Add failing test for grow merkle tree

eth2/utils/ssz/src/cached_tree_hash.rs

@@ -16,6 +16,8 @@ pub enum Error {
     ShouldNotProduceOffsetHandler,
     NoFirstNode,
     NoBytesForRoot,
+    UnableToObtainSlices,
+    UnableToGrowMerkleTree,
     BytesAreNotEvenChunks(usize),
     NoModifiedFieldForChunk(usize),
     NoBytesForChunk(usize),
@@ -74,6 +76,13 @@ impl TreeHashCache {
         item.build_tree_hash_cache()
     }
 
+    pub fn from_elems(cache: Vec<u8>, chunk_modified: Vec<bool>) -> Self {
+        Self {
+            cache,
+            chunk_modified,
+        }
+    }
+
     pub fn from_leaves_and_subtrees<T>(
         item: &T,
         leaves_and_subtrees: Vec<Self>,
@@ -149,7 +158,7 @@ impl TreeHashCache {
         // Update the `chunk_modified` vec, marking all spliced-in nodes as changed.
         self.chunk_modified.splice(chunk_range.clone(), bools);
         self.cache
-            .splice(node_range_to_byte_range(chunk_range), bytes);
+            .splice(node_range_to_byte_range(&chunk_range), bytes);
     }
 
     pub fn maybe_update_chunk(&mut self, chunk: usize, to: &[u8]) -> Result<(), Error> {
@@ -167,6 +176,13 @@ impl TreeHashCache {
         Ok(())
     }
 
+    pub fn slices(&self, chunk_range: Range<usize>) -> Option<(&[u8], &[bool])> {
+        Some((
+            self.cache.get(node_range_to_byte_range(&chunk_range))?,
+            self.chunk_modified.get(chunk_range)?,
+        ))
+    }
+
     pub fn modify_chunk(&mut self, chunk: usize, to: &[u8]) -> Result<(), Error> {
         let start = chunk * BYTES_PER_CHUNK;
         let end = start + BYTES_PER_CHUNK;
@@ -231,7 +247,7 @@ fn num_nodes(num_leaves: usize) -> usize {
     2 * num_leaves - 1
 }
 
-fn node_range_to_byte_range(node_range: Range<usize>) -> Range<usize> {
+fn node_range_to_byte_range(node_range: &Range<usize>) -> Range<usize> {
     node_range.start * HASHSIZE..node_range.end * HASHSIZE
 }
 
@@ -281,6 +297,10 @@ impl OffsetHandler {
         })
     }
 
+    pub fn node_range(&self) -> Result<Range<usize>, Error> {
+        Ok(*self.offsets.first().ok_or_else(|| Error::NoFirstNode)?..self.next_node())
+    }
+
     pub fn total_nodes(&self) -> usize {
         self.num_internal_nodes + self.num_leaf_nodes
     }

eth2/utils/ssz/src/cached_tree_hash/impls.rs

@@ -113,9 +113,27 @@ where
     ) -> Result<usize, Error> {
         let offset_handler = OffsetHandler::new(self, chunk)?;
 
-        if other.len().next_power_of_two() > self.len().next_power_of_two() {
+        if self.len().next_power_of_two() > other.len().next_power_of_two() {
-            //
+            // Get slices of the exsiting tree from the cache.
-        } else if other.len().next_power_of_two() < self.len().next_power_of_two() {
+            let (old_bytes, old_flags) = cache
+                .slices(offset_handler.node_range()?)
+                .ok_or_else(|| Error::UnableToObtainSlices)?;
+
+            // From the existing slices build new, expanded Vecs.
+            let (new_bytes, new_flags) = grow_merkle_cache(
+                old_bytes,
+                old_flags,
+                other.len().next_power_of_two().leading_zeros() as usize,
+                self.len().next_power_of_two().leading_zeros() as usize,
+            ).ok_or_else(|| Error::UnableToGrowMerkleTree)?;
+
+            // Create a `TreeHashCache` from the raw elements.
+            let expanded_cache = TreeHashCache::from_elems(new_bytes, new_flags);
+
+            // Splice the newly created `TreeHashCache` over the existing, smaller elements.
+            cache.splice(offset_handler.node_range()?, expanded_cache);
+        //
+        } else if self.len().next_power_of_two() < other.len().next_power_of_two() {
             panic!("shrinking below power of two is not implemented")
         }
 

eth2/utils/ssz/src/cached_tree_hash/tests.rs

@@ -408,7 +408,6 @@ fn extended_u64_vec_len_within_pow_2_boundary() {
     test_u64_vec_modifications(original_vec, modified_vec);
 }
 
-/*
 #[test]
 fn extended_u64_vec_len_outside_pow_2_boundary() {
     let original_vec: Vec<u64> = (0..2_u64.pow(5)).collect();
@@ -417,7 +416,6 @@ fn extended_u64_vec_len_outside_pow_2_boundary() {
 
     test_u64_vec_modifications(original_vec, modified_vec);
 }
-*/
 
 #[test]
 fn large_vec_of_u64_builds() {