Approve multiple candidates with a single signature

The pr migrates:
- paritytech/polkadot#7554

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

cumulus/client/relay-chain-minimal-node/src/blockchain_rpc_client.rs

@@ -23,7 +23,7 @@ use polkadot_core_primitives::{Block, BlockNumber, Hash, Header};
 use polkadot_overseer::RuntimeApiSubsystemClient;
 use polkadot_primitives::{
 	slashing,
-	vstaging::{AsyncBackingParams, BackingState},
+	vstaging::{ApprovalVotingParams, AsyncBackingParams, BackingState},
 };
 use sc_authority_discovery::{AuthorityDiscovery, Error as AuthorityDiscoveryError};
 use sp_api::{ApiError, RuntimeApiInfo};
@@ -349,6 +349,10 @@ impl RuntimeApiSubsystemClient for BlockChainRpcClient {
 	) -> Result<Option<BackingState>, ApiError> {
 		Ok(self.rpc_client.parachain_host_staging_para_backing_state(at, para_id).await?)
 	}
+	/// Approval voting configuration parameters
+	async fn approval_voting_params(&self, _at: Hash) -> Result<ApprovalVotingParams, ApiError> {
+		Ok(ApprovalVotingParams { max_approval_coalesce_count: 1 })
+	}
 }
 
 #[async_trait::async_trait]

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

@@ -64,7 +64,7 @@ pub enum RequiredTranches {
 }
 
 /// The result of a check.
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone, Copy, PartialEq)]
 pub enum Check {
 	/// The candidate is unapproved.
 	Unapproved,
@@ -372,19 +372,22 @@ pub fn tranches_to_approve(
 	block_tick: Tick,
 	no_show_duration: Tick,
 	needed_approvals: usize,
-) -> RequiredTranches {
+) -> (RequiredTranches, usize) {
 	let tick_now = tranche_now as Tick + block_tick;
 	let n_validators = approval_entry.n_validators();
 
-	let initial_state = State {
-		assignments: 0,
-		depth: 0,
-		covered: 0,
-		covering: needed_approvals,
-		uncovered: 0,
-		next_no_show: None,
-		last_assignment_tick: None,
-	};
+	let initial_state = (
+		State {
+			assignments: 0,
+			depth: 0,
+			covered: 0,
+			covering: needed_approvals,
+			uncovered: 0,
+			next_no_show: None,
+			last_assignment_tick: None,
+		},
+		0usize,
+	);
 
 	// The `ApprovalEntry` doesn't have any data for empty tranches. We still want to iterate over
 	// these empty tranches, so we create an iterator to fill the gaps.
@@ -395,7 +398,7 @@ pub fn tranches_to_approve(
 	tranches_with_gaps_filled
 		.scan(Some(initial_state), |state, (tranche, assignments)| {
 			// The `Option` here is used for early exit.
-			let s = state.take()?;
+			let (s, prev_no_shows) = state.take()?;
 
 			let clock_drift = s.clock_drift(no_show_duration);
 			let drifted_tick_now = tick_now.saturating_sub(clock_drift);
@@ -444,11 +447,11 @@ pub fn tranches_to_approve(
 				RequiredTranches::Pending { .. } => {
 					// Pending results are only interesting when they are the last result of the iterator
 					// i.e. we never achieve a satisfactory level of assignment.
-					Some(s)
+					Some((s, no_shows + prev_no_shows))
 				}
 			};
 
