Merge branch 'fix/45' into 'master'

Resolve "Update rebalance conditions"

Closes #45

See merge request aave-tech/protocol-v2!54

contracts/interfaces/IReserveInterestRateStrategy.sol

@@ -10,9 +10,13 @@ interface IReserveInterestRateStrategy {
   /**
    * @dev returns the base variable borrow rate, in rays
    */
-
   function baseVariableBorrowRate() external view returns (uint256);
 
+  /**
+   * @dev returns the maximum variable borrow rate
+   */
+  function getMaxVariableBorrowRate() external view returns (uint256);
+
   /**
    * @dev calculates the liquidity, stable, and variable rates depending on the current utilization rate
    *      and the base parameters

contracts/lendingpool/DefaultReserveInterestRateStrategy.sol

@@ -91,6 +91,10 @@ contract DefaultReserveInterestRateStrategy is IReserveInterestRateStrategy {
     return _baseVariableBorrowRate;
   }
 
+  function getMaxVariableBorrowRate() external override view returns (uint256) {
+    return _baseVariableBorrowRate.add(_variableRateSlope1).add(_variableRateSlope2);
+  }
+  
   struct CalcInterestRatesLocalVars {
 
     uint256 totalBorrows;

contracts/lendingpool/LendingPool.sol

@@ -28,21 +28,22 @@ import {IPriceOracleGetter} from '../interfaces/IPriceOracleGetter.sol';
 import {SafeERC20} from '@openzeppelin/contracts/token/ERC20/SafeERC20.sol';
 import {ILendingPool} from '../interfaces/ILendingPool.sol';
 import {LendingPoolStorage} from './LendingPoolStorage.sol';
-
+import {IReserveInterestRateStrategy} from '../interfaces/IReserveInterestRateStrategy.sol';
 /**
  * @title LendingPool contract
  * @notice Implements the actions of the LendingPool, and exposes accessory methods to fetch the users and reserve data
  * @author Aave
  **/
-
 contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage {
   using SafeMath for uint256;
   using WadRayMath for uint256;
+  using PercentageMath for uint256;
   using SafeERC20 for IERC20;
 
   //main configuration parameters
-  uint256 public constant REBALANCE_DOWN_RATE_DELTA = (1e27) / 5;
+  uint256 public constant REBALANCE_UP_LIQUIDITY_RATE_THRESHOLD = 4000;
-  uint256 public constant MAX_STABLE_RATE_BORROW_SIZE_PERCENT = 25;
+  uint256 public constant REBALANCE_UP_USAGE_RATIO_THRESHOLD = 0.95 * 1e27; //usage ratio of 95%
+  uint256 public constant MAX_STABLE_RATE_BORROW_SIZE_PERCENT = 2500;
   uint256 public constant FLASHLOAN_PREMIUM_TOTAL = 9;
   uint256 public constant MAX_NUMBER_RESERVES = 128;
   uint256 public constant LENDINGPOOL_REVISION = 0x2;
@@ -50,13 +51,12 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
   /**
    * @dev only lending pools configurator can use functions affected by this modifier
    **/
-  function onlyLendingPoolConfigurator() internal view {
+  function _onlyLendingPoolConfigurator() internal view {
     require(
       _addressesProvider.getLendingPoolConfigurator() == msg.sender,
       Errors.CALLER_NOT_LENDING_POOL_CONFIGURATOR
     );
   }
-
   /**
    * @dev Function to make a function callable only when the contract is not paused.
    *
@@ -64,7 +64,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
    *
    * - The contract must not be paused.
    */
-  function whenNotPaused() internal view {
+  function _whenNotPaused() internal view {
     require(!_paused, Errors.IS_PAUSED);
   }
 
@@ -94,7 +94,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
     address onBehalfOf,
     uint16 referralCode
   ) external override {
-    whenNotPaused();
+    _whenNotPaused();
     ReserveLogic.ReserveData storage reserve = _reserves[asset];
 
