Add keep_alive parameter to can_hold

frame/balances/src/lib.rs

@@ -1169,19 +1169,24 @@ impl<T: Config<I>, I: 'static> fungible::InspectHold<T::AccountId> for Pallet<T,
 	fn balance_on_hold(who: &T::AccountId) -> T::Balance {
 		Self::account(who).reserved
 	}
-	fn can_hold(who: &T::AccountId, amount: T::Balance) -> bool {
+	fn can_hold(who: &T::AccountId, amount: T::Balance, keep_alive: bool) -> bool {
 		let a = Self::account(who);
-		let min_balance = T::ExistentialDeposit::get().max(a.frozen(Reasons::All));
 		if a.reserved.checked_add(&amount).is_none() {
 			return false
 		}
-		// We require it to be min_balance + amount to ensure that the full reserved funds may be
-		// slashed without compromising locked funds or destroying the account.
-		let required_free = match min_balance.checked_add(&amount) {
-			Some(x) => x,
-			None => return false,
-		};
-		a.free >= required_free
+
+		if keep_alive {
+			let min_balance = T::ExistentialDeposit::get().max(a.frozen(Reasons::All));
+			// We require it to be min_balance + amount to ensure that the full reserved funds may
+			// be slashed without compromising locked funds or destroying the account.
+			let required_free = match min_balance.checked_add(&amount) {
+				Some(x) => x,
+				None => return false,
+			};
+			a.free >= required_free
+		} else {
+			a.free >= amount
+		}
 	}
 }
 impl<T: Config<I>, I: 'static> fungible::MutateHold<T::AccountId> for Pallet<T, I> {
@@ -1190,7 +1195,7 @@ impl<T: Config<I>, I: 'static> fungible::MutateHold<T::AccountId> for Pallet<T,
 			return Ok(())
 		}
 		ensure!(
-			<Self as fungible::InspectHold<T::AccountId>>::can_hold(who, amount),
+			<Self as fungible::InspectHold<T::AccountId>>::can_hold(who, amount, false),
 			Error::<T, I>::InsufficientBalance,
 		);
 		Self::try_mutate_account(who, |a, _| -> DispatchResult {

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

@@ -128,7 +128,7 @@ pub trait InspectHold<AccountId>: Inspect<AccountId> {
 	fn balance_on_hold(who: &AccountId) -> Self::Balance;
 
 	/// Check to see if some `amount` of funds of `who` may be placed on hold.
-	fn can_hold(who: &AccountId, amount: Self::Balance) -> bool;
+	fn can_hold(who: &AccountId, amount: Self::Balance, keep_alive: bool) -> bool;
 }
 
 /// Trait for mutating a fungible asset which can be reserved.
@@ -269,8 +269,8 @@ impl<
 	fn balance_on_hold(who: &AccountId) -> Self::Balance {
 		<F as fungibles::InspectHold<AccountId>>::balance_on_hold(A::get(), who)
 	}
-	fn can_hold(who: &AccountId, amount: Self::Balance) -> bool {
-		<F as fungibles::InspectHold<AccountId>>::can_hold(A::get(), who, amount)
+	fn can_hold(who: &AccountId, amount: Self::Balance, keep_alive: bool) -> bool {
+		<F as fungibles::InspectHold<AccountId>>::can_hold(A::get(), who, amount, keep_alive)
 	}
 }
 

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

@@ -183,7 +183,15 @@ pub trait InspectHold<AccountId>: Inspect<AccountId> {
 	fn balance_on_hold(asset: Self::AssetId, who: &AccountId) -> Self::Balance;
 
 	/// Check to see if some `amount` of `asset` may be held on the account of `who`.
-	fn can_hold(asset: Self::AssetId, who: &AccountId, amount: Self::Balance) -> bool;
+	///
+	/// If `keep_alive` is set to `true`, then it also checks so that the free balance of `asset`
+	/// does not go below its existential deposit after holding `amount`.
+	fn can_hold(
+		asset: Self::AssetId,
+		who: &AccountId,
+		amount: Self::Balance,
+		keep_alive: bool,
+	) -> bool;
 }
 
 /// Trait for mutating a set of named fungible assets which can be placed on hold.