From 7ea2ca6c405ae7c49837b54438757f9e745d563b Mon Sep 17 00:00:00 2001
From: Andrzej Krzemienski <akrzemi1@gmail.com>
Date: Sat, 19 Nov 2016 14:57:40 +0100
Subject: [PATCH] Fix #12563

---
 include/boost/optional/optional.hpp           | 14 ++++++++--
 test/optional_test_convert_from_T.cpp         | 26 ++++++++++++++++++-
 ...tional_test_sfinae_friendly_value_ctor.cpp | 17 +++++++++---
 3 files changed, 50 insertions(+), 7 deletions(-)

diff --git a/include/boost/optional/optional.hpp b/include/boost/optional/optional.hpp
index 021588f..ef62aa7 100644
--- a/include/boost/optional/optional.hpp
+++ b/include/boost/optional/optional.hpp
@@ -745,6 +745,10 @@ struct is_convertible_to_T_or_factory
                       , boost::true_type, boost::false_type>::type
 {};
 
+template <typename T, typename U>
+struct is_optional_constructible : boost::is_constructible<T, U>
+{};
+
 #else
 
 #define BOOST_OPTIONAL_DETAIL_NO_IS_CONSTRUCTIBLE_TRAIT
@@ -753,6 +757,10 @@ template <typename, typename>
 struct is_convertible_to_T_or_factory : boost::true_type
 {};
 
+template <typename T, typename U>
+struct is_optional_constructible : boost::true_type
+{};
+
 #endif // is_convertible condition
 
 template <typename T, typename U>
@@ -812,7 +820,8 @@ class optional : public optional_detail::optional_base<T>
     // Requires a valid conversion from U to T.
     // Can throw if T::T(U const&) does
     template<class U>
-    explicit optional ( optional<U> const& rhs )
+    explicit optional ( optional<U> const& rhs,
+                        typename boost::enable_if< optional_detail::is_optional_constructible<T, U const&> >::type* = 0)
       :
       base()
     {
@@ -825,7 +834,8 @@ class optional : public optional_detail::optional_base<T>
     // Requires a valid conversion from U to T.
     // Can throw if T::T(U&&) does
     template<class U>
-    explicit optional ( optional<U> && rhs )
+    explicit optional ( optional<U> && rhs,
+                        typename boost::enable_if< optional_detail::is_optional_constructible<T, U> >::type* = 0 )
       :
       base()
     {
diff --git a/test/optional_test_convert_from_T.cpp b/test/optional_test_convert_from_T.cpp
index d4ce4bb..2abe7e5 100644
--- a/test/optional_test_convert_from_T.cpp
+++ b/test/optional_test_convert_from_T.cpp
@@ -23,6 +23,29 @@
 using boost::optional;
 using boost::none;
 
+template <typename U>
+struct superconv
+{
+  #ifndef BOOST_OPTIONAL_DETAIL_NO_RVALUE_REFERENCES
+  template <typename T>
+    superconv(T&&) { BOOST_STATIC_ASSERT(sizeof(T) == 0); }
+  #else
+  template <typename T>
+    superconv(const T&) { BOOST_STATIC_ASSERT(sizeof(T) == 0); }
+  template <typename T>
+    superconv(      T&) { BOOST_STATIC_ASSERT(sizeof(T) == 0); }
+  #endif
+  
+  superconv() {}
+};
+
+void test_optional_of_superconverting_T() // compile-time test
+{
+  superconv<optional<int> > s;
+   superconv<optional<int> > & rs = s;
+  optional<superconv<optional<int> > > os = rs;
+}
+
 void test_optional_optional_T()
 {
   optional<int> oi1 (1), oiN;
@@ -39,6 +62,7 @@ void test_optional_optional_T()
 int main()
 {
     test_optional_optional_T();
-  
+    test_optional_of_superconverting_T();
+    
     return boost::report_errors();
 }
diff --git a/test/optional_test_sfinae_friendly_value_ctor.cpp b/test/optional_test_sfinae_friendly_value_ctor.cpp
index d7af15d..6c2abda 100644
--- a/test/optional_test_sfinae_friendly_value_ctor.cpp
+++ b/test/optional_test_sfinae_friendly_value_ctor.cpp
@@ -27,11 +27,20 @@ struct Resource
   explicit Resource(const X&) {}
 };
 
-BOOST_STATIC_ASSERT(( boost::is_constructible<Resource, const X&>::value));
-BOOST_STATIC_ASSERT((!boost::is_constructible<Resource, const Y&>::value));
+BOOST_STATIC_ASSERT((  boost::is_constructible<Resource, const X&>::value ));
+BOOST_STATIC_ASSERT(( !boost::is_constructible<Resource, const Y&>::value ));
 
-BOOST_STATIC_ASSERT(( boost::is_constructible<optional<Resource>, const X&>::value));
-BOOST_STATIC_ASSERT((!boost::is_constructible<optional<Resource>, const Y&>::value));
+BOOST_STATIC_ASSERT((  boost::is_constructible<optional<Resource>, const X&>::value ));
+BOOST_STATIC_ASSERT(( !boost::is_constructible<optional<Resource>, const Y&>::value ));
+
+BOOST_STATIC_ASSERT((  boost::is_constructible< optional< optional<int> >, optional<int> >::value ));
+BOOST_STATIC_ASSERT(( !boost::is_constructible< optional<int>, optional< optional<int> > >::value ));
+
+BOOST_STATIC_ASSERT((  boost::is_constructible< optional< optional<int> >, const optional<int>& >::value ));
+BOOST_STATIC_ASSERT(( !boost::is_constructible< optional<int>, const optional< optional<int> >& >::value ));
+
+BOOST_STATIC_ASSERT((  boost::is_constructible<optional<Resource>, const optional<X>&>::value ));
+BOOST_STATIC_ASSERT(( !boost::is_constructible<optional<Resource>, const optional<Y>&>::value ));
   
 #endif