Add a check for GCC to the _LIBCPP_EXPLICIT define

[mdaniels]

Summary

When using libc++ with GCC functions are not getting the explicit specifier as expected. This change adds a GCC check to resolve the problem.

I was unable to figure out exactly when GCC added support for the explicit keyword, but I found messages on the mailing list suggesting it was implemented and working in at lease GCC 3.3, so it just defaults to any GCC version.

A test case is included to reproduce the problem. While it could be demonstrated with any explicit function, this just happened to be the one we were having problem with.

Tested with GCC 5.4.0 and clang 3.8.0 using libc++ from ToT as well as GCC 5.4 using libc++ 3.7.1.

[mdaniels]

Did some more digging to find the right version check..

[mclow.lists]

test/std/diagnostics/syserr/syserr.errcode/syserr.errcode.observers/bool.fail.cpp

19

I think this test would be better making the bool conversion clear; instead of relying on the double conversion error_code --> bool --> int.

bool whatever()
{
    const std::error_code ec(0, std::generic_category());
    return ec;
}

int main () {}

[mdaniels]

Update based on feedback.

[mclow.lists]

LGTM

[mdaniels]

I don't have commit access, could I trouble someone to do it on my behalf?

[mclow.lists]

Ok, this is weird. It looks like the changes to <__config> got committed, but not the test.

[EricWF]

I think I may have committed these changes as part of another change set.

[mclow.lists]

Yes, this appears to have been landed. Closing.

include/__config

 #define _NOALIAS
 #endif
 
-#if __has_feature(cxx_explicit_conversions) || defined(__IBMCPP__)
+#if __has_feature(cxx_explicit_conversions) || defined(__IBMCPP__) || _GNUC_VER >= 406
 #   define _LIBCPP_EXPLICIT explicit
 #else
 #   define _LIBCPP_EXPLICIT

test/std/diagnostics/syserr/syserr.errcode/syserr.errcode.observers/bool.fail.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.
+//
+//===----------------------------------------------------------------------===//
+
+// <system_error>
+
+// class error_code
+
+// explicit operator bool() const;
+
+#include <system_error>
+
+int main()
+{
+    const std::error_code ec(0, std::generic_category());
+    return ec;
+}
+