[Staking] Cleanups and some improvements (#8701)

## Changes
- Introduced a new `min_bond` value, which is the minimum of
`MinValidatorBond` and `MinNominatorBond`, with a fallback to
`ExistentialDeposit`. Since ED on AH is much lower than on RC, this
ensures we enforce some min bonds for staking to cover storage costs for
staking ledger and related data.
- Added an upper bound on era duration, protecting against anomalous
conditions that could otherwise lead to excessive inflation.
- Some refactors to gracefully handle unexpected validator activation in
RC.


## TODO
- [ ] Set `MaxEraDuration` in WAH.
- [ ] Port [full
unbond](#3811) (will do
in a separate PR)

---------

Co-authored-by: cmd[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: 2 people

substrate/frame/staking-async/ahm-test/src/ah/mock.rs

@@ -83,11 +83,10 @@ pub fn roll_until_matches(criteria: impl Fn() -> bool, with_rc: bool) {
 /// Use the given `end_index` as the first session report, and increment as per needed.
 pub(crate) fn roll_until_next_active(mut end_index: SessionIndex) -> Vec<AccountId> {
 	// receive enough session reports, such that we plan a new era
-	let planned_era = pallet_staking_async::session_rotation::Rotator::<Runtime>::planning_era();
+	let planned_era = pallet_staking_async::session_rotation::Rotator::<Runtime>::planned_era();
 	let active_era = pallet_staking_async::session_rotation::Rotator::<Runtime>::active_era();
 
-	while pallet_staking_async::session_rotation::Rotator::<Runtime>::planning_era() == planned_era
-	{
+	while pallet_staking_async::session_rotation::Rotator::<Runtime>::planned_era() == planned_era {
 		let report = SessionReport {
 			end_index,
 			activation_timestamp: None,
@@ -342,6 +341,7 @@ impl pallet_staking_async::Config for Runtime {
 	type RewardRemainder = ();
 	type Slash = ();
 	type SlashDeferDuration = SlashDeferredDuration;
+	type MaxEraDuration = ();
 
 	type HistoryDepth = ConstU32<7>;
 	type MaxControllersInDeprecationBatch = ();

substrate/frame/staking-async/runtimes/parachain/src/staking.rs

@@ -244,6 +244,10 @@ parameter_types! {
 	// of nominators.
 	pub const MaxControllersInDeprecationBatch: u32 = 751;
 	pub const MaxNominations: u32 = <NposCompactSolution16 as frame_election_provider_support::NposSolution>::LIMIT as u32;
+	// Note: In WAH, this should be set closer to the ideal era duration to trigger capping more
+	// frequently. On Kusama and Polkadot, a higher value like 7 × ideal_era_duration is more
+	// appropriate.
+	pub const MaxEraDuration: u64 = RelaySessionDuration::get() as u64 * RELAY_CHAIN_SLOT_DURATION_MILLIS as u64 * SessionsPerEra::get() as u64;
 }
 
 impl pallet_staking_async::Config for Runtime {
@@ -273,6 +277,7 @@ impl pallet_staking_async::Config for Runtime {
 	type EventListeners = (NominationPools, DelegatedStaking);
 	type WeightInfo = weights::pallet_staking_async::WeightInfo<Runtime>;
 	type MaxInvulnerables = frame_support::traits::ConstU32<20>;
+	type MaxEraDuration = MaxEraDuration;
 	type MaxDisabledValidators = ConstU32<100>;
 	type PlanningEraOffset =
 		pallet_staking_async::PlanningEraOffsetOf<Self, RelaySessionDuration, ConstU32<10>>;

substrate/frame/staking-async/src/benchmarking.rs

@@ -229,7 +229,7 @@ mod benchmarks {
 		// clean up any existing state.
 		clear_validators_and_nominators::<T>();
 
-		let origin_weight = MinNominatorBond::<T>::get().max(asset::existential_deposit::<T>());
+		let origin_weight = Staking::<T>::min_nominator_bond();
 
 		// setup the worst case list scenario.
 
