Support Mutate, Unbalanced, Balanced fungible related traits fo…

…r `pallet-evm-balances` (#102)

* Move currencies implementation into separate mod

* [substrate=apply] Deprecate Currency; introduce holds and freezing into fungible traits #12951

* Apply new balances logic to currency trait implementation

* Use DustRemoval over Credit instead of NegativeImbalance

* Implement Balanced, Unbalanced, Mutate fungible traits for pallet

* Revert using negative imbalance

* Apply formatter

* Fix withdraw_consequence method

* Move currency related tests to separate mod

* Add transfer_fails_funds_unavailable test to currency tests

* Add transfer_works_full_balance test to currency tests

* Fix slashing conditions

* Add slash_works_full_balance test to currency tests

* Add deposit_into_existing related fails tests

* Add withdraw_works_full_balance test to currency tests

* Add withdraw fails related tests to currency tests

* Add basic fungible tests

* Add reducable balance test to fungible tests

* Add can deposit related tests

* Fix can_withdraw logic

* Add can_withdraw related tests

* Add write_balance_works test

* Add set_total_issuance_works test

* Add decrease_balance related tests

* Add increase_balance related tests

* Add deactivate_reactivate_works test

* Add mint_into related tests

* Add burn_from related tests

* Add shelve related tests

* Add restored related tests

* Add transfer related tests

* Add balanced related tests

* Undo formatting

* Simplify reducible logic implementation

* Simplify can_deposit implementation

* Simplify can_withdraw implementation

* Properly use semantics of total and free balances

* Improve reducable_balance_works test

* Fix test race conditions

frame/evm-balances/src/impl_currency.rs

@@ -0,0 +1,300 @@
+//! Currency trait implementation.
+
+use frame_support::traits::Currency;
+
+use super::*;
+
+impl<T: Config<I>, I: 'static> Currency<<T as Config<I>>::AccountId> for Pallet<T, I>
+where
+	T::Balance: MaybeSerializeDeserialize + Debug,
+{
+	type Balance = T::Balance;
+	type PositiveImbalance = PositiveImbalance<T, I>;
+	type NegativeImbalance = NegativeImbalance<T, I>;
+
+	fn total_balance(who: &<T as Config<I>>::AccountId) -> Self::Balance {
+		Self::account(who).total()
+	}
+
+	fn can_slash(who: &<T as Config<I>>::AccountId, value: Self::Balance) -> bool {
+		if value.is_zero() {
+			return true;
+		}
+		Self::free_balance(who) >= value
+	}
+
+	fn total_issuance() -> Self::Balance {
+		TotalIssuance::<T, I>::get()
+	}
+
+	fn active_issuance() -> Self::Balance {
+		<Self as fungible::Inspect<_>>::active_issuance()
+	}
+
+	fn deactivate(amount: Self::Balance) {
+		<Self as fungible::Unbalanced<_>>::deactivate(amount);
+	}
+
+	fn reactivate(amount: Self::Balance) {
+		<Self as fungible::Unbalanced<_>>::reactivate(amount);
+	}
+
+	fn minimum_balance() -> Self::Balance {
+		T::ExistentialDeposit::get()
+	}
+
+	// Burn funds from the total issuance, returning a positive imbalance for the amount burned.
+	// Is a no-op if amount to be burned is zero.
+	fn burn(mut amount: Self::Balance) -> Self::PositiveImbalance {
+		if amount.is_zero() {
+			return PositiveImbalance::zero();
+		}
+		<TotalIssuance<T, I>>::mutate(|issued| {
+			*issued = issued.checked_sub(&amount).unwrap_or_else(|| {
+				amount = *issued;
+				Zero::zero()
+			});
+		});
+		PositiveImbalance::new(amount)
+	}
+
+	// Create new funds into the total issuance, returning a negative imbalance
+	// for the amount issued.
+	// Is a no-op if amount to be issued it zero.
+	fn issue(mut amount: Self::Balance) -> Self::NegativeImbalance {
+		if amount.is_zero() {
+			return NegativeImbalance::zero();
+		}
+		<TotalIssuance<T, I>>::mutate(|issued| {
+			*issued = issued.checked_add(&amount).unwrap_or_else(|| {
+				amount = Self::Balance::max_value() - *issued;
+				Self::Balance::max_value()
+			})
+		});
+		NegativeImbalance::new(amount)
