From a6e879f0914e98db2c5d94fff2a33ce0539a06ab Mon Sep 17 00:00:00 2001
From: John Maddock <john@johnmaddock.co.uk>
Date: Thu, 25 Jan 2018 13:18:38 +0000
Subject: [PATCH] Add tests and tentative fix for issue with clang
 mis-identifying pairs of non-constructible types.  See github #51.

---
 include/boost/type_traits/is_default_constructible.hpp | 6 ++++++
 test/has_trivial_constr_test.cpp                       | 1 +
 test/is_default_constr_test.cpp                        | 2 ++
 3 files changed, 9 insertions(+)

diff --git a/include/boost/type_traits/is_default_constructible.hpp b/include/boost/type_traits/is_default_constructible.hpp
index fa5d76a..99c911f 100644
--- a/include/boost/type_traits/is_default_constructible.hpp
+++ b/include/boost/type_traits/is_default_constructible.hpp
@@ -16,6 +16,9 @@
 #if BOOST_WORKAROUND(BOOST_GCC_VERSION, < 40700)
 #include <boost/type_traits/is_abstract.hpp>
 #endif
+#ifdef  __clang__
+#include <utility> // std::pair
+#endif
 
 #if !defined(BOOST_NO_CXX11_DECLTYPE) && !BOOST_WORKAROUND(BOOST_MSVC, < 1800) && !BOOST_WORKAROUND(BOOST_GCC_VERSION, < 40500)
 
@@ -55,6 +58,9 @@ namespace boost{
    template <class T, std::size_t N> struct is_default_constructible<T[N]> : public is_default_constructible<T>{};
    template <class T> struct is_default_constructible<T[]> : public is_default_constructible<T>{};
    template <class T> struct is_default_constructible<T&> : public integral_constant<bool, false>{};
+#ifdef  __clang__
+   template <class T, class U> struct is_default_constructible<std::pair<T,U> > : public integral_constant<bool, is_default_constructible<T>::value && is_default_constructible<U>::value>{};
+#endif
 #if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES) 
    template <class T> struct is_default_constructible<T&&> : public integral_constant<bool, false>{};
 #endif
diff --git a/test/has_trivial_constr_test.cpp b/test/has_trivial_constr_test.cpp
index 9328b51..455ee95 100644
--- a/test/has_trivial_constr_test.cpp
+++ b/test/has_trivial_constr_test.cpp
@@ -207,6 +207,7 @@ BOOST_CHECK_INTEGRAL_CONSTANT(::tt::has_trivial_constructor<bug11324_derived>::v
 BOOST_CHECK_INTEGRAL_CONSTANT(::tt::has_trivial_constructor<private_construct>::value, false);
 #ifndef BOOST_NO_CXX11_DELETED_FUNCTIONS
 BOOST_CHECK_INTEGRAL_CONSTANT(::tt::has_trivial_constructor<deleted_construct>::value, false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::has_trivial_constructor<std::pair<deleted_construct, int> >::value), false);
 #endif
 
 TT_TEST_END
diff --git a/test/is_default_constr_test.cpp b/test/is_default_constr_test.cpp
index 9992d4a..ba54e32 100644
--- a/test/is_default_constr_test.cpp
+++ b/test/is_default_constr_test.cpp
@@ -197,9 +197,11 @@ BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_default_constructible<test_abc1>::value,
 BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_default_constructible<bug11324_derived>::value, false);
 #ifndef BOOST_NO_CXX11_DELETED_FUNCTIONS
 BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_default_constructible<deleted_default_construct>::value, false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_default_constructible<std::pair<deleted_default_construct, int> >::value), false);
 #endif
 #if !BOOST_WORKAROUND(BOOST_GCC_VERSION, < 40800)
 BOOST_CHECK_INTEGRAL_CONSTANT(::tt::is_default_constructible<private_default_construct>::value, false);
+BOOST_CHECK_INTEGRAL_CONSTANT((::tt::is_default_constructible<std::pair<private_default_construct, int> >::value), false);
 #endif
 
 TT_TEST_END