Fix failing struct vec vectors

eth2/utils/ssz/src/cached_tree_hash.rs

@@ -145,30 +145,20 @@ impl TreeHashCache {
         })
     }
 
-    pub fn single_chunk_splice<I>(&mut self, chunk: usize, replace_with: I) -> Splice<I::IntoIter>
+    pub fn single_chunk_splice<I>(&mut self, chunk: usize, replace_with: Vec<u8>) {
-    where
+        self.chunk_splice(chunk..chunk + 1, replace_with);
-        I: IntoIterator<Item = u8>,
-    {
-        self.chunk_splice(chunk..chunk + 1, replace_with)
     }
 
-    pub fn chunk_splice<I>(
+    pub fn chunk_splice(&mut self, chunk_range: Range<usize>, replace_with: Vec<u8>) {
-        &mut self,
-        chunk_range: Range<usize>,
-        replace_with: I,
-    ) -> Splice<I::IntoIter>
-    where
-        I: IntoIterator<Item = u8>,
-    {
         let byte_start = chunk_range.start * BYTES_PER_CHUNK;
         let byte_end = chunk_range.end * BYTES_PER_CHUNK;
 
         // Update the `chunk_modified` vec, marking all spliced-in nodes as changed.
         self.chunk_modified.splice(
             chunk_range.clone(),
-            vec![true; chunk_range.end - chunk_range.start],
+            vec![true; replace_with.len() / HASHSIZE],
         );
-        self.cache.splice(byte_start..byte_end, replace_with)
+        self.cache.splice(byte_start..byte_end, replace_with);
     }
 
     pub fn maybe_update_chunk(&mut self, chunk: usize, to: &[u8]) -> Result<(), Error> {

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

@@ -153,7 +153,6 @@ where
                         // The item didn't exist in the old list and doesn't exist in the new list,
                         // nothing to do.
                         (None, None) => {}
-                        _ => panic!("variable sized lists not implemented"),
                     };
                 }
             }

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

@@ -473,9 +473,14 @@ fn test_inner_vec_modifications(original: Vec<Inner>, modified: Vec<Inner>, refe
         full_bytes.append(&mut merkle);
     }
 
+    let num_leaves = leaves.len() / HASHSIZE;
+
     let mut expected = merkleize(leaves);
     expected.splice(3 * HASHSIZE.., full_bytes);
+
+    for _ in num_leaves..num_leaves.next_power_of_two() {
         expected.append(&mut vec![0; HASHSIZE]);
+    }
 
     // Compare the cached tree to the reference tree.
     assert_trees_eq(&expected, &modified_cache);