[COMMITTED] c++: Fix decltype of empty pack expansion of parm.

[COMMITTED] c++: Fix decltype of empty pack expansion of parm.

[Jason Merrill]

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.

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

	PR c++/93140
	* pt.c (tsubst_decl) [PARM_DECL]: Check cp_unevaluated_operand in
	handling of TREE_CHAIN for empty pack.
---
 gcc/cp/pt.c                                 |  2 +-
 gcc/testsuite/g++.dg/cpp0x/variadic-parm1.C | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/variadic-parm1.C

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 40ff3c3a089..01bade85cdf 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -14076,7 +14076,7 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
 
                 /* Zero-length parameter packs are boring. Just substitute
                    into the chain.  */
-                if (len == 0)
+		if (len == 0 && !cp_unevaluated_operand)
                   RETURN (tsubst (TREE_CHAIN (t), args, complain,
 				  TREE_CHAIN (t)));
               }
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 00000000000..4300c781400
--- /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);
+}

base-commit: 5a8ad97b6e4823d4ded00a3ce8d80e4bf93368d4
-- 
2.18.1