@@ -318,7 +318,7 @@ mod benchmarks {
 		// clean up any existing state.
 		clear_validators_and_nominators::<T>();
 
-		let origin_weight = MinNominatorBond::<T>::get().max(asset::existential_deposit::<T>());
+		let origin_weight = Staking::<T>::min_nominator_bond();
 
 		// setup a worst case list scenario. Note that we don't care about the setup of the
 		// destination position because we are doing a removal from the list but no insert.
@@ -442,7 +442,7 @@ mod benchmarks {
 		// clean up any existing state.
 		clear_validators_and_nominators::<T>();
 
-		let origin_weight = MinNominatorBond::<T>::get().max(asset::existential_deposit::<T>());
+		let origin_weight = Staking::<T>::min_nominator_bond();
 
 		// setup a worst case list scenario. Note we don't care about the destination position,
 		// because we are just doing an insert into the origin position.
@@ -475,7 +475,7 @@ mod benchmarks {
 		// clean up any existing state.
 		clear_validators_and_nominators::<T>();
 
-		let origin_weight = MinNominatorBond::<T>::get().max(asset::existential_deposit::<T>());
+		let origin_weight = Staking::<T>::min_nominator_bond();
 
 		// setup a worst case list scenario. Note that we don't care about the setup of the
 		// destination position because we are doing a removal from the list but no insert.
@@ -633,7 +633,7 @@ mod benchmarks {
 		// Clean up any existing state.
 		clear_validators_and_nominators::<T>();
 
-		let origin_weight = MinNominatorBond::<T>::get().max(asset::existential_deposit::<T>());
+		let origin_weight = Staking::<T>::min_nominator_bond();
 
 		// setup a worst case list scenario. Note that we don't care about the setup of the
 		// destination position because we are doing a removal from the list but no insert.
@@ -734,8 +734,7 @@ mod benchmarks {
 		// clean up any existing state.
 		clear_validators_and_nominators::<T>();
 
-		let origin_weight = MinNominatorBond::<T>::get()
-			.max(asset::existential_deposit::<T>())
+		let origin_weight = Pallet::<T>::min_nominator_bond()
 			// we use 100 to play friendly with the list threshold values in the mock
 			.max(100u32.into());
 
@@ -781,7 +780,7 @@ mod benchmarks {
 		// clean up any existing state.
 		clear_validators_and_nominators::<T>();
 
-		let origin_weight = MinNominatorBond::<T>::get().max(asset::existential_deposit::<T>());
+		let origin_weight = Staking::<T>::min_nominator_bond();
 
 		// setup a worst case list scenario. Note that we don't care about the setup of the
 		// destination position because we are doing a removal from the list but no insert.
@@ -858,7 +857,7 @@ mod benchmarks {
 		// clean up any existing state.
 		clear_validators_and_nominators::<T>();
 
-		let origin_weight = MinNominatorBond::<T>::get().max(asset::existential_deposit::<T>());
+		let origin_weight = Staking::<T>::min_nominator_bond();
 
 		// setup a worst case list scenario. Note that we don't care about the setup of the
 		// destination position because we are doing a removal from the list but no insert.
@@ -1024,14 +1023,14 @@ mod benchmarks {
 		let _new_validators = Rotator::<T>::legacy_insta_plan_era();
 		// activate the previous one
 		Rotator::<T>::start_era(
-			crate::ActiveEraInfo { index: Rotator::<T>::planning_era() - 1, start: Some(1) },
+			crate::ActiveEraInfo { index: Rotator::<T>::planned_era() - 1, start: Some(1) },
 			42, // start session index doesn't really matter,
 			2,  // timestamp doesn't really matter
 		);
 
 		// ensure our offender has at least a full exposure page
 		let offender_exposure =
-			Eras::<T>::get_full_exposure(Rotator::<T>::planning_era(), &offender);
+			Eras::<T>::get_full_exposure(Rotator::<T>::planned_era(), &offender);
 		ensure!(
 			offender_exposure.others.len() as u32 == 2 * T::MaxExposurePageSize::get(),
 			"exposure not created"
@@ -1073,7 +1072,7 @@ mod benchmarks {
 	fn rc_on_offence(
 		v: Linear<2, { T::MaxValidatorSet::get() / 2 }>,
 	) -> Result<(), BenchmarkError> {
-		let initial_era = Rotator::<T>::planning_era();
+		let initial_era = Rotator::<T>::planned_era();
 		let _ = crate::testing_utils::create_validators_with_nominators_for_era::<T>(
 			2 * v,
 			// number of nominators is irrelevant here, so we hardcode these
@@ -1085,7 +1084,7 @@ mod benchmarks {
 
