XCM remote lock consumers (#6947)

* xcm remote lock consumers

* update xcm pallet config setups

* fix import

* update xcm pallet config setups

* rename consumers to users

* rename

* rename users to consumers, more docs

* correct doc

---------

Co-authored-by: parity-processbot <>

runtime/kusama/src/xcm_config.rs

@@ -422,6 +422,8 @@ impl pallet_xcm::Config for Runtime {
 	type TrustedLockers = ();
 	type SovereignAccountOf = SovereignAccountOf;
 	type MaxLockers = ConstU32<8>;
+	type MaxRemoteLockConsumers = ConstU32<0>;
+	type RemoteLockConsumerIdentifier = ();
 	type WeightInfo = crate::weights::pallet_xcm::WeightInfo<Runtime>;
 	#[cfg(feature = "runtime-benchmarks")]
 	type ReachableDest = ReachableDest;

runtime/polkadot/src/xcm_config.rs

@@ -417,6 +417,8 @@ impl pallet_xcm::Config for Runtime {
 	type TrustedLockers = ();
 	type SovereignAccountOf = SovereignAccountOf;
 	type MaxLockers = ConstU32<8>;
+	type MaxRemoteLockConsumers = ConstU32<0>;
+	type RemoteLockConsumerIdentifier = ();
 	type WeightInfo = crate::weights::pallet_xcm::WeightInfo<Runtime>;
 	#[cfg(feature = "runtime-benchmarks")]
 	type ReachableDest = ReachableDest;

runtime/rococo/src/xcm_config.rs

@@ -384,6 +384,8 @@ impl pallet_xcm::Config for Runtime {
 	type TrustedLockers = ();
 	type SovereignAccountOf = LocationConverter;
 	type MaxLockers = ConstU32<8>;
+	type MaxRemoteLockConsumers = ConstU32<0>;
+	type RemoteLockConsumerIdentifier = ();
 	type WeightInfo = crate::weights::pallet_xcm::WeightInfo<Runtime>;
 	#[cfg(feature = "runtime-benchmarks")]
 	type ReachableDest = ReachableDest;

runtime/test-runtime/src/xcm_config.rs

@@ -144,6 +144,8 @@ impl pallet_xcm::Config for crate::Runtime {
 	type TrustedLockers = ();
 	type SovereignAccountOf = ();
 	type MaxLockers = frame_support::traits::ConstU32<8>;
+	type MaxRemoteLockConsumers = frame_support::traits::ConstU32<0>;
+	type RemoteLockConsumerIdentifier = ();
 	type WeightInfo = pallet_xcm::TestWeightInfo;
 	#[cfg(feature = "runtime-benchmarks")]
 	type ReachableDest = ReachableDest;

runtime/westend/src/xcm_config.rs

@@ -300,6 +300,8 @@ impl pallet_xcm::Config for Runtime {
 	type TrustedLockers = ();
 	type SovereignAccountOf = LocationConverter;
 	type MaxLockers = ConstU32<8>;
+	type MaxRemoteLockConsumers = ConstU32<0>;
+	type RemoteLockConsumerIdentifier = ();
 	type WeightInfo = crate::weights::pallet_xcm::WeightInfo<Runtime>;
 	#[cfg(feature = "runtime-benchmarks")]
 	type ReachableDest = ReachableDest;

xcm/pallet-xcm/src/lib.rs

@@ -250,6 +250,12 @@ pub mod pallet {
 		/// The maximum number of local XCM locks that a single account may have.
 		type MaxLockers: Get<u32>;
 
+		/// The maximum number of consumers a single remote lock may have.
+		type MaxRemoteLockConsumers: Get<u32>;
+
+		/// The ID type for local consumers of remote locks.
+		type RemoteLockConsumerIdentifier: Parameter + Member + MaxEncodedLen + Ord + Copy;
+
 		/// Weight information for extrinsics in this pallet.
 		type WeightInfo: WeightInfo;
 
@@ -445,7 +451,7 @@ pub mod pallet {
 		FeesNotMet,
 		/// A remote lock with the corresponding data could not be found.
 		LockNotFound,
-		/// The unlock operation cannot succeed because there are still users of the lock.
+		/// The unlock operation cannot succeed because there are still consumers of the lock.
 		InUse,
 	}
 