     ValidationLogic.validateDeposit(reserve, amount);
@@ -123,7 +123,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
    * @param amount the underlying amount to be redeemed
    **/
   function withdraw(address asset, uint256 amount) external override {
-    whenNotPaused();
+    _whenNotPaused();
     ReserveLogic.ReserveData storage reserve = _reserves[asset];
 
     address aToken = reserve.aTokenAddress;
@@ -139,7 +139,6 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
 
     ValidationLogic.validateWithdraw(
       asset,
-      aToken,
       amountToWithdraw,
       userBalance,
       _reserves,
@@ -161,6 +160,14 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
     emit Withdraw(asset, msg.sender, amount);
   }
 
+  /**
+   * @dev returns the borrow allowance of the user
+   * @param asset The underlying asset of the debt token
+   * @param fromUser The user to giving allowance
+   * @param toUser The user to give allowance to
+   * @param interestRateMode Type of debt: 1 for stable, 2 for variable
+   * @return the current allowance of toUser
+   **/
   function getBorrowAllowance(
     address fromUser,
     address toUser,
@@ -184,7 +191,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
     uint256 interestRateMode,
     uint256 amount
   ) external override {
-    whenNotPaused();
+    _whenNotPaused();
     address debtToken = _reserves[asset].getDebtTokenAddress(interestRateMode);
 
     _borrowAllowance[debtToken][msg.sender][user] = amount;
@@ -207,7 +214,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
     uint16 referralCode,
     address onBehalfOf
   ) external override {
-    whenNotPaused();
+    _whenNotPaused();
     ReserveLogic.ReserveData storage reserve = _reserves[asset];
 
     if (onBehalfOf != msg.sender) {
@@ -247,7 +254,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
     uint256 rateMode,
     address onBehalfOf
   ) external override {
-    whenNotPaused();
+    _whenNotPaused();
 
     ReserveLogic.ReserveData storage reserve = _reserves[asset];
 
@@ -304,7 +311,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
    * @param rateMode the rate mode that the user wants to swap
    **/
   function swapBorrowRateMode(address asset, uint256 rateMode) external override {
-    whenNotPaused();
+    _whenNotPaused();
     ReserveLogic.ReserveData storage reserve = _reserves[asset];
 
     (uint256 stableDebt, uint256 variableDebt) = Helpers.getUserCurrentDebt(msg.sender, reserve);
@@ -356,43 +363,50 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
    * @param user the address of the user to be rebalanced
    **/
   function rebalanceStableBorrowRate(address asset, address user) external override {
-    whenNotPaused();
+    
+    _whenNotPaused();
+    
     ReserveLogic.ReserveData storage reserve = _reserves[asset];
 
-    IStableDebtToken stableDebtToken = IStableDebtToken(reserve.stableDebtTokenAddress);
+    IERC20 stableDebtToken = IERC20(reserve.stableDebtTokenAddress);
+    IERC20 variableDebtToken = IERC20(reserve.variableDebtTokenAddress);
+    address aTokenAddress = reserve.aTokenAddress;
 
-    uint256 stableBorrowBalance = IERC20(address(stableDebtToken)).balanceOf(user);
+    uint256 stableBorrowBalance = IERC20(stableDebtToken).balanceOf(user);
 
-    // user must be borrowing on asset at a stable rate
+    //if the utilization rate is below 95%, no rebalances are needed
-    require(stableBorrowBalance > 0, Errors.NOT_ENOUGH_STABLE_BORROW_BALANCE);
+    uint256 totalBorrows = stableDebtToken.totalSupply().add(variableDebtToken.totalSupply()).wadToRay();
+    uint256 availableLiquidity = IERC20(asset).balanceOf(aTokenAddress).wadToRay();
+    uint256 usageRatio = totalBorrows == 0
+      ? 0
+      : totalBorrows.rayDiv(availableLiquidity.add(totalBorrows));
 
