From cc205a58e9385373729ebf91718dffef5097982c Mon Sep 17 00:00:00 2001
From: Marek Polacek <polacek@redhat.com>
Date: Sat, 28 Sep 2019 11:50:11 +0000
Subject: [PATCH] PR c++/91923 - failure-to-SFINAE with class type NTTP in
 C++17.

	* pt.c (invalid_nontype_parm_type_p): Only emit errors when
	tf_error.

	* g++.dg/cpp0x/nontype5.C: New test.

From-SVN: r276250
---
 gcc/cp/ChangeLog                      |  9 +++++++++
 gcc/cp/pt.c                           |  5 +++--
 gcc/testsuite/g++.dg/cpp0x/nontype5.C | 17 +++++++++++++++++
 3 files changed, 29 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp0x/nontype5.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 8bd42b839731..297eb6f0e9b2 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,12 @@
+2019-09-28  Marek Polacek  <polacek@redhat.com>
+
+	Backported from mainline
+	2019-09-28  Marek Polacek  <polacek@redhat.com>
+
+	PR c++/91923 - failure-to-SFINAE with class type NTTP in C++17.
+	* pt.c (invalid_nontype_parm_type_p): Only emit errors when
+	tf_error.
+
 2019-09-10  Marek Polacek  <polacek@redhat.com>
 
 	Backported from mainline
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index b3fe901097c8..34d440c7eb58 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -25231,8 +25231,9 @@ invalid_nontype_parm_type_p (tree type, tsubst_flags_t complain)
     {
       if (cxx_dialect < cxx2a)
 	{
-	  error ("non-type template parameters of class type only available "
-		 "with %<-std=c++2a%> or %<-std=gnu++2a%>");
+	  if (complain & tf_error)
+	    error ("non-type template parameters of class type only available "
+		   "with %<-std=c++2a%> or %<-std=gnu++2a%>");
 	  return true;
 	}
       if (dependent_type_p (type))
diff --git a/gcc/testsuite/g++.dg/cpp0x/nontype5.C b/gcc/testsuite/g++.dg/cpp0x/nontype5.C
new file mode 100644
index 000000000000..c31134581aa4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/nontype5.C
@@ -0,0 +1,17 @@
+// PR c++/91923 - failure-to-SFINAE with class type NTTP in C++17.
+// { dg-do compile { target c++11 } }
+
+template<typename T>
+constexpr bool is_integral_(...) {
+    return false;
+}
+template<typename T, T = 1>
+constexpr bool is_integral_(long) {
+    return true;
+}
+
+static_assert(is_integral_<int>(42), "");
+static_assert(!is_integral_<void>(42), "");
+
+struct S {};
+static_assert(!is_integral_<S>(42), "");
-- 
2.47.2