Emit event when changing total locked value in pallet-balances (#12287)

* Emit Locked/Unlocked events

* Implement lock event tests

* Adhere to style guide

* Use saturating math

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Fix typo

* Emit event on change locks and add tests

* Adjust event docstring

---------

Co-authored-by: Kian Paimani <5588131+kianenigma@users.noreply.github.com>
Co-authored-by: parity-processbot <>

frame/balances/src/lib.rs

@@ -330,6 +330,10 @@ pub mod pallet {
 		Issued { amount: T::Balance },
 		/// Total issuance was decreased by `amount`, creating a debt to be balanced.
 		Rescinded { amount: T::Balance },
+		/// Some balance was locked.
+		Locked { who: T::AccountId, amount: T::Balance },
+		/// Some balance was unlocked.
+		Unlocked { who: T::AccountId, amount: T::Balance },
 	}
 
 	#[pallet::error]
@@ -1016,16 +1020,20 @@ pub mod pallet {
 				);
 			}
 			let freezes = Freezes::<T, I>::get(who);
+			let mut prev_frozen = Zero::zero();
+			let mut after_frozen = Zero::zero();
 			// TODO: Revisit this assumption. We no manipulate consumer/provider refs.
 			// No way this can fail since we do not alter the existential balances.
 			let res = Self::mutate_account(who, |b| {
+				prev_frozen = b.frozen;
 				b.frozen = Zero::zero();
 				for l in locks.iter() {
 					b.frozen = b.frozen.max(l.amount);
 				}
 				for l in freezes.iter() {
 					b.frozen = b.frozen.max(l.amount);
 				}
+				after_frozen = b.frozen;
 			});
 			debug_assert!(res.is_ok());
 			if let Ok((_, maybe_dust)) = res {
@@ -1053,6 +1061,14 @@ pub mod pallet {
 					);
 				}
 			}
+
+			if prev_frozen > after_frozen {
+				let amount = prev_frozen.saturating_sub(after_frozen);
+				Self::deposit_event(Event::Unlocked { who: who.clone(), amount });
+			} else if after_frozen > prev_frozen {
+				let amount = after_frozen.saturating_sub(prev_frozen);
+				Self::deposit_event(Event::Locked { who: who.clone(), amount });
+			}
 		}
 
 		/// Update the account entry for `who`, given the locks.

frame/balances/src/tests/currency_tests.rs

@@ -754,6 +754,61 @@ fn emit_events_with_reserve_and_unreserve() {
 	});
 }
 
+#[test]
+fn emit_events_with_changing_locks() {
+	ExtBuilder::default().build_and_execute_with(|| {
+		let _ = Balances::deposit_creating(&1, 100);
+		System::reset_events();
+
+		// Locks = [] --> [10]
+		Balances::set_lock(*b"LOCK_000", &1, 10, WithdrawReasons::TRANSFER);
+		assert_eq!(events(), [RuntimeEvent::Balances(crate::Event::Locked { who: 1, amount: 10 })]);
+
+		// Locks = [10] --> [15]
+		Balances::set_lock(*b"LOCK_000", &1, 15, WithdrawReasons::TRANSFER);
+		assert_eq!(events(), [RuntimeEvent::Balances(crate::Event::Locked { who: 1, amount: 5 })]);
+
+		// Locks = [15] --> [15, 20]
+		Balances::set_lock(*b"LOCK_001", &1, 20, WithdrawReasons::TRANSACTION_PAYMENT);
+		assert_eq!(events(), [RuntimeEvent::Balances(crate::Event::Locked { who: 1, amount: 5 })]);
+
+		// Locks = [15, 20] --> [17, 20]
+		Balances::set_lock(*b"LOCK_000", &1, 17, WithdrawReasons::TRANSACTION_PAYMENT);
+		for event in events() {
+			match event {
+				RuntimeEvent::Balances(crate::Event::Locked { .. }) => {
+					assert!(false, "unexpected lock event")
+				},
+				RuntimeEvent::Balances(crate::Event::Unlocked { .. }) => {
+					assert!(false, "unexpected unlock event")
+				},
+				_ => continue,
+			}
+		}
+
+		// Locks = [17, 20] --> [17, 15]
+		Balances::set_lock(*b"LOCK_001", &1, 15, WithdrawReasons::TRANSFER);
+		assert_eq!(
+			events(),
+			[RuntimeEvent::Balances(crate::Event::Unlocked { who: 1, amount: 3 })]
+		);
+
+		// Locks = [17, 15] --> [15]
+		Balances::remove_lock(*b"LOCK_000", &1);
+		assert_eq!(
+			events(),
+			[RuntimeEvent::Balances(crate::Event::Unlocked { who: 1, amount: 2 })]
+		);
+
+		// Locks = [15] --> []
+		Balances::remove_lock(*b"LOCK_001", &1);
+		assert_eq!(
+			events(),
+			[RuntimeEvent::Balances(crate::Event::Unlocked { who: 1, amount: 15 })]
+		);
+	});
+}
+
 #[test]
 fn emit_events_with_existential_deposit() {
 	ExtBuilder::default().existential_deposit(100).build_and_execute_with(|| {