Patch to warn about __private_extern__ on tentative definitions

as it does something unexpected (but gcc compatible).
Suggest use of __attribute__((visibility("hidden")))
on declaration instead. // rdar://7703982

llvm-svn: 161972

clang/include/clang/Basic/DiagnosticGroups.td

@@ -155,6 +155,7 @@ def MethodAccess : DiagGroup<"objc-method-access">;
 def ObjCReceiver : DiagGroup<"receiver-expr">;
 def OverlengthStrings : DiagGroup<"overlength-strings">;
 def OverloadedVirtual : DiagGroup<"overloaded-virtual">;
+def PrivateExtern : DiagGroup<"private-extern">;
 def ObjCPropertyImpl : DiagGroup<"objc-property-implementation">;
 def ObjCPropertyNoAttribute : DiagGroup<"objc-property-no-attribute">;
 def ObjCMissingSuperCalls : DiagGroup<"objc-missing-super-calls">;
@@ -371,7 +372,8 @@ def Most : DiagGroup<"most", [
     Unused,
     VolatileRegisterVar,
     ObjCMissingSuperCalls,
-    OverloadedVirtual
+    OverloadedVirtual,
+    PrivateExtern
  ]>;
 
 // Thread Safety warnings 

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -1489,6 +1489,11 @@ def note_non_literal_user_provided_dtor : Note<
   "%0 is not literal because it has a user-provided destructor">;
 def note_non_literal_nontrivial_dtor : Note<
   "%0 is not literal because it has a non-trivial destructor">;
+def warn_private_extern : Warning<
+  "Use of __private_extern__ on tentative definition has unexpected"
+  " behaviour - use __attribute__((visibility(\"hidden\"))) on extern"
+  " declaration or definition instead">,
+  InGroup<PrivateExtern>, DefaultIgnore;
 
 // C++11 char16_t/char32_t
 def warn_cxx98_compat_unicode_type : Warning<

clang/lib/Sema/SemaDecl.cpp

@@ -6754,6 +6754,10 @@ void Sema::ActOnUninitializedDecl(Decl *RealDecl,
                                  diag::err_abstract_type_in_decl,
                                  AbstractVariableType))
         Var->setInvalidDecl();
+      if (!Type->isDependentType() && !Var->isInvalidDecl() &&
+          Var->getStorageClass() == SC_PrivateExtern)
+        Diag(Var->getLocation(), diag::warn_private_extern);
+        
       return;
 
     case VarDecl::TentativeDefinition:

clang/test/Sema/tentative-decls.c

@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 %s -fsyntax-only -verify
+// RUN: %clang_cc1 %s -fsyntax-only -Wprivate-extern -verify
 
 // PR3310
 struct a x1; // expected-note 2{{forward declaration of 'struct a'}}
@@ -32,7 +32,8 @@ int i2 = 3; // expected-error{{non-static declaration of 'i2' follows static dec
 static int i3 = 5;
 extern int i3;
 
-__private_extern__ int pExtern;
+// rdar://7703982
+__private_extern__ int pExtern; // expected-warning {{Use of __private_extern__ on tentative definition has unexpected behaviour}}
 int pExtern = 0;
 
 int i4;