From 16bd101dd1542d18f051c4198e97c5cd44dfd2fa Mon Sep 17 00:00:00 2001
From: dim <dim@FreeBSD.org>
Date: Mon, 30 Mar 2015 19:36:33 +0000
Subject: [PATCH] Pull in r233552 from upstream libc++ trunk (by Eric
 Fiselier):

  [libcxx] Fix PR22771 - Support access control SFINAE in the library
  version of is_convertible.

  Summary:
  Currently the conversion check does not take place in a context where
  access control SFINAE is applied. This patch changes the context of
  the test expression so that SFINAE occurs if access control does not
  permit the conversion.

  Related bug: https://llvm.org/bugs/show_bug.cgi?id=22771

  Reviewers: mclow.lists, rsmith, dim

  Reviewed By: dim

  Subscribers: dim, rodrigc, emaste, cfe-commits

  Differential Revision: http://reviews.llvm.org/D8461

This fixes building clang, and other programs using libc++, with newer
versions of gcc (specifically, gcc 4.8 and higher).

Reported by:	rodrigc
MFC after:	1 week
---
 contrib/libc++/include/type_traits | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/contrib/libc++/include/type_traits b/contrib/libc++/include/type_traits
index f4677358a560..8612e57b77da 100644
--- a/contrib/libc++/include/type_traits
+++ b/contrib/libc++/include/type_traits
@@ -842,7 +842,16 @@ template <class _T1, class _T2> struct _LIBCPP_TYPE_VIS_ONLY is_convertible
 
 namespace __is_convertible_imp
 {
-template <class _Tp> char  __test(_Tp);
+template <class _Tp> void  __test_convert(_Tp);
+
+template <class _From, class _To, class = void>
+struct __is_convertible_test : public false_type {};
+
+template <class _From, class _To>
+struct __is_convertible_test<_From, _To,
+    decltype(__test_convert<_To>(_VSTD::declval<_From>()))> : public true_type
+{};
+
 template <class _Tp> __two __test(...);
 #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
 template <class _Tp> _Tp&& __source();
@@ -877,10 +886,8 @@ template <class _T1, class _T2,
     unsigned _T2_is_array_function_or_void = __is_convertible_imp::__is_array_function_or_void<_T2>::value>
 struct __is_convertible
     : public integral_constant<bool,
-#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
-        sizeof(__is_convertible_imp::__test<_T2>(__is_convertible_imp::__source<_T1>())) == 1
-#else
-        sizeof(__is_convertible_imp::__test<_T2>(__is_convertible_imp::__source<_T1>())) == 1
+        __is_convertible_imp::__is_convertible_test<_T1, _T2>::value
+#if defined(_LIBCPP_HAS_NO_RVALUE_REFERENCES)
          && !(!is_function<_T1>::value && !is_reference<_T1>::value && is_reference<_T2>::value
               && (!is_const<typename remove_reference<_T2>::type>::value
                   || is_volatile<typename remove_reference<_T2>::type>::value)