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, 9 insertions, 0 deletions

diff --git a/absl/container/internal/container_memory.h b/absl/container/internal/container_memory.h
index e67529ec..df492236 100644
--- a/absl/container/internal/container_memory.h
+++ b/absl/container/internal/container_memory.h
@@ -402,6 +402,15 @@ struct map_slot_policy {
     }
   }
 
+  // Construct this slot by copying from another slot.
+  template <class Allocator>
+  static void construct(Allocator* alloc, slot_type* slot,
+                        const slot_type* other) {
+    emplace(slot);
+    absl::allocator_traits<Allocator>::construct(*alloc, &slot->value,
+                                                 other->value);
+  }
+
   template <class Allocator>
   static void destroy(Allocator* alloc, slot_type* slot) {
     if (kMutableKeys::value) {