Fix parsing :: in method parameter type.

Author: qiongsiwu

clang/lib/Parse/Parser.cpp

@@ -2222,8 +2222,14 @@ bool Parser::TryAnnotateTypeOrScopeTokenAfterScopeSpec(
     }
   }
 
-  if (SS.isEmpty())
+  if (SS.isEmpty()) {
+    if (getLangOpts().ObjC && Tok.is(tok::coloncolon)) {
+      // ObjectiveC does not allow :: as as a scope token.
+      Diag(ConsumeToken(), diag::err_expected_type);
+      return true;
+    }
     return false;
+  }
 
   // A C++ scope specifier that isn't followed by a typename.
   AnnotateScopeToken(SS, IsNewScope);

clang/test/Parser/objc-coloncolon.m

@@ -0,0 +1,5 @@
+// RUN: %clang_cc1 -x objective-c -fsyntax-only -verify %s
+
+@interface A
+- (instancetype)init:(::A *) foo; // expected-error {{expected a type}} 
+@end