feat(tree): enhance tree structure with debug traits and new methods

- Add `Debug` implementations for tree-related structs and enums
- Introduce new methods for node manipulation, including `make_internal_node`
- Refactor `Tree::entry` to support key insertion and retrieval
- Improve internal node handling with enhanced parent-child link management
- Add test cases for tree operations and debug output

src/lib.rs

@@ -1,7 +1,12 @@
 #![cfg_attr(not(feature = "std"), no_std)]
 #![cfg_attr(
     feature = "nightly",
-    feature(strict_provenance_atomic_ptr, box_vec_non_null, maybe_uninit_slice)
+    feature(
+        strict_provenance_atomic_ptr,
+        box_vec_non_null,
+        maybe_uninit_slice,
+        debug_closure_helpers
+    )
 )]
 #![cfg_attr(feature = "transposed-option", feature(try_trait_v2))]
 

src/tree.rs

@@ -24,18 +24,29 @@ use core::{
 mod marker {
     use core::marker::PhantomData;
 
+    #[derive(Debug)]
     pub struct LeafOrInternal;
+    #[derive(Debug)]
     pub struct Leaf;
+    #[derive(Debug)]
     pub struct Internal;
 
+    #[derive(Debug)]
     pub struct Edge;
+    #[derive(Debug)]
     pub struct Value;
 
+    #[derive(Debug)]
     pub struct Owned;
+    #[derive(Debug)]
     pub struct Mut<'a>(PhantomData<&'a mut ()>);
+    #[derive(Debug)]
     pub struct ValMut<'a>(PhantomData<&'a mut ()>);
+    #[derive(Debug)]
     pub struct Immut<'a>(PhantomData<&'a ()>);
+    #[derive(Debug)]
     pub struct Dying;
+    #[derive(Debug)]
     pub struct DormantMut;
 
     pub trait BorrowType {
@@ -55,13 +66,15 @@ mod marker {
 
 const CAPACITY: usize = 16;
 
+#[derive(Debug)]
 struct LeafNode<K, V> {
     parent: Option<NonNull<InternalNode<K, V>>>,
     parent_idx: MaybeUninit<u16>,
-    value: Option<MaybeUninit<V>>,
+    value: Option<V>,
     leaf: bool,
 }
 
+#[derive(Debug)]
 struct InternalNode<K, V> {
     data: LeafNode<K, V>,
     next: Option<NonNull<InternalNode<K, V>>>,
@@ -72,11 +85,13 @@ struct InternalNode<K, V> {
 
 type BoxedNode<K, V> = NonNull<LeafNode<K, V>>;
 
+#[derive(Debug)]
 struct NodeRef<BorrowType, K, V, Type> {
     node: NonNull<LeafNode<K, V>>,
     _marker: PhantomData<(BorrowType, Type)>,
 }
 
+#[derive(Debug)]
 struct Handle<Node, Type> {
     node: Node,
     idx: usize,
@@ -140,6 +155,7 @@ impl<K, V> InternalNode<K, V> {
     unsafe fn init(this: *mut Self) {
         unsafe {
             LeafNode::init(&raw mut (*this).data);
+            (&raw mut (*this).data.leaf).write(false);
             (&raw mut (*this).next).write(None);
             (&raw mut (*this).len).write(0);
             // keys and edges may be left uninitialized
@@ -150,6 +166,7 @@ impl<K, V> InternalNode<K, V> {
         let mut uninit: Box<MaybeUninit<LeafNode<K, V>>> = unsafe { core::mem::transmute(leaf) };
         unsafe {
             core::ptr::swap(&raw mut (*this).data, uninit.as_mut_ptr());
+            (&raw mut (*this).data.leaf).write(false);
             (&raw mut (*this).next).write(None);
             (&raw mut (*this).len).write(1);
         }
@@ -183,11 +200,15 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::Leaf> {
 }
 
 impl<K, V> NodeRef<marker::Owned, K, V, marker::Internal> {
-    fn new_internal(child: Root<K, V>) -> Self {
+    fn new_internal_with_child(child: Root<K, V>) -> Self {
         let mut node = InternalNode::new();
         node.edges[0].write(child.node);
 
