From 0003e469d4664397b65080a66ad7d6557bd7ffce Mon Sep 17 00:00:00 2001
From: Simon Martin <simon-l.martin@laposte.net>
Date: Mon, 6 May 2024 15:20:10 +0200
Subject: [PATCH] c++: ICE in build_deduction_guide for invalid template
 [PR105760]

We currently ICE upon the following invalid snippet because we fail to
properly handle tsubst_arg_types returning error_mark_node in
build_deduction_guide.

== cut ==
template<class... Ts, class>
struct A { A(Ts...); };
A a;
== cut ==

This patch fixes this, and has been successfully tested on x86_64-pc-linux-gnu.

	PR c++/105760

gcc/cp/ChangeLog:

	* pt.cc (build_deduction_guide): Check for error_mark_node
	result from tsubst_arg_types.

gcc/testsuite/ChangeLog:

	* g++.dg/parse/error66.C: New test.
---
 gcc/cp/pt.cc                         | 2 ++
 gcc/testsuite/g++.dg/parse/error66.C | 6 ++++++
 2 files changed, 8 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/parse/error66.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 4b71e199d27..32640f8e946 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -30031,6 +30031,8 @@ build_deduction_guide (tree type, tree ctor, tree outer_args, tsubst_flags_t com
 	     references to members of an unknown specialization.  */
 	  cp_evaluated ev;
 	  fparms = tsubst_arg_types (fparms, targs, NULL_TREE, complain, ctor);
+	 if (fparms == error_mark_node)
+	   ok = false;
 	  fargs = tsubst (fargs, targs, complain, ctor);
 	  if (ci)
 	    {
diff --git a/gcc/testsuite/g++.dg/parse/error66.C b/gcc/testsuite/g++.dg/parse/error66.C
new file mode 100644
index 00000000000..82f4b8b8a53
--- /dev/null
+++ b/gcc/testsuite/g++.dg/parse/error66.C
@@ -0,0 +1,6 @@
+// PR c++/105760
+// { dg-do compile { target c++17 } }
+
+template<class... Ts, class> // { dg-error "must be at the end of the template parameter list" }
+struct A { A(Ts...); };
+A a;