From 50bee766bc9f4020cf1f814178155d16e80dccaa Mon Sep 17 00:00:00 2001
From: Marek Polacek <polacek@redhat.com>
Date: Thu, 16 Jul 2020 09:15:37 -0400
Subject: [PATCH] c++: Variable template and template parameter pack [PR96218]

This is DR 2032 which says that the restrictions regarding template
parameter packs and default arguments apply to variable templates as
well, but we weren't detecting that.

gcc/cp/ChangeLog:

	DR 2032
	PR c++/96218
	* pt.c (check_default_tmpl_args): Also consider variable
	templates.

gcc/testsuite/ChangeLog:

	DR 2032
	PR c++/96218
	* g++.dg/cpp1y/var-templ67.C: New test.
---
 gcc/cp/pt.c                              |  5 +++--
 gcc/testsuite/g++.dg/cpp1y/var-templ67.C | 16 ++++++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/var-templ67.C

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 72bdf869b55..bd2af8b6679 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -5482,14 +5482,15 @@ check_default_tmpl_args (tree decl, tree parms, bool is_primary,
 		       /* Don't complain about an enclosing partial
 			  specialization.  */
 		       && parm_level == parms
-		       && TREE_CODE (decl) == TYPE_DECL
+		       && (TREE_CODE (decl) == TYPE_DECL || VAR_P (decl))
 		       && i < ntparms - 1
 		       && template_parameter_pack_p (TREE_VALUE (parm))
 		       /* A fixed parameter pack will be partially
 			  instantiated into a fixed length list.  */
 		       && !fixed_parameter_pack_p (TREE_VALUE (parm)))
 		{
-		  /* A primary class template can only have one
+		  /* A primary class template, primary variable template
+		     (DR 2032), or alias template can only have one
 		     parameter pack, at the end of the template
 		     parameter list.  */
 
diff --git a/gcc/testsuite/g++.dg/cpp1y/var-templ67.C b/gcc/testsuite/g++.dg/cpp1y/var-templ67.C
new file mode 100644
index 00000000000..f36af39bc19
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/var-templ67.C
@@ -0,0 +1,16 @@
+// DR 2032 - Default template-arguments of variable templates
+// PR c++/96218
+// { dg-do compile { target c++14 } }
+
+// [temp.param]/14: If a template-parameter of a class template, variable
+// template, or alias template has a default template-argument, each subsequent
+// template-parameter shall either have a default template-argument supplied or
+// be a template parameter pack.
+template<typename T = int, typename U>
+T vt; // { dg-error "no default argument" }
+
+// [temp.param]/14: If a template-parameter of a primary class template,
+// primary variable template, or alias template is a template parameter pack,
+// it shall be the last template-parameter.
+template<typename... Ts, typename U> // { dg-error "must be at the end" }
+int vt2;
-- 
2.30.2