+	}
+
+	fn free_balance(who: &<T as Config<I>>::AccountId) -> Self::Balance {
+		Self::account(who).free
+	}
+
+	// We don't have any existing withdrawal restrictions like locked and reserved balance.
+	// Is a no-op if amount to be withdrawn is zero.
+	fn ensure_can_withdraw(
+		_who: &<T as Config<I>>::AccountId,
+		_amount: T::Balance,
+		_reasons: WithdrawReasons,
+		_new_balance: T::Balance,
+	) -> DispatchResult {
+		Ok(())
+	}
+
+	// Transfer some free balance from `transactor` to `dest`, respecting existence requirements.
+	// Is a no-op if value to be transferred is zero or the `transactor` is the same as `dest`.
+	fn transfer(
+		transactor: &<T as Config<I>>::AccountId,
+		dest: &<T as Config<I>>::AccountId,
+		value: Self::Balance,
+		existence_requirement: ExistenceRequirement,
+	) -> DispatchResult {
+		if value.is_zero() || transactor == dest {
+			return Ok(());
+		}
+		let keep_alive = match existence_requirement {
+			ExistenceRequirement::KeepAlive => Preservation::Preserve,
+			ExistenceRequirement::AllowDeath => Preservation::Expendable,
+		};
+		<Self as fungible::Mutate<_>>::transfer(transactor, dest, value, keep_alive)?;
+		Ok(())
+	}
+
+	/// Slash a target account `who`, returning the negative imbalance created and any left over
+	/// amount that could not be slashed.
+	///
+	/// Is a no-op if `value` to be slashed is zero or the account does not exist.
+	///
+	/// NOTE: `slash()` prefers free balance, but assumes that reserve balance can be drawn
+	/// from in extreme circumstances. `can_slash()` should be used prior to `slash()` to avoid
+	/// having to draw from reserved funds, however we err on the side of punishment if things are
+	/// inconsistent or `can_slash` wasn't used appropriately.
+	fn slash(
+		who: &<T as Config<I>>::AccountId,
+		value: Self::Balance,
+	) -> (Self::NegativeImbalance, Self::Balance) {
+		if value.is_zero() {
+			return (NegativeImbalance::zero(), Zero::zero());
+		}
+
+		if Self::total_balance(who).is_zero() {
+			return (NegativeImbalance::zero(), value);
+		}
+
+		let result = match Self::try_mutate_account_handling_dust(
+			who,
+			|account, _is_new| -> Result<(Self::NegativeImbalance, Self::Balance), DispatchError> {
+				// Best value is the most amount we can slash following liveness rules.
+				let actual = value.min(account.free);
+				account.free.saturating_reduce(actual);
+				let remaining = value.saturating_sub(actual);
+				Ok((NegativeImbalance::new(actual), remaining))
+			},
+		) {
+			Ok((imbalance, remaining)) => {
+				Self::deposit_event(Event::Slashed {
+					who: who.clone(),
+					amount: value.saturating_sub(remaining),
+				});
+				(imbalance, remaining)
+			}
+			Err(_) => (Self::NegativeImbalance::zero(), value),
+		};
+		result
+	}
+
+	/// Deposit some `value` into the free balance of an existing target account `who`.
+	///
+	/// Is a no-op if the `value` to be deposited is zero.
+	fn deposit_into_existing(
+		who: &<T as Config<I>>::AccountId,
+		value: Self::Balance,
+	) -> Result<Self::PositiveImbalance, DispatchError> {
+		if value.is_zero() {
+			return Ok(PositiveImbalance::zero());
+		}
+
+		Self::try_mutate_account_handling_dust(
+			who,
+			|account, is_new| -> Result<Self::PositiveImbalance, DispatchError> {
+				ensure!(!is_new, Error::<T, I>::DeadAccount);
+				account.free = account
+					.free
+					.checked_add(&value)
+					.ok_or(ArithmeticError::Overflow)?;
+				Self::deposit_event(Event::Deposit {
+					who: who.clone(),
+					amount: value,
+				});
+				Ok(PositiveImbalance::new(value))
+			},
+		)
+	}
+
+	/// Deposit some `value` into the free balance of `who`, possibly creating a new account.
+	///
+	/// This function is a no-op if:
+	/// - the `value` to be deposited is zero; or
+	/// - the `value` to be deposited is less than the required ED and the account does not yet
+	///   exist; or
