Add feature flag to enable v2 assignments

Scaffold everything, so that we can enable v2 assignments via a node
feature bit, once all nodes have upgraded to the new protocol.

Implements: #628

Signed-off-by: Alexandru Gheorghe <alexandru.gheorghe@parity.io>

polkadot/node/core/approval-voting/src/criteria.rs

@@ -259,6 +259,7 @@ pub(crate) trait AssignmentCriteria {
 		relay_vrf_story: RelayVRFStory,
 		config: &Config,
 		leaving_cores: Vec<(CandidateHash, CoreIndex, GroupIndex)>,
+		enable_v2_assignments: bool,
 	) -> HashMap<CoreIndex, OurAssignment>;
 
 	fn check_assignment_cert(
@@ -282,8 +283,9 @@ impl AssignmentCriteria for RealAssignmentCriteria {
 		relay_vrf_story: RelayVRFStory,
 		config: &Config,
 		leaving_cores: Vec<(CandidateHash, CoreIndex, GroupIndex)>,
+		enable_v2_assignments: bool,
 	) -> HashMap<CoreIndex, OurAssignment> {
-		compute_assignments(keystore, relay_vrf_story, config, leaving_cores, false)
+		compute_assignments(keystore, relay_vrf_story, config, leaving_cores, enable_v2_assignments)
 	}
 
 	fn check_assignment_cert(

polkadot/node/core/approval-voting/src/import.rs

@@ -43,10 +43,13 @@ use polkadot_node_subsystem::{
 	},
 	overseer, RuntimeApiError, SubsystemError, SubsystemResult,
 };
-use polkadot_node_subsystem_util::{determine_new_blocks, runtime::RuntimeInfo};
+use polkadot_node_subsystem_util::{
+	determine_new_blocks,
+	runtime::{request_node_features, RuntimeInfo},
+};
 use polkadot_primitives::{
-	BlockNumber, CandidateEvent, CandidateHash, CandidateReceipt, ConsensusLog, CoreIndex,
-	GroupIndex, Hash, Header, SessionIndex,
+	vstaging::node_features, BlockNumber, CandidateEvent, CandidateHash, CandidateReceipt,
+	ConsensusLog, CoreIndex, GroupIndex, Hash, Header, SessionIndex,
 };
 use sc_keystore::LocalKeystore;
 use sp_consensus_slots::Slot;
@@ -217,7 +220,17 @@ async fn imported_block_info<Context>(
 	let session_info = get_session_info(env.runtime_info, ctx.sender(), block_hash, session_index)
 		.await
 		.ok_or(ImportedBlockInfoError::SessionInfoUnavailable)?;
-
+	let enable_v2_assignments = request_node_features(block_hash, session_index, ctx.sender())
+		.await
+		.ok()
+		.flatten()
+		.map_or(false, |node_features| {
+			*node_features
+				.get(node_features::ENABLE_ASSIGNMENTS_V2 as usize)
+				.as_deref()
+				.unwrap_or(&false)
+		});
+	gum::debug!(target: LOG_TARGET, ?enable_v2_assignments, "V2 assignments");
 	let (assignments, slot, relay_vrf_story) = {
 		let unsafe_vrf = approval_types::v1::babe_unsafe_vrf_info(&block_header);
 
@@ -239,6 +252,7 @@ async fn imported_block_info<Context>(
 								.iter()
 								.map(|(c_hash, _, core, group)| (*c_hash, *core, *group))
 								.collect(),
+							enable_v2_assignments,
 						);
 
 						(assignments, slot, relay_vrf)
@@ -667,6 +681,7 @@ pub(crate) mod tests {
 				polkadot_primitives::CoreIndex,
 				polkadot_primitives::GroupIndex,
 			)>,
+			_enable_assignments_v2: bool,
 		) -> HashMap<polkadot_primitives::CoreIndex, criteria::OurAssignment> {
 			HashMap::new()
 		}

polkadot/node/core/approval-voting/src/tests.rs

@@ -243,6 +243,7 @@ where
 			polkadot_primitives::CoreIndex,
 			polkadot_primitives::GroupIndex,
 		)>,
+		_enable_assignments_v2: bool,
 	) -> HashMap<polkadot_primitives::CoreIndex, criteria::OurAssignment> {
 		self.0()
 	}

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

@@ -28,7 +28,7 @@ use polkadot_node_subsystem::{
 	overseer, FromOrchestra, OverseerSignal, SpawnedSubsystem, SubsystemError, SubsystemResult,
 };
 use polkadot_node_subsystem_types::RuntimeApiSubsystemClient;
-use polkadot_primitives::Hash;
+use polkadot_primitives::{vstaging::node_features::FIRST_UNASSIGNED, Hash};
 
 use cache::{RequestResult, RequestResultCache};
 use futures::{channel::oneshot, prelude::*, select, stream::FuturesUnordered};
@@ -173,8 +173,13 @@ where
 				.cache_para_backing_state((relay_parent, para_id), constraints),
 			AsyncBackingParams(relay_parent, params) =>
 				self.requests_cache.cache_async_backing_params(relay_parent, params),
-			NodeFeatures(session_index, params) =>
-				self.requests_cache.cache_node_features(session_index, params),
+			NodeFeatures(session_index, params) => {
+				let last_set_index = params.iter_ones().last().unwrap_or_default();
+				if last_set_index >= FIRST_UNASSIGNED as usize {
+					gum::warn!(target: LOG_TARGET, "Runtime requires feature bit {} that node doesn't support, please upgrade node version", last_set_index);
+				}
+				self.requests_cache.cache_node_features(session_index, params)
+			},
 		}
 	}
 

polkadot/primitives/src/vstaging/mod.rs

@@ -22,3 +22,14 @@ use bitvec::vec::BitVec;
 
 /// Bit indices in the `HostConfiguration.node_features` that correspond to different node features.
 pub type NodeFeatures = BitVec<u8, bitvec::order::Lsb0>;
+
+/// Module containing feature-specific bit indices into the `NodeFeatures` bitvec.
+pub mod node_features {
+	/// Tells if tranch0 assignments could be sent in a single certificate.
+	/// Reserved for: https://github.com/paritytech/polkadot-sdk/issues/628
+	pub const ENABLE_ASSIGNMENTS_V2: u8 = 0;
+	/// First unassigned feature bit.
+	/// Every time a new feature flag is assigned it should take this value.
+	/// and this should be incremented.
+	pub const FIRST_UNASSIGNED: u8 = 1;
+}