runtime/session_info: keep track of stash keys (#5473)

polkadot/runtime/kusama/src/lib.rs

@@ -1256,7 +1256,9 @@ impl parachains_configuration::Config for Runtime {
 
 impl parachains_shared::Config for Runtime {}
 
-impl parachains_session_info::Config for Runtime {}
+impl parachains_session_info::Config for Runtime {
+	type ValidatorSet = Historical;
+}
 
 impl parachains_inclusion::Config for Runtime {
 	type Event = Event;

polkadot/runtime/parachains/src/mock.rs

@@ -25,7 +25,7 @@ use crate::{
 
 use frame_support::{
 	parameter_types,
-	traits::{GenesisBuild, KeyOwnerProofSystem},
+	traits::{GenesisBuild, KeyOwnerProofSystem, ValidatorSet, ValidatorSetWithIdentification},
 	weights::Weight,
 };
 use frame_support_test::TestRandomness;
@@ -301,7 +301,41 @@ impl crate::paras_inherent::Config for Test {
 	type WeightInfo = crate::paras_inherent::TestWeightInfo;
 }
 
-impl crate::session_info::Config for Test {}
+pub struct MockValidatorSet;
+
+impl ValidatorSet<AccountId> for MockValidatorSet {
+	type ValidatorId = AccountId;
+	type ValidatorIdOf = ValidatorIdOf;
+	fn session_index() -> SessionIndex {
+		0
+	}
+	fn validators() -> Vec<Self::ValidatorId> {
+		Vec::new()
+	}
+}
+
+impl ValidatorSetWithIdentification<AccountId> for MockValidatorSet {
+	type Identification = ();
+	type IdentificationOf = FoolIdentificationOf;
+}
+
+pub struct FoolIdentificationOf;
+impl sp_runtime::traits::Convert<AccountId, Option<()>> for FoolIdentificationOf {
+	fn convert(_: AccountId) -> Option<()> {
+		Some(())
+	}
+}
+
+pub struct ValidatorIdOf;
+impl sp_runtime::traits::Convert<AccountId, Option<AccountId>> for ValidatorIdOf {
+	fn convert(a: AccountId) -> Option<AccountId> {
+		Some(a)
+	}
+}
+
+impl crate::session_info::Config for Test {
+	type ValidatorSet = MockValidatorSet;
+}
 
 thread_local! {
 	pub static DISCOVERY_AUTHORITIES: RefCell<Vec<AuthorityDiscoveryId>> = RefCell::new(Vec::new());

polkadot/runtime/parachains/src/session_info.rs

@@ -23,7 +23,10 @@ use crate::{
 	configuration, paras, scheduler, shared,
 	util::{take_active_subset, take_active_subset_and_inactive},
 };
-use frame_support::{pallet_prelude::*, traits::OneSessionHandler};
+use frame_support::{
+	pallet_prelude::*,
+	traits::{OneSessionHandler, ValidatorSet, ValidatorSetWithIdentification},
+};
 use primitives::v2::{AssignmentId, AuthorityDiscoveryId, SessionIndex, SessionInfo};
 use sp_std::vec::Vec;
 
@@ -34,6 +37,20 @@ pub mod migration;
 #[cfg(test)]
 mod tests;
 
+/// A type for representing the validator account id in a session.
+pub type AccountId<T> = <<T as Config>::ValidatorSet as ValidatorSet<
+	<T as frame_system::Config>::AccountId,
+>>::ValidatorId;
+
+/// A tuple of `(AccountId, Identification)` where `Identification`
+/// is the full identification of `AccountId`.
+pub type IdentificationTuple<T> = (
+	AccountId<T>,
+	<<T as Config>::ValidatorSet as ValidatorSetWithIdentification<
+		<T as frame_system::Config>::AccountId,
+	>>::Identification,
+);
+
 #[frame_support::pallet]
 pub mod pallet {
 	use super::*;
@@ -53,6 +70,10 @@ pub mod pallet {
 		+ scheduler::Config
 		+ AuthorityDiscoveryConfig
 	{
+		/// A type for retrieving `AccountId`s of the validators in the current session.
+		/// These are stash keys of the validators.
+		/// It's used for rewards and slashing. `Identification` is only needed for slashing.
+		type ValidatorSet: ValidatorSetWithIdentification<Self::AccountId>;
 	}
 
