merging child info in the overlay when possible.

primitives/core/storage/src/lib.rs

@@ -273,6 +273,14 @@ impl OwnedChildInfo {
 		})
 	}
 
+	/// Try to update with another instance, return false if both instance
+	/// are not compatible.
+	pub fn try_update(&mut self, other: ChildInfo) -> bool {
+		match self {
+			OwnedChildInfo::Default(owned_child_trie) => owned_child_trie.try_update(other),
+		}
+	}
+
 	/// Get `ChildInfo` reference to this owned child info.
 	pub fn as_ref(&self) -> ChildInfo {
 		match self {
@@ -311,3 +319,22 @@ pub struct OwnedChildTrie {
 	/// See `ChildTrie` reference field documentation.
 	pub unique_id: Vec<u8>,
 }
+
+impl OwnedChildTrie {
+	/// Try to update with another instance, return false if both instance
+	/// are not compatible.
+	fn try_update(&mut self, other: ChildInfo) -> bool {
+		match other {
+			ChildInfo::Default(other) => {
+				if self.unique_id != other.unique_id {
+					return false;
+				}
+				if self.root.is_none() {
+					self.root = other.root.as_ref().map(|s| s.to_vec());
+				}
+				debug_assert!(self.root.as_ref().map(|v| v.as_slice()) == other.root);
+			},
+		}
+		true
+	}
+}

primitives/sr-primitives/src/lib.rs

@@ -154,6 +154,9 @@ impl BuildStorage for (StorageOverlay, ChildrenStorageOverlay) {
 			let k = k.clone();
 			if let Some(map) = storage.1.get_mut(&k) {
 				map.0.extend(other_map.0.iter().map(|(k, v)| (k.clone(), v.clone())));
+				if !map.1.try_update(other_map.1.as_ref()) {
+					return Err("Incompatible child info update".to_string());
+				}
 			} else {
 				storage.1.insert(k, other_map.clone());
 			}

primitives/state-machine/src/basic.rs

@@ -240,7 +240,7 @@ impl Externalities for BasicExternalities {
 			if &empty_hash[..] == &child_root[..] {
 				top.remove(storage_key.as_slice());
 			} else {
-				top.insert(storage_key.clone(), child_root);
+				top.insert(storage_key, child_root);
 			}
 		}
 

primitives/state-machine/src/overlayed_changes.rs

@@ -159,6 +159,9 @@ impl OverlayedChanges {
 		let extrinsic_index = self.extrinsic_index();
 		let map_entry = self.prospective.children.entry(storage_key)
 			.or_insert_with(|| (Default::default(), child_info.to_owned()));
+		let updatable = map_entry.1.try_update(child_info);
+		debug_assert!(updatable);
+
 		let entry = map_entry.0.entry(key).or_default();
 		entry.value = val;
 
@@ -182,6 +185,8 @@ impl OverlayedChanges {
 		let extrinsic_index = self.extrinsic_index();
 		let map_entry = self.prospective.children.entry(storage_key.to_vec())
 			.or_insert_with(|| (Default::default(), child_info.to_owned()));
+		let updatable = map_entry.1.try_update(child_info);
+		debug_assert!(updatable);
 
 		map_entry.0.values_mut().for_each(|e| {
 			if let Some(extrinsic) = extrinsic_index {
@@ -255,6 +260,8 @@ impl OverlayedChanges {
 		let extrinsic_index = self.extrinsic_index();
 		let map_entry = self.prospective.children.entry(storage_key.to_vec())
 			.or_insert_with(|| (Default::default(), child_info.to_owned()));
+		let updatable = map_entry.1.try_update(child_info);
+		debug_assert!(updatable);
 
 		for (key, entry) in map_entry.0.iter_mut() {
 			if key.starts_with(prefix) {