a forward class declaration matching a typedef name of a class

refers to the underlying class.
This is radar 6859726. Steve, please read the radar for my rational.

llvm-svn: 71181

clang/lib/Sema/SemaDeclObjC.cpp

@@ -1075,6 +1075,13 @@ Sema::ActOnForwardClassDeclaration(SourceLocation AtClassLoc,
         Diag(AtClassLoc, diag::err_redefinition_different_kind) << IdentList[i];
         Diag(PrevDecl->getLocation(), diag::note_previous_definition);
       }
+      else if (TDD) {
+        // a forward class declaration matching a typedef name of a class
+        // refers to the underlying class.
+        if (ObjCInterfaceType * OI = 
+              dyn_cast<ObjCInterfaceType>(TDD->getUnderlyingType()))
+          PrevDecl = OI->getDecl();
+      }
     }
     ObjCInterfaceDecl *IDecl = dyn_cast_or_null<ObjCInterfaceDecl>(PrevDecl); 
     if (!IDecl) {  // Not already seen?  Make a forward decl.

clang/test/SemaObjC/forward-class-1.m

@@ -22,3 +22,26 @@
 
 @interface INTF2 : INTF1 // expected-error {{duplicate interface definition for class 'INTF2'}}
 @end
+
+// 2nd test of a forward class declaration matching a typedef name
+// referring to class object.
+// FIXME. This may become a negative test should we decide to make this an error.
+//
+@interface NSObject @end
+
+@protocol XCElementP @end
+
+typedef NSObject <XCElementP> XCElement;
+
+@interface XCElementMainImp  {
+  XCElement * _editingElement;
+}
+@end
+
+@class XCElement;
+
+@implementation XCElementMainImp
+- (XCElement *)editingElement  { return _editingElement;  }
+@end
+
+