4 files changed, 51 insertions, 1 deletions
diff --git a/lib/AST/NSAPI.cpp b/lib/AST/NSAPI.cpp
index 8f03711f4d..f5ea2c54ee 100644
--- a/lib/AST/NSAPI.cpp
+++ b/lib/AST/NSAPI.cpp
@@ -18,6 +18,7 @@ NSAPI::NSAPI(ASTContext &ctx)
 
 IdentifierInfo *NSAPI::getNSClassId(NSClassIdKindKind K) const {
   static const char *ClassName[NumClassIds] = {
+    "NSObject",
     "NSString",
     "NSArray",
     "NSMutableArray",
diff --git a/lib/Parse/ParseObjc.cpp b/lib/Parse/ParseObjc.cpp
index c664c64b67..11417fb66f 100644
--- a/lib/Parse/ParseObjc.cpp
+++ b/lib/Parse/ParseObjc.cpp
@@ -161,6 +161,7 @@ void Parser::CheckNestedObjCContexts(SourceLocation AtLoc)
 ///     __attribute__((deprecated))
 ///     __attribute__((unavailable))
 ///     __attribute__((objc_exception)) - used by NSException on 64-bit
+///     __attribute__((objc_root_class))
 ///
 Decl *Parser::ParseObjCAtInterfaceDeclaration(SourceLocation AtLoc,
                                               ParsedAttributes &attrs) {
diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index 081c93f8c2..77809e153f 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -1593,6 +1593,22 @@ static void handleArcWeakrefUnavailableAttr(Sema &S, Decl *D,
                                           Attr.getRange(), S.Context));
 }
 
+static void handleObjCRootClassAttr(Sema &S, Decl *D, 
+                                    const AttributeList &Attr) {
+  if (!isa<ObjCInterfaceDecl>(D)) {
+    S.Diag(Attr.getLoc(), diag::err_attribute_requires_objc_interface);
+    return;
+  }
+  
+  unsigned NumArgs = Attr.getNumArgs();
+  if (NumArgs > 0) {
+    S.Diag(Attr.getLoc(), diag::err_attribute_too_many_arguments) << 0;
+    return;
+  }
+  
+  D->addAttr(::new (S.Context) ObjCRootClassAttr(Attr.getRange(), S.Context));
+}
+
 static void handleObjCRequiresPropertyDefsAttr(Sema &S, Decl *D, 
                                             const AttributeList &Attr) {
   if (!isa<ObjCInterfaceDecl>(D)) {
@@ -3658,6 +3674,9 @@ static void ProcessInheritableDeclAttr(Sema &S, Scope *scope, Decl *D,
   case AttributeList::AT_objc_arc_weak_reference_unavailable: 
     handleArcWeakrefUnavailableAttr (S, D, Attr); 
     break;
+  case AttributeList::AT_objc_root_class:
+    handleObjCRootClassAttr(S, D, Attr);
+    break;
   case AttributeList::AT_objc_requires_property_definitions: 
     handleObjCRequiresPropertyDefsAttr (S, D, Attr); 
     break;
diff --git a/lib/Sema/SemaDeclObjC.cpp b/lib/Sema/SemaDeclObjC.cpp
index 6be9c7ceeb..a942d4979d 100644
--- a/lib/Sema/SemaDeclObjC.cpp
+++ b/lib/Sema/SemaDeclObjC.cpp
@@ -24,6 +24,7 @@
 #include "clang/AST/ASTMutationListener.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Sema/DeclSpec.h"
+#include "clang/Lex/Preprocessor.h"
 #include "llvm/ADT/DenseSet.h"
 
 using namespace clang;
@@ -2371,11 +2372,39 @@ Decl *Sema::ActOnAtEnd(Scope *S, SourceRange AtEnd,
       AtomicPropertySetterGetterRules(IC, IDecl);
       DiagnoseOwningPropertyGetterSynthesis(IC);
   
-      if (LangOpts.ObjCNonFragileABI2)
+      bool HasRootClassAttr = IDecl->hasAttr<ObjCRootClassAttr>();
+      if (IDecl->getSuperClass() == NULL) {
+        // This class has no superclass, so check that it has been marked with
+        // __attribute((objc_root_class)).
+        if (!HasRootClassAttr) {
+          SourceLocation DeclLoc(IDecl->getLocation());
+          SourceLocation SuperClassLoc(PP.getLocForEndOfToken(DeclLoc));
+          Diag(DeclLoc, diag::warn_objc_root_class_missing)
+            << IDecl->getIdentifier();
+          // See if NSObject is in the current scope, and if it is, suggest
+          // adding " : NSObject " to the class declaration.
+          NamedDecl *IF = LookupSingleName(TUScope,
+                                           NSAPIObj->getNSClassId(NSAPI::ClassId_NSObject),
+                                           DeclLoc, LookupOrdinaryName);
+          ObjCInterfaceDecl *NSObjectDecl = dyn_cast_or_null<ObjCInterfaceDecl>(IF);
+          if (NSObjectDecl && NSObjectDecl->getDefinition()) {
+            Diag(SuperClassLoc, diag::note_objc_needs_superclass)
+              << FixItHint::CreateInsertion(SuperClassLoc, " : NSObject ");
+          } else {
+            Diag(SuperClassLoc, diag::note_objc_needs_superclass);
+          }
+        }
+      } else if (HasRootClassAttr) {
+        // Complain that only root classes may have this attribute.
+        Diag(IDecl->getLocation(), diag::err_objc_root_class_subclass);
+      }
+
+      if (LangOpts.ObjCNonFragileABI2) {
         while (IDecl->getSuperClass()) {
           DiagnoseDuplicateIvars(IDecl, IDecl->getSuperClass());
           IDecl = IDecl->getSuperClass();
         }
+      }
     }
     SetIvarInitializers(IC);
   } else if (ObjCCategoryImplDecl* CatImplClass =