Merge pull request #85 from liquity/apply_and_mint_interest_rebase

Apply and mint interest

contracts/src/ActivePool.sol

@@ -4,12 +4,15 @@ pragma solidity 0.8.18;
 
 import "openzeppelin-contracts/contracts/token/ERC20/utils/SafeERC20.sol";
 
+import './Interfaces/IActivePool.sol';
+import './Interfaces/IBoldToken.sol';
+import "./Interfaces/IInterestRouter.sol";
 import "./Dependencies/Ownable.sol";
 import "./Dependencies/CheckContract.sol";
 import './Interfaces/IDefaultPool.sol';
 import './Interfaces/IActivePool.sol';
 
-// import "forge-std/console.sol";
+//import "forge-std/console2.sol";
 
 /*
  * The Active Pool holds the ETH collateral and Bold debt (but not Bold tokens) for all active troves.
@@ -28,8 +31,31 @@ contract ActivePool is Ownable, CheckContract, IActivePool {
  address public troveManagerAddress;
  address public stabilityPoolAddress;
  address public defaultPoolAddress;
+
+ IBoldToken boldToken;
+
+ IInterestRouter public interestRouter;
+
+ uint256 constant public SECONDS_IN_ONE_YEAR = 31536000; // 60 * 60 * 24 * 365,
+
  uint256 internal ETHBalance; // deposited ether tracker
- uint256 internal boldDebt;
+
+ // Sum of individual recorded Trove debts. Updated only at individual Trove operations.
+ // "G" in the spec.
+ uint256 internal recordedDebtSum;
+
+ // Aggregate recorded debt tracker. Updated whenever a Trove's debt is touched AND whenever the aggregate pending interest is minted.
+ // "D" in the spec.
+ uint256 public aggRecordedDebt;
+
+ /* Sum of individual recorded Trove debts weighted by their respective chosen interest rates.
+ * Updated at individual Trove operations.
+ * "S" in the spec.
+ */
+ uint256 public aggWeightedDebtSum;
+
+ // Last time at which the aggregate recorded debt and weighted sum were updated
+ uint256 public lastAggUpdateTime;
 
  // --- Events ---
 
@@ -38,21 +64,24 @@ contract ActivePool is Ownable, CheckContract, IActivePool {
  event EtherSent(address _to, uint _amount);
  event BorrowerOperationsAddressChanged(address _newBorrowerOperationsAddress);
  event TroveManagerAddressChanged(address _newTroveManagerAddress);
- event ActivePoolBoldDebtUpdated(uint _boldDebt);
+ event ActivePoolBoldDebtUpdated(uint _recordedDebtSum);
  event ActivePoolETHBalanceUpdated(uint _ETHBalance);
 
  constructor(address _ETHAddress) {
  checkContract(_ETHAddress);
  ETH = IERC20(_ETHAddress);
  }
 
+
  // --- Contract setters ---
 
  function setAddresses(
  address _borrowerOperationsAddress,
  address _troveManagerAddress,
  address _stabilityPoolAddress,
- address _defaultPoolAddress
+ address _defaultPoolAddress,
+ address _boldTokenAddress,
+ address _interestRouterAddress
  )
  external
  onlyOwner
@@ -61,11 +90,15 @@ contract ActivePool is Ownable, CheckContract, IActivePool {
  checkContract(_troveManagerAddress);
  checkContract(_stabilityPoolAddress);
  checkContract(_defaultPoolAddress);
+ checkContract(_boldTokenAddress);
+ checkContract(_interestRouterAddress);
 
  borrowerOperationsAddress = _borrowerOperationsAddress;
  troveManagerAddress = _troveManagerAddress;
  stabilityPoolAddress = _stabilityPoolAddress;
  defaultPoolAddress = _defaultPoolAddress;
+ boldToken = IBoldToken(_boldTokenAddress);
+ interestRouter = IInterestRouter(_interestRouterAddress);
 
  emit BorrowerOperationsAddressChanged(_borrowerOperationsAddress);
  emit TroveManagerAddressChanged(_troveManagerAddress);
@@ -89,8 +122,17 @@ contract ActivePool is Ownable, CheckContract, IActivePool {
  return ETHBalance;
  }
 
- function getBoldDebt() external view override returns (uint) {
- return boldDebt;
+ function getRecordedDebtSum() external view override returns (uint) {
+ return recordedDebtSum;
+ }
+
+ function calcPendingAggInterest() public view returns (uint256) {
+ return aggWeightedDebtSum * (block.timestamp - lastAggUpdateTime) / SECONDS_IN_ONE_YEAR / 1e18;
+ }
+
+ // Returns sum of agg.recorded debt plus agg. pending interest. Excludes pending redist. gains.
+ function getTotalActiveDebt() public view returns (uint256) {
+ return aggRecordedDebt + calcPendingAggInterest();
  }
 
  // --- Pool functionality ---
@@ -131,16 +173,54 @@ contract ActivePool is Ownable, CheckContract, IActivePool {
  emit ActivePoolETHBalanceUpdated(newETHBalance);
  }
 
