Fix clear prefix check to avoid erasing child trie roots.

primitives/state-machine/src/ext.rs

@@ -454,8 +454,9 @@ where
 			HexDisplay::from(&prefix),
 		);
 		let _guard = guard();
-		if is_child_storage_key(prefix) {
-			warn!(target: "trie", "Refuse to directly clear prefix that is part of child storage key");
+
+		if sp_core::storage::well_known_keys::can_contain_child_storage_key(prefix) {
+			warn!(target: "trie", "Refuse to directly clear prefix that is part or contains of child storage key");
 			return;
 		}
 
@@ -1022,6 +1023,24 @@ mod tests {
 			ext.child_storage_hash(child_info, &[30]),
 			Some(Blake2Hasher::hash(&[31]).as_ref().to_vec()),
 		);
+
+		// check clear prefix is ignored on conflict
+		use sp_core::storage::well_known_keys;
+		let mut ext = ext;
+		let mut not_under_prefix = well_known_keys::CHILD_STORAGE_KEY_PREFIX.to_vec();
+		not_under_prefix[4] = 88;
+		not_under_prefix.extend(b"path");
+		ext.set_storage(not_under_prefix.clone(), vec![10]);
+
+		ext.clear_prefix(&[]);
+		ext.clear_prefix(&well_known_keys::CHILD_STORAGE_KEY_PREFIX[..4]);
+		let mut under_prefix = well_known_keys::CHILD_STORAGE_KEY_PREFIX.to_vec();
+		under_prefix.extend(b"path");
+		ext.clear_prefix(&well_known_keys::CHILD_STORAGE_KEY_PREFIX[..4]);
+		assert_eq!(ext.child_storage(child_info, &[30]), Some(vec![31]));
+		assert_eq!(ext.storage(not_under_prefix.as_slice()), Some(vec![10]));
+		ext.clear_prefix(&not_under_prefix[..5]);
+		assert_eq!(ext.storage(not_under_prefix.as_slice()), None);
 	}
 
 	#[test]

primitives/storage/src/lib.rs

@@ -180,6 +180,16 @@ pub mod well_known_keys {
 		// Other code might depend on this, so be careful changing this.
 		key.starts_with(CHILD_STORAGE_KEY_PREFIX)
 	}
+
+	/// Whether a prefix potentially contains child storage keys.
+	pub fn can_contain_child_storage_key(prefix: &[u8]) -> bool {
+		if prefix.len() > CHILD_STORAGE_KEY_PREFIX.len() {
+			prefix.starts_with(CHILD_STORAGE_KEY_PREFIX)
+		} else {
+			CHILD_STORAGE_KEY_PREFIX.starts_with(prefix)
+		}
+	}
+
 }
 
 /// Information related to a child state.