From 8a1df3ca0cbb3d30125c0e011219923c8dc15e1d Mon Sep 17 00:00:00 2001
From: Howard Hinnant <hhinnant@apple.com>
Date: Thu, 22 Aug 2013 17:41:48 +0000
Subject: [PATCH] David Blaikie suggested this test for detecting constexpr on
 the error_category default constructor.  Additionally I decided to make this
 constructor trivial as well, as I could not come up with a rationale for not
 doing so.  Fully tested with both current Apple clang and tip-of-trunk clang.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@189034 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/system_error                          |  3 +-
 .../default_ctor.pass.cpp                     | 40 +++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)
 create mode 100644 test/diagnostics/syserr/syserr.errcat/syserr.errcat.nonvirtuals/default_ctor.pass.cpp

diff --git a/include/system_error b/include/system_error
index df668cc6..afc73f29 100644
--- a/include/system_error
+++ b/include/system_error
@@ -370,7 +370,8 @@ public:
 #ifdef _LIBCPP_BUILDING_SYSTEM_ERROR
     error_category() _NOEXCEPT;
 #else
-    _LIBCPP_ALWAYS_INLINE _LIBCPP_CONSTEXPR_AFTER_CXX11 error_category() _NOEXCEPT {}
+    _LIBCPP_ALWAYS_INLINE
+    _LIBCPP_CONSTEXPR_AFTER_CXX11 error_category() _NOEXCEPT = default;
 #endif
 private:
     error_category(const error_category&);// = delete;
diff --git a/test/diagnostics/syserr/syserr.errcat/syserr.errcat.nonvirtuals/default_ctor.pass.cpp b/test/diagnostics/syserr/syserr.errcat/syserr.errcat.nonvirtuals/default_ctor.pass.cpp
new file mode 100644
index 00000000..0573ef86
--- /dev/null
+++ b/test/diagnostics/syserr/syserr.errcat/syserr.errcat.nonvirtuals/default_ctor.pass.cpp
@@ -0,0 +1,40 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+// <system_error>
+
+// class error_category
+
+// constexpr error_category() noexcept;
+
+#include <system_error>
+#include <type_traits>
+#include <string>
+#include <cassert>
+
+#if _LIBCPP_STD_VER > 11
+
+class test1
+    : public std::error_category
+{
+public:
+    constexpr test1() = default;  // won't compile if error_category() is not constexpr
+    virtual const char* name() const noexcept {return nullptr;}
+    virtual std::string message(int ev) const {return std::string();}
+};
+
+#endif  // _LIBCPP_STD_VER > 11
+
+int main()
+{
+#if _LIBCPP_STD_VER > 11
+    static_assert(std::is_nothrow_default_constructible<test1>::value,
+                                 "error_category() must exist and be noexcept");
+#endif  // _LIBCPP_STD_VER > 11
+}