Fix bug with num_nodes/num_chunks

eth2/utils/tree_hash/src/cached_tree_hash.rs

@@ -316,7 +316,7 @@ impl TreeHashCache {
                 old_flags,
                 old_overlay.height(),
                 new_overlay.height(),
-                new_overlay.total_chunks(),
+                new_overlay.num_chunks(),
             )
             .ok_or_else(|| Error::UnableToShrinkMerkleTree)?
         };

eth2/utils/tree_hash/src/cached_tree_hash/btree_overlay.rs

@@ -42,6 +42,10 @@ impl BTreeOverlay {
         self.num_leaf_nodes() - self.lengths.len()
     }
 
+    /// Returns the number of nodes in the tree.
+    ///
+    /// Note: this is distinct from `num_chunks`, which returns the total number of chunks in
+    /// this tree.
     pub fn num_nodes(&self) -> usize {
         2 * self.num_leaf_nodes() - 1
     }
@@ -71,7 +75,11 @@ impl BTreeOverlay {
         self.first_node()..self.next_node()
     }
 
-    pub fn total_chunks(&self) -> usize {
+    /// Returns the number of chunks inside this tree (including subtrees).
+    ///
+    /// Note: this is distinct from `num_nodes` which returns the number of nodes in the binary
+    /// tree.
+    pub fn num_chunks(&self) -> usize {
         self.next_node() - self.first_node()
     }
 

eth2/utils/tree_hash/src/cached_tree_hash/impls/vec.rs

@@ -48,7 +48,7 @@ where
                 let mut lengths = vec![];
 
                 for item in self {
-                    lengths.push(BTreeOverlay::new(item, 0, depth)?.num_nodes())
+                    lengths.push(BTreeOverlay::new(item, 0, depth)?.num_chunks())
                 }
 
                 // Disallow zero-length as an empty list still has one all-padding node.
@@ -177,8 +177,6 @@ where
 
         cache.update_internal_nodes(&new_overlay)?;
 
-        dbg!(&new_overlay);
-
         // Mix in length.
         let root_node = new_overlay.root();
         if cache.changed(root_node)? {