-			Some(output)
+			Some((output, no_shows + prev_no_shows))
 		})
 		.last()
 		.expect("the underlying iterator is infinite, starts at 0, and never exits early before tranche 1; qed")
@@ -675,7 +678,8 @@ mod tests {
 				block_tick,
 				no_show_duration,
 				needed_approvals,
-			),
+			)
+			.0,
 			RequiredTranches::Exact {
 				needed: 1,
 				tolerated_missing: 0,
@@ -715,7 +719,8 @@ mod tests {
 				block_tick,
 				no_show_duration,
 				needed_approvals,
-			),
+			)
+			.0,
 			RequiredTranches::Pending {
 				considered: 2,
 				next_no_show: Some(block_tick + no_show_duration),
@@ -759,7 +764,8 @@ mod tests {
 				block_tick,
 				no_show_duration,
 				needed_approvals,
-			),
+			)
+			.0,
 			RequiredTranches::Pending {
 				considered: 11,
 				next_no_show: None,
@@ -807,7 +813,8 @@ mod tests {
 				block_tick,
 				no_show_duration,
 				needed_approvals,
-			),
+			)
+			.0,
 			RequiredTranches::Pending {
 				considered: 1,
 				next_no_show: None,
@@ -826,7 +833,8 @@ mod tests {
 				block_tick,
 				no_show_duration,
 				needed_approvals,
-			),
+			)
+			.0,
 			RequiredTranches::Pending {
 				considered: 1,
 				next_no_show: None,
@@ -879,7 +887,8 @@ mod tests {
 				block_tick,
 				no_show_duration,
 				needed_approvals,
-			),
+			)
+			.0,
 			RequiredTranches::Exact {
 				needed: 1,
 				tolerated_missing: 0,
@@ -898,7 +907,8 @@ mod tests {
 				block_tick,
 				no_show_duration,
 				needed_approvals,
-			),
+			)
+			.0,
 			RequiredTranches::Exact {
 				needed: 2,
 				tolerated_missing: 1,
@@ -917,7 +927,8 @@ mod tests {
 				block_tick,
 				no_show_duration,
 				needed_approvals,
-			),
+			)
+			.0,
 			RequiredTranches::Pending {
 				considered: 2,
 				next_no_show: None,
@@ -970,7 +981,8 @@ mod tests {
 				block_tick,
 				no_show_duration,
 				needed_approvals,
-			),
+			)
+			.0,
 			RequiredTranches::Exact {
 				needed: 2,
 				tolerated_missing: 1,
@@ -992,7 +1004,8 @@ mod tests {
 				block_tick,
 				no_show_duration,
 				needed_approvals,
-			),
+			)
+			.0,
 			RequiredTranches::Pending {
 				considered: 2,
 				next_no_show: None,
@@ -1013,7 +1026,8 @@ mod tests {
 				block_tick,
 				no_show_duration,
 				needed_approvals,
-			),
+			)
+			.0,
 			RequiredTranches::Exact {
 				needed: 3,
 				tolerated_missing: 2,
@@ -1068,7 +1082,8 @@ mod tests {
 				block_tick,
 				no_show_duration,
 				needed_approvals,
-			),
+			)
+			.0,
 			RequiredTranches::Pending {
 				considered: 10,
 				next_no_show: None,

polkadot/node/core/approval-voting/src/approval_db/v2/mod.rs

@@ -17,12 +17,15 @@
 //! Version 2 of the DB schema.
 
 use parity_scale_codec::{Decode, Encode};
-use polkadot_node_primitives::approval::{v1::DelayTranche, v2::AssignmentCertV2};
+use polkadot_node_primitives::approval::{
+	v1::DelayTranche,
+	v2::{AssignmentCertV2, CandidateBitfield},
+};
 use polkadot_node_subsystem::{SubsystemError, SubsystemResult};
 use polkadot_node_subsystem_util::database::{DBTransaction, Database};
 use polkadot_primitives::{
-	BlockNumber, CandidateHash, CandidateReceipt, CoreIndex, GroupIndex, Hash, SessionIndex,
-	ValidatorIndex, ValidatorSignature,
+	BlockNumber, CandidateHash, CandidateIndex, CandidateReceipt, CoreIndex, GroupIndex, Hash,
+	SessionIndex, ValidatorIndex, ValidatorSignature,
 };
 
 use sp_consensus_slots::Slot;
@@ -197,14 +200,24 @@ pub struct TrancheEntry {
 	pub assignments: Vec<(ValidatorIndex, Tick)>,
 }
 
