PR c++/51427 - Better diagnostic when union/struct tags conflicts

gcc/cp/

	PR c++/51427
	* parser.c (cp_parser_check_class_key): Add note about earlier
	declaration.

gcc/testsuite/

	PR c++/51427
	* g++.dg/diagnostic/wrong-tag-1.C

From-SVN: r182043

gcc/cp/ChangeLog

+2011-12-06  Dodji Seketeli  <dodji@redhat.com>
+
+	PR c++/51427
+	* parser.c (cp_parser_check_class_key): Add note about earlier
+	declaration.
+
 2011-12-05  Fabien Chêne  <fabien@gcc.gnu.org>
 
 	PR c++/51319

gcc/cp/parser.c

@@ -22544,10 +22544,14 @@ static void
 cp_parser_check_class_key (enum tag_types class_key, tree type)
 {
   if ((TREE_CODE (type) == UNION_TYPE) != (class_key == union_type))
-    permerror (input_location, "%qs tag used in naming %q#T",
-	    class_key == union_type ? "union"
-	     : class_key == record_type ? "struct" : "class",
-	     type);
+    {
+      permerror (input_location, "%qs tag used in naming %q#T",
+		 class_key == union_type ? "union"
+		 : class_key == record_type ? "struct" : "class",
+		 type);
+      inform (DECL_SOURCE_LOCATION (TYPE_NAME (type)),
+	      "%q#T was previously declared here", type);
+    }
 }
 
 /* Issue an error message if DECL is redeclared with different

gcc/testsuite/ChangeLog

+2011-12-06  Dodji Seketeli  <dodji@redhat.com>
+
+	PR c++/51427
+	* g++.dg/diagnostic/wrong-tag-1.C
+
 2011-12-05  Fabien Chêne  <fabien@gcc.gnu.org>
 
 	PR c++/51319

gcc/testsuite/g++.dg/diagnostic/wrong-tag-1.C

+// Origin PR c++/51427
+
+typedef struct _GMutex GMutex; // { dg-message "previously declared here"}
+typedef union _GMutex GMutex; // { dg-error "tag used in naming" }