Dust Account Detection Strategy?

[aurexav]

Account {
	ring: 0,
	kton: 100_000_000,
}

Got killed?

[hackfisher]

In this case, the account should definitely be kept.

For now, let's follow strict and safe strategy:

Only Account.ring < existential_deposit and account.kton == 0 will get killed.

For KTON, there is no existential_deposit, or the default existential_deposit is zero.

[aurexav]

Implement ExistentialCheck for darwinia-ring and darwinia-kton.

Will be solved in #307.

Example:

// support.rs
pub trait ExistentialCheck<AccountId, Balance> {
	fn try_drop(who: &AccountId) -> (bool, Balance);
}

// kton.rs
impl<T: Trait<I>, I: Instance> ExistentialCheck<T::AccountId, T::Balance> for Module<T, I>
where
	T::Balance: MaybeSerializeDeserialize + Debug,
{
	fn try_drop(who: &T::AccountId) -> (bool, T::Balance) {
		let dropped_kton = Self::total_balance(who);
		let dropped = !dropped_kton.is_zero() && dropped_kton < T::ExistentialDeposit::get();
		if dropped {
			T::DustRemoval::on_unbalanced(NegativeImbalance::new(dropped_kton));
		}

		(dropped, dropped_kton)
	}
}

// ring.rs
fn post_mutation(who: &T::AccountId, new: ActiveBalance<T::Balance>) -> Option<ActiveBalance<T::Balance>> {
	let total = new.total();
	if total < T::ExistentialDeposit::get() {
		if !total.is_zero() {
			let (dropped, dropped_kton) = T::ExistentialCheck::try_drop(who);
			if dropped {
				T::DustRemoval::on_unbalanced(NegativeImbalance::new(total));
				Self::deposit_event(RawEvent::DustLost(who.clone(), total, dropped_kton));
			}
		}
		None
	} else {
		Some(new)
	}
}

[hackfisher]

Implement ExistentialCheck for darwinia-ring and darwinia-kton.

Will be solved in #307.

Example:

// support.rs
pub trait ExistentialCheck<AccountId, Balance> {
	fn try_drop(who: &AccountId) -> (bool, Balance);
}

// kton.rs
impl<T: Trait<I>, I: Instance> ExistentialCheck<T::AccountId, T::Balance> for Module<T, I>
where
	T::Balance: MaybeSerializeDeserialize + Debug,
{
	fn try_drop(who: &T::AccountId) -> (bool, T::Balance) {
		let dropped_kton = Self::total_balance(who);
		let dropped = !dropped_kton.is_zero() && dropped_kton < T::ExistentialDeposit::get();
		if dropped {
			T::DustRemoval::on_unbalanced(NegativeImbalance::new(dropped_kton));
		}

		(drop, dropped_kton)
	}
}

// ring.rs
fn post_mutation(who: &T::AccountId, new: ActiveBalance<T::Balance>) -> Option<ActiveBalance<T::Balance>> {
	let total = new.total();
	if total < T::ExistentialDeposit::get() {
		if !total.is_zero() {
			let (dropped, dropped_kton) T::ExistentialCheck::try_drop(who);
			if dropped {
				T::DustRemoval::on_unbalanced(NegativeImbalance::new(total));
				Self::deposit_event(RawEvent::DustLost(who.clone(), total, dropped_kton));
			}
		}
		None
	} else {
		Some(new)
	}
}

// ring.rs
fn post_mutation(who: &T::AccountId, new: ActiveBalance<T::Balance>) -> Option<ActiveBalance<T::Balance>> {
	let total = new.total();
	if total < T::ExistentialDeposit::get() {
                 let (dropped, dropped_kton) = T::ExistentialCheck::try_drop(who);
		if dropped {
                          if !total.is_zero(){
				T::DustRemoval::on_unbalanced(NegativeImbalance::new(total));
				Self::deposit_event(RawEvent::DustLost(who.clone(), total, dropped_kton));
			}
                          None
                 } else {
                          Some(new)
                 }
	} else {
		Some(new)
	}
}