Add vector type to tree hashing

eth2/types/src/beacon_state.rs

@@ -60,7 +60,7 @@ pub struct BeaconState {
     pub validator_registry_update_epoch: Epoch,
 
     // Randomness and committees
-    pub latest_randao_mixes: Vec<Hash256>,
+    pub latest_randao_mixes: TreeHashVector<Hash256>,
     pub previous_shuffling_start_shard: u64,
     pub current_shuffling_start_shard: u64,
     pub previous_shuffling_epoch: Epoch,
@@ -80,11 +80,11 @@ pub struct BeaconState {
     pub finalized_root: Hash256,
 
     // Recent state
-    pub latest_crosslinks: Vec<Crosslink>,
-    latest_block_roots: Vec<Hash256>,
-    latest_state_roots: Vec<Hash256>,
-    latest_active_index_roots: Vec<Hash256>,
-    latest_slashed_balances: Vec<u64>,
+    pub latest_crosslinks: TreeHashVector<Crosslink>,
+    latest_block_roots: TreeHashVector<Hash256>,
+    latest_state_roots: TreeHashVector<Hash256>,
+    latest_active_index_roots: TreeHashVector<Hash256>,
+    latest_slashed_balances: TreeHashVector<u64>,
     pub latest_block_header: BeaconBlockHeader,
     pub historical_roots: Vec<Hash256>,
 
@@ -139,7 +139,8 @@ impl BeaconState {
             validator_registry_update_epoch: spec.genesis_epoch,
 
             // Randomness and committees
-            latest_randao_mixes: vec![spec.zero_hash; spec.latest_randao_mixes_length as usize],
+            latest_randao_mixes: vec![spec.zero_hash; spec.latest_randao_mixes_length as usize]
+                .into(),
             previous_shuffling_start_shard: spec.genesis_start_shard,
             current_shuffling_start_shard: spec.genesis_start_shard,
             previous_shuffling_epoch: spec.genesis_epoch,
@@ -159,11 +160,12 @@ impl BeaconState {
             finalized_root: spec.zero_hash,
 
             // Recent state
-            latest_crosslinks: vec![initial_crosslink; spec.shard_count as usize],
-            latest_block_roots: vec![spec.zero_hash; spec.slots_per_historical_root],
-            latest_state_roots: vec![spec.zero_hash; spec.slots_per_historical_root],
-            latest_active_index_roots: vec![spec.zero_hash; spec.latest_active_index_roots_length],
-            latest_slashed_balances: vec![0; spec.latest_slashed_exit_length],
+            latest_crosslinks: vec![initial_crosslink; spec.shard_count as usize].into(),
+            latest_block_roots: vec![spec.zero_hash; spec.slots_per_historical_root].into(),
+            latest_state_roots: vec![spec.zero_hash; spec.slots_per_historical_root].into(),
+            latest_active_index_roots: vec![spec.zero_hash; spec.latest_active_index_roots_length]
+                .into(),
+            latest_slashed_balances: vec![0; spec.latest_slashed_exit_length].into(),
             latest_block_header: BeaconBlock::empty(spec).temporary_block_header(spec),
             historical_roots: vec![],
 
@@ -505,7 +507,7 @@ impl BeaconState {
     /// Spec v0.5.0
     pub fn fill_active_index_roots_with(&mut self, index_root: Hash256, spec: &ChainSpec) {
         self.latest_active_index_roots =
-            vec![index_root; spec.latest_active_index_roots_length as usize]
+            vec![index_root; spec.latest_active_index_roots_length as usize].into()
     }
 
     /// Safely obtains the index for latest state roots, given some `slot`.

eth2/types/src/historical_batch.rs

@@ -1,5 +1,5 @@
 use crate::test_utils::TestRandom;
-use crate::Hash256;
+use crate::{Hash256, TreeHashVector};
 use rand::RngCore;
 use serde_derive::{Deserialize, Serialize};
 use ssz_derive::{Decode, Encode};
@@ -11,8 +11,8 @@ use tree_hash_derive::TreeHash;
 /// Spec v0.5.0
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize, Encode, Decode, TreeHash, TestRandom)]
 pub struct HistoricalBatch {
-    pub block_roots: Vec<Hash256>,
-    pub state_roots: Vec<Hash256>,
+    pub block_roots: TreeHashVector<Hash256>,
+    pub state_roots: TreeHashVector<Hash256>,
 }
 
