Changes tries build cache (#2933)

* changes tries build cache

added CT build cache test

* fix lines width

* fixed some grumbles

* clear cache when: digests disabled, top-level or skewed digest is built

* cached_changed_keys -> with_cached_changed_keys

substrate/core/client/src/light/backend.rs

@@ -22,7 +22,7 @@ use std::sync::{Arc, Weak};
 use parking_lot::{RwLock, Mutex};
 
 use sr_primitives::{generic::BlockId, Justification, StorageOverlay, ChildrenStorageOverlay};
-use state_machine::{Backend as StateBackend, TrieBackend, backend::InMemory as InMemoryState};
+use state_machine::{Backend as StateBackend, TrieBackend, backend::InMemory as InMemoryState, ChangesTrieTransaction};
 use sr_primitives::traits::{Block as BlockT, NumberFor, Zero, Header};
 use crate::in_mem::{self, check_genesis_storage};
 use crate::backend::{
@@ -284,7 +284,7 @@ where
 		Ok(())
 	}
 
-	fn update_changes_trie(&mut self, _update: MemoryDB<H>) -> ClientResult<()> {
+	fn update_changes_trie(&mut self, _update: ChangesTrieTransaction<H, NumberFor<Block>>) -> ClientResult<()> {
 		// we're not storing anything locally => ignore changes
 		Ok(())
 	}

substrate/core/client/src/light/call_executor.rs

@@ -25,10 +25,10 @@ use std::{
 use codec::{Encode, Decode};
 use primitives::{offchain, H256, Blake2Hasher, convert_hash, NativeOrEncoded};
 use sr_primitives::generic::BlockId;
-use sr_primitives::traits::{One, Block as BlockT, Header as HeaderT};
+use sr_primitives::traits::{One, Block as BlockT, Header as HeaderT, NumberFor};
 use state_machine::{
 	self, Backend as StateBackend, CodeExecutor, OverlayedChanges,
-	ExecutionStrategy, create_proof_check_backend,
+	ExecutionStrategy, ChangesTrieTransaction, create_proof_check_backend,
 	execution_proof_check_on_trie_backend, ExecutionManager, NeverOffchainExt
 };
 use hash_db::Hasher;
@@ -40,7 +40,6 @@ use crate::call_executor::CallExecutor;
 use crate::error::{Error as ClientError, Result as ClientResult};
 use crate::light::fetcher::{Fetcher, RemoteCallRequest};
 use executor::{RuntimeVersion, NativeVersion};
-use trie::MemoryDB;
 
 /// Call executor that executes methods on remote node, querying execution proof
 /// and checking proof by re-executing locally.
@@ -185,7 +184,7 @@ where
 	) -> ClientResult<(
 		NativeOrEncoded<R>,
 		(S::Transaction, <Blake2Hasher as Hasher>::Out),
-		Option<MemoryDB<Blake2Hasher>>,
+		Option<ChangesTrieTransaction<Blake2Hasher, NumberFor<Block>>>,
 	)> {
 		Err(ClientError::NotAvailableOnLightClient.into())
 	}
@@ -365,7 +364,7 @@ impl<Block, B, Remote, Local> CallExecutor<Block, Blake2Hasher> for
 	) -> ClientResult<(
 		NativeOrEncoded<R>,
 		(S::Transaction, <Blake2Hasher as Hasher>::Out),
-		Option<MemoryDB<Blake2Hasher>>,
+		Option<ChangesTrieTransaction<Blake2Hasher, NumberFor<Block>>>,
 	)> {
 		// there's no actual way/need to specify native/wasm execution strategy on light node
 		// => we can safely ignore passed values

substrate/core/client/src/light/fetcher.rs

@@ -460,7 +460,7 @@ struct RootsStorage<'a, Number: SimpleArithmetic, Hash: 'a> {
 impl<'a, H, Number, Hash> ChangesTrieRootsStorage<H, Number> for RootsStorage<'a, Number, Hash>
 	where
 		H: Hasher,
-		Number: ::std::fmt::Display + Clone + SimpleArithmetic + Encode + Decode + Send + Sync + 'static,
+		Number: ::std::fmt::Display + ::std::hash::Hash + Clone + SimpleArithmetic + Encode + Decode + Send + Sync + 'static,
 		Hash: 'a + Send + Sync + Clone + AsRef<[u8]>,
 {
 	fn build_anchor(