PR c++/51145 - Alias template in elaborated-type-specifier

diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
index b77963b..7170072 100644
--- a/gcc/cp/decl.c
+++ b/gcc/cp/decl.c
@@ -11342,6 +11342,9 @@  check_elaborated_type_specifier (enum tag_types tag_code,
 {
   tree type;
 
+  if (decl == error_mark_node)
+    return error_mark_node;
+
   /* In the case of:
 
        struct S { struct S *p; };
@@ -11361,10 +11364,15 @@  check_elaborated_type_specifier (enum tag_types tag_code,
 	     type, tag_name (tag_code));
       return error_mark_node;
     }
+  /* Accept bound template template parameters.  */
+  else if (allow_template_p
+	   && TREE_CODE (type) == BOUND_TEMPLATE_TEMPLATE_PARM)
+    ;
   /*   [dcl.type.elab]
 
-       If the identifier resolves to a typedef-name or a template
-       type-parameter, the elaborated-type-specifier is ill-formed.
+       If the identifier resolves to a typedef-name or the
+       simple-template-id resolves to an alias template
+       specialization, the elaborated-type-specifier is ill-formed.
 
      In other words, the only legitimate declaration to use in the
      elaborated type specifier is the implicit typedef created when
@@ -11373,8 +11381,14 @@  check_elaborated_type_specifier (enum tag_types tag_code,
 	   && !DECL_SELF_REFERENCE_P (decl)
 	   && tag_code != typename_type)
     {
-      error ("using typedef-name %qD after %qs", decl, tag_name (tag_code));
-      error ("%q+D has a previous declaration here", decl);
+      if (alias_template_specialization_p (type))
+	error ("using alias template specialization %qT after %qs",
+	       type, tag_name (tag_code));
+      else
+	{
+	  error ("using typedef-name %qD after %qs", decl, tag_name (tag_code));
+	  error ("%q+D has a previous declaration here", decl);
+	}
       return error_mark_node;
     }
   else if (TREE_CODE (type) != RECORD_TYPE
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index f839112..08b9c13 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -13933,7 +13933,8 @@  cp_parser_elaborated_type_specifier (cp_parser* parser,
       else if (tag_type == typename_type && TREE_CODE (decl) != TYPE_DECL)
         type = NULL_TREE; 
       else 
-	type = TREE_TYPE (decl);
+	type = check_elaborated_type_specifier (tag_type, decl,
+						/*allow_template_p=*/true);
     }
 
   if (!type)
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-10.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-10.C
index 856e429..6adb785 100644
--- a/gcc/testsuite/g++.dg/cpp0x/alias-decl-10.C
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-10.C
@@ -3,16 +3,24 @@ 
 template <class T> using Ptr = T*;
 Ptr<unsigned>; // { dg-error "does not declare anything" }
 Ptr<char><int>; // { dg-error "not a template|does not declare anything" }
-template class Ptr<int>;//{ dg-error "explicit instantiation|non-class templ|does not decl|anything" }
+template class Ptr<int>;//{ dg-error "alias templ|specialization|Ptr<int>|after|class" }
 
 template <class T> using Arg = T;
 struct A {};
-template class Arg<A>;// { dg-error "explicit instantiation|non-class templ" }
+template class Arg<A>;// { dg-error "alias templ|specialization|Arg<A>|after|class" }
 
 template <template <class> class TT, class T> using Instantiate = TT<T>;
 template <class> struct Vector {};
-template class Instantiate<Vector, int>; // OK Vector<int> can be explicitely instantiated
+
+// The below is not OK, because of [dcl.type.elab]:
+// 
+//     If the identifier resolves to a typedef-name or the
+//     simple-template-id resolves to an alias template
+//     specialization, the elaborated-type-specifier is ill-formed.
+//
+template class Instantiate<Vector, int>;//{ dg-error "alias templ|after|class" }
 
 template <class T> struct S {};
 template<class T> using SFor = S<T>;
-template class SFor<int>; // OK, S<int> can be explicitely instantiated
+// Likewise, this is not OK.
+template class SFor<int>; //{ dg-error "alias tmpl|after|class" }
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-14.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-14.C
new file mode 100644
index 0000000..485802e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-14.C
@@ -0,0 +1,14 @@ 
+// Origin: PR c++/51145
+// { dg-options "-std=c++0x" }
+
+struct A {};
+
+template<class>
+using X = A;
+
+struct X<int>* px; // { dg-error "invalid|alias|specialization|X<int>|after struct" }
+
+template<int>
+using Y = A;
+
+struct Y<0>* py;// { dg-error "invalid|alias|specialization|Y<0>|after struct" }
diff --git a/gcc/testsuite/g++.dg/cpp0x/alias-decl-2.C b/gcc/testsuite/g++.dg/cpp0x/alias-decl-2.C
index 2e03dd8..1d5a996 100644
--- a/gcc/testsuite/g++.dg/cpp0x/alias-decl-2.C
+++ b/gcc/testsuite/g++.dg/cpp0x/alias-decl-2.C
@@ -6,7 +6,7 @@  template<class T> using AS0 = S0<T>;
 template<template<class> class TT>
 void f(TT<int>);
 
-template class AS0<char>;
+template class AS0<char>; // { dg-error "alias templ|specialization|after|class" }
 
 void
 foo()