 #[cfg(test)]

eth2/types/src/lib.rs

@@ -27,6 +27,7 @@ pub mod pending_attestation;
 pub mod proposer_slashing;
 pub mod slashable_attestation;
 pub mod transfer;
+pub mod tree_hash_vector;
 pub mod voluntary_exit;
 #[macro_use]
 pub mod slot_epoch_macros;
@@ -65,6 +66,7 @@ pub use crate::slashable_attestation::SlashableAttestation;
 pub use crate::slot_epoch::{Epoch, Slot};
 pub use crate::slot_height::SlotHeight;
 pub use crate::transfer::Transfer;
+pub use crate::tree_hash_vector::TreeHashVector;
 pub use crate::validator::Validator;
 pub use crate::voluntary_exit::VoluntaryExit;
 

eth2/types/src/test_utils/mod.rs

@@ -17,7 +17,10 @@ mod testing_voluntary_exit_builder;
 
 pub use generate_deterministic_keypairs::generate_deterministic_keypairs;
 pub use keypairs_file::KeypairsFile;
-pub use rand::{prng::XorShiftRng, SeedableRng};
+pub use rand::{
+    RngCore,
+    {prng::XorShiftRng, SeedableRng},
+};
 pub use serde_utils::{fork_from_hex_str, u8_from_hex_str};
 pub use test_random::TestRandom;
 pub use testing_attestation_builder::TestingAttestationBuilder;

eth2/types/src/tree_hash_vector.rs

@@ -0,0 +1,82 @@
+use crate::test_utils::{RngCore, TestRandom};
+use serde_derive::{Deserialize, Serialize};
+use ssz::{Decodable, DecodeError, Encodable, SszStream};
+use std::ops::{Deref, DerefMut};
+use tree_hash::TreeHash;
+
+#[derive(Debug, PartialEq, Clone, Serialize, Deserialize)]
+pub struct TreeHashVector<T>(Vec<T>);
+
+impl<T> From<Vec<T>> for TreeHashVector<T> {
+    fn from(vec: Vec<T>) -> TreeHashVector<T> {
+        TreeHashVector(vec)
+    }
+}
+
+impl<T> Into<Vec<T>> for TreeHashVector<T> {
+    fn into(self) -> Vec<T> {
+        self.0
+    }
+}
+
+impl<T> Deref for TreeHashVector<T> {
+    type Target = Vec<T>;
+
+    fn deref(&self) -> &Vec<T> {
+        &self.0
+    }
+}
+
+impl<T> DerefMut for TreeHashVector<T> {
+    fn deref_mut(&mut self) -> &mut Vec<T> {
+        &mut self.0
+    }
+}
+
+impl<T> tree_hash::TreeHash for TreeHashVector<T>
+where
+    T: TreeHash,
+{
+    fn tree_hash_type() -> tree_hash::TreeHashType {
+        tree_hash::TreeHashType::Vector
+    }
+
+    fn tree_hash_packed_encoding(&self) -> Vec<u8> {
+        unreachable!("Vector should never be packed.")
+    }
+
+    fn tree_hash_packing_factor() -> usize {
+        unreachable!("Vector should never be packed.")
+    }
+
+    fn tree_hash_root(&self) -> Vec<u8> {
+        tree_hash::standard_tree_hash::vec_tree_hash_root(self)
+    }
+}
+
+impl<T> Encodable for TreeHashVector<T>
+where
+    T: Encodable,
+{
+    fn ssz_append(&self, s: &mut SszStream) {
+        s.append_vec(self)
+    }
+}
+
+impl<T> Decodable for TreeHashVector<T>
+where
+    T: Decodable,
+{
+    fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError> {
+        ssz::decode_ssz_list(bytes, index).and_then(|(vec, i)| Ok((vec.into(), i)))
+    }
+}
+
+impl<T: RngCore, U> TestRandom<T> for TreeHashVector<U>
+where
+    U: TestRandom<T>,
+{
+    fn random_for_test(rng: &mut T) -> Self {
+        Vec::random_for_test(rng).into()
+    }
+}