-        // SAFETY: `height` isn't zero
+        unsafe { NodeRef::from_new_internal(node) }
+    }
+
+    fn new_internal() -> Self {
+        let node = InternalNode::new();
         unsafe { NodeRef::from_new_internal(node) }
     }
 
@@ -199,7 +220,6 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::Internal> {
             node,
             _marker: PhantomData,
         };
-        this.borrow_mut().correct_all_childrens_parent_links();
         this
     }
 }
@@ -295,41 +315,34 @@ impl<BorrowType: marker::BorrowType, K, V>
     }
 }
 
-impl<'a, K, V> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, marker::Edge> {
-    /// Fixes the parent pointer and index in the child node that this edge
-    /// links to. This is useful when the ordering of edges has been changed,
-    fn correct_parent_link(self) {
-        // Create backpointer without invalidating other references to the node.
-        let ptr = unsafe { NonNull::new_unchecked(NodeRef::as_internal_ptr(&self.node)) };
-        let idx = self.idx;
-        let mut child = self.descend();
-        child.set_parent_link(ptr, idx);
-    }
-}
-
-impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
-    /// Sets the node's link to its parent edge,
-    /// without invalidating other references to the node.
-    fn set_parent_link(&mut self, parent: NonNull<InternalNode<K, V>>, parent_idx: usize) {
-        let leaf = Self::as_leaf_ptr(self);
-        unsafe { (*leaf).parent = Some(parent) };
-        unsafe { (*leaf).parent_idx.write(parent_idx as u16) };
-    }
-}
-
-impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
-    /// # Safety
-    /// Every item returned by `range` is a valid edge index for the node.
-    unsafe fn correct_childrens_parent_links<R: Iterator<Item = usize>>(&mut self, range: R) {
-        for i in range {
-            debug_assert!(i <= self.len());
-            unsafe { Handle::new_edge(self.reborrow_mut(), i) }.correct_parent_link();
+impl<'a, K, V, NodeType, HandleType> Handle<NodeRef<marker::Mut<'a>, K, V, NodeType>, HandleType> {
+    /// Temporarily takes out another mutable handle on the same location. Beware, as
+    /// this method is very dangerous, doubly so since it might not immediately appear
+    /// dangerous.
+    ///
+    /// For details, see `NodeRef::reborrow_mut`.
+    pub(super) unsafe fn reborrow_mut(
+        &mut self,
+    ) -> Handle<NodeRef<marker::Mut<'_>, K, V, NodeType>, HandleType> {
+        // We can't use Handle::new_kv or Handle::new_edge because we don't know our type
+        Handle {
+            node: unsafe { self.node.reborrow_mut() },
+            idx: self.idx,
+            _marker: PhantomData,
         }
     }
 
-    fn correct_all_childrens_parent_links(&mut self) {
-        let len = self.len();
-        unsafe { self.correct_childrens_parent_links(0..=len) };
+    /// Returns a dormant copy of this handle which can be reawakened later.
+    ///
+    /// See `DormantMutRef` for more details.
+    pub(super) fn dormant(
+        &self,
+    ) -> Handle<NodeRef<marker::DormantMut, K, V, NodeType>, HandleType> {
+        Handle {
+            node: self.node.dormant(),
+            idx: self.idx,
+            _marker: PhantomData,
+        }
     }
 }
 
