PR c++/81843 - ICE with variadic member template.

	PR c++/72801
	* pt.c (unify_pack_expansion): Don't try to deduce enclosing
	template args.

From-SVN: r256802

gcc/cp/ChangeLog

+2018-01-17  Jason Merrill  <jason@redhat.com>
+
+	PR c++/81843 - ICE with variadic member template.
+	PR c++/72801
+	* pt.c (unify_pack_expansion): Don't try to deduce enclosing
+	template args.
+
 2018-01-17  David Malcolm  <dmalcolm@redhat.com>
 
 	PR c++/83799

gcc/cp/pt.c

@@ -20370,6 +20370,7 @@ unify_pack_expansion (tree tparms, tree targs, tree packed_parms,
 
   /* Add in any args remembered from an earlier partial instantiation.  */
   targs = add_to_template_args (PACK_EXPANSION_EXTRA_ARGS (parm), targs);
+  int levels = TMPL_ARGS_DEPTH (targs);
 
   packed_args = expand_template_argument_pack (packed_args);
 
@@ -20385,6 +20386,8 @@ unify_pack_expansion (tree tparms, tree targs, tree packed_parms,
 
       /* Determine the index and level of this parameter pack.  */
       template_parm_level_and_index (parm_pack, &level, &idx);
+      if (level < levels)
+	continue;
 
       /* Keep track of the parameter packs and their corresponding
          argument packs.  */

gcc/testsuite/g++.dg/cpp0x/variadic171.C

+// PR c++/81843
+// { dg-do compile { target c++11 } }
+
+template < typename > struct A;
+template < typename, typename > struct B;
+template < typename ... S > struct C
+{
+  template < typename > struct D {};
+  template < typename ... T > struct D < A < B < S, T > ... > >;
+};
+
+C <>::D < A < B < int, int > > > c;