Fix for move_assign

Author: vinay-deshmukh

libcxx/include/__tree

@@ -1053,11 +1053,11 @@ public:
     #if _LIBCPP_STD_VER >= 26
     if (__libcpp_is_constant_evaluated()) {
       // static_assert(std::same_as_v<decltype(__value.first), double>);
-      // __emplace_hint_unique(__p, std::move(__value.first), std::move(__value.second));
+      __emplace_hint_unique(__p, std::move(__value.first), std::move(__value.second));
 
-      __sfinae_call_emplace_hint_unique(__p, std::move(__value),
-        integral_constant<bool, is_copy_constructible<decltype(__value.first)>::value >()
-      );
+      // __sfinae_call_emplace_hint_unique(__p, std::move(__value),
+      //   integral_constant<bool, is_copy_constructible<decltype(__value.first)>::value >()
+      // );
     } else 
     #endif
     {
@@ -1239,30 +1239,66 @@ private:
 
 
 // todo; mark consteval?
-#ifdef FAKE_VINAY
+// #ifdef FAKE_VINAY
 
   template <class _From, class _ValueT = _Tp, 
   __enable_if_t<__is_tree_value_type<_ValueT>::value, int> = 0
-  , __enable_if_t< ! is_copy_constructible_v< typename _From::first_type  >, int> = 0
+
+// , typename = std::enable_if_t<
+//               !std::is_copy_constructible_v<
+//                   std::remove_cvref_t<decltype(std::declval<_From>().first)>
+//               >
+//             >
   >
+  requires (!std::is_copy_constructible_v<
+            std::remove_cvref_t<decltype(std::declval<_From>().first)>
+          >)
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void __move_from_value_type(
      __get_node_value_type_t<value_type>& __lhs, _From&& __rhs/*, false_type*/) _NOEXCEPT {
       (void)__lhs;
       (void)__rhs;
-      static_assert(false, "Can not move from a pair<const T, T>");
+      // static_assert(false, "Can not move from a pair<const T, U>");
+      // TODO: how do I flag this code to NOT run at compile time?
+      // Using static_assert means this can't compile _at all_, regardless of whether this code is actually going to execute at compile time or not
   }
 
   template <class _From, class _ValueT = _Tp, 
   __enable_if_t<__is_tree_value_type<_ValueT>::value, int> = 0
 
   // Check if first type can be copy constructed
-  , __enable_if_t< is_copy_constructible_v< typename _From::first_type >, int> = 0
+
+// , typename = std::enable_if_t<
+//               std::is_copy_constructible_v<
+//                   std::remove_cvref_t<decltype(std::declval<_From>().first)>
+//               >
+//             >
   >
+  requires ( std::is_copy_constructible_v<
+            std::remove_cvref_t<decltype(std::declval<_From>().first)>
+          >)
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void __move_from_value_type(
      __get_node_value_type_t<value_type>& __lhs, _From&& __rhs/*, true_type*/) _NOEXCEPT {
 
+
+      // const_cast is not allowed at constexpr time.
+      // we get around this by deleting __lhs and creating a new node in-place
+      // to avoid const_cast -ing __lhs.first
+
+      // note: this does not work for `const MoveOnly` keys at constexpr time
+
+
+      __node_allocator& __na = __node_alloc();
+      __node_traits::destroy(__na, std::addressof(__lhs));
+
+      // __get_node_value_type_t<value_type> __tmp(__rhs);
+      using __node_value_type = __get_node_value_type_t<value_type>;
+      __get_node_value_type_t<value_type> __tmp(__rhs.first, __rhs.second);
+      __node_traits::construct(__na, std::addressof(__lhs), std::move(__tmp));
+
+
+
   }
-  #endif
+  // #endif
 
 
 
@@ -1280,25 +1316,9 @@ error: no matching constructor for initialization of '__get_node_value_type_t<va
 # |  1225 |       __get_node_value_type_t<value_type> __tmp(__rhs.first, __rhs.second);
      */
     if (__libcpp_is_constant_evaluated()) {
-      // __move_from_value_type(__lhs, __rhs
+      __move_from_value_type(__lhs, __rhs
       // , integral_constant<bool, is_copy_constructible_v<_From> >()
-      // );
-
-      using __node_value_type = __get_node_value_type_t<value_type>;
-      __get_node_value_type_t<value_type> __tmp(__rhs.first, __rhs.second);
-      // __get_node_value_type_t<value_type> __tmp(__rhs);
-
-      // const_cast is not allowed at constexpr time.
-      // we get around this by deleting __lhs and creating a new node in-place
-      // to avoid const_cast -ing __lhs.first
-
-      // note: this does not work for `const MoveOnly` keys at constexpr time
-
-      // __lhs.~__node_value_type();
-      __node_allocator& __na = __node_alloc();
-      __node_traits::destroy(__na, std::addressof(__lhs));
-      __node_traits::construct(__na, std::addressof(__lhs), std::move(__tmp));
-
+      );