Dependency Injection Trait Locker for Uniques Pallet (#11025)

* Create a dependency injection trait named Locker that can be implemented downstream to enable locking of an asset. Use case defined in RMRK substrate pallet PR76

* Formatting

* Change impl Locker function name to is_locked

* Remove unused import

* Add docstring header

* Remove impl_locker file and add Locker trait to frame_support::traits

* Expose Locker from frame_support::traits::misc

* Formatting

* Move to tokens folder

* Move to tokens folder

* Format and remove Locker from misc traits

* Punctuation

* Update frame/support/src/traits/tokens/misc.rs

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>
Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Giles Cope <gilescope@gmail.com>

bin/node/runtime/src/lib.rs

@@ -1407,6 +1407,7 @@ impl pallet_uniques::Config for Runtime {
 	#[cfg(feature = "runtime-benchmarks")]
 	type Helper = ();
 	type CreateOrigin = AsEnsureOriginWithArg<EnsureSigned<AccountId>>;
+	type Locker = ();
 }
 
 impl pallet_transaction_storage::Config for Runtime {

frame/support/src/traits.rs

@@ -27,7 +27,7 @@ pub use tokens::{
 	},
 	fungible, fungibles,
 	imbalance::{Imbalance, OnUnbalanced, SignedImbalance},
-	BalanceStatus, ExistenceRequirement, WithdrawReasons,
+	BalanceStatus, ExistenceRequirement, Locker, WithdrawReasons,
 };
 
 mod members;

frame/support/src/traits/tokens.rs

@@ -27,5 +27,5 @@ pub mod nonfungibles;
 pub use imbalance::Imbalance;
 pub use misc::{
 	AssetId, Balance, BalanceConversion, BalanceStatus, DepositConsequence, ExistenceRequirement,
-	WithdrawConsequence, WithdrawReasons,
+	Locker, WithdrawConsequence, WithdrawReasons,
 };

frame/support/src/traits/tokens/misc.rs

@@ -179,3 +179,19 @@ pub trait BalanceConversion<InBalance, AssetId, OutBalance> {
 	type Error;
 	fn to_asset_balance(balance: InBalance, asset_id: AssetId) -> Result<OutBalance, Self::Error>;
 }
+
+/// Trait to handle asset locking mechanism to ensure interactions with the asset can be implemented
+/// downstream to extend logic of Uniques current functionality.
+pub trait Locker<ClassId, InstanceId> {
+	/// Check if the asset should be locked and prevent interactions with the asset from executing.
+	fn is_locked(class: ClassId, instance: InstanceId) -> bool;
+}
+
+impl<ClassId, InstanceId> Locker<ClassId, InstanceId> for () {
+	// Default will be false if not implemented downstream.
+	// Note: The logic check in this function must be constant time and consistent for benchmarks
+	// to work.
+	fn is_locked(_class: ClassId, _instance: InstanceId) -> bool {
+		false
+	}
+}

frame/uniques/src/functions.rs

@@ -33,6 +33,7 @@ impl<T: Config<I>, I: 'static> Pallet<T, I> {
 	) -> DispatchResult {
 		let class_details = Class::<T, I>::get(&class).ok_or(Error::<T, I>::UnknownClass)?;
 		ensure!(!class_details.is_frozen, Error::<T, I>::Frozen);
+		ensure!(!T::Locker::is_locked(class, instance), Error::<T, I>::Locked);
 
 		let mut details =
 			Asset::<T, I>::get(&class, &instance).ok_or(Error::<T, I>::UnknownClass)?;

frame/uniques/src/lib.rs

@@ -43,7 +43,7 @@ pub mod weights;
 
 use codec::{Decode, Encode};
 use frame_support::traits::{
-	BalanceStatus::Reserved, Currency, EnsureOriginWithArg, ReservableCurrency,
+	tokens::Locker, BalanceStatus::Reserved, Currency, EnsureOriginWithArg, ReservableCurrency,
 };
 use frame_system::Config as SystemConfig;
 use sp_runtime::{
@@ -108,6 +108,9 @@ pub mod pallet {
 			Self::ClassId,
 		>;
 
+		/// Locker trait to enable Locking mechanism downstream.
+		type Locker: Locker<Self::ClassId, Self::InstanceId>;
+
 		/// The basic amount of funds that must be reserved for an asset class.
 		#[pallet::constant]
 		type ClassDeposit: Get<DepositBalanceOf<Self, I>>;
@@ -352,6 +355,8 @@ pub mod pallet {
 		Unapproved,
 		/// The named owner has not signed ownership of the class is acceptable.
 		Unaccepted,
+		/// The asset instance is locked.
+		Locked,
 	}
 
 	impl<T: Config<I>, I: 'static> Pallet<T, I> {

frame/uniques/src/mock.rs

@@ -91,6 +91,7 @@ impl Config for Test {
 	type Currency = Balances;
 	type CreateOrigin = AsEnsureOriginWithArg<frame_system::EnsureSigned<u64>>;
 	type ForceOrigin = frame_system::EnsureRoot<u64>;
+	type Locker = ();
 	type ClassDeposit = ConstU64<2>;
 	type InstanceDeposit = ConstU64<1>;
 	type MetadataDepositBase = ConstU64<1>;