Add relay parent to inherent and to digest

collator/src/lib.rs

@@ -297,6 +297,7 @@ where
 				horizontal_messages,
 				validation_data: validation_data.clone(),
 				relay_chain_state,
+				relay_parent,
 			}
 		};
 

parachain-system/src/lib.rs

@@ -44,6 +44,8 @@ use sp_std::{vec::Vec, cmp};
 
 mod relay_state_snapshot;
 use relay_state_snapshot::MessagingStateSnapshot;
+use sp_runtime::DigestItem;
+use codec::Encode;
 
 /// The pallet's configuration trait.
 pub trait Config: frame_system::Config {
@@ -153,6 +155,7 @@ decl_module! {
 				relay_chain_state,
 				downward_messages,
 				horizontal_messages,
+				relay_parent,
 			} = data;
 
 			// initialization logic: we know that this runs exactly once every block,
@@ -219,6 +222,12 @@ decl_module! {
 				);
 			}
 
+			// Add the relay parent to a digest to track which parents this block was built on.
+			frame_system::Module::<T>::deposit_log(DigestItem::<T::Hash>::Consensus(
+				*b"rlyp", // "rlyp" -> "relay parent"
+				relay_parent.encode(),
+			));
+
 			Ok(())
 		}
 
@@ -932,6 +941,7 @@ mod tests {
 								relay_chain_state,
 							    downward_messages: Default::default(),
 							    horizontal_messages: Default::default(),
+								relay_parent: Default::default(),
 							})
 							.expect("failed to put VFP inherent");
 						inherent_data

primitives/src/lib.rs

@@ -45,6 +45,7 @@ pub mod inherents {
 	use super::{InboundDownwardMessage, InboundHrmpMessage, ParaId};
 	use sp_inherents::InherentIdentifier;
 	use sp_std::{collections::btree_map::BTreeMap, vec::Vec};
+	use polkadot_primitives::v1::Hash as PHash;
 
 	/// The identifier for the parachain-system inherent.
 	pub const SYSTEM_INHERENT_IDENTIFIER: InherentIdentifier = *b"sysi1337";
@@ -68,6 +69,8 @@ pub mod inherents {
 		/// were sent. In combination with the rule of no more than one message in a channel per block,
 		/// this means `sent_at` is **strictly** greater than the previous one (if any).
 		pub horizontal_messages: BTreeMap<ParaId, Vec<InboundHrmpMessage>>,
+		/// The hash of the relay parent block on which this block is built.
+		pub relay_parent: PHash,
 	}
 }
 

test/client/src/block_builder.rs

@@ -107,6 +107,7 @@ impl InitBlockBuilder for Client {
 					relay_chain_state,
 					downward_messages: Default::default(),
 					horizontal_messages: Default::default(),
+					relay_parent: Default::default(),
 				},
 			)
 			.expect("Put validation function params failed");