[C++] PR 57397

Index: cp/pt.c
===================================================================
--- cp/pt.c	(revision 213287)
+++ cp/pt.c	(working copy)
@@ -5517,13 +5517,21 @@  unify_method_type_error (bool explain_p, tree arg)
 }
 
 static int
-unify_arity (bool explain_p, int have, int wanted)
+unify_arity (bool explain_p, int have, int wanted, bool least_p = false)
 {
   if (explain_p)
-    inform_n (input_location, wanted,
-	      "  candidate expects %d argument, %d provided",
-	      "  candidate expects %d arguments, %d provided",
-	      wanted, have);
+    {
+      if (least_p)
+	inform_n (input_location, wanted,
+		  "  candidate expects at least %d argument, %d provided",
+		  "  candidate expects at least %d arguments, %d provided",
+		  wanted, have);
+      else
+	inform_n (input_location, wanted,
+		  "  candidate expects %d argument, %d provided",
+		  "  candidate expects %d arguments, %d provided",
+		  wanted, have);
+    }
   return 1;
 }
 
@@ -5534,9 +5542,10 @@  unify_too_many_arguments (bool explain_p, int have
 }
 
 static int
-unify_too_few_arguments (bool explain_p, int have, int wanted)
+unify_too_few_arguments (bool explain_p, int have, int wanted,
+			 bool least_p = false)
 {
-  return unify_arity (explain_p, have, wanted);
+  return unify_arity (explain_p, have, wanted, least_p);
 }
 
 static int
@@ -16546,6 +16555,7 @@  type_unification_real (tree tparms,
   const tree *args;
   unsigned int nargs;
   unsigned int ia;
+  bool non_deduced_pack;
 
   gcc_assert (TREE_CODE (tparms) == TREE_VEC);
   gcc_assert (xparms == NULL_TREE || TREE_CODE (xparms) == TREE_LIST);
@@ -16559,6 +16569,7 @@  type_unification_real (tree tparms,
   parms = xparms;
   args = xargs;
   nargs = xnargs;
+  non_deduced_pack = false;
 
   ia = 0;
   while (parms && parms != void_list_node
@@ -16577,10 +16588,13 @@  type_unification_real (tree tparms,
       parms = TREE_CHAIN (parms);
 
       if (TREE_CODE (parm) == TYPE_PACK_EXPANSION)
-	/* For a function parameter pack that does not occur at the
-	   end of the parameter-declaration-list, the type of the
-	   parameter pack is a non-deduced context.  */
-	continue;
+	{
+	  /* For a function parameter pack that does not occur at the
+	     end of the parameter-declaration-list, the type of the
+	     parameter pack is a non-deduced context.  */
+	  non_deduced_pack = true;
+	  continue;
+	}
 
       arg = args[ia];
       ++ia;
@@ -16594,6 +16608,18 @@  type_unification_real (tree tparms,
       && parms != void_list_node
       && TREE_CODE (TREE_VALUE (parms)) == TYPE_PACK_EXPANSION)
     {
+      /* Eg (c++/57397):
+
+      template<class T1, class... Tn, class... Tm>
+      void foo(T1, Tn..., Tm...);
+
+      int main()
+      {
+        foo(1, 2);
+      }  */
+      if (ia < nargs && non_deduced_pack)
+	return unify_too_many_arguments (explain_p, nargs, ia);
+
       /* Unify the remaining arguments with the pack expansion type.  */
       tree argvec;
       tree parmvec = make_tree_vec (1);
@@ -16617,18 +16643,33 @@  type_unification_real (tree tparms,
      are present, and the parm list isn't variadic.  */
   if (ia < nargs && parms == void_list_node)
     return unify_too_many_arguments (explain_p, nargs, ia);
-  /* Fail if parms are left and they don't have default values.  */
+  /* Fail if parms are left and they don't have default values and
+     they aren't all deduced as empty packs, eg (c++/57397):
+
+     template<class T1, class... Tn, class... Tm>
+     void foo(T1, Tn..., Tm...);
+
+     int main()
+     {
+       foo(1);
+     }  */
   if (parms && parms != void_list_node
       && TREE_PURPOSE (parms) == NULL_TREE)
     {
       unsigned int count = nargs;
+      bool trailing_packs = false;
       tree p = parms;
       while (p && p != void_list_node)
 	{
-	  count++;
+	  if (TREE_CODE (TREE_VALUE (p)) == TYPE_PACK_EXPANSION)
+	    trailing_packs = true;
+	  else
+	    count++;
 	  p = TREE_CHAIN (p);
 	}
-      return unify_too_few_arguments (explain_p, ia, count);
+      if (count != nargs)
+	return unify_too_few_arguments (explain_p, ia, count,
+					trailing_packs);
     }
 
   if (!subr)
Index: testsuite/g++.dg/cpp0x/vt-57397-1.C
===================================================================
--- testsuite/g++.dg/cpp0x/vt-57397-1.C	(revision 0)
+++ testsuite/g++.dg/cpp0x/vt-57397-1.C	(working copy)
@@ -0,0 +1,22 @@ 
+// PR c++/57397
+// { dg-do compile { target c++11 } }
+
+template<class T1, class... Tn>
+void foo(T1, Tn...);
+
+template<class T1, class T2, class... Tn>
+void bar(T1, T2, Tn...);
+
+int main()
+{
+  foo();   // { dg-error "no matching" }
+  // { dg-message "candidate expects at least 1 argument, 0 provided" "" { target *-*-* } 12 }
+  foo(1);
+  foo(1, 2);
+  bar();   // { dg-error "no matching" }
+  // { dg-message "candidate expects at least 2 arguments, 0 provided" "" { target *-*-* } 16 }
+  bar(1);  // { dg-error "no matching" }
+  // { dg-message "candidate expects at least 2 arguments, 1 provided" "" { target *-*-* } 18 }
+  bar(1, 2);
+  bar(1, 2, 3);
+}
Index: testsuite/g++.dg/cpp0x/vt-57397-2.C
===================================================================
--- testsuite/g++.dg/cpp0x/vt-57397-2.C	(revision 0)
+++ testsuite/g++.dg/cpp0x/vt-57397-2.C	(working copy)
@@ -0,0 +1,22 @@ 
+// PR c++/57397
+// { dg-do compile { target c++11 } }
+
+template<class T1, class... Tn, class... Tm>
+void foo(T1, Tn..., Tm...);
+
+template<class T1, class T2, class... Tn, class... Tm>
+void bar(T1, T2, Tn..., Tm...);
+
+int main()
+{
+  foo(1);
+  foo(1, 2);        // { dg-error "no matching" }
+  // { dg-message "candidate expects 1 argument, 2 provided" "" { target *-*-* } 13 }
+  foo(1, 2, 3);     // { dg-error "no matching" }
+  // { dg-message "candidate expects 1 argument, 3 provided" "" { target *-*-* } 15 }
+  bar(1, 2);
+  bar(1, 2, 3);     // { dg-error "no matching" }
+  // { dg-message "candidate expects 2 arguments, 3 provided" "" { target *-*-* } 18 }
+  bar(1, 2, 3, 4);  // { dg-error "no matching" }
+  // { dg-message "candidate expects 2 arguments, 4 provided" "" { target *-*-* } 20 }
+}