c++: Fix decltype of empty pack expansion of parm.

In unevaluated context, we only substitute a single PARM_DECL, not the
entire chain, but the handling of an empty pack expansion was missing that
check.

	PR c++/93140
	* pt.c (tsubst_decl) [PARM_DECL]: Check cp_unevaluated_operand in
	handling of TREE_CHAIN for empty pack.

1 files changed, 17 insertions, 0 deletions

diff --git a/gcc/testsuite/g++.dg/cpp0x/variadic-parm1.C b/gcc/testsuite/g++.dg/cpp0x/variadic-parm1.C
new file mode 100644
index 0000000..4300c78
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/variadic-parm1.C
@@ -0,0 +1,17 @@
+// PR c++/93140
+// { dg-do compile { target c++11 } }
+
+int
+bar ()
+{
+  return 42;
+}
+
+template <typename... R>
+void foo (R... r, decltype (bar (r...)) x = 0) {}
+
+int
+main ()
+{
+  foo (3);
+}