[Bug c++/20420] Incorrectly Accepts double declarations

["paolo.carlini at oracle dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20420

--- Comment #8 from Paolo Carlini <paolo.carlini at oracle dot com> 2012-08-22 00:01:27 UTC ---
For Comment #4: the validate_nonmember_using_decl call at the beginning of
do_local_using_decl returns NULL_TREE for the second using declaration, but we 
ignore that and return without error. That doesn't seem right for VAR_DECLs.

This combo patchlet passes testing:

Index: name-lookup.c
===================================================================
--- name-lookup.c    (revision 190569)
+++ name-lookup.c    (working copy)
@@ -441,7 +441,8 @@ supplement_binding_1 (cxx_binding *binding, tree d
          template in order to handle late matching of underlying
          type on an opaque-enum-declaration followed by an
          enum-specifier.  */
-      || (TREE_CODE (TREE_TYPE (target_decl)) == ENUMERAL_TYPE
+      || (processing_template_decl
+          && TREE_CODE (TREE_TYPE (target_decl)) == ENUMERAL_TYPE
           && TREE_CODE (TREE_TYPE (target_bval)) == ENUMERAL_TYPE
           && (dependent_type_p (ENUM_UNDERLYING_TYPE
                     (TREE_TYPE (target_decl)))
@@ -2581,7 +2582,11 @@ do_local_using_decl (tree decl, tree scope, tree n

   decl = validate_nonmember_using_decl (decl, scope, name);
   if (decl == NULL_TREE)
-    return;
+    {
+      if (TREE_CODE (orig_decl) == VAR_DECL)
+    error ("%qD is already declared in this scope", name);
+      return;
+    }

   if (building_stmt_list_p ()
       && at_function_scope_p ())