@@ -341,6 +354,11 @@ impl<BorrowType, K, V> NodeRef<BorrowType, K, V, marker::Internal> {
         // SAFETY: the static node type is `Internal`.
         this.node.as_ptr() as *mut InternalNode<K, V>
     }
+
+    fn as_internal_non_null(this: &Self) -> NonNull<InternalNode<K, V>> {
+        // SAFETY: the static node type is `Internal`.
+        unsafe { NonNull::new_unchecked(Self::as_internal_ptr(this)) }
+    }
 }
 
 impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
@@ -349,6 +367,19 @@ impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
         let ptr = Self::as_internal_ptr(self);
         unsafe { &mut *ptr }
     }
+
+    pub(super) fn len_mut(&mut self) -> &mut u16 {
+        // SAFETY: we have exclusive access to the entire node.
+        unsafe { &mut (*Self::as_internal_ptr(self)).len }
+    }
+
+    pub(super) fn next_mut(&mut self) -> Option<NodeRef<marker::Mut<'a>, K, V, marker::Internal>> {
+        let internal = self.as_internal_mut();
+        internal.next.map(|next| NodeRef {
+            node: next.cast(),
+            _marker: PhantomData,
+        })
+    }
 }
 
 impl<K, V, Type> NodeRef<marker::Owned, K, V, Type> {
@@ -422,6 +453,46 @@ impl<'a, K, V, Type> NodeRef<marker::Mut<'a>, K, V, Type> {
     }
 }
 
+impl<'a, K: 'a, V: 'a> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
+    /// Borrows exclusive access to an element of the key storage area.
+    ///
+    /// # Safety
+    /// `index` is in bounds of 0..CAPACITY
+    unsafe fn key_area_mut<I, Output: ?Sized>(&mut self, index: I) -> &mut Output
+    where
+        I: core::slice::SliceIndex<[MaybeUninit<K>], Output = Output>,
+    {
+        // SAFETY: the caller will not be able to call further methods on self
+        // until the key slice reference is dropped, as we have unique access
+        // for the lifetime of the borrow.
+        unsafe {
+            self.as_internal_mut()
+                .keys
+                .as_mut_slice()
+                .get_unchecked_mut(index)
+        }
+    }
+
+    /// Borrows exclusive access to an element or slice of the node's value storage area.
+    ///
+    /// # Safety
+    /// `index` is in bounds of 0..CAPACITY
+    unsafe fn edge_area_mut<I, Output: ?Sized>(&mut self, index: I) -> &mut Output
+    where
+        I: core::slice::SliceIndex<[MaybeUninit<BoxedNode<K, V>>], Output = Output>,
+    {
+        // SAFETY: the caller will not be able to call further methods on self
+        // until the value slice reference is dropped, as we have unique access
+        // for the lifetime of the borrow.
+        unsafe {
+            self.as_internal_mut()
+                .edges
+                .as_mut_slice()
+                .get_unchecked_mut(index)
+        }
+    }
+}
+
 impl<K, V, Type> NodeRef<marker::DormantMut, K, V, Type> {
     /// Revert to the unique borrow initially captured.
     ///
@@ -492,13 +563,6 @@ impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
 }
 
 impl<'a, K: 'a, V: 'a> NodeRef<marker::Immut<'a>, K, V, marker::Internal> {
-    /// Exposes the leaf portion of any leaf or internal node in an immutable tree.
-    fn into_leaf(self) -> &'a LeafNode<K, V> {
-        let ptr = Self::as_leaf_ptr(&self);
-        // SAFETY: there can be no mutable references into this tree borrowed as `Immut`.
-        unsafe { &*ptr }
-    }
-
     fn into_internal(self) -> &'a InternalNode<K, V> {
         // SAFETY: the static node type is `Internal`.
         unsafe { &*Self::as_internal_ptr(&self) }
@@ -514,6 +578,24 @@ impl<'a, K: 'a, V: 'a> NodeRef<marker::Immut<'a>, K, V, marker::Internal> {
                 .assume_init_ref()
         }
     }
+
+    pub(super) fn edges(&self) -> &[BoxedNode<K, V>] {
+        let internal = self.into_internal();
+        unsafe {
+            internal
+                .edges
+                .get_unchecked(..usize::from(internal.len + 1))
+                .assume_init_ref()
+        }
+    }
+
+    pub(super) fn next(&self) -> Option<NodeRef<marker::Immut<'a>, K, V, marker::Internal>> {
+        let internal = self.into_internal();
+        internal.next.map(|next| NodeRef {
+            node: next.cast(),
+            _marker: PhantomData,
+        })
+    }
 }
 
