C++ PATCH for c++/48292 (variadics and member templates)

[Jason Merrill <jason@redhat.com>]

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Several parts of the variadic template code have had trouble dealing 
with partial instantiation; this is another one.

Tested x86_64-pc-linux-gnu, applying to trunk.

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commit 0bbe297555a3e6585f1668266d965745df352ba4
Author: Jason Merrill <jason@redhat.com>
Date:   Tue May 24 23:20:29 2011 -0400

    	PR c++/48292
    	* pt.c (tsubst_decl) [PARM_DECL]: Handle partial instantiation of
    	function parameter pack.
    	(tsubst_pack_expansion): Likewise.

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index bd9aeba..fc84314 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -8711,7 +8711,12 @@ tsubst_pack_expansion (tree t, tree args, tsubst_flags_t complain,
 		 have the wrong value for a recursive call.  Just make a
 		 dummy decl, since it's only used for its type.  */
 	      arg_pack = tsubst_decl (parm_pack, args, complain);
-	      arg_pack = make_fnparm_pack (arg_pack);
+	      if (arg_pack && FUNCTION_PARAMETER_PACK_P (arg_pack))
+		/* Partial instantiation of the parm_pack, we can't build
+		   up an argument pack yet.  */
+		arg_pack = NULL_TREE;
+	      else
+		arg_pack = make_fnparm_pack (arg_pack);
 	    }
 	}
       else
@@ -9801,14 +9806,14 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
             if (DECL_TEMPLATE_PARM_P (t))
               SET_DECL_TEMPLATE_PARM_P (r);
 
-	    /* An argument of a function parameter pack is not a parameter
-	       pack.  */
-	    FUNCTION_PARAMETER_PACK_P (r) = false;
-
             if (expanded_types)
               /* We're on the Ith parameter of the function parameter
                  pack.  */
               {
+		/* An argument of a function parameter pack is not a parameter
+		   pack.  */
+		FUNCTION_PARAMETER_PACK_P (r) = false;
+
                 /* Get the Ith type.  */
                 type = TREE_VEC_ELT (expanded_types, i);
 
diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic109.C b/gcc/testsuite/g++.dg/cpp0x/variadic109.C
new file mode 100644
index 0000000..0ec69af
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/variadic109.C
@@ -0,0 +1,17 @@
+// PR c++/48292
+// { dg-options -std=c++0x }
+
+template <typename... Args> int g(Args...);
+
+template <int N = 0>
+struct A
+{
+    template <typename... Args>
+    static auto f(Args... args) -> decltype(g(args...));
+};
+
+int main()
+{
+    A<>::f();
+    return 0;
+}