mock-sdk: -sdk %S/../../test/Inputs/clang-importer-sdk -I %t) -emit-module -o %t %S/Inputs/reintroduced-new.swift -disable-objc-attr-requires-foundation-module -module-name main
-// RUN: %target-swift-frontend(mock-sdk: -sdk %S/../../test/Inputs/clang-importer-sdk -I %t) -parse-as-library %t/main.swiftmodule -typecheck -emit-objc-header-path %t/generated.h -disable-objc-attr-requires-foundation-module
-// RUN: not %clang -fsyntax-only -x objective-c %s -include %t/generated.h -fobjc-arc -fmodules -Werror -isysroot %S/../../test/Inputs/clang-importer-sdk 2>&1 | %FileCheck %s
+// RUN: %target-swift-frontend(mock-sdk: -sdk %S/../../test/Inputs/clang-importer-sdk -I %t) -emit-module -o %t %S/Inputs/reintroduced-new.swift -swift-version 4 -disable-objc-attr-requires-foundation-module -module-name main
+// RUN: %target-swift-frontend(mock-sdk: -sdk %S/../../test/Inputs/clang-importer-sdk -I %t) -parse-as-library %t/main.swiftmodule -typecheck -emit-objc-header-path %t/generated.h -disable-objc-attr-requires-foundation-module -swift-version 4
+// RUN: not %clang -fsyntax-only -x objective-c %s -include %t/generated.h -fobjc-arc -fmodules -Werror -isysroot %S/../../test/Inputs/clang-importer-sdk 2>&1 | %FileCheck -check-prefix=CHECK -check-prefix=CHECK-4 %s
+
+// RUN: %target-swift-frontend(mock-sdk: -sdk %S/../../test/Inputs/clang-importer-sdk -I %t) -emit-module -o %t %S/Inputs/reintroduced-new.swift -disable-objc-attr-requires-foundation-module -module-name main -swift-version 5
+// RUN: %target-swift-frontend(mock-sdk: -sdk %S/../../test/Inputs/clang-importer-sdk -I %t) -parse-as-library %t/main.swiftmodule -typecheck -emit-objc-header-path %t/generated.h -disable-objc-attr-requires-foundation-module -swift-version 5
+// RUN: not %clang -fsyntax-only -x objective-c %s -include %t/generated.h -fobjc-arc -fmodules -Werror -isysroot %S/../../test/Inputs/clang-importer-sdk 2>&1 | %FileCheck  -check-prefix=CHECK -check-prefix=CHECK-5 %s
 
 // CHECK-NOT: error:
 
@@ -17,7 +21,8 @@ void test() {
   (void)[[Base alloc] init];
    // CHECK-NOT: error:
   (void)[[Sub alloc] init];
-  // CHECK: :[[@LINE+1]]:{{[0-9]+}}: error: 'new' is unavailable: -init is unavailable
+  // CHECK-4: :[[@LINE+2]]:{{[0-9]+}}: error: 'new' is deprecated: -init is unavailable
+  // CHECK-5: :[[@LINE+1]]:{{[0-9]+}}: error: 'new' is unavailable: -init is unavailable
   (void)[Base new];
    // CHECK-NOT: error:
   (void)[Sub new];