Use Merkle Tree instead of Merkle Patricia Tree for execution trace

Fixes #236 (comment)

crates/sp-executor/src/lib.rs

@@ -25,7 +25,7 @@ use sp_runtime::traits::{BlakeTwo256, Hash as HashT};
 use sp_runtime::{OpaqueExtrinsic, RuntimeDebug};
 use sp_std::vec::Vec;
 use sp_trie::StorageProof;
-use subspace_core_primitives::Randomness;
+use subspace_core_primitives::{Randomness, Sha256Hash};
 use subspace_runtime_primitives::AccountId;
 
 /// Header of transaction bundle.
@@ -103,7 +103,7 @@ pub struct ExecutionReceipt<Hash> {
     /// List of storage roots collected during the block execution.
     pub trace: Vec<Hash>,
     /// The merkle root of `trace`.
-    pub trace_root: H256,
+    pub trace_root: Sha256Hash,
 }
 
 impl<Hash: Encode> ExecutionReceipt<Hash> {

cumulus/client/cirrus-executor/Cargo.toml

@@ -30,7 +30,9 @@ futures = { version = "0.3.19", features = ["compat"] }
 futures-timer = "3.0.1"
 rand = "0.8.4"
 rand_chacha = "0.3.1"
+merkletree = "0.21.0"
 parking_lot = "0.12.0"
+sha2 = "0.10.0"
 tracing = "0.1.25"
 thiserror = "1.0.29"
 tokio = "1.10"

cumulus/client/cirrus-executor/src/lib.rs

@@ -19,6 +19,7 @@
 
 mod aux_schema;
 mod bundler;
+mod merkle_tree;
 mod processor;
 
 use sc_client_api::{AuxStore, BlockBackend};

cumulus/client/cirrus-executor/src/merkle_tree.rs

@@ -0,0 +1,43 @@
+use merkletree::hash::Algorithm;
+use sha2::{Digest, Sha256};
+use std::hash::Hasher;
+use subspace_core_primitives::Sha256Hash;
+
+#[derive(Default, Clone)]
+pub(super) struct Sha256Algorithm(Sha256);
+
+impl Hasher for Sha256Algorithm {
+	#[inline]
+	fn write(&mut self, msg: &[u8]) {
+		self.0.update(msg);
+	}
+
+	#[inline]
+	fn finish(&self) -> u64 {
+		unimplemented!()
+	}
+}
+
+impl Algorithm<Sha256Hash> for Sha256Algorithm {
+	#[inline]
+	fn hash(&mut self) -> Sha256Hash {
+		self.0
+			.clone()
+			.finalize()
+			.as_slice()
+			.try_into()
+			.expect("Sha256 output is always 32 bytes; qed")
+	}
+
+	#[inline]
+	fn reset(&mut self) {
+		self.0.reset();
+	}
+}
+
+/// Merkle tree type for execution trace.
+pub(super) type MerkleTree = merkletree::merkle::MerkleTree<
+	Sha256Hash,
+	Sha256Algorithm,
+	merkletree::store::VecStore<Sha256Hash>,
+>;

cumulus/client/cirrus-executor/src/processor.rs

@@ -9,7 +9,7 @@ use sp_consensus::BlockOrigin;
 use sp_inherents::{CreateInherentDataProviders, InherentData, InherentDataProvider};
 use sp_runtime::{
 	generic::BlockId,
-	traits::{BlakeTwo256, Block as BlockT, Hash as HashT, Header as HeaderT},
+	traits::{Block as BlockT, Header as HeaderT},
 };
 use std::{
 	collections::{BTreeMap, VecDeque},
@@ -194,8 +194,13 @@ where
 			self.client.runtime_api().intermediate_roots(&BlockId::Hash(parent_hash))?;
 		roots.push(state_root.encode());
 
-		let trace_root =
-			BlakeTwo256::ordered_trie_root(roots.clone(), sp_core::storage::StateVersion::V1);
+		let trace_root = crate::merkle_tree::MerkleTree::new(
+			roots
+				.iter()
+				.map(|r| r.as_slice().try_into().expect("Storage root type is [u8; 32]; qed")),
+		)
+		.expect("Failed to construct merkle tree for execution trace")
+		.root();
 
 		let trace = roots
 			.into_iter()