PrintAsObjC: Add support for classes with resilient ancestry

Without -enable-resilient-objc-class-stubs, don't print classes with
resilient ancestry at all, since they're not actually visible to
Clang and referencing one will not actually work.

When the flag is specified, such classes do appear in the generated
header with the new objc_class_stub Clang attribute.

Author: slavapestov

lib/PrintAsObjC/PrintAsObjC.cpp

@@ -322,14 +322,22 @@ class ObjCPrinter : private DeclVisitor<ObjCPrinter>,
   void visitClassDecl(ClassDecl *CD) {
     printDocumentationComment(CD);
 
+    bool hasResilientAncestry =
+      CD->checkAncestry().contains(AncestryFlags::ResilientOther);
+    if (hasResilientAncestry) {
+      os << "SWIFT_RESILIENT_CLASS";
+    } else {
+      os << "SWIFT_CLASS";
+    }
+
     StringRef customName = getNameForObjC(CD, CustomNamesOnly);
     if (customName.empty()) {
       llvm::SmallString<32> scratch;
-      os << "SWIFT_CLASS(\"" << CD->getObjCRuntimeName(scratch) << "\")";
+      os << "(\"" << CD->getObjCRuntimeName(scratch) << "\")";
       printAvailability(CD);
       os << "\n@interface " << CD->getName();
     } else {
-      os << "SWIFT_CLASS_NAMED(\"" << CD->getName() << "\")";
+      os << "_NAMED(\"" << CD->getName() << "\")";
       printAvailability(CD);
       os << "\n@interface " << customName;
     }
@@ -2640,6 +2648,20 @@ class ModuleWriter {
              "SWIFT_CLASS_EXTRA\n"
            "# endif\n"
            "#endif\n"
+           "#if !defined(SWIFT_RESILIENT_CLASS)\n"
+           "# if __has_attribute(objc_class_stub)\n"
+           "#  define SWIFT_RESILIENT_CLASS(SWIFT_NAME) SWIFT_CLASS(SWIFT_NAME) "
+             "__attribute__((objc_class_stub))\n"
+           "#  define SWIFT_RESILIENT_CLASS_NAMED(SWIFT_NAME) "
+             "__attribute__((objc_class_stub)) "
+             "SWIFT_CLASS_NAMED(SWIFT_NAME)\n"
+           "# else\n"
+           "#  define SWIFT_RESILIENT_CLASS(SWIFT_NAME) "
+             "SWIFT_CLASS(SWIFT_NAME)\n"
+           "#  define SWIFT_RESILIENT_CLASS_NAMED(SWIFT_NAME) "
+             "SWIFT_CLASS_NAMED(SWIFT_NAME)\n"
+           "# endif\n"
+           "#endif\n"
            "\n"
            "#if !defined(SWIFT_PROTOCOL)\n"
            "# define SWIFT_PROTOCOL(SWIFT_NAME) SWIFT_RUNTIME_NAME(SWIFT_NAME) "

test/PrintAsObjC/Inputs/custom-modules/module.map

@@ -42,3 +42,8 @@ module VersionedFMWK {
   header "VersionedFMWK.h"
   export *
 }
+
+module resilient_objc_class {
+  header "resilient_objc_class.h"
+  export *
+}

test/PrintAsObjC/resilient-ancestry.swift

@@ -0,0 +1,52 @@
+// Please keep this file in alphabetical order!
+
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-module-path %t/resilient_struct.swiftmodule %S/../Inputs/resilient_struct.swift -enable-library-evolution
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -emit-module-path %t/resilient_objc_class.swiftmodule %S/../Inputs/resilient_objc_class.swift -I %t -enable-library-evolution -emit-objc-header-path %t/resilient_objc_class.h
+
+// RUN: cp %S/Inputs/custom-modules/module.map %t/module.map
+
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck %s -module-name resilient -emit-objc-header-path %t/resilient.h -I %t -enable-library-evolution
+// RUN: %FileCheck %s --check-prefix=NO-STUBS < %t/resilient.h
+// RUN: %check-in-clang %t/resilient.h -I %t
+
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -typecheck %s -module-name resilient -emit-objc-header-path %t/resilient.h -I %t -enable-library-evolution -enable-resilient-objc-class-stubs
+// RUN: %FileCheck %s < %t/resilient.h
+// RUN: %check-in-clang %t/resilient.h -I %t
+
+// REQUIRES: objc_interop
+
+import Foundation
+import resilient_objc_class
+
+// Note: @_fixed_layout on a class only applies to the storage layout and
+// not metadata, which remains resilient.
+
+// NO-STUBS-NOT: FixedLayoutNSObjectSubclass
+
+// CHECK-LABEL: SWIFT_RESILIENT_CLASS("_TtC9resilient27FixedLayoutNSObjectSubclass")
+// CHECK-NEXT: @interface FixedLayoutNSObjectSubclass : FixedLayoutNSObjectOutsideParent
+// CHECK-NEXT:   - (nonnull instancetype)init OBJC_DESIGNATED_INITIALIZER;
+// CHECK-NEXT: @end
+
+@_fixed_layout
+public class FixedLayoutNSObjectSubclass : FixedLayoutNSObjectOutsideParent {}
+
+// NO-STUBS-NOT: ResilientNSObjectSubclass
+
+// CHECK-LABEL: SWIFT_RESILIENT_CLASS("_TtC9resilient25ResilientNSObjectSubclass")
+// CHECK-NEXT: @interface ResilientNSObjectSubclass : ResilientNSObjectOutsideParent
+// CHECK-NEXT:   - (nonnull instancetype)init OBJC_DESIGNATED_INITIALIZER;
+// CHECK-NEXT: @end
+
+public class ResilientNSObjectSubclass : ResilientNSObjectOutsideParent {}
+
+// NO-STUBS-NOT: RenamedNSObjectSubclass
+
+// CHECK-LABEL: SWIFT_RESILIENT_CLASS_NAMED("UnrenamedNSObjectSubclass")
+// CHECK-NEXT: @interface RenamedNSObjectSubclass : ResilientNSObjectOutsideParent
+// CHECK-NEXT:   - (nonnull instancetype)init OBJC_DESIGNATED_INITIALIZER;
+// CHECK-NEXT: @end
+
+@objc(RenamedNSObjectSubclass)
+public class UnrenamedNSObjectSubclass : ResilientNSObjectOutsideParent {}