Pallet session new API (#4609)

* Initial work

* Fix most things

* fix test

* fix old comment

* migration

* fix

* remove useless stuff

* fix

* less spaghetti implementation

* fix initial session

* fix

substrate/frame/staking/src/lib.rs

@@ -265,7 +265,7 @@ use frame_support::{
 		WithdrawReasons, OnUnbalanced, Imbalance, Get, Time
 	}
 };
-use pallet_session::{historical::OnSessionEnding, SelectInitialValidators};
+use pallet_session::historical::SessionManager;
 use sp_runtime::{
 	Perbill,
 	RuntimeDebug,
@@ -575,8 +575,7 @@ impl<T: Trait> SessionInterface<<T as frame_system::Trait>::AccountId> for T whe
 		FullIdentificationOf = ExposureOf<T>,
 	>,
 	T::SessionHandler: pallet_session::SessionHandler<<T as frame_system::Trait>::AccountId>,
-	T::OnSessionEnding: pallet_session::OnSessionEnding<<T as frame_system::Trait>::AccountId>,
-	T::SelectInitialValidators: pallet_session::SelectInitialValidators<<T as frame_system::Trait>::AccountId>,
+	T::SessionManager: pallet_session::SessionManager<<T as frame_system::Trait>::AccountId>,
 	T::ValidatorIdOf: Convert<<T as frame_system::Trait>::AccountId, Option<<T as frame_system::Trait>::AccountId>>
 {
 	fn disable_validator(validator: &<T as frame_system::Trait>::AccountId) -> Result<bool, ()> {
@@ -1346,11 +1345,8 @@ impl<T: Trait> Module<T> {
 		imbalance
 	}
 
-	/// Session has just ended. Provide the validator set for the next session if it's an era-end, along
-	/// with the exposure of the prior validator set.
-	fn new_session(session_index: SessionIndex)
-		-> Option<(Vec<T::AccountId>, Vec<(T::AccountId, Exposure<T::AccountId, BalanceOf<T>>)>)>
-	{
+	/// Session has just ended. Provide the validator set for the next session if it's an era-end.
+	fn new_session(session_index: SessionIndex) -> Option<Vec<T::AccountId>> {
 		let era_length = session_index.checked_sub(Self::current_era_start_session_index()).unwrap_or(0);
 		match ForceEra::get() {
 			Forcing::ForceNew => ForceEra::kill(),
@@ -1358,12 +1354,17 @@ impl<T: Trait> Module<T> {
 			Forcing::NotForcing if era_length >= T::SessionsPerEra::get() => (),
 			_ => return None,
 		}
-		let validators = T::SessionInterface::validators();
-		let prior = validators.into_iter()
-			.map(|v| { let e = Self::stakers(&v); (v, e) })
-			.collect();
 
-		Self::new_era(session_index).map(move |new| (new, prior))
+		Self::new_era(session_index)
+	}
+
+	/// Initialise the first session (and consequently the first era)
+	fn initial_session() -> Option<Vec<T::AccountId>> {
+		// note: `CurrentEraStart` is set in `on_finalize` of the first block because now is not
+		// available yet.
+		CurrentEraStartSessionIndex::put(0);
+		BondedEras::mutate(|bonded| bonded.push((0, 0)));
+		Self::select_validators().1
 	}
 
 	/// The era has changed - enact new staking set.
@@ -1646,19 +1647,30 @@ impl<T: Trait> Module<T> {
 	}
 }
 
-impl<T: Trait> pallet_session::OnSessionEnding<T::AccountId> for Module<T> {
-	fn on_session_ending(_ending: SessionIndex, start_session: SessionIndex) -> Option<Vec<T::AccountId>> {
+impl<T: Trait> pallet_session::SessionManager<T::AccountId> for Module<T> {
+	fn new_session(new_index: SessionIndex) -> Option<Vec<T::AccountId>> {
 		Self::ensure_storage_upgraded();
-		Self::new_session(start_session - 1).map(|(new, _old)| new)
+		if new_index == 0 {
+			return Self::initial_session();
+		}
+		Self::new_session(new_index - 1)
 	}
+	fn end_session(_end_index: SessionIndex) {}
 }
 