+	/// - the deposit would necessitate the account to exist and there are no provider references;
+	///   or
+	/// - `value` is so large it would cause the balance of `who` to overflow.
+	fn deposit_creating(
+		who: &<T as Config<I>>::AccountId,
+		value: Self::Balance,
+	) -> Self::PositiveImbalance {
+		if value.is_zero() {
+			return Self::PositiveImbalance::zero();
+		}
+
+		Self::try_mutate_account_handling_dust(
+			who,
+			|account, is_new| -> Result<Self::PositiveImbalance, DispatchError> {
+				let ed = T::ExistentialDeposit::get();
+				ensure!(value >= ed || !is_new, Error::<T, I>::ExistentialDeposit);
+
+				// defensive only: overflow should never happen, however in case it does, then this
+				// operation is a no-op.
+				account.free = match account.free.checked_add(&value) {
+					Some(x) => x,
+					None => return Ok(Self::PositiveImbalance::zero()),
+				};
+
+				Self::deposit_event(Event::Deposit {
+					who: who.clone(),
+					amount: value,
+				});
+				Ok(PositiveImbalance::new(value))
+			},
+		)
+		.unwrap_or_else(|_| Self::PositiveImbalance::zero())
+	}
+
+	/// Withdraw some free balance from an account, respecting existence requirements.
+	///
+	/// Is a no-op if value to be withdrawn is zero.
+	fn withdraw(
+		who: &<T as Config<I>>::AccountId,
+		value: Self::Balance,
+		reasons: WithdrawReasons,
+		liveness: ExistenceRequirement,
+	) -> result::Result<Self::NegativeImbalance, DispatchError> {
+		if value.is_zero() {
+			return Ok(NegativeImbalance::zero());
+		}
+
+		Self::try_mutate_account_handling_dust(
+			who,
+			|account, _| -> Result<Self::NegativeImbalance, DispatchError> {
+				let new_free_account = account
+					.free
+					.checked_sub(&value)
+					.ok_or(Error::<T, I>::InsufficientBalance)?;
+
+				// bail if we need to keep the account alive and this would kill it.
+				let ed = T::ExistentialDeposit::get();
+				let would_be_dead = new_free_account < ed;
+				let would_kill = would_be_dead && account.free >= ed;
+				ensure!(
+					liveness == ExistenceRequirement::AllowDeath || !would_kill,
+					Error::<T, I>::Expendability
+				);
+
+				Self::ensure_can_withdraw(who, value, reasons, new_free_account)?;
+
+				account.free = new_free_account;
+
+				Self::deposit_event(Event::Withdraw {
+					who: who.clone(),
+					amount: value,
+				});
+				Ok(NegativeImbalance::new(value))
+			},
+		)
+	}
+
+	/// Force the new free balance of a target account `who` to some new value `balance`.
+	fn make_free_balance_be(
+		who: &<T as Config<I>>::AccountId,
+		value: Self::Balance,
+	) -> SignedImbalance<Self::Balance, Self::PositiveImbalance> {
+		Self::try_mutate_account_handling_dust(
+			who,
+			|account,
+			 is_new|
+			 -> Result<SignedImbalance<Self::Balance, Self::PositiveImbalance>, DispatchError> {
+				let ed = T::ExistentialDeposit::get();
+				// If we're attempting to set an existing account to less than ED, then
+				// bypass the entire operation. It's a no-op if you follow it through, but
+				// since this is an instance where we might account for a negative imbalance
+				// (in the dust cleaner of set_account) before we account for its actual
+				// equal and opposite cause (returned as an Imbalance), then in the
+				// instance that there's no other accounts on the system at all, we might
+				// underflow the issuance and our arithmetic will be off.
+				ensure!(value >= ed || !is_new, Error::<T, I>::ExistentialDeposit);
+
+				let imbalance = if account.free <= value {
+					SignedImbalance::Positive(PositiveImbalance::new(value - account.free))
+				} else {
+					SignedImbalance::Negative(NegativeImbalance::new(account.free - value))
+				};
+				account.free = value;
+				Self::deposit_event(Event::BalanceSet {
+					who: who.clone(),
+					free: account.free,
+				});
+				Ok(imbalance)
+			},
+		)
+		.unwrap_or_else(|_| SignedImbalance::Positive(Self::PositiveImbalance::zero()))
+	}
+}