 impl<BorrowType, K, V, NodeType, HandleType>
@@ -545,11 +627,35 @@ impl<'a, K: 'a, V: 'a, NodeType> Handle<NodeRef<marker::Immut<'a>, K, V, NodeTyp
     /// SAFETY: the caller must ensure that `idx < node.len()`
     pub(super) unsafe fn into_value(self) -> &'a V {
         let leaf = self.node.into_leaf();
-        let v = unsafe { leaf.value.as_ref().unwrap().assume_init_ref() };
+        let v = leaf.value.as_ref().unwrap();
         v
     }
 }
 
+impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Edge> {
+    pub(super) fn forget_node_type(
+        self,
+    ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::Edge> {
+        unsafe { Handle::new_edge(self.node.forget_type(), self.idx) }
+    }
+}
+
+impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Internal>, marker::Edge> {
+    pub(super) fn forget_node_type(
+        self,
+    ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::Edge> {
+        unsafe { Handle::new_edge(self.node.forget_type(), self.idx) }
+    }
+}
+
+impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::Leaf>, marker::Value> {
+    pub(super) fn forget_node_type(
+        self,
+    ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::Value> {
+        unsafe { Handle::new_value(self.node.forget_type()) }
+    }
+}
+
 pub(super) enum ForceResult<Leaf, Internal> {
     Leaf(Leaf),
     Internal(Internal),
@@ -629,6 +735,50 @@ impl<BorrowType, K, V, Type> NodeRef<BorrowType, K, V, Type> {
     }
 }
 
+impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::Leaf> {
+    /// node must have parent/ be a leaf node.
+    pub(super) unsafe fn make_internal_node(
+        self,
+    ) -> NodeRef<marker::Mut<'a>, K, V, marker::Internal> {
+        let leaf = self.node;
+
+        let mut parent = self.ascend().ok().unwrap();
+        let internal = Box::into_non_null(InternalNode::new_with_leaf(unsafe {
+            Box::from_non_null(leaf)
+        }))
+        .cast();
+
+        parent.node.as_internal_mut().edges[parent.idx].write(internal);
+
+        NodeRef {
+            node: internal,
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<'a, K, V, Type> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, Type> {
+    /// node must have parent/ be a leaf node.
+    pub(super) unsafe fn make_internal_node(
+        self,
+    ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Internal>, Type> {
+        Handle {
+            node: unsafe { self.node.make_internal_node() },
+            idx: self.idx,
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<BorrowType, K, V> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::Edge> {
+    /// Converts this edge handle into a value handle.
+    pub(super) fn into_value(
+        self,
+    ) -> Handle<NodeRef<BorrowType, K, V, marker::LeafOrInternal>, marker::Value> {
+        unsafe { Handle::new_value(self.node) }
+    }
+}
+
 impl<'a, K, V> NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal> {
     /// Unsafely asserts to the compiler the static information that this node is a `Leaf`.
     pub(super) unsafe fn cast_to_leaf_unchecked(
@@ -653,22 +803,89 @@ impl<'a, K: 'a, V: 'a, Type> Handle<NodeRef<marker::Mut<'a>, K, V, Type>, marker
     /// Inserts a key-value pair into
     pub(super) unsafe fn insert_recursing<Q>(
         mut self,
-        mut key: Q,
+        mut key_seq: Q,
         val: V,
-    ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, marker::Value>
+    ) -> Handle<NodeRef<marker::Mut<'a>, K, V, marker::LeafOrInternal>, marker::Value>
     where
         Q: Iterator<Item = K>,
         K: Ord,
     {
+        let Some(key) = key_seq.next() else {
+            // key has run out: insert value here.
+            self.node.as_leaf_mut().value = Some(val);
+            // TODO: handle occupied values.
+            return unsafe { Handle::new_value(self.node.as_leaf_or_internal()) };
+        };
+
         let idx = self.idx;
-        match unsafe { self.force() } {
+        let mut internal = match self.force() {
             ForceResult::Leaf(leaf) => {
                 // need to turn the leaf into an internal node.
-            }
-            ForceResult::Internal(internal) => todo!(),
-        }
 
