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>

substrate/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;

substrate/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,
 };

substrate/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
+	}
+}