@@ -588,11 +594,26 @@ pub mod pallet {
 		StorageValue<_, VersionMigrationStage, OptionQuery>;
 
 	#[derive(Clone, Encode, Decode, Eq, PartialEq, Ord, PartialOrd, TypeInfo, MaxEncodedLen)]
-	pub struct RemoteLockedFungibleRecord {
+	#[scale_info(skip_type_params(MaxConsumers))]
+	pub struct RemoteLockedFungibleRecord<ConsumerIdentifier, MaxConsumers: Get<u32>> {
+		/// Total amount of the asset held by the remote lock.
 		pub amount: u128,
+		/// The owner of the locked asset.
 		pub owner: VersionedMultiLocation,
+		/// The location which holds the original lock.
 		pub locker: VersionedMultiLocation,
-		pub users: u32,
+		/// Local consumers of the remote lock with a consumer identifier and the amount
+		/// of fungible asset every consumer holds.
+		/// Every consumer can hold up to total amount of the remote lock.
+		pub consumers: BoundedVec<(ConsumerIdentifier, u128), MaxConsumers>,
+	}
+
+	impl<LockId, MaxConsumers: Get<u32>> RemoteLockedFungibleRecord<LockId, MaxConsumers> {
+		/// Amount of the remote lock in use by consumers.
+		/// Returns `None` if the remote lock has no consumers.
+		pub fn amount_held(&self) -> Option<u128> {
+			self.consumers.iter().max_by(|x, y| x.1.cmp(&y.1)).map(|max| max.1)
+		}
 	}
 
 	/// Fungible assets which we know are locked on a remote chain.
@@ -604,7 +625,7 @@ pub mod pallet {
 			NMapKey<Blake2_128Concat, T::AccountId>,
 			NMapKey<Blake2_128Concat, VersionedAssetId>,
 		),
-		RemoteLockedFungibleRecord,
+		RemoteLockedFungibleRecord<T::RemoteLockConsumerIdentifier, T::MaxRemoteLockConsumers>,
 		OptionQuery,
 	>;
 
@@ -1693,11 +1714,12 @@ impl<T: Config> xcm_executor::traits::Enact for ReduceTicket<T> {
 		use xcm_executor::traits::LockError::UnexpectedState;
 		let mut record = RemoteLockedFungibles::<T>::get(&self.key).ok_or(UnexpectedState)?;
 		ensure!(self.locker == record.locker && self.owner == record.owner, UnexpectedState);
-		ensure!(record.users == 0, UnexpectedState);
-		record.amount = record.amount.checked_sub(self.amount).ok_or(UnexpectedState)?;
-		if record.amount == 0 {
+		let new_amount = record.amount.checked_sub(self.amount).ok_or(UnexpectedState)?;
+		ensure!(record.amount_held().map_or(true, |h| new_amount >= h), UnexpectedState);
+		if new_amount == 0 {
 			RemoteLockedFungibles::<T>::remove(&self.key);
 		} else {
+			record.amount = new_amount;
 			RemoteLockedFungibles::<T>::insert(&self.key, &record);
 		}
 		Ok(())
@@ -1757,11 +1779,12 @@ impl<T: Config> xcm_executor::traits::AssetLock for Pallet<T> {
 		let owner = owner.into();
 		let id: VersionedAssetId = asset.id.into();
 		let key = (XCM_VERSION, account, id);
-		let mut record = RemoteLockedFungibleRecord { amount, owner, locker, users: 0 };
+		let mut record =
+			RemoteLockedFungibleRecord { amount, owner, locker, consumers: BoundedVec::default() };
 		if let Some(old) = RemoteLockedFungibles::<T>::get(&key) {
 			// Make sure that the new record wouldn't clobber any old data.
 			ensure!(old.locker == record.locker && old.owner == record.owner, WouldClobber);
-			record.users = old.users;
+			record.consumers = old.consumers;
 			record.amount = record.amount.max(old.amount);
 		}
 		RemoteLockedFungibles::<T>::insert(&key, record);
@@ -1788,8 +1811,11 @@ impl<T: Config> xcm_executor::traits::AssetLock for Pallet<T> {
 		let record = RemoteLockedFungibles::<T>::get(&key).ok_or(NotLocked)?;
 		// Make sure that the record contains what we expect and there's enough to unlock.
 		ensure!(locker == record.locker && owner == record.owner, WouldClobber);
-		ensure!(record.users == 0, InUse);
 		ensure!(record.amount >= amount, NotEnoughLocked);
+		ensure!(
+			record.amount_held().map_or(true, |h| record.amount.saturating_sub(amount) >= h),
+			InUse
+		);
 		Ok(ReduceTicket { key, amount, locker, owner })
 	}
 }

