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/subsystem-types/src/messages.rs

@@ -670,7 +670,7 @@ pub enum RuntimeApiRequest {
 	/// Get validation code by its hash, either past, current or future code can be returned, as
 	/// long as state is still available.
 	ValidationCodeByHash(ValidationCodeHash, RuntimeApiSender<Option<ValidationCode>>),
-	/// Get a the candidate pending availability for a particular parachain by parachain / core
+	/// Get the candidate pending availability for a particular parachain by parachain / core
 	/// index
 	CandidatePendingAvailability(ParaId, RuntimeApiSender<Option<CommittedCandidateReceipt>>),
 	/// Get all events concerning candidates (backing, inclusion, time-out) in the parent of
@@ -739,6 +739,9 @@ pub enum RuntimeApiRequest {
 	/// Fetch the `ClaimQueue` from scheduler pallet
 	/// `V11`
 	ClaimQueue(RuntimeApiSender<BTreeMap<CoreIndex, VecDeque<ParaId>>>),
+	/// Get the candidates pending availability for a particular parachain
+	/// `V11`
+	CandidatesPendingAvailability(ParaId, RuntimeApiSender<Vec<CommittedCandidateReceipt>>),
 }
 
 impl RuntimeApiRequest {
@@ -776,6 +779,9 @@ impl RuntimeApiRequest {
 
 	/// `ClaimQueue`
 	pub const CLAIM_QUEUE_RUNTIME_REQUIREMENT: u32 = 11;
+
+	/// `candidates_pending_availability`
+	pub const CANDIDATES_PENDING_AVAILABILITY_RUNTIME_REQUIREMENT: u32 = 11;
 }
 
 /// A message to the Runtime API subsystem.

polkadot/node/subsystem-types/src/runtime_client.rs

@@ -333,6 +333,14 @@ pub trait RuntimeApiSubsystemClient {
 	// == v11: Claim queue ==
 	/// Fetch the `ClaimQueue` from scheduler pallet
 	async fn claim_queue(&self, at: Hash) -> Result<BTreeMap<CoreIndex, VecDeque<Id>>, ApiError>;
+
+	// == v11: Elastic scaling support ==
+	/// Get the receipts of all candidates pending availability for a `ParaId`.
+	async fn candidates_pending_availability(
+		&self,
+		at: Hash,
+		para_id: Id,
+	) -> Result<Vec<CommittedCandidateReceipt<Hash>>, ApiError>;
 }
 
 /// Default implementation of [`RuntimeApiSubsystemClient`] using the client.
@@ -428,6 +436,14 @@ where
 		self.client.runtime_api().candidate_pending_availability(at, para_id)
 	}
 
+	async fn candidates_pending_availability(
+		&self,
+		at: Hash,
+		para_id: Id,
+	) -> Result<Vec<CommittedCandidateReceipt<Hash>>, ApiError> {
+		self.client.runtime_api().candidates_pending_availability(at, para_id)
+	}
+
 	async fn candidate_events(&self, at: Hash) -> Result<Vec<CandidateEvent<Hash>>, ApiError> {
 		self.client.runtime_api().candidate_events(at)
 	}