 	/// Assignment keys for the current session.
@@ -73,6 +94,14 @@ pub mod pallet {
 	#[pallet::storage]
 	#[pallet::getter(fn session_info)]
 	pub(crate) type Sessions<T: Config> = StorageMap<_, Identity, SessionIndex, SessionInfo>;
+
+	/// The validator account keys of the validators actively participating in parachain consensus.
+	// We do not store this in `SessionInfo` to avoid leaking the `AccountId` type to the client,
+	// which would complicate the migration process if we are to change it in the future.
+	#[pallet::storage]
+	#[pallet::getter(fn account_keys)]
+	pub(crate) type AccountKeys<T: Config> =
+		StorageMap<_, Identity, SessionIndex, Vec<AccountId<T>>>;
 }
 
 /// An abstraction for the authority discovery pallet
@@ -121,6 +150,9 @@ impl<T: Config> Pallet<T> {
 		if old_earliest_stored_session != 0 || Sessions::<T>::get(0).is_some() {
 			for idx in old_earliest_stored_session..new_earliest_stored_session {
 				Sessions::<T>::remove(&idx);
+				// Idx will be missing for a few sessions after the runtime upgrade.
+				// But it shouldn'be be a problem.
+				AccountKeys::<T>::remove(&idx);
 			}
 			// update `EarliestStoredSession` based on `config.dispute_period`
 			EarliestStoredSession::<T>::set(new_earliest_stored_session);
@@ -128,6 +160,13 @@ impl<T: Config> Pallet<T> {
 			// just introduced on a live chain
 			EarliestStoredSession::<T>::set(new_session_index);
 		}
+
+		// The validator set is guaranteed to be of the current session
+		// because we delay `on_new_session` till the end of the block.
+		let account_ids = T::ValidatorSet::validators();
+		let active_account_ids = take_active_subset(&active_set, &account_ids);
+		AccountKeys::<T>::insert(&new_session_index, &active_account_ids);
+
 		// create a new entry in `Sessions` with information about the current session
 		let new_session_info = SessionInfo {
 			validators, // these are from the notification and are thus already correct.

polkadot/runtime/polkadot/src/lib.rs

@@ -1238,7 +1238,9 @@ impl parachains_configuration::Config for Runtime {
 
 impl parachains_shared::Config for Runtime {}
 
-impl parachains_session_info::Config for Runtime {}
+impl parachains_session_info::Config for Runtime {
+	type ValidatorSet = Historical;
+}
 
 impl parachains_inclusion::Config for Runtime {
 	type Event = Event;

polkadot/runtime/rococo/src/lib.rs

@@ -603,7 +603,9 @@ impl parachains_paras::Config for Runtime {
 	type NextSessionRotation = Babe;
 }
 
-impl parachains_session_info::Config for Runtime {}
+impl parachains_session_info::Config for Runtime {
+	type ValidatorSet = Historical;
+}
 
 parameter_types! {
 	pub const FirstMessageFactorPercent: u64 = 100;

polkadot/runtime/test-runtime/src/lib.rs

@@ -499,7 +499,9 @@ impl parachains_initializer::Config for Runtime {
 	type WeightInfo = ();
 }
 
-impl parachains_session_info::Config for Runtime {}
+impl parachains_session_info::Config for Runtime {
+	type ValidatorSet = Historical;
+}
 
 parameter_types! {
 	pub const ParasUnsignedPriority: TransactionPriority = TransactionPriority::max_value();

polkadot/runtime/westend/src/lib.rs

@@ -852,7 +852,9 @@ impl parachains_configuration::Config for Runtime {
 
 impl parachains_shared::Config for Runtime {}
 
-impl parachains_session_info::Config for Runtime {}
+impl parachains_session_info::Config for Runtime {
+	type ValidatorSet = Historical;
+}
 
 impl parachains_inclusion::Config for Runtime {
 	type Event = Event;