xcm/pallet-xcm/src/mock.rs

@@ -342,6 +342,8 @@ impl pallet_xcm::Config for Test {
 	type Currency = Balances;
 	type CurrencyMatcher = IsConcrete<RelayLocation>;
 	type MaxLockers = frame_support::traits::ConstU32<8>;
+	type MaxRemoteLockConsumers = frame_support::traits::ConstU32<0>;
+	type RemoteLockConsumerIdentifier = ();
 	type WeightInfo = TestWeightInfo;
 	#[cfg(feature = "runtime-benchmarks")]
 	type ReachableDest = ReachableDest;

xcm/xcm-builder/tests/mock/mod.rs

@@ -233,6 +233,8 @@ impl pallet_xcm::Config for Runtime {
 	type Currency = Balances;
 	type CurrencyMatcher = IsConcrete<KsmLocation>;
 	type MaxLockers = frame_support::traits::ConstU32<8>;
+	type MaxRemoteLockConsumers = frame_support::traits::ConstU32<0>;
+	type RemoteLockConsumerIdentifier = ();
 	type WeightInfo = pallet_xcm::TestWeightInfo;
 	#[cfg(feature = "runtime-benchmarks")]
 	type ReachableDest = ReachableDest;

xcm/xcm-simulator/example/src/parachain.rs

@@ -423,6 +423,8 @@ impl pallet_xcm::Config for Runtime {
 	type TrustedLockers = ();
 	type SovereignAccountOf = LocationToAccountId;
 	type MaxLockers = ConstU32<8>;
+	type MaxRemoteLockConsumers = ConstU32<0>;
+	type RemoteLockConsumerIdentifier = ();
 	type WeightInfo = pallet_xcm::TestWeightInfo;
 	#[cfg(feature = "runtime-benchmarks")]
 	type ReachableDest = ReachableDest;

xcm/xcm-simulator/example/src/relay_chain.rs

@@ -220,6 +220,8 @@ impl pallet_xcm::Config for Runtime {
 	type TrustedLockers = ();
 	type SovereignAccountOf = LocationToAccountId;
 	type MaxLockers = ConstU32<8>;
+	type MaxRemoteLockConsumers = ConstU32<0>;
+	type RemoteLockConsumerIdentifier = ();
 	type WeightInfo = pallet_xcm::TestWeightInfo;
 	#[cfg(feature = "runtime-benchmarks")]
 	type ReachableDest = ReachableDest;

xcm/xcm-simulator/fuzzer/src/parachain.rs

@@ -338,6 +338,8 @@ impl pallet_xcm::Config for Runtime {
 	type TrustedLockers = ();
 	type SovereignAccountOf = LocationToAccountId;
 	type MaxLockers = frame_support::traits::ConstU32<8>;
+	type MaxRemoteLockConsumers = frame_support::traits::ConstU32<0>;
+	type RemoteLockConsumerIdentifier = ();
 	type WeightInfo = pallet_xcm::TestWeightInfo;
 	#[cfg(feature = "runtime-benchmarks")]
 	type ReachableDest = ReachableDest;

xcm/xcm-simulator/fuzzer/src/relay_chain.rs

@@ -184,6 +184,8 @@ impl pallet_xcm::Config for Runtime {
 	type TrustedLockers = ();
 	type SovereignAccountOf = SovereignAccountOf;
 	type MaxLockers = ConstU32<8>;
+	type MaxRemoteLockConsumers = ConstU32<0>;
+	type RemoteLockConsumerIdentifier = ();
 	type WeightInfo = pallet_xcm::TestWeightInfo;
 	#[cfg(feature = "runtime-benchmarks")]
 	type ReachableDest = ReachableDest;