Warn if forward class is used as a receiver.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@71278 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Basic/DiagnosticSemaKinds.td

@@ -1690,6 +1690,8 @@ def err_collection_expr_type : Error<
 
 // Type
 def ext_invalid_sign_spec : Extension<"'%0' cannot be signed or unsigned">;
+def warn_receiver_forward_class : Warning<
+    "receiver %0 is a forward class and corresponding @interface may not exist">;
 def warn_missing_declspec : Warning<
   "declaration specifier missing, defaulting to 'int'">;
 def warn_missing_type_specifier : Warning<

lib/Sema/SemaExprObjC.cpp

@@ -422,7 +422,15 @@ Sema::ExprResult Sema::ActOnClassMessage(
   assert(ClassDecl && "missing interface declaration");
   ObjCMethodDecl *Method = 0;
   QualType returnType;
-  Method = ClassDecl->lookupClassMethod(Context, Sel);
+  if (ClassDecl->isForwardDecl()) {
+    // A forward class used in messaging is tread as a 'Class'
+    Method = LookupFactoryMethodInGlobalPool(Sel, SourceRange(lbrac,rbrac));
+    if (Method)
+      Diag(lbrac, diag::warn_receiver_forward_class) 
+        << ClassDecl->getDeclName();
+  }
+  if (!Method)
+    Method = ClassDecl->lookupClassMethod(Context, Sel);
   
   // If we have an implementation in scope, check "private" methods.
   if (!Method)

test/SemaObjC/forward-class-receiver.m

@@ -0,0 +1,13 @@
+// RUN: clang-cc  -fsyntax-only -verify %s
+
+@interface I
++ new;
+@end
+Class isa;
+
+@class NotKnown;
+
+void foo(NotKnown *n) {
+  [isa new];
+  [NotKnown new];	   /* expected-warning {{receiver 'NotKnown' is a forward class and corresponding}} */
+}