+/// Metadata about our approval signature
+#[derive(Encode, Decode, Debug, Clone, PartialEq)]
+pub struct OurApproval {
+	/// The signature for the candidates hashes pointed by indices.
+	pub signature: ValidatorSignature,
+	/// The indices of the candidates signed in this approval, an empty value means only
+	/// the candidate referred by this approval entry was signed.
+	pub signed_candidates_indices: Option<CandidateBitfield>,
+}
+
 /// Metadata regarding approval of a particular candidate within the context of some
 /// particular block.
 #[derive(Encode, Decode, Debug, Clone, PartialEq)]
 pub struct ApprovalEntry {
 	pub tranches: Vec<TrancheEntry>,
 	pub backing_group: GroupIndex,
 	pub our_assignment: Option<OurAssignment>,
-	pub our_approval_sig: Option<ValidatorSignature>,
+	pub our_approval_sig: Option<OurApproval>,
 	// `n_validators` bits.
 	pub assigned_validators: Bitfield,
 	pub approved: bool,
@@ -241,12 +254,25 @@ pub struct BlockEntry {
 	// block. The block can be considered approved if the bitfield has all bits set to `true`.
 	pub approved_bitfield: Bitfield,
 	pub children: Vec<Hash>,
+	// A list of candidates that has been approved, but we didn't not sign and
+	// advertise the vote yet.
+	pub candidates_pending_signature: BTreeMap<CandidateIndex, CandidateSigningContext>,
 	// Assignments we already distributed. A 1 bit means the candidate index for which
 	// we already have sent out an assignment. We need this to avoid distributing
 	// multiple core assignments more than once.
 	pub distributed_assignments: Bitfield,
 }
 
+#[derive(Encode, Decode, Debug, Clone, PartialEq)]
+
+/// Context needed for creating an approval signature  for a given candidate.
+pub struct CandidateSigningContext {
+	/// The candidate hash, to be included in the signature.
+	pub candidate_hash: CandidateHash,
+	/// The latest tick we have to create and send the approval.
+	pub send_no_later_than_tick: Tick,
+}
+
 impl From<crate::Tick> for Tick {
 	fn from(tick: crate::Tick) -> Tick {
 		Tick(tick)

polkadot/node/core/approval-voting/src/approval_db/v2/tests.rs

@@ -56,6 +56,7 @@ fn make_block_entry(
 		approved_bitfield: make_bitvec(candidates.len()),
 		candidates,
 		children: Vec::new(),
+		candidates_pending_signature: Default::default(),
 		distributed_assignments: Default::default(),
 	}
 }

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

@@ -278,7 +278,7 @@ impl AssignmentCriteria for RealAssignmentCriteria {
 		config: &Config,
 		leaving_cores: Vec<(CandidateHash, CoreIndex, GroupIndex)>,
 	) -> HashMap<CoreIndex, OurAssignment> {
-		compute_assignments(keystore, relay_vrf_story, config, leaving_cores, false)
+		compute_assignments(keystore, relay_vrf_story, config, leaving_cores, true)
 	}
 
 	fn check_assignment_cert(

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

@@ -513,6 +513,7 @@ pub(crate) async fn handle_new_head<Context, B: Backend>(
 				.collect(),
 			approved_bitfield,
 			children: Vec::new(),
+			candidates_pending_signature: Default::default(),
 			distributed_assignments: Default::default(),
 		};
 
@@ -639,6 +640,7 @@ pub(crate) mod tests {
 			clock: Box::new(MockClock::default()),
 			assignment_criteria: Box::new(MockAssignmentCriteria),
 			spans: HashMap::new(),
+			approval_voting_params_cache: None,
 		}
 	}
 
@@ -1267,6 +1269,7 @@ pub(crate) mod tests {
 				candidates: Vec::new(),
 				approved_bitfield: Default::default(),
 				children: Vec::new(),
+				candidates_pending_signature: Default::default(),
 				distributed_assignments: Default::default(),
 			}
 			.into(),