move_alloc and move_assign, fail in __insert_unique_from_orphaned_node, need to place the SFINAE there, not in __assign_value

Author: vinay-deshmukh

libcxx/include/__tree

@@ -1027,14 +1027,12 @@ public:
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void
   __insert_unique_from_orphaned_node(const_iterator __p, __get_node_value_type_t<_Tp>&& __value) {
     // fails here for move_alloc.pass.cpp
-    if ( 
-      (
-        _LIBCPP_STD_VER >= 26
-      )
-      && 
-      __libcpp_is_constant_evaluated()) {
+
+    #if _LIBCPP_STD_VER >= 26
+    if (__libcpp_is_constant_evaluated()) {
       __emplace_hint_unique(__p, std::move(__value.first), std::move(__value.second));
     } else 
+    #endif
     {
       __emplace_hint_unique(__p, const_cast<key_type&&>(__value.first), std::move(__value.second));
     }
@@ -1212,6 +1210,35 @@ private:
   }
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void __move_assign_alloc(__tree&, false_type) _NOEXCEPT {}
 
+
+// todo; mark consteval?
+#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
+  >
+  _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>");
+  }
+
+  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
+  >
+  _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 {
+
+  }
+  #endif
+
+
+
   template <class _From, class _ValueT = _Tp, __enable_if_t<__is_tree_value_type<_ValueT>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void
   __assign_value( __get_node_value_type_t<value_type>& __lhs, _From&& __rhs) {
@@ -1226,16 +1253,29 @@ 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
+      // , 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 and creating a new node value
+      // 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));
+
+
+
+
+
     } else 
     #endif
     {
@@ -1915,14 +1955,13 @@ __tree<_Tp, _Compare, _Allocator>::__construct_node(_Args&&... __args) {
   // for container_test_types.h
   // but I don't know how to placement new to avoid instantiation
 
-  } else {
+  } else 
   #endif
-
+  {
   __node_traits::construct(__na, std::addressof(__h->__value_), std::forward<_Args>(__args)...);
-
-
-  #if _LIBCPP_STD_VER >= 26
   }
+  #if _LIBCPP_STD_VER >= 26
+  
   #endif