-        todo!()
+                // SAFETY: root is allocated as an internal node.
+                // the only node that doesn't have a parent is the root node,
+                // all parent nodes are internal nodes.
+                let internal = unsafe { leaf.make_internal_node() };
+
+                internal
+            }
+            ForceResult::Internal(mut internal) => {
+                if idx >= CAPACITY {
+                    // create a sibling node
+                    let mut sibling = NodeRef::new_internal();
+                    let mut sibling = sibling.borrow_mut();
+                    // let sibling = Box::into_non_null(InternalNode::new());
+                    // set parent link
+                    unsafe {
+                        core::ptr::copy_nonoverlapping(
+                            &raw mut internal.node.as_leaf_mut().parent,
+                            &raw mut sibling.as_leaf_mut().parent,
+                            1,
+                        );
+                        core::ptr::copy_nonoverlapping(
+                            &raw mut internal.node.as_leaf_mut().parent_idx,
+                            &raw mut sibling.as_leaf_mut().parent_idx,
+                            1,
+                        );
+                    }
+
+                    internal.node.as_internal_mut().next =
+                        Some(NodeRef::as_internal_non_null(&sibling));
+
+                    unsafe { Handle::new_edge(sibling.dormant(), 0).awaken() }
+                } else {
+                    internal
+                }
+            }
+        };
+
+        let last = unsafe {
+            let mut child = NodeRef::new_leaf();
+
+            // set parent link
+            child.borrow_mut().as_leaf_mut().parent =
+                Some(NodeRef::as_internal_non_null(&internal.node));
+            child
+                .borrow_mut()
+                .as_leaf_mut()
+                .parent_idx
+                .write(internal.idx as u16);
+
+            let new_len = internal.node.len() + 1;
+
+            slice_insert(internal.node.key_area_mut(..new_len), internal.idx, key);
+            slice_insert(
+                internal.node.edge_area_mut(..new_len),
+                internal.idx,
+                child.node,
+            );
+            *internal.node.len_mut() = new_len as u16;
+
+            let child = Handle::new_edge(child.borrow_mut(), 0);
+            child.insert_recursing(key_seq, val).dormant()
+        };
+
+        unsafe { last.awaken() }
     }
 }
 
@@ -697,7 +914,7 @@ mod search {
     }
 
     impl<BorrowType: marker::BorrowType, K, V> NodeRef<BorrowType, K, V, marker::LeafOrInternal> {
-        fn search_tree<Q>(
+        pub(super) fn search_tree<Q>(
             mut self,
             mut key: Q,
         ) -> SearchResult<BorrowType, K, V, marker::LeafOrInternal, marker::Leaf>
@@ -774,24 +991,51 @@ mod search {
             {
                 match key.cmp(k.borrow()) {
                     Ordering::Greater => {}
-                    Ordering::Equal => return IndexResult::Edge(start_index + offset),
-                    Ordering::Less => return IndexResult::Insert(start_index + offset),
+                    Ordering::Equal => {
+                        std::eprintln!("found key at index {}", start_index + offset);
+                        return IndexResult::Edge(start_index + offset);
+                    }
+                    Ordering::Less => {
+                        std::eprintln!("insert key at index {}", start_index + offset);
+                        return IndexResult::Insert(start_index + offset);
+                    }
                 }
             }
 
