[PATCH] PR libstdc++/87538 fix std::not_fn exception specifications

[Jonathan Wakely]

	PR libstdc++/87538
	* include/std/functional (_Not_fn::operator()): Check value of
	__is_nothrow_invocable as well.
	* testsuite/20_util/function_objects/not_fn/87538.cc: New test.

Tested x86_64-linux, committed to trunk.

I'll backport this to gcc-7 and gcc-8 too.

-------------- next part --------------
commit ece63ca7236e5a85dfa6464ef7ca0a7b7b77b16d
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Oct 8 12:13:30 2018 +0100

    PR libstdc++/87538 fix std::not_fn exception specifications
    
            PR libstdc++/87538
            * include/std/functional (_Not_fn::operator()): Check value of
            __is_nothrow_invocable as well.
            * testsuite/20_util/function_objects/not_fn/87538.cc: New test.

diff --git a/libstdc++-v3/include/std/functional b/libstdc++-v3/include/std/functional
index 2b46ba899dd..093528bcc4f 100644
--- a/libstdc++-v3/include/std/functional
+++ b/libstdc++-v3/include/std/functional
@@ -864,7 +864,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       template<typename... _Args>					\
 	decltype(_S_not<__inv_res_t<_Fn _QUALS, _Args...>>())		\
 	operator()(_Args&&... __args) _QUALS				\
-	noexcept(noexcept(_S_not<__inv_res_t<_Fn _QUALS, _Args...>>()))	\
+	noexcept(__is_nothrow_invocable<_Fn _QUALS, _Args...>::value	\
+	    && noexcept(_S_not<__inv_res_t<_Fn _QUALS, _Args...>>()))	\
 	{								\
 	  return !std::__invoke(std::forward< _Fn _QUALS >(_M_fn),	\
 				std::forward<_Args>(__args)...);	\
diff --git a/libstdc++-v3/testsuite/20_util/function_objects/not_fn/87538.cc b/libstdc++-v3/testsuite/20_util/function_objects/not_fn/87538.cc
new file mode 100644
index 00000000000..7f4f0df54ae
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/function_objects/not_fn/87538.cc
@@ -0,0 +1,49 @@
+// Copyright (C) 2018 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do run { target c++17 } }
+
+#include <functional>
+#include <testsuite_hooks.h>
+
+struct N {
+  int operator()(int i) { if (i == 0) throw -1; return i; }
+};
+
+void
+test01()
+{
+  N n;
+  auto not_n = std::not_fn(n);
+  static_assert( !noexcept(not_n(1)) );
+  VERIFY(not_n(1) == 0);
+  int exception = 0;
+  try {
+    not_n(0);
+  }
+  catch (int e) {
+    exception = e;
+  }
+  VERIFY(exception == -1);
+}
+
+int
+main()
+{
+  test01();
+}