Merge pull request #2696 from subspace/treasury_fix

Staking - 1: Accumulate and then mint funds in to treasury when they cross minimum balance

crates/pallet-domains/src/bundle_storage_fund.rs

@@ -1,6 +1,7 @@
 //! Bundle storage fund
 
 use crate::staking::NewDeposit;
+use crate::staking_epoch::mint_into_treasury;
 use crate::{BalanceOf, Config, Event, HoldIdentifier, Operators, Pallet};
 use codec::{Decode, Encode};
 use frame_support::traits::fungible::{Inspect, Mutate, MutateHold};
@@ -124,8 +125,7 @@ pub fn refund_storage_fee<T: Config>(
 
     // Drop any dust and deregistered/slashed operator's bundle storage fee to the treasury
     if !remaining_fee.is_zero() {
-        T::Currency::mint_into(&T::TreasuryAccount::get(), remaining_fee)
-            .map_err(|_| Error::MintBalance)?;
+        mint_into_treasury::<T>(remaining_fee).ok_or(Error::MintBalance)?;
     }
 
     Ok(())

crates/pallet-domains/src/lib.rs

@@ -636,6 +636,11 @@ mod pallet {
     pub(super) type PermissionedActionAllowedBy<T: Config> =
         StorageValue<_, sp_domains::PermissionedActionAllowedBy<T::AccountId>, OptionQuery>;
 
+    /// Accumulate treasury funds temporarily until the funds are above Existential despoit.
+    /// We do this to ensure minting small amounts into treasury would not fail.
+    #[pallet::storage]
+    pub(super) type AccumulatedTreasuryFunds<T> = StorageValue<_, BalanceOf<T>, ValueQuery>;
+
     #[derive(TypeInfo, Encode, Decode, PalletError, Debug, PartialEq)]
     pub enum BundleError {
         /// Can not find the operator for given operator id.

crates/pallet-domains/src/staking.rs

@@ -9,7 +9,7 @@ use crate::pallet::{
     NominatorCount, OperatorIdOwner, OperatorSigningKey, Operators, PendingOperatorSwitches,
     PendingSlashes, PendingStakingOperationCount, Withdrawals,
 };
-use crate::staking_epoch::mint_funds;
+use crate::staking_epoch::{mint_funds, mint_into_treasury};
 use crate::{
     BalanceOf, Config, DomainBlockNumberFor, Event, HoldIdentifier, NominatorId,
     OperatorEpochSharePrice, Pallet, ReceiptHashFor, SlashedReason,
@@ -1181,7 +1181,7 @@ pub(crate) fn do_unlock_operator<T: Config>(operator_id: OperatorId) -> Result<u
             .map_err(Error::BundleStorageFund)?;
 
         // transfer any remaining amount to treasury
-        mint_funds::<T>(&T::TreasuryAccount::get(), total_stake)?;
+        mint_into_treasury::<T>(total_stake).ok_or(Error::MintBalance)?;
 
         // remove OperatorOwner Details
         OperatorIdOwner::<T>::remove(operator_id);
@@ -1234,7 +1234,7 @@ pub(crate) fn do_reward_operators<T: Config>(
                 .ok_or(Error::BalanceUnderflow)?;
         }
 
-        mint_funds::<T>(&T::TreasuryAccount::get(), rewards)
+        mint_into_treasury::<T>(rewards).ok_or(Error::MintBalance)
     })
 }
 

crates/pallet-domains/src/staking_epoch.rs

@@ -1,8 +1,9 @@
 //! Staking epoch transition for domain
 use crate::bundle_storage_fund::deposit_reserve_for_storage_fund;
 use crate::pallet::{
-    Deposits, DomainStakingSummary, LastEpochStakingDistribution, OperatorIdOwner, Operators,
-    PendingOperatorSwitches, PendingSlashes, PendingStakingOperationCount, Withdrawals,
+    AccumulatedTreasuryFunds, Deposits, DomainStakingSummary, LastEpochStakingDistribution,
+    OperatorIdOwner, Operators, PendingOperatorSwitches, PendingSlashes,
+    PendingStakingOperationCount, Withdrawals,
 };
 use crate::staking::{
     do_convert_previous_epoch_deposits, do_convert_previous_epoch_withdrawal, DomainEpoch,
@@ -13,8 +14,10 @@ use crate::{
     OperatorEpochSharePrice, Pallet,
 };
 use codec::{Decode, Encode};
-use frame_support::traits::fungible::{InspectHold, Mutate, MutateHold};
-use frame_support::traits::tokens::{Fortitude, Precision, Restriction};
+use frame_support::traits::fungible::{Inspect, InspectHold, Mutate, MutateHold};
+use frame_support::traits::tokens::{
+    DepositConsequence, Fortitude, Precision, Provenance, Restriction,
+};
 use frame_support::PalletError;
 use scale_info::TypeInfo;
 use sp_core::Get;
@@ -365,6 +368,25 @@ pub(crate) fn mint_funds<T: Config>(
     Ok(())
 }
 
+pub(crate) fn mint_into_treasury<T: Config>(amount: BalanceOf<T>) -> Option<()> {
+    let existing_funds = AccumulatedTreasuryFunds::<T>::get();
+    let total_funds = existing_funds.checked_add(&amount)?;
+    if total_funds.is_zero() {
+        return Some(());
+    }
+
+    match T::Currency::can_deposit(&T::TreasuryAccount::get(), total_funds, Provenance::Minted) {
+        // Deposit is possible, so we mint the funds into treasury.
+        DepositConsequence::Success => {
+            T::Currency::mint_into(&T::TreasuryAccount::get(), total_funds).ok()?;
+            AccumulatedTreasuryFunds::<T>::kill();
+        }
+        // Deposit cannot be done to treasury, so hold the funds until we can.
+        _ => AccumulatedTreasuryFunds::<T>::set(total_funds),
+    }
+    Some(())
+}
+
 pub(crate) fn do_finalize_slashed_operators<T: Config>(
     domain_id: DomainId,
 ) -> Result<u32, TransitionError> {
@@ -461,7 +483,8 @@ pub(crate) fn do_finalize_slashed_operators<T: Config>(
                         .ok_or(TransitionError::BalanceOverflow)?
                         .checked_sub(&amount_to_slash_in_holding)
                         .ok_or(TransitionError::BalanceUnderflow)?;
-                    mint_funds::<T>(&T::TreasuryAccount::get(), nominator_reward)?;
+                    mint_into_treasury::<T>(nominator_reward)
+                        .ok_or(TransitionError::MintBalance)?;
 
                     total_stake = total_stake.saturating_sub(nominator_staked_amount);
 
@@ -507,7 +530,7 @@ pub(crate) fn do_finalize_slashed_operators<T: Config>(
             )?;
 
             // mint any gains to treasury account
-            mint_funds::<T>(&T::TreasuryAccount::get(), total_stake)?;
+            mint_into_treasury::<T>(total_stake).ok_or(TransitionError::MintBalance)?;
 
             // Transfer all the storage fund to treasury
             bundle_storage_fund::transfer_all_to_treasury::<T>(operator_id)