[FRAME] Make core-fellowship ans salary work for swapped members (#3156)

Fixup for https://github.com/paritytech/polkadot-sdk/pull/2587 to make
the `core-fellowship` crate work with swapped members.

Adds a `MemberSwappedHandler` to the `ranked-collective` pallet that are
implemented by `core-fellowship+salary`.
There is are exhaustive tests
[here](https://github.com/paritytech/polkadot-sdk/blob/72aa7ac17a0e5b16faab5d2992aa2db2e01b05d0/substrate/frame/core-fellowship/src/tests/integration.rs#L338)
and
[here](https://github.com/paritytech/polkadot-sdk/blob/ab3cdb05a5ebc1ff841f8dda67edef0ea40bbba5/substrate/frame/salary/src/tests/integration.rs#L224)
to check that adding member `1` is equivalent to adding member `0` and
then swapping.

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

substrate/frame/ranked-collective/src/benchmarking.rs

@@ -33,6 +33,10 @@ fn assert_last_event<T: Config<I>, I: 'static>(generic_event: <T as Config<I>>::
 	frame_system::Pallet::<T>::assert_last_event(generic_event.into());
 }
 
+fn assert_has_event<T: Config<I>, I: 'static>(generic_event: <T as Config<I>>::RuntimeEvent) {
+	frame_system::Pallet::<T>::assert_has_event(generic_event.into());
+}
+
 fn make_member<T: Config<I>, I: 'static>(rank: Rank) -> T::AccountId {
 	let who = account::<T::AccountId>("member", MemberCount::<T, I>::get(0), SEED);
 	let who_lookup = T::Lookup::unlookup(who.clone());
@@ -175,17 +179,18 @@ benchmarks_instance_pallet! {
 
 	exchange_member {
 		let who = make_member::<T, I>(1);
+		T::BenchmarkSetup::ensure_member(&who);
 		let who_lookup = T::Lookup::unlookup(who.clone());
 		let new_who = account::<T::AccountId>("new-member", 0, SEED);
 		let new_who_lookup = T::Lookup::unlookup(new_who.clone());
 		let origin =
 			T::ExchangeOrigin::try_successful_origin().map_err(|_| BenchmarkError::Weightless)?;
-		let call = Call::<T, I>::exchange_member { who: who_lookup, new_who:new_who_lookup};
+		let call = Call::<T, I>::exchange_member { who: who_lookup, new_who: new_who_lookup };
 	}: { call.dispatch_bypass_filter(origin)? }
 	verify {
 		assert_eq!(Members::<T, I>::get(&new_who).unwrap().rank, 1);
 		assert_eq!(Members::<T, I>::get(&who), None);
-		assert_last_event::<T, I>(Event::MemberExchanged { who, new_who }.into());
+		assert_has_event::<T, I>(Event::MemberExchanged { who, new_who }.into());
 	}
 
 	impl_benchmark_test_suite!(RankedCollective, crate::tests::new_test_ext(), crate::tests::Test);

substrate/frame/ranked-collective/src/lib.rs

@@ -54,7 +54,10 @@ use sp_std::{marker::PhantomData, prelude::*};
 use frame_support::{
 	dispatch::{DispatchResultWithPostInfo, PostDispatchInfo},
 	ensure, impl_ensure_origin_with_arg_ignoring_arg,
-	traits::{EnsureOrigin, EnsureOriginWithArg, PollStatus, Polling, RankedMembers, VoteTally},
+	traits::{
+		EnsureOrigin, EnsureOriginWithArg, PollStatus, Polling, RankedMembers,
+		RankedMembersSwapHandler, VoteTally,
+	},
 	CloneNoBound, EqNoBound, PartialEqNoBound, RuntimeDebugNoBound,
 };
 
@@ -365,6 +368,13 @@ impl_ensure_origin_with_arg_ignoring_arg! {
 	{}
 }
 
+/// Helper functions to setup benchmarking.
+#[impl_trait_for_tuples::impl_for_tuples(8)]
+pub trait BenchmarkSetup<AccountId> {
+	/// Ensure that this member is registered correctly.
+	fn ensure_member(acc: &AccountId);
+}
+
 #[frame_support::pallet]
 pub mod pallet {
 	use super::*;
@@ -402,11 +412,21 @@ pub mod pallet {
 		/// "a rank of at least the poll class".
 		type MinRankOfClass: Convert<ClassOf<Self, I>, Rank>;
 
+		/// An external handler that will be notified when two members are swapped.
+		type MemberSwappedHandler: RankedMembersSwapHandler<
+			<Pallet<Self, I> as RankedMembers>::AccountId,
+			<Pallet<Self, I> as RankedMembers>::Rank,
+		>;
+
 		/// Convert a rank_delta into a number of votes the rank gets.
 		///
 		/// Rank_delta is defined as the number of ranks above the minimum required to take part
 		/// in the poll.
 		type VoteWeight: Convert<Rank, Votes>;
+
+		/// Setup a member for benchmarking.
+		#[cfg(feature = "runtime-benchmarks")]
+		type BenchmarkSetup: BenchmarkSetup<Self::AccountId>;
 	}
 
 	/// The number of members in the collective who have at least the rank according to the index
@@ -679,7 +699,12 @@ pub mod pallet {
 			Self::do_remove_member_from_rank(&who, rank)?;
 			Self::do_add_member_to_rank(new_who.clone(), rank, false)?;
 
-			Self::deposit_event(Event::MemberExchanged { who, new_who });
+			Self::deposit_event(Event::MemberExchanged {
+				who: who.clone(),
+				new_who: new_who.clone(),
+			});
+			T::MemberSwappedHandler::swapped(&who, &new_who, rank);
+
 			Ok(())
 		}
 	}

substrate/frame/ranked-collective/src/tests.rs

@@ -172,7 +172,10 @@ impl Config for Test {
 	>;
 	type Polls = TestPolls;
 	type MinRankOfClass = MinRankOfClass<MinRankOfClassDelta>;
+	type MemberSwappedHandler = ();
 	type VoteWeight = Geometric;
+	#[cfg(feature = "runtime-benchmarks")]
+	type BenchmarkSetup = ();
 }
 
 pub fn new_test_ext() -> sp_io::TestExternalities {
@@ -602,3 +605,21 @@ fn exchange_member_works() {
 		);
 	});
 }
+
+#[test]
+fn exchange_member_same_noops() {
+	new_test_ext().execute_with(|| {
+		assert_ok!(Club::add_member(RuntimeOrigin::root(), 1));
+		assert_ok!(Club::promote_member(RuntimeOrigin::root(), 1));
+		assert_ok!(Club::add_member(RuntimeOrigin::root(), 2));
+		assert_ok!(Club::promote_member(RuntimeOrigin::root(), 2));
+
+		// Swapping the same accounts is a noop:
+		assert_noop!(Club::exchange_member(RuntimeOrigin::root(), 1, 1), Error::<Test>::SameMember);
+		// Swapping with a different member is a noop:
+		assert_noop!(
+			Club::exchange_member(RuntimeOrigin::root(), 1, 2),
+			Error::<Test>::AlreadyMember
+		);
+	});
+}