+            std::eprintln!("insert key at index {}", keys.len());
             IndexResult::Insert(keys.len())
         }
     }
 
     #[cfg(test)]
     mod tests {
+        use super::super::Tree;
         use super::*;
 
-        fn build_test_node() {
-            let mut root = NodeRef::<marker::Owned, char, u32, _>::new_leaf();
+        #[test]
+        fn asdf() {
+            let mut tree = Tree::new();
+            let entry = tree.entry("+".chars());
+            std::dbg!(&entry);
+            entry.or_insert("Plus");
 
-            let root_mut = root.borrow_mut();
-            // root_mut.as_leaf_mut().
+            let entry = tree.entry("++".chars());
+            std::dbg!(&entry);
+            entry.or_insert("PlusPlus");
+
+            let entry = tree.entry("+=".chars());
+            std::dbg!(&entry);
+            entry.or_insert("PlusEqual");
+
+            std::dbg!(tree.entry("++".chars()));
+
+            std::eprintln!("tree: {:?}", &tree);
+
+            assert_eq!(
+                tree.entry("++".chars()).or_insert("asdf").get(),
+                &"PlusPlus"
+            );
+            assert_eq!(tree.entry("+".chars()).or_insert("asdf").get(), &"Plus");
         }
     }
 }
@@ -809,6 +1053,41 @@ mod entry {
         Occupied(OccupiedEntry<'a, K, V>),
     }
 
+    use core::fmt::Debug;
+
+    impl<Q: Debug, K: Debug, V: Debug> Debug for Entry<'_, Q, K, V>
+    where
+        Q: Iterator<Item = K>,
+    {
+        fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+            match self {
+                Entry::Vacant(vacant) => write!(f, "Vacant({:?})", vacant),
+                Entry::Occupied(occupied) => write!(f, "Occupied({:?})", occupied),
+            }
+        }
+    }
+
+    impl<Q: Debug, K: Debug, V: Debug> Debug for VacantEntry<'_, Q, K, V>
+    where
+        Q: Iterator<Item = K>,
+    {
+        fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+            f.debug_struct("VacantEntry")
+                .field("key", &self.key)
+                .field("handle", &self.handle)
+                .finish()
+        }
+    }
+
+    impl<K: Debug, V: Debug> Debug for OccupiedEntry<'_, K, V> {
+        fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+            f.debug_struct("OccupiedEntry")
+                .field("value", &self.get())
+                .field("handle", &self.handle)
+                .finish()
+        }
+    }
+
     pub struct VacantEntry<'a, Q, K, V>
     where
         Q: Iterator<Item = K>,
@@ -827,9 +1106,21 @@ mod entry {
         pub(super) _marker: PhantomData<&'a mut (K, V)>,
     }
 
-    impl<'a, K: Ord, V> OccupiedEntry<'a, K, V> {
-        pub fn key(&self) -> Option<&K> {
-            unsafe { self.handle.reborrow().into_kv().0 }
+    impl<'a, K, V> OccupiedEntry<'a, K, V> {
+        pub fn get(&self) -> &V {
+            unsafe { self.handle.reborrow().into_value() }
+        }
+    }
+
+    impl<'a, Q, K: Ord, V> Entry<'a, Q, K, V>
+    where
+        Q: Iterator<Item = K>,
+    {
+        pub fn or_insert(self, value: V) -> OccupiedEntry<'a, K, V> {
+            match self {
+                Entry::Vacant(vacant) => vacant.insert_entry(value),
+                Entry::Occupied(occupied) => occupied,
+            }
         }
     }
 