-impl<T: Trait> OnSessionEnding<T::AccountId, Exposure<T::AccountId, BalanceOf<T>>> for Module<T> {
-	fn on_session_ending(_ending: SessionIndex, start_session: SessionIndex)
-		-> Option<(Vec<T::AccountId>, Vec<(T::AccountId, Exposure<T::AccountId, BalanceOf<T>>)>)>
+impl<T: Trait> SessionManager<T::AccountId, Exposure<T::AccountId, BalanceOf<T>>> for Module<T> {
+	fn new_session(new_index: SessionIndex)
+		-> Option<Vec<(T::AccountId, Exposure<T::AccountId, BalanceOf<T>>)>>
 	{
-		Self::ensure_storage_upgraded();
-		Self::new_session(start_session - 1)
+		<Self as pallet_session::SessionManager<_>>::new_session(new_index).map(|validators| {
+			validators.into_iter().map(|v| {
+				let exposure = <Stakers<T>>::get(&v);
+				(v, exposure)
+			}).collect()
+		})
+	}
+	fn end_session(end_index: SessionIndex) {
+		<Self as pallet_session::SessionManager<_>>::end_session(end_index)
 	}
 }
 
@@ -1707,12 +1719,6 @@ impl<T: Trait> Convert<T::AccountId, Option<Exposure<T::AccountId, BalanceOf<T>>
 	}
 }
 
-impl<T: Trait> SelectInitialValidators<T::AccountId> for Module<T> {
-	fn select_initial_validators() -> Option<Vec<T::AccountId>> {
-		<Module<T>>::select_validators().1
-	}
-}
-
 /// This is intended to be used with `FilterHistoricalOffences`.
 impl <T: Trait> OnOffenceHandler<T::AccountId, pallet_session::historical::IdentificationTuple<T>> for Module<T> where
 	T: pallet_session::Trait<ValidatorId = <T as frame_system::Trait>::AccountId>,
@@ -1721,8 +1727,7 @@ impl <T: Trait> OnOffenceHandler<T::AccountId, pallet_session::historical::Ident
 		FullIdentificationOf = ExposureOf<T>,
 	>,
 	T::SessionHandler: pallet_session::SessionHandler<<T as frame_system::Trait>::AccountId>,
-	T::OnSessionEnding: pallet_session::OnSessionEnding<<T as frame_system::Trait>::AccountId>,
-	T::SelectInitialValidators: pallet_session::SelectInitialValidators<<T as frame_system::Trait>::AccountId>,
+	T::SessionManager: pallet_session::SessionManager<<T as frame_system::Trait>::AccountId>,
 	T::ValidatorIdOf: Convert<<T as frame_system::Trait>::AccountId, Option<<T as frame_system::Trait>::AccountId>>
 {
 	fn on_offence(

substrate/frame/staking/src/mock.rs

@@ -162,14 +162,13 @@ parameter_types! {
 	pub const DisabledValidatorsThreshold: Perbill = Perbill::from_percent(25);
 }
 impl pallet_session::Trait for Test {
-	type OnSessionEnding = pallet_session::historical::NoteHistoricalRoot<Test, Staking>;
+	type SessionManager = pallet_session::historical::NoteHistoricalRoot<Test, Staking>;
 	type Keys = UintAuthorityId;
 	type ShouldEndSession = pallet_session::PeriodicSessions<Period, Offset>;
 	type SessionHandler = TestSessionHandler;
 	type Event = ();
 	type ValidatorId = AccountId;
 	type ValidatorIdOf = crate::StashOf<Test>;
-	type SelectInitialValidators = Staking;
 	type DisabledValidatorsThreshold = DisabledValidatorsThreshold;
 }
 

substrate/frame/staking/src/tests.rs

@@ -365,7 +365,7 @@ fn less_than_needed_candidates_works() {
 #[test]
 fn no_candidate_emergency_condition() {
 	ExtBuilder::default()
-		.minimum_validator_count(10)
+		.minimum_validator_count(1)
 		.validator_count(15)
 		.num_validators(4)
 		.validator_pool(true)
@@ -374,21 +374,21 @@ fn no_candidate_emergency_condition() {
 		.execute_with(|| {
 			// initial validators
 			assert_eq_uvec!(validator_controllers(), vec![10, 20, 30, 40]);
+			let prefs = ValidatorPrefs { commission: Perbill::one() };
+			<Staking as crate::Store>::Validators::insert(11, prefs.clone());
 
 			// set the minimum validator count.
 			<Staking as crate::Store>::MinimumValidatorCount::put(10);
-			<Staking as crate::Store>::ValidatorCount::put(15);
-			assert_eq!(Staking::validator_count(), 15);
 
 			let _ = Staking::chill(Origin::signed(10));
 
 			// trigger era
-			System::set_block_number(1);
-			Session::on_initialize(System::block_number());
+			start_era(1);
 
 			// Previous ones are elected. chill is invalidates. TODO: #2494
 			assert_eq_uvec!(validator_controllers(), vec![10, 20, 30, 40]);
-			assert_eq!(Staking::current_elected().len(), 0);
+			// Though the validator preferences has been removed.
+			assert!(Staking::validators(11) != prefs);
 		});
 }