-    uint256 rebalanceDownRateThreshold = WadRayMath.ray().add(REBALANCE_DOWN_RATE_DELTA).rayMul(
+    //if the liquidity rate is below REBALANCE_UP_THRESHOLD of the max variable APR at 95% usage,
-      reserve.currentStableBorrowRate
+    //then we allow rebalancing of the stable rate positions.
-    );
 
-    //1. user stable borrow rate is below the current liquidity rate. The loan needs to be rebalanced,
+    uint256 currentLiquidityRate = reserve.currentLiquidityRate;
-    //as this situation can be abused (user putting back the borrowed liquidity in the same reserve to earn on it)
+    uint256 maxVariableBorrowRate = IReserveInterestRateStrategy(
-    //2. user stable rate is above the market avg borrow rate of a certain delta, and utilization rate is low.
+      reserve
-    //In this case, the user is paying an interest that is too high, and needs to be rescaled down.
+        .interestRateStrategyAddress
-
+    )
-    uint256 userStableRate = stableDebtToken.getUserStableRate(user);
+      .getMaxVariableBorrowRate();
 
     require(
-      userStableRate < reserve.currentLiquidityRate || userStableRate > rebalanceDownRateThreshold,
+      usageRatio >= REBALANCE_UP_USAGE_RATIO_THRESHOLD &&
+      currentLiquidityRate <=
+        maxVariableBorrowRate.percentMul(REBALANCE_UP_LIQUIDITY_RATE_THRESHOLD),
       Errors.INTEREST_RATE_REBALANCE_CONDITIONS_NOT_MET
     );
 
     reserve.updateState();
 
-    //burn old debt tokens, mint new ones
+    IStableDebtToken(address(stableDebtToken)).burn(user, stableBorrowBalance);
-    stableDebtToken.burn(user, stableBorrowBalance);
+    IStableDebtToken(address(stableDebtToken)).mint(user, stableBorrowBalance, reserve.currentStableBorrowRate);
-    stableDebtToken.mint(user, stableBorrowBalance, reserve.currentStableBorrowRate);
 
-    reserve.updateInterestRates(asset, reserve.aTokenAddress, 0, 0);
+    reserve.updateInterestRates(asset, aTokenAddress, 0, 0);
 
     emit RebalanceStableBorrowRate(asset, user);
 
-    return;
   }
 
   /**
@@ -401,7 +415,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
    * @param useAsCollateral true if the user wants to user the deposit as collateral, false otherwise.
    **/
   function setUserUseReserveAsCollateral(address asset, bool useAsCollateral) external override {
-    whenNotPaused();
+    _whenNotPaused();
     ReserveLogic.ReserveData storage reserve = _reserves[asset];
 
     ValidationLogic.validateSetUseReserveAsCollateral(
@@ -438,7 +452,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
     uint256 purchaseAmount,
     bool receiveAToken
   ) external override {
-    whenNotPaused();
+    _whenNotPaused();
     address collateralManager = _addressesProvider.getLendingPoolCollateralManager();
 
     //solium-disable-next-line
@@ -482,7 +496,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
     address receiver,
     bytes calldata params
   ) external override {
-    whenNotPaused();
+    _whenNotPaused();
     require(!_flashLiquidationLocked, Errors.REENTRANCY_NOT_ALLOWED);
     _flashLiquidationLocked = true;
 
@@ -538,7 +552,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
     bytes calldata params,
     uint16 referralCode
   ) external override {
-    whenNotPaused();
+    _whenNotPaused();
     ReserveLogic.ReserveData storage reserve = _reserves[asset];
     FlashLoanLocalVars memory vars;
 
@@ -600,7 +614,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
     uint256 amountToSwap,
     bytes calldata params
   ) external override {
-    whenNotPaused();
+    _whenNotPaused();
     address collateralManager = _addressesProvider.getLendingPoolCollateralManager();
 
