This is LWG issue 3349.
Backport from mainline
2019-12-10 Jonathan Wakely <jwakely@redhat.com>
* include/std/complex (__cpp_lib_constexpr_complex): Define.
* include/std/version (__cpp_lib_constexpr_complex): Likewise.
* testsuite/26_numerics/complex/1.cc: New test.
* testsuite/26_numerics/complex/2.cc: New test.
2020-04-23 Jonathan Wakely <jwakely@redhat.com>
+ Backport from mainline
+ 2019-12-10 Jonathan Wakely <jwakely@redhat.com>
+
+ * include/std/complex (__cpp_lib_constexpr_complex): Define.
+ * include/std/version (__cpp_lib_constexpr_complex): Likewise.
+ * testsuite/26_numerics/complex/1.cc: New test.
+ * testsuite/26_numerics/complex/2.cc: New test.
+
Backport from mainline
2019-11-05 Jonathan Wakely <jwakely@redhat.com>
// Get rid of a macro possibly defined in <complex.h>
#undef complex
+#if __cplusplus > 201703L
+# define __cpp_lib_constexpr_complex 201711L
+#endif
+
namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
#if _GLIBCXX_HOSTED
#define __cpp_lib_bind_front 201907L
+#define __cpp_lib_constexpr_complex 201711L
#define __cpp_lib_erase_if 202002L
#define __cpp_lib_interpolate 201902L
#define __cpp_lib_list_remove_return_type 201806L
--- /dev/null
+// Copyright (C) 2019 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++2a" }
+// { dg-do preprocess { target c++2a } }
+
+#include <complex>
+
+#ifndef __cpp_lib_constexpr_complex
+# error "Feature test macro for constexpr complex is missing in <complex>"
+#elif __cpp_lib_constexpr_complex < 201711L
+# error "Feature test macro for constexpr complex has wrong value in <complex>"
+#endif
--- /dev/null
+// Copyright (C) 2019 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++2a" }
+// { dg-do preprocess { target c++2a } }
+
+#include <version>
+
+#ifndef __cpp_lib_constexpr_complex
+# error "Feature test macro for constexpr complex is missing in <version>"
+#elif __cpp_lib_constexpr_complex < 201711L
+# error "Feature test macro for constexpr complex has wrong value in <version>"
+#endif