- function increaseBoldDebt(uint _amount) external override {
+ function increaseRecordedDebtSum(uint _amount) external override {
+ _requireCallerIsBOorTroveM();
+ uint256 newRecordedDebtSum = recordedDebtSum + _amount;
+ recordedDebtSum = newRecordedDebtSum;
+ emit ActivePoolBoldDebtUpdated(newRecordedDebtSum);
+ }
+
+ function decreaseRecordedDebtSum(uint _amount) external override {
+ _requireCallerIsBOorTroveMorSP();
+ uint256 newRecordedDebtSum = recordedDebtSum - _amount;
+
+ recordedDebtSum = newRecordedDebtSum;
+
+ emit ActivePoolBoldDebtUpdated(newRecordedDebtSum);
+ }
+
+ function changeAggWeightedDebtSum(uint256 _oldWeightedRecordedTroveDebt, uint256 _newTroveWeightedRecordedTroveDebt) external {
  _requireCallerIsBOorTroveM();
- boldDebt = boldDebt + _amount;
- emit ActivePoolBoldDebtUpdated(boldDebt);
+ // Do the arithmetic in 2 steps here to avoid overflow from the decrease
+ uint256 newAggWeightedDebtSum = aggWeightedDebtSum + _newTroveWeightedRecordedTroveDebt; // 1 SLOAD
+ newAggWeightedDebtSum -= _oldWeightedRecordedTroveDebt;
+ aggWeightedDebtSum = newAggWeightedDebtSum; // 1 SSTORE
  }
 
- function decreaseBoldDebt(uint _amount) external override {
+ // --- Aggregate interest operations ---
+
+ // This function is called inside all state-changing user ops: borrower ops, liquidations, redemptions and SP deposits/withdrawals.
+ // Some user ops trigger debt changes to Trove(s), in which case _troveDebtChange will be non-zero.
+ // The aggregate recorded debt is incremented by the aggregate pending interest, plus the net Trove debt change.
+ // The net Trove debt change consists of the sum of a) any debt issued/repaid and b) any redistribution debt gain applied in the encapsulating operation.
+ // It does *not* include the Trove's individual accrued interest - this gets accounted for in the aggregate accrued interest.
+ // The net Trove debt change could be positive or negative in a repayment (depending on whether its redistribution gain or repayment amount is larger),
+ // so this function accepts both the increase and the decrease to avoid using (and converting to/from) signed ints.
+ function mintAggInterest(uint256 _troveDebtIncrease, uint256 _troveDebtDecrease) public {
  _requireCallerIsBOorTroveMorSP();
- boldDebt = boldDebt - _amount;
- emit ActivePoolBoldDebtUpdated(boldDebt);
+ uint256 aggInterest = calcPendingAggInterest();
+ // Mint the new BOLD interest to a mock interest router that would split it and send it onward to SP, LP staking, etc.
+ // TODO: implement interest routing and SP Bold reward tracking
+ if (aggInterest > 0) {boldToken.mint(address(interestRouter), aggInterest);}
+
+ // Do the arithmetic in 2 steps here to avoid overflow from the decrease
+ uint256 newAggRecordedDebt = aggRecordedDebt + aggInterest + _troveDebtIncrease; // 1 SLOAD
+ newAggRecordedDebt -=_troveDebtDecrease;
+ aggRecordedDebt = newAggRecordedDebt; // 1 SSTORE
+ // assert(aggRecordedDebt >= 0) // This should never be negative. If all redistribution gians and all aggregate interest was applied
+ // and all Trove debts were repaid, it should become 0.
+
+ lastAggUpdateTime = block.timestamp;
  }
 
  // --- 'require' functions ---

contracts/src/BoldToken.sol

@@ -56,7 +56,9 @@ contract BoldToken is CheckContract, IBoldToken {
  address public immutable troveManagerAddress;
  address public immutable stabilityPoolAddress;
  address public immutable borrowerOperationsAddress;
+ address public immutable activePoolAddress;
 
+
  // --- Events ---
  event TroveManagerAddressChanged(address _troveManagerAddress);
  event StabilityPoolAddressChanged(address _newStabilityPoolAddress);
@@ -66,11 +68,13 @@ contract BoldToken is CheckContract, IBoldToken {
  ( 
  address _troveManagerAddress,
  address _stabilityPoolAddress,
- address _borrowerOperationsAddress
+ address _borrowerOperationsAddress,
+ address _activePoolAddress
  ) {
  checkContract(_troveManagerAddress);
  checkContract(_stabilityPoolAddress);
  checkContract(_borrowerOperationsAddress);
+ checkContract(_activePoolAddress);
 
  troveManagerAddress = _troveManagerAddress;
  emit TroveManagerAddressChanged(_troveManagerAddress);
@@ -80,6 +84,8 @@ contract BoldToken is CheckContract, IBoldToken {
 
  borrowerOperationsAddress = _borrowerOperationsAddress; 
  emit BorrowerOperationsAddressChanged(_borrowerOperationsAddress);
+
+ activePoolAddress = _activePoolAddress;
 
  bytes32 hashedName = keccak256(bytes(_NAME));
  bytes32 hashedVersion = keccak256(bytes(_VERSION));
@@ -95,7 +101,7 @@ contract BoldToken is CheckContract, IBoldToken {
  // --- Functions for intra-Liquity calls ---
 
  function mint(address _account, uint256 _amount) external override {
- _requireCallerIsBorrowerOperations();
+ _requireCallerIsBOorAP();
  _mint(_account, _amount);
  }
 
@@ -258,8 +264,10 @@ contract BoldToken is CheckContract, IBoldToken {
  );
  }
 
- function _requireCallerIsBorrowerOperations() internal view {
- require(msg.sender == borrowerOperationsAddress, "BoldToken: Caller is not BorrowerOperations");
+ function _requireCallerIsBOorAP() internal view {
+ require(msg.sender == borrowerOperationsAddress ||
+ msg.sender == activePoolAddress,
+ "BoldToken: Caller is not BO or AP");
  }
 
  function _requireCallerIsBOorTroveMorSP() internal view {