Runtime API: introduce candidates_pending_availability (#4027)

Fixes https://github.com/paritytech/polkadot-sdk/issues/3576

Required by elastic scaling collators.
Deprecates old API: `candidate_pending_availability`.

TODO:
- [x] PRDoc

---------

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

polkadot/node/core/runtime-api/src/cache.rs

@@ -48,6 +48,7 @@ pub(crate) struct RequestResultCache {
 	validation_code: LruMap<(Hash, ParaId, OccupiedCoreAssumption), Option<ValidationCode>>,
 	validation_code_by_hash: LruMap<ValidationCodeHash, Option<ValidationCode>>,
 	candidate_pending_availability: LruMap<(Hash, ParaId), Option<CommittedCandidateReceipt>>,
+	candidates_pending_availability: LruMap<(Hash, ParaId), Vec<CommittedCandidateReceipt>>,
 	candidate_events: LruMap<Hash, Vec<CandidateEvent>>,
 	session_executor_params: LruMap<SessionIndex, Option<ExecutorParams>>,
 	session_info: LruMap<SessionIndex, SessionInfo>,
@@ -86,6 +87,7 @@ impl Default for RequestResultCache {
 			validation_code: LruMap::new(ByLength::new(DEFAULT_CACHE_CAP)),
 			validation_code_by_hash: LruMap::new(ByLength::new(DEFAULT_CACHE_CAP)),
 			candidate_pending_availability: LruMap::new(ByLength::new(DEFAULT_CACHE_CAP)),
+			candidates_pending_availability: LruMap::new(ByLength::new(DEFAULT_CACHE_CAP)),
 			candidate_events: LruMap::new(ByLength::new(DEFAULT_CACHE_CAP)),
 			session_executor_params: LruMap::new(ByLength::new(DEFAULT_CACHE_CAP)),
 			session_info: LruMap::new(ByLength::new(DEFAULT_CACHE_CAP)),
@@ -261,6 +263,21 @@ impl RequestResultCache {
 		self.candidate_pending_availability.insert(key, value);
 	}
 
+	pub(crate) fn candidates_pending_availability(
+		&mut self,
+		key: (Hash, ParaId),
+	) -> Option<&Vec<CommittedCandidateReceipt>> {
+		self.candidates_pending_availability.get(&key).map(|v| &*v)
+	}
+
+	pub(crate) fn cache_candidates_pending_availability(
+		&mut self,
+		key: (Hash, ParaId),
+		value: Vec<CommittedCandidateReceipt>,
+	) {
+		self.candidates_pending_availability.insert(key, value);
+	}
+
 	pub(crate) fn candidate_events(&mut self, relay_parent: &Hash) -> Option<&Vec<CandidateEvent>> {
 		self.candidate_events.get(relay_parent).map(|v| &*v)
 	}
@@ -591,4 +608,5 @@ pub(crate) enum RequestResult {
 	AsyncBackingParams(Hash, async_backing::AsyncBackingParams),
 	NodeFeatures(SessionIndex, NodeFeatures),
 	ClaimQueue(Hash, BTreeMap<CoreIndex, VecDeque<ParaId>>),
+	CandidatesPendingAvailability(Hash, ParaId, Vec<CommittedCandidateReceipt>),
 }

polkadot/node/core/runtime-api/src/lib.rs

@@ -133,6 +133,9 @@ where
 			CandidatePendingAvailability(relay_parent, para_id, candidate) => self
 				.requests_cache
 				.cache_candidate_pending_availability((relay_parent, para_id), candidate),
+			CandidatesPendingAvailability(relay_parent, para_id, candidates) => self
+				.requests_cache
+				.cache_candidates_pending_availability((relay_parent, para_id), candidates),
 			CandidateEvents(relay_parent, events) =>
 				self.requests_cache.cache_candidate_events(relay_parent, events),
 			SessionExecutorParams(_relay_parent, session_index, index) =>
@@ -252,6 +255,9 @@ where
 			Request::CandidatePendingAvailability(para, sender) =>
 				query!(candidate_pending_availability(para), sender)
 					.map(|sender| Request::CandidatePendingAvailability(para, sender)),
+			Request::CandidatesPendingAvailability(para, sender) =>
+				query!(candidates_pending_availability(para), sender)
+					.map(|sender| Request::CandidatesPendingAvailability(para, sender)),
 			Request::CandidateEvents(sender) =>
 				query!(candidate_events(), sender).map(|sender| Request::CandidateEvents(sender)),
 			Request::SessionExecutorParams(session_index, sender) => {
@@ -531,6 +537,12 @@ where
 			ver = 1,
 			sender
 		),
+		Request::CandidatesPendingAvailability(para, sender) => query!(
+			CandidatesPendingAvailability,
+			candidates_pending_availability(para),
+			ver = Request::CANDIDATES_PENDING_AVAILABILITY_RUNTIME_REQUIREMENT,
+			sender
+		),
 		Request::CandidateEvents(sender) => {
 			query!(CandidateEvents, candidate_events(), ver = 1, sender)
 		},

polkadot/node/core/runtime-api/src/tests.rs

@@ -47,6 +47,7 @@ struct MockSubsystemClient {
 	validation_outputs_results: HashMap<ParaId, bool>,
 	session_index_for_child: SessionIndex,
 	candidate_pending_availability: HashMap<ParaId, CommittedCandidateReceipt>,
+	candidates_pending_availability: HashMap<ParaId, Vec<CommittedCandidateReceipt>>,
 	dmq_contents: HashMap<ParaId, Vec<InboundDownwardMessage>>,
 	hrmp_channels: HashMap<ParaId, BTreeMap<ParaId, Vec<InboundHrmpMessage>>>,
 	validation_code_by_hash: HashMap<ValidationCodeHash, ValidationCode>,
@@ -140,6 +141,14 @@ impl RuntimeApiSubsystemClient for MockSubsystemClient {
 		Ok(self.candidate_pending_availability.get(&para_id).cloned())
 	}
 
+	async fn candidates_pending_availability(
+		&self,
+		_: Hash,
+		para_id: ParaId,
+	) -> Result<Vec<CommittedCandidateReceipt<Hash>>, ApiError> {
+		Ok(self.candidates_pending_availability.get(&para_id).cloned().unwrap_or_default())
+	}
+
 	async fn candidate_events(&self, _: Hash) -> Result<Vec<CandidateEvent<Hash>>, ApiError> {
 		Ok(self.candidate_events.clone())
 	}