 		// plan new era
 		let new_validators = Rotator::<T>::legacy_insta_plan_era();
-		ensure!(Rotator::<T>::planning_era() == initial_era + 1, "era should be incremented");
+		ensure!(Rotator::<T>::planned_era() == initial_era + 1, "era should be incremented");
 		// activate the previous one
 		Rotator::<T>::start_era(
 			crate::ActiveEraInfo { index: initial_era, start: Some(1) },
@@ -1135,7 +1134,7 @@ mod benchmarks {
 
 	#[benchmark]
 	fn rc_on_session_report() -> Result<(), BenchmarkError> {
-		let initial_planned_era = Rotator::<T>::planning_era();
+		let initial_planned_era = Rotator::<T>::planned_era();
 		let initial_active_era = Rotator::<T>::active_era();
 
 		// create a small, arbitrary number of stakers. This is just for sanity of the era planning,

substrate/frame/staking-async/src/mock.rs

@@ -312,16 +312,29 @@ pub mod session_mock {
 				if QueuedBufferSessions::get() == 0 {
 					// buffer time has passed
 					Active::set(q);
-					Rotator::<Test>::end_session(ending, Some((Timestamp::get(), id)));
+					<Staking as rc_client::AHStakingInterface>::on_relay_session_report(
+						rc_client::SessionReport::new_terminal(
+							ending,
+							// TODO: currently we use `Eras::reward_active_era()` to set validator
+							// points in our tests. We should improve this and find a good way to
+							// set this value instead.
+							vec![],
+							Some((Timestamp::get(), id)),
+						),
+					);
 					Queued::reset();
 					QueuedId::reset();
 				} else {
 					QueuedBufferSessions::mutate(|s| *s -= 1);
-					Rotator::<Test>::end_session(ending, None);
+					<Staking as rc_client::AHStakingInterface>::on_relay_session_report(
+						rc_client::SessionReport::new_terminal(ending, vec![], None),
+					);
 				}
 			} else {
 				// just end the session.
-				Rotator::<Test>::end_session(ending, None);
+				<Staking as rc_client::AHStakingInterface>::on_relay_session_report(
+					rc_client::SessionReport::new_terminal(ending, vec![], None),
+				);
 			}
 			CurrentIndex::set(ending + 1);
 		}
@@ -385,6 +398,7 @@ ord_parameter_types! {
 
 parameter_types! {
 	pub static RemainderRatio: Perbill = Perbill::from_percent(50);
+	pub static MaxEraDuration: u64 = time_per_era() * 7;
 }
 pub struct OneTokenPerMillisecond;
 impl EraPayout<Balance> for OneTokenPerMillisecond {
@@ -423,6 +437,7 @@ impl crate::pallet::pallet::Config for Test {
 	type EventListeners = EventListenerMock;
 	type MaxInvulnerables = ConstU32<20>;
 	type MaxDisabledValidators = ConstU32<100>;
+	type MaxEraDuration = MaxEraDuration;
 	type PlanningEraOffset = PlanningEraOffset;
 	type Filter = MockedRestrictList;
 	type RcClientInterface = session_mock::Session;

substrate/frame/staking-async/src/pallet/impls.rs

@@ -72,6 +72,30 @@ use sp_runtime::TryRuntimeError;
 const NPOS_MAX_ITERATIONS_COEFFICIENT: u32 = 2;
 
 impl<T: Config> Pallet<T> {
+	/// Returns the minimum required bond for participation, considering nominators,
+	/// and the chain’s existential deposit.
+	///
+	/// This function computes the smallest allowed bond among `MinValidatorBond` and
+	/// `MinNominatorBond`, but ensures it is not below the existential deposit required to keep an
+	/// account alive.
+	pub(crate) fn min_chilled_bond() -> BalanceOf<T> {
+		MinValidatorBond::<T>::get()
+			.min(MinNominatorBond::<T>::get())
+			.max(asset::existential_deposit::<T>())
+	}
+
+	/// Returns the minimum required bond for validators, defaulting to `MinNominatorBond` if not
+	/// set or less than `MinNominatorBond`.
+	pub(crate) fn min_validator_bond() -> BalanceOf<T> {
+		MinValidatorBond::<T>::get().max(Self::min_nominator_bond())
+	}
+
+	/// Returns the minimum required bond for nominators, considering the chain’s existential
+	/// deposit.
+	pub(crate) fn min_nominator_bond() -> BalanceOf<T> {
+		MinNominatorBond::<T>::get().max(asset::existential_deposit::<T>())
+	}
+
 	/// Fetches the ledger associated with a controller or stash account, if any.
 	pub fn ledger(account: StakingAccount<T::AccountId>) -> Result<StakingLedger<T>, Error<T>> {
 		StakingLedger::<T>::get(account)
@@ -169,8 +193,8 @@ impl<T: Config> Pallet<T> {
 
