Check that the validation code matches the parachain code (#3433)

This introduces a check to ensure that the parachain code matches the
validation code stored in the relay chain state. If not, it will print a
warning. This should be mainly useful for parachain builders to make
sure they have setup everything correctly.

cumulus/client/relay-chain-interface/src/lib.rs

@@ -30,7 +30,7 @@ use cumulus_primitives_core::relay_chain::BlockId;
 pub use cumulus_primitives_core::{
 	relay_chain::{
 		CommittedCandidateReceipt, Hash as PHash, Header as PHeader, InboundHrmpMessage,
-		OccupiedCoreAssumption, SessionIndex, ValidatorId,
+		OccupiedCoreAssumption, SessionIndex, ValidationCodeHash, ValidatorId,
 	},
 	InboundDownwardMessage, ParaId, PersistedValidationData,
 };
@@ -194,6 +194,15 @@ pub trait RelayChainInterface: Send + Sync {
 		relay_parent: PHash,
 		relevant_keys: &Vec<Vec<u8>>,
 	) -> RelayChainResult<StorageProof>;
+
+	/// Returns the validation code hash for the given `para_id` using the given
+	/// `occupied_core_assumption`.
+	async fn validation_code_hash(
+		&self,
+		relay_parent: PHash,
+		para_id: ParaId,
+		occupied_core_assumption: OccupiedCoreAssumption,
+	) -> RelayChainResult<Option<ValidationCodeHash>>;
 }
 
 #[async_trait]
@@ -301,4 +310,15 @@ where
 	async fn header(&self, block_id: BlockId) -> RelayChainResult<Option<PHeader>> {
 		(**self).header(block_id).await
 	}
+
+	async fn validation_code_hash(
+		&self,
+		relay_parent: PHash,
+		para_id: ParaId,
+		occupied_core_assumption: OccupiedCoreAssumption,
+	) -> RelayChainResult<Option<ValidationCodeHash>> {
+		(**self)
+			.validation_code_hash(relay_parent, para_id, occupied_core_assumption)
+			.await
+	}
 }