     //solium-disable-next-line
@@ -799,7 +813,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
     address variableDebtAddress,
     address interestRateStrategyAddress
   ) external override {
-    onlyLendingPoolConfigurator();
+    _onlyLendingPoolConfigurator();
     _reserves[asset].init(
       aTokenAddress,
       stableDebtAddress,
@@ -819,12 +833,12 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
     external
     override
   {
-    onlyLendingPoolConfigurator();
+    _onlyLendingPoolConfigurator();
     _reserves[asset].interestRateStrategyAddress = rateStrategyAddress;
   }
 
   function setConfiguration(address asset, uint256 configuration) external override {
-    onlyLendingPoolConfigurator();
+    _onlyLendingPoolConfigurator();
     _reserves[asset].configuration.data = configuration;
   }
 
@@ -980,7 +994,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
     address user,
     uint256 amount
   ) external override view returns (bool) {
-    whenNotPaused();
+    _whenNotPaused();
     return
       GenericLogic.balanceDecreaseAllowed(
         asset,
@@ -998,7 +1012,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
    * @param val the boolean value to set the current pause state of LendingPool
    */
   function setPause(bool val) external override {
-    onlyLendingPoolConfigurator();
+    _onlyLendingPoolConfigurator();
 
     _paused = val;
     if (_paused) {

contracts/libraries/configuration/ReserveConfiguration.sol

@@ -6,7 +6,6 @@ import {IERC20} from '@openzeppelin/contracts/token/ERC20/IERC20.sol';
 import {ReserveLogic} from '../logic/ReserveLogic.sol';
 import {WadRayMath} from '../math/WadRayMath.sol';
 import {IPriceOracleGetter} from '../../interfaces/IPriceOracleGetter.sol';
-import "@nomiclabs/buidler/console.sol";
 
 /**
  * @title ReserveConfiguration library
@@ -143,7 +142,7 @@ library ReserveConfiguration {
    * @param self the reserve configuration
    * @param active the active state
    **/
-  function setActive(ReserveConfiguration.Map memory self, bool active) internal {
+  function setActive(ReserveConfiguration.Map memory self, bool active) internal pure {
     self.data = (self.data & ACTIVE_MASK) | (uint256(active ? 1 : 0) << 56);
   }
 

contracts/libraries/logic/ReserveLogic.sol

@@ -127,7 +127,7 @@ library ReserveLogic {
    * @return an address of the corresponding debt token from reserve configuration
    **/
   function getDebtTokenAddress(ReserveLogic.ReserveData storage reserve, uint256 interestRateMode)
-    internal
+    external
     view
     returns (address)
   {
@@ -371,7 +371,6 @@ library ReserveLogic {
     uint256 liquidityIndex,
     uint256 variableBorrowIndex
   ) internal returns (uint256, uint256) {
-
     uint40 timestamp = reserve.lastUpdateTimestamp;
 
     uint256 currentLiquidityRate = reserve.currentLiquidityRate;

contracts/libraries/logic/ValidationLogic.sol

@@ -34,7 +34,7 @@ library ValidationLogic {
    * @param reserve the reserve state on which the user is depositing
    * @param amount the amount to be deposited
    */
-  function validateDeposit(ReserveLogic.ReserveData storage reserve, uint256 amount) internal view {
+  function validateDeposit(ReserveLogic.ReserveData storage reserve, uint256 amount) external view {
     (bool isActive, bool isFreezed, , ) = reserve.configuration.getFlags();
 
     require(amount > 0, Errors.AMOUNT_NOT_GREATER_THAN_0);
@@ -45,13 +45,11 @@ library ValidationLogic {
   /**
    * @dev validates a withdraw action.
    * @param reserveAddress the address of the reserve
-   * @param aTokenAddress the address of the aToken for the reserve
    * @param amount the amount to be withdrawn
    * @param userBalance the balance of the user
    */
   function validateWithdraw(
     address reserveAddress,
-    address aTokenAddress,
     uint256 amount,
     uint256 userBalance,
     mapping(address => ReserveLogic.ReserveData) storage reservesData,

contracts/tokenization/StableDebtToken.sol

@@ -8,7 +8,6 @@ import {DebtTokenBase} from './base/DebtTokenBase.sol';
 import {MathUtils} from '../libraries/math/MathUtils.sol';
 import {WadRayMath} from '../libraries/math/WadRayMath.sol';
 import {IStableDebtToken} from './interfaces/IStableDebtToken.sol';
-import "@nomiclabs/buidler/console.sol";
 