 		ledger.total = ledger.total.checked_add(&extra).ok_or(ArithmeticError::Overflow)?;
 		ledger.active = ledger.active.checked_add(&extra).ok_or(ArithmeticError::Overflow)?;
-		// last check: the new active amount of ledger must be more than ED.
-		ensure!(ledger.active >= asset::existential_deposit::<T>(), Error::<T>::InsufficientBond);
+		// last check: the new active amount of ledger must be more than min bond.
+		ensure!(ledger.active >= Self::min_chilled_bond(), Error::<T>::InsufficientBond);
 
 		// NOTE: ledger must be updated prior to calling `Self::weight_of`.
 		ledger.update()?;
@@ -193,22 +217,22 @@ impl<T: Config> Pallet<T> {
 		}
 		let new_total = ledger.total;
 
-		let ed = asset::existential_deposit::<T>();
-		let used_weight =
-			if ledger.unlocking.is_empty() && (ledger.active < ed || ledger.active.is_zero()) {
-				// This account must have called `unbond()` with some value that caused the active
-				// portion to fall below existential deposit + will have no more unlocking chunks
-				// left. We can now safely remove all staking-related information.
-				Self::kill_stash(&ledger.stash)?;
+		let used_weight = if ledger.unlocking.is_empty() &&
+			(ledger.active < Self::min_chilled_bond() || ledger.active.is_zero())
+		{
+			// This account must have called `unbond()` with some value that caused the active
+			// portion to fall below existential deposit + will have no more unlocking chunks
+			// left. We can now safely remove all staking-related information.
+			Self::kill_stash(&ledger.stash)?;
 
-				T::WeightInfo::withdraw_unbonded_kill()
-			} else {
-				// This was the consequence of a partial unbond. just update the ledger and move on.
-				ledger.update()?;
+			T::WeightInfo::withdraw_unbonded_kill()
+		} else {
+			// This was the consequence of a partial unbond. just update the ledger and move on.
+			ledger.update()?;
 
-				// This is only an update, so we use less overall weight.
-				T::WeightInfo::withdraw_unbonded_update()
-			};
+			// This is only an update, so we use less overall weight.
+			T::WeightInfo::withdraw_unbonded_update()
+		};
 
 		// `old_total` should never be less than the new total because
 		// `consolidate_unlocked` strictly subtracts balance.
@@ -972,7 +996,7 @@ impl<T: Config> ElectionDataProvider for Pallet<T> {
 
 	#[cfg(feature = "runtime-benchmarks")]
 	fn add_target(target: T::AccountId) {
-		let stake = (MinValidatorBond::<T>::get() + 1u32.into()) * 100u32.into();
+		let stake = (Self::min_validator_bond() + 1u32.into()) * 100u32.into();
 		<Bonded<T>>::insert(target.clone(), target.clone());
 		<Ledger<T>>::insert(target.clone(), StakingLedger::<T>::new(target.clone(), stake));
 		Self::do_add_validator(
@@ -1004,7 +1028,7 @@ impl<T: Config> ElectionDataProvider for Pallet<T> {
 		targets.into_iter().for_each(|v| {
 			let stake: BalanceOf<T> = target_stake
 				.and_then(|w| <BalanceOf<T>>::try_from(w).ok())
-				.unwrap_or_else(|| MinNominatorBond::<T>::get() * 100u32.into());
+				.unwrap_or_else(|| Self::min_nominator_bond() * 100u32.into());
 			<Bonded<T>>::insert(v.clone(), v.clone());
 			<Ledger<T>>::insert(v.clone(), StakingLedger::<T>::new(v.clone(), stake));
 			Self::do_add_validator(
@@ -1425,11 +1449,11 @@ impl<T: Config> StakingInterface for Pallet<T> {
 	type CurrencyToVote = T::CurrencyToVote;
 
 	fn minimum_nominator_bond() -> Self::Balance {
-		MinNominatorBond::<T>::get()
+		Self::min_nominator_bond()
 	}
 
 	fn minimum_validator_bond() -> Self::Balance {
-		MinValidatorBond::<T>::get()
+		Self::min_validator_bond()
 	}
 
 	fn stash_by_ctrl(controller: &Self::AccountId) -> Result<Self::AccountId, DispatchError> {