From: Jason Merrill <jason@redhat.com>
Date: Wed, 26 Feb 2020 18:03:23 +0000 (-0500)
Subject: c++: Fix decltype of empty pack expansion of parm.
X-Git-Tag: releases/gcc-9.3.0~70
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1a8996b0a7b238180f4a10b19b1e90b33e5b2df0;p=thirdparty%2Fgcc.git

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.

gcc/cp/ChangeLog
2020-02-26  Jason Merrill  <jason@redhat.com>

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

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index ca4bc4cc1b50..8c4d662d7ec9 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2020-02-26  Jason Merrill  <jason@redhat.com>
+
+	PR c++/93140
+	* pt.c (tsubst_decl) [PARM_DECL]: Check cp_unevaluated_operand in
+	handling of TREE_CHAIN for empty pack.
+
 2020-02-26  Jason Merrill  <jason@redhat.com>
 
 	PR c++/92852
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index c7245efa2b26..c7ca7e419ea0 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -13495,7 +13495,7 @@ 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 000000000000..4300c781400c
--- /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);
+}