Allow for using b-tree with `value_type`s that can only be constructed by the allocator (ignoring copy/move constructors).

We were using `init_type`s for temp values that we would move into slots, but in this case, we need to have actual slots. We use node handles for managing slots outside of nodes.

Also, in btree::copy_or_move_values_in_order, pass the slots from the iterators rather than references to values. This allows for moving from map keys instead of copying for standard layout types.

In the test, fix a couple of ClangTidy warnings from missing includes and calling `new` instead of `make_unique`.

PiperOrigin-RevId: 452062967
Change-Id: I870e89ae1aa5b3cfa62ae6e75b73ffc3d52e731c

1 files changed, 10 insertions, 14 deletions

diff --git a/absl/container/internal/btree.h b/absl/container/internal/btree.h
index cb39b161..79b56e0d 100644
--- a/absl/container/internal/btree.h
+++ b/absl/container/internal/btree.h
@@ -1196,7 +1196,9 @@ class btree_iterator {
   }
 
   const key_type &key() const { return node_->key(position_); }
-  slot_type *slot() { return node_->slot(position_); }
+  decltype(std::declval<Node *>()->slot(0)) slot() {
+    return node_->slot(position_);
+  }
 
   void assert_valid_generation() const {
 #ifdef ABSL_BTREE_ENABLE_GENERATIONS
@@ -1225,7 +1227,6 @@ template <typename Params>
 class btree {
   using node_type = btree_node<Params>;
   using is_key_compare_to = typename Params::is_key_compare_to;
-  using init_type = typename Params::init_type;
   using field_type = typename node_type::field_type;
 
   // We use a static empty node for the root/leftmost/rightmost of empty btrees
@@ -1309,14 +1310,6 @@ class btree {
   using slot_type = typename Params::slot_type;
 
  private:
-  // For use in copy_or_move_values_in_order.
-  const value_type &maybe_move_from_iterator(const_iterator it) { return *it; }
-  value_type &&maybe_move_from_iterator(iterator it) {
-    // This is a destructive operation on the other container so it's safe for
-    // us to const_cast and move from the keys here even if it's a set.
-    return std::move(const_cast<value_type &>(*it));
-  }
-
   // Copies or moves (depending on the template parameter) the values in
   // other into this btree in their order in other. This btree must be empty
   // before this method is called. This method is used in copy construction,
@@ -2063,12 +2056,12 @@ void btree<P>::copy_or_move_values_in_order(Btree &other) {
   // values is the same order we'll store them in.
   auto iter = other.begin();
   if (iter == other.end()) return;
-  insert_multi(maybe_move_from_iterator(iter));
+  insert_multi(iter.slot());
   ++iter;
   for (; iter != other.end(); ++iter) {
     // If the btree is not empty, we can just insert the new value at the end
     // of the tree.
-    internal_emplace(end(), maybe_move_from_iterator(iter));
+    internal_emplace(end(), iter.slot());
   }
 }
 
@@ -2205,8 +2198,11 @@ template <typename P>
 template <typename InputIterator>
 void btree<P>::insert_iterator_unique(InputIterator b, InputIterator e, char) {
   for (; b != e; ++b) {
-    init_type value(*b);
-    insert_hint_unique(end(), params_type::key(value), std::move(value));
+    // Use a node handle to manage a temp slot.
+    auto node_handle =
+        CommonAccess::Construct<node_handle_type>(get_allocator(), *b);
+    slot_type *slot = CommonAccess::GetSlot(node_handle);
+    insert_hint_unique(end(), params_type::key(slot), slot);
   }
 }