diff --git a/rust/hg-core/src/revlog/nodemap.rs b/rust/hg-core/src/revlog/nodemap.rs
--- a/rust/hg-core/src/revlog/nodemap.rs
+++ b/rust/hg-core/src/revlog/nodemap.rs
@@ -15,6 +15,7 @@
 use super::{NodeError, NodePrefix, NodePrefixRef, Revision, RevlogIndex};
 use std::fmt;
 use std::ops::Deref;
+use std::ops::Index;
 
 #[derive(Debug, PartialEq)]
 pub enum NodeMapError {
@@ -152,6 +153,14 @@
     readonly: Box<dyn Deref<Target = [Block]> + Send>,
 }
 
+impl Index<usize> for NodeTree {
+    type Output = Block;
+
+    fn index(&self, i: usize) -> &Block {
+        &self.readonly[i]
+    }
+}
+
 /// Return `None` unless the `Node` for `rev` has given prefix in `index`.
 fn has_prefix_or_none<'p>(
     idx: &impl RevlogIndex,
@@ -170,6 +179,10 @@
 }
 
 impl NodeTree {
+    fn len(&self) -> usize {
+        self.readonly.len()
+    }
+
     /// Main working method for `NodeTree` searches
     ///
     /// This partial implementation lacks
@@ -178,14 +191,14 @@
         &self,
         prefix: NodePrefixRef<'p>,
     ) -> Result<Option<Revision>, NodeMapError> {
-        let blocks: &[Block] = &*self.readonly;
-        if blocks.is_empty() {
+        let len = self.len();
+        if len == 0 {
             return Ok(None);
         }
-        let mut visit = blocks.len() - 1;
+        let mut visit = len - 1;
         for i in 0..prefix.len() {
             let nybble = prefix.get_nybble(i);
-            match blocks[visit].read(nybble) {
+            match self[visit].read(nybble) {
                 Element::None => return Ok(None),
                 Element::Rev(r) => return Ok(Some(r)),
                 Element::Block(idx) => visit = idx,