PR c++/88312 - pack expansion of decltype.

The standard doesn't really talk about an expression depending on the number
of elements of a pack, but that's definitely an important form of template
argument dependence.

	* pt.c (instantiation_dependent_r): A template non-type parameter
	pack is instantiation-dependent.

From-SVN: r267860

gcc/cp/ChangeLog

 2019-01-11  Jason Merrill  <jason@redhat.com>
 
+	PR c++/88312 - pack expansion of decltype.
+	* pt.c (instantiation_dependent_r): A template non-type parameter
+	pack is instantiation-dependent.
+
+2019-01-11  Jason Merrill  <jason@redhat.com>
+
 	PR c++/88613 - ICE with use of const var in lambda.
 	* expr.c (mark_use): Fix location wrapper handling.
 	* cp-gimplify.c (cp_fold_maybe_rvalue): Call mark_rvalue_use.

gcc/cp/pt.c

@@ -25736,6 +25736,8 @@ instantiation_dependent_r (tree *tp, int *walk_subtrees,
     case TEMPLATE_PARM_INDEX:
       if (dependent_type_p (TREE_TYPE (*tp)))
 	return *tp;
+      if (TEMPLATE_PARM_PARAMETER_PACK (*tp))
+	return *tp;
       /* We'll check value-dependence separately.  */
       return NULL_TREE;
 

gcc/testsuite/g++.dg/cpp0x/variadic-decltype1.C

+// PR c++/88555
+// { dg-do compile { target c++11 } }
+
+template <class ...> struct T {};
+
+template <int ...Indices>
+void test() {
+    using Test = T<decltype((Indices, char(0)))...>;
+}