@@ -837,16 +1128,25 @@ mod entry {
     where
         Q: Iterator<Item = K>,
     {
-        pub fn insert(self, value: V) -> OccupiedEntry<'a, K, V> {
+        pub fn insert_entry(mut self, value: V) -> OccupiedEntry<'a, K, V> {
             let handle = match self.handle {
                 // no root node yet
                 None => {
-                    unimplemented!()
+                    let tree = unsafe { self.dormant_map.reborrow() };
+                    let root = tree.root.insert(NodeRef::new_internal());
+
+                    unsafe {
+                        Handle::new_edge(root.borrow_mut(), 0).insert_recursing(self.key, value)
+                    }
                 }
-                Some(handle) => {}
+                Some(handle) => unsafe { handle.insert_recursing(self.key, value) },
             };
 
-            todo!()
+            OccupiedEntry {
+                handle,
+                dormant_map: self.dormant_map,
+                _marker: PhantomData,
+            }
         }
     }
 }
@@ -925,13 +1225,71 @@ mod borrow {
     }
 }
 
-type Root<K, V> = NodeRef<marker::Owned, K, V, marker::LeafOrInternal>;
+type Root<K, V> = NodeRef<marker::Owned, K, V, marker::Internal>;
 
 struct Tree<K, V> {
     root: Option<Root<K, V>>,
     _marker: PhantomData<alloc::boxed::Box<(K, V)>>,
 }
 
+impl<'a, K: core::fmt::Debug + 'a, V: core::fmt::Debug + 'a> core::fmt::Debug for &'a Tree<K, V> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        let mut map = f.debug_map();
+
+        fn format_node_ref<'a, K: 'a, V: 'a>(
+            f: &mut core::fmt::Formatter<'_>,
+            node: &NodeRef<marker::Immut<'a>, K, V, marker::LeafOrInternal>,
+        ) -> core::fmt::Result
+        where
+            K: core::fmt::Debug,
+            V: core::fmt::Debug,
+        {
+            match node.force() {
+                ForceResult::Leaf(leaf) => f
+                    .debug_struct("Leaf")
+                    .field("value", &leaf.into_leaf().value)
+                    .finish(),
+                ForceResult::Internal(internal) => f
+                    .debug_struct("Internal")
+                    .field("value", &internal.into_leaf().value)
+                    .field_with("edges", |f| {
+                        let mut list = f.debug_list();
+                        for (key, edge) in internal.keys().iter().zip(internal.edges()) {
+                            list.entry_with(|f| {
+                                f.debug_set()
+                                    .entry(key)
+                                    .entry_with(|f| {
+                                        format_node_ref(
+                                            f,
+                                            &NodeRef {
+                                                node: *edge,
+                                                _marker: PhantomData,
+                                            },
+                                        )
+                                    })
+                                    .finish()
+                            });
+                        }
+                        list.finish()
+                    })
+                    .finish(),
+            }
+        }
+
+        match self.root {
+            Some(ref root) => {
+                map.key(&"root").value_with(|f| {
+                    let internal = root.reborrow();
+                    format_node_ref(f, &internal.as_leaf_or_internal())
+                });
+
+                map.finish()
+            }
+            None => map.finish(),
+        }
+    }
+}
+
 impl<K, V> Tree<K, V> {
     pub fn new() -> Self {
         Self {
@@ -941,6 +1299,141 @@ impl<K, V> Tree<K, V> {
     }
 }
 
