From 30d974d0fc447b627cf29d50268136d1d6460ff3 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Tue, 26 Feb 2019 15:12:37 +0200
Subject: [PATCH] Fix exception safety issue in copy/move/converting
 constructor

---
 include/boost/variant2/variant.hpp | 36 ++++++++++++++++++++++++++----
 1 file changed, 32 insertions(+), 4 deletions(-)

diff --git a/include/boost/variant2/variant.hpp b/include/boost/variant2/variant.hpp
index b0f759f..de9b8d3 100644
--- a/include/boost/variant2/variant.hpp
+++ b/include/boost/variant2/variant.hpp
@@ -608,6 +608,13 @@ template<class... T> struct variant_base_impl<true, true, T...>
     {
     }
 
+    // requires: ix_ == 0
+    template<class I, class... A> void _replace( I, A&&... a )
+    {
+        ::new( &st1_ ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );
+        ix_ = I::value + 1;
+    }
+
     constexpr std::size_t index() const noexcept
     {
         return ix_ - 1;
@@ -700,6 +707,13 @@ template<class... T> struct variant_base_impl<true, false, T...>
     {
     }
 
+    // requires: ix_ == 0
+    template<class I, class... A> void _replace( I, A&&... a )
+    {
+        ::new( &st1_ ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );
+        ix_ = I::value + 1;
+    }
+
     constexpr std::size_t index() const noexcept
     {
         return ix_ >= 0? ix_ - 1: -ix_ - 1;
@@ -755,6 +769,13 @@ template<class... T> struct variant_base_impl<false, true, T...>
     {
     }
 
+    // requires: ix_ == 0
+    template<class I, class... A> void _replace( I, A&&... a )
+    {
+        ::new( &st1_ ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );
+        ix_ = I::value + 1;
+    }
+
     //[&]( auto I ){
     //    using U = mp_at_c<mp_list<none, T...>, I>;
     //    st1_.get( I ).~U();
@@ -869,6 +890,13 @@ template<class... T> struct variant_base_impl<false, false, T...>
     {
     }
 
+    // requires: ix_ == 0
+    template<class I, class... A> void _replace( I, A&&... a )
+    {
+        ::new( &st1_ ) variant_storage<none, T...>( mp11::mp_size_t<I::value + 1>(), std::forward<A>(a)... );
+        ix_ = I::value + 1;
+    }
+
     //[&]( auto I ){
     //    using U = mp_at_c<mp_list<none, T...>, I>;
     //    st1_.get( I ).~U();
@@ -1090,7 +1118,7 @@ private:
 
         template<class I> void operator()( I i ) const
         {
-            ::new( static_cast<void*>( this_ ) ) variant_base( i, r._get_impl( i ) );
+            this_->_replace( i, r._get_impl( i ) );
         }
     };
 
@@ -1123,7 +1151,7 @@ private:
 
         template<class I> void operator()( I i ) const
         {
-            ::new( static_cast<void*>( this_ ) ) variant_base( i, std::move( r._get_impl( i ) ) );
+            this_->_replace( i, std::move( r._get_impl( i ) ) );
         }
     };
 
@@ -1369,7 +1397,7 @@ private:
         template<class I> void operator()( I i ) const
         {
             using J = mp11::mp_find<mp11::mp_list<T...>, mp11::mp_at<mp11::mp_list<U...>, I>>;
-            ::new( static_cast<void*>(this_) ) variant_base( J{}, r._get_impl( i ) );
+            this_->_replace( J{}, r._get_impl( i ) );
         }
     };
 
@@ -1393,7 +1421,7 @@ private:
         template<class I> void operator()( I i ) const
         {
             using J = mp11::mp_find<mp11::mp_list<T...>, mp11::mp_at<mp11::mp_list<U...>, I>>;
-            ::new( static_cast<void*>(this_) ) variant_base( J{}, std::move( r._get_impl( i ) ) );
+            this_->_replace( J{}, std::move( r._get_impl( i ) ) );
         }
     };