Assets pallet: Giving the asset owner the ability to set minimum balance

frame/assets/src/benchmarking.rs

@@ -471,5 +471,12 @@ benchmarks_instance_pallet! {
 		assert_last_event::<T, I>(Event::ApprovalCancelled { asset_id: asset_id.into(), owner: caller, delegate }.into());
 	}
 
+	set_min_balance {
+		let (asset_id, caller, caller_lookup) = create_default_asset::<T, I>(true);
+	}: _(SystemOrigin::Signed(caller.clone()), asset_id, 50u32.into())
+	verify {
+		assert_last_event::<T, I>(Event::AssetMinBalanceChanged { asset_id: asset_id.into(), new_min_balance: 50u32.into() }.into());
+	}
+
 	impl_benchmark_test_suite!(Assets, crate::mock::new_test_ext(), crate::mock::Test)
 }

frame/assets/src/lib.rs

@@ -514,6 +514,8 @@ pub mod pallet {
 		},
 		/// An asset has had its attributes changed by the `Force` origin.
 		AssetStatusChanged { asset_id: T::AssetId },
+		/// The min_balance of an asset has been updated by the asset owner.
+		AssetMinBalanceChanged { asset_id: T::AssetId, new_min_balance: T::Balance },
 	}
 
 	#[pallet::error]
@@ -1511,6 +1513,48 @@ pub mod pallet {
 			let id: T::AssetId = id.into();
 			Self::do_refund(id, ensure_signed(origin)?, allow_burn)
 		}
+
+		/// Sets the minimum balance of an asset. Only works if there aren't any
+		/// accounts that are holding the asset or if the new vlaue of new_balance
+		/// is less than the old one.
+		///
+		/// Origin must be Signed and the sender has to be the Owner of the
+		/// asset `id`.
+		///
+		/// - `id`: The identifier of the asset.
+		/// - `min_balance`: The new value of `min_balance`.
+		///
+		/// Emits `AssetStatusChanged` event when successful.
+		#[pallet::call_index(28)]
+		#[pallet::weight(10_000)]
+		pub fn set_min_balance(
+			origin: OriginFor<T>,
+			id: T::AssetIdParameter,
+			min_balance: T::Balance,
+		) -> DispatchResult {
+			let origin = ensure_signed(origin)?;
+			let id: T::AssetId = id.into();
+
+			let mut details = Asset::<T, I>::get(id).ok_or(Error::<T, I>::Unknown)?;
+			ensure!(origin == details.owner, Error::<T, I>::NoPermission);
+
+			let old_min_balance = details.min_balance;
+			// Ensure that either the new min_balance is less than old min_balance or there aren't
+			// any accounts holding the asset.
+			ensure!(
+				min_balance < old_min_balance || details.accounts == 0,
+				Error::<T, I>::NoPermission
+			);
+
+			details.min_balance = min_balance;
+			Asset::<T, I>::insert(&id, details);
+
+			Self::deposit_event(Event::AssetMinBalanceChanged {
+				asset_id: id,
+				new_min_balance: min_balance,
+			});
+			Ok(())
+		}
 	}
 }
 

frame/assets/src/tests.rs

@@ -1091,6 +1091,35 @@ fn force_asset_status_should_work() {
 	});
 }
 
+#[test]
+fn set_min_balance_should_work() {
+	new_test_ext().execute_with(|| {
+		let id = 42;
+		Balances::make_free_balance_be(&1, 10);
+		assert_ok!(Assets::create(RuntimeOrigin::signed(1), id, 1, 30));
+
+		assert_ok!(Assets::mint(RuntimeOrigin::signed(1), id, 1, 50));
+		// won't execute because there is an asset holder.
+		assert_noop!(
+			Assets::set_min_balance(RuntimeOrigin::signed(1), id, 50),
+			Error::<Test>::NoPermission
+		);
+
+		// will execute because the new value of min_balance is less than the
+		// old value. 10 < 30
+		assert_ok!(Assets::mint(RuntimeOrigin::signed(1), id, 1, 10));
+
+		assert_ok!(Assets::burn(RuntimeOrigin::signed(1), id, 1, 50));
+		assert_noop!(
+			Assets::set_min_balance(RuntimeOrigin::signed(2), id, 50),
+			Error::<Test>::NoPermission
+		);
+
+		assert_ok!(Assets::set_min_balance(RuntimeOrigin::signed(1), id, 50));
+		assert_eq!(Asset::<Test>::get(id).unwrap().min_balance, 50);
+	});
+}
+
 #[test]
 fn balance_conversion_should_work() {
 	new_test_ext().execute_with(|| {