+#[derive(Debug)]
+pub struct OnceAndIter<I, T>
+where
+    I: Iterator<Item = T>,
+{
+    once: Option<T>,
+    iter: I,
+}
+
+impl<I, T> Iterator for OnceAndIter<I, T>
+where
+    I: Iterator<Item = T>,
+{
+    type Item = T;
+
+    fn next(&mut self) -> Option<T> {
+        if let Some(once) = self.once.take() {
+            Some(once)
+        } else {
+            self.iter.next()
+        }
+    }
+}
+
+impl<I> From<I> for OnceAndIter<I, I::Item>
+where
+    I: Iterator,
+{
+    fn from(iter: I) -> Self {
+        Self { once: None, iter }
+    }
+}
+
+impl<I, T> OnceAndIter<I, T>
+where
+    I: Iterator<Item = T>,
+{
+    pub fn once(once: T, iter: I) -> Self {
+        Self {
+            once: Some(once),
+            iter,
+        }
+    }
+}
+
+impl<K, V> Tree<K, V>
+where
+    K: Ord,
+{
+    // pub fn closest_entry<Q>(
+    //     &mut self,
+    //     mut key_seq: Q,
+    // ) -> Option<entry::Entry<OnceAndIter<Q, K>, K, V>>
+    // where
+    //     Q: Iterator<Item = K>,
+    // {
+    //     use borrow::DormantMutRef;
+    //     use entry::Entry;
+
+    //     let (tree, dormant) = DormantMutRef::new(self);
+
+    //     match tree.root {
+    //         None => None,
+    //         Some(ref mut root) => match root.borrow_mut().forget_type().search_tree(&mut key_seq) {
+    //             search::SearchResult::Found(handle) => {
+    //                 Some(Entry::Occupied(entry::OccupiedEntry {
+    //                     handle,
+    //                     dormant_map: dormant,
+    //                     _marker: PhantomData,
+    //                 }))
+    //             }
+    //             search::SearchResult::GoDown(handle) => match key_seq.next() {
+    //                 None => Some(Entry::Occupied(entry::OccupiedEntry {
+    //                     handle: handle.forget_node_type().into_value(),
+    //                     dormant_map: dormant,
+    //                     _marker: PhantomData,
+    //                 })),
+    //                 Some(key) => Some(Entry::Vacant(entry::VacantEntry {
+    //                     key: OnceAndIter::once(key, key_seq),
+    //                     handle: Some(handle.forget_node_type()),
+    //                     dormant_map: dormant,
+    //                     _marker: PhantomData,
+    //                 })),
+    //             },
+    //             search::SearchResult::Insert(key, handle) => {
+    //                 Some(Entry::Vacant(entry::VacantEntry {
+    //                     key: OnceAndIter::once(key, key_seq),
+    //                     handle: Some(handle),
+    //                     dormant_map: dormant,
+    //                     _marker: PhantomData,
+    //                 }))
+    //             }
+    //         },
+    //     }
+    // }
+
+    pub fn entry<Q>(&'_ mut self, mut key_seq: Q) -> entry::Entry<'_, OnceAndIter<Q, K>, K, V>
+    where
+        Q: Iterator<Item = K>,
+    {
+        use borrow::DormantMutRef;
+        use entry::{Entry::*, OccupiedEntry, VacantEntry};
+
+        let (tree, dormant) = DormantMutRef::new(self);
+
+        match tree.root {
+            None => Vacant(VacantEntry {
+                key: key_seq.into(),
+                handle: None,
+                dormant_map: dormant,
+                _marker: PhantomData,
+            }),
+            Some(ref mut root) => match root.borrow_mut().forget_type().search_tree(&mut key_seq) {
+                search::SearchResult::Found(handle) => Occupied(OccupiedEntry {
+                    handle,
+                    dormant_map: dormant,
+                    _marker: PhantomData,
+                }),
+                search::SearchResult::GoDown(handle) => Vacant(VacantEntry {
+                    key: key_seq.into(),
+                    handle: Some(handle.forget_node_type()),
+                    dormant_map: dormant,
+                    _marker: PhantomData,
+                }),
+                search::SearchResult::Insert(key, handle) => Vacant(VacantEntry {
+                    key: OnceAndIter::once(key, key_seq),
+                    handle: Some(handle),
+                    dormant_map: dormant,
+                    _marker: PhantomData,
+                }),
+            },
+        }
+    }
+}
+
 unsafe fn slice_insert<T>(slice: &mut [MaybeUninit<T>], idx: usize, value: T) {
     unsafe {
         let len = slice.len();