[libcxx] Add <experimental/system_error>

[EricWF]

Summary

This patch just adds the variable templates in <experimental/system_error>.

see: https://rawgit.com/cplusplus/fundamentals-ts/v1/fundamentals-ts.html#syserror

[mclow.lists]

LGTM. I think the whole "static assertion on three lines" coding style is hard(er) to read, but the checks are there and are fine.

[EricWF]

I think @chandlerc said the hardest part of C++ is where to split the line. I'll try and come up with something better in the tests without violating the 80 col limit.

[EricWF]

I let clang-format take a pass at it and cleaned up what came out. It still doesn't look nice but it is better(?).

[mclow.lists]

Looks good to me.

test/std/experimental/utilities/syserror/header.system_error.synop/is_error_condition_enum.pass.cpp

25

You know, if I was writing this, I would align stuff to make it clear what's the same and what's different.

static_assert( ex::is_error_condition_enum_v<std::errc> ==
              std::is_error_condition_enum  <std::errc>::value, "" );

But that might just be me indulging my OCD.

include/experimental/system_error

+// -*- C++ -*-
+//===-------------------------- system_error ------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef _LIBCPP_EXPERIMENTAL_SYSTEM_ERROR
+#define _LIBCPP_EXPERIMENTAL_SYSTEM_ERROR
+
+/**
+    experimental/system_error synopsis
+
+// C++1y
+
+#include <system_error>
+
+namespace std {
+namespace experimental {
+inline namespace fundamentals_v1 {
+
+  // See C++14 19.5, System error support
+  template <class T> constexpr bool is_error_code_enum_v
+    = is_error_code_enum<T>::value;
+  template <class T> constexpr bool is_error_condition_enum_v
+    = is_error_condition_enum<T>::value;
+
+} // namespace fundamentals_v1
+} // namespace experimental
+} // namespace std
+
+*/
+
+#include <experimental/__config>
+
+#if _LIBCPP_STD_VER > 11
+
+#include <system_error>
+
+_LIBCPP_BEGIN_NAMESPACE_LFTS
+
+#if __has_feature(cxx_variable_templates)
+
+template <class _Tp> _LIBCPP_CONSTEXPR bool is_error_code_enum_v
+    = is_error_code_enum<_Tp>::value;
+
+template <class _Tp> _LIBCPP_CONSTEXPR bool is_error_condition_enum_v
+    = is_error_condition_enum<_Tp>::value;
+
+#endif /* __has_feature(cxx_variable_templates) */
+
+_LIBCPP_END_NAMESPACE_LFTS
+
+#endif /* _LIBCPP_STD_VER > 11 */
+
+#endif /* _LIBCPP_EXPERIMENTAL_SYSTEM_ERROR */
 No newline at end of file

test/libcxx/experimental/utilities/syserror/header.system_error.synop/includes.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <experimental/system_error>
+
+#include <experimental/system_error>
+
+#ifndef _LIBCPP_STD_VER > 11
+# ifndef _LIBCPP_SYSTEM_ERROR
+#   error "<experimental/system_error> must include <system_error>"
+# endif
+#endif
+
+int main()
+{
+}

test/libcxx/experimental/utilities/syserror/version.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <experimental/system_error>
+
+#include <experimental/system_error>
+
+#ifndef _LIBCPP_VERSION
+#error _LIBCPP_VERSION not defined
+#endif
+
+int main()
+{
+}

test/std/experimental/utilities/syserror/header.system_error.synop/includes.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11
+
+// <experimental/system_error>
+
+#include <experimental/system_error>
+
+int main()
+{
+  // Check that <system_error> has been included
+  std::error_code ec;
+  ((void)ec);
+}

test/std/experimental/utilities/syserror/header.system_error.synop/is_error_code_enum_v.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11
+
+// <experimental/system_error>
+
+// template <class T> constexpr bool is_error_code_enum_v;
+
+#include <experimental/system_error>
+#include <ios> /* for std::io_errc */
+
+namespace ex = std::experimental;
+
+int main()
+{
+  {
+    static_assert(
+      ex::is_error_code_enum_v<std::io_errc>, ""
+    );
+    static_assert(
+      ex::is_error_code_enum_v<std::io_errc>
+      == std::is_error_code_enum<std::io_errc>::value, ""
+    );
+    static_assert(
+      std::is_same<
+        decltype(ex::is_error_code_enum_v<std::io_errc>),  const bool
+      >::value, ""
+    );
+  }
+  {
+    static_assert(
+      !ex::is_error_code_enum_v<int>, ""
+    );
+    static_assert(
+      ex::is_error_code_enum_v<int>
+      == std::is_error_code_enum<int>::value, ""
+    );
+  }
+}

test/std/experimental/utilities/syserror/header.system_error.synop/is_error_condition_enum.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11
+
+// <experimental/system_error>
+
+// template <class T> constexpr bool is_error_condition_enum_v;
+
+#include <experimental/system_error>
+#include <type_traits>
+namespace ex = std::experimental;
+
+int main()
+{
+  {
+    static_assert(
+      ex::is_error_condition_enum_v<std::errc>, ""
+    );
+    static_assert(
+      ex::is_error_condition_enum_v<std::errc>
+      == std::is_error_condition_enum<std::errc>::value, ""
+    );
+    static_assert(
+      std::is_same<
+        decltype(ex::is_error_condition_enum_v<std::errc>),  const bool
+      >::value, ""
+    );
+  }
+  {
+    static_assert(
+      !ex::is_error_condition_enum_v<int>, ""
+    );
+    static_assert(
+      ex::is_error_condition_enum_v<int>
+      == std::is_error_condition_enum<int>::value, ""
+    );
+  }
+}