 /**
  * @title contract StableDebtToken

test/helpers/scenarios/rebalance-stable-rate.json

@@ -19,7 +19,7 @@
       ]
     },
     {
-      "description": "User 0 deposits 1000 DAI, user 1 deposits 1 ETH, borrows 100 DAI at a variable rate, user 0 rebalances user 1 (revert expected)",
+      "description": "User 0 deposits 1000 DAI, user 1 deposits 5 ETH, borrows 600 DAI at a variable rate, user 0 rebalances user 1 (revert expected)",
       "actions": [
         {
           "name": "mint",
@@ -51,7 +51,7 @@
           "name": "mint",
           "args": {
             "reserve": "WETH",
-            "amount": "1",
+            "amount": "5",
             "user": "1"
           },
           "expected": "success"
@@ -69,7 +69,7 @@
           "args": {
             "reserve": "WETH",
 
-            "amount": "1",
+            "amount": "5",
             "user": "1"
           },
           "expected": "success"
@@ -78,8 +78,8 @@
           "name": "borrow",
           "args": {
             "reserve": "DAI",
-            "amount": "100",
+            "amount": "250",
-            "borrowRateMode": "variable",
+            "borrowRateMode": "stable",
             "user": "1",
             "timeTravel": "365"
           },
@@ -98,14 +98,16 @@
       ]
     },
     {
-      "description": "User 1 swaps to stable, user 0 tries to rebalance but the conditions are not met (revert expected)",
+      "description": "User 1 borrows another 200 at stable, user 0 tries to rebalance but the conditions are not met (revert expected)",
       "actions": [
         {
-          "name": "swapBorrowRateMode",
+          "name": "borrow",
           "args": {
             "reserve": "DAI",
+            "amount": "200",
+            "borrowRateMode": "stable",
             "user": "1",
-            "borrowRateMode": "variable"
+            "timeTravel": "365"
           },
           "expected": "success"
         },
@@ -122,40 +124,92 @@
       ]
     },
     {
-      "description": "User 2 deposits ETH and borrows the remaining DAI, causing the stable rates to rise (liquidity rate < user 1 borrow rate). User 0 tries to rebalance user 1 (revert expected)",
+      "description": "User 1 borrows another 200 at stable, user 0 tries to rebalance but the conditions are not met (revert expected)",
       "actions": [
         {
-          "name": "mint",
+          "name": "borrow",
           "args": {
-            "reserve": "WETH",
+            "reserve": "DAI",
-            "amount": "5",
+            "amount": "200",
-            "user": "2"
+            "borrowRateMode": "stable",
+            "user": "1",
+            "timeTravel": "365"
           },
           "expected": "success"
         },
         {
-          "name": "approve",
+          "name": "rebalanceStableBorrowRate",
           "args": {
-            "reserve": "WETH",
+            "reserve": "DAI",
-            "user": "2"
+            "user": "0",
+            "target": "1"
           },
-          "expected": "success"
+          "expected": "revert",
+          "revertMessage": "Interest rate rebalance conditions were not met"
+        }
+      ]
     },
     {
-          "name": "deposit",
+      "description": "User 1 borrows another 100 at stable, user 0 tries to rebalance but the conditions are not met (revert expected)",
-          "args": {
+      "actions": [
-            "reserve": "WETH",
-
-            "amount": "5",
-            "user": "2"
-          },
-          "expected": "success"
-        },
         {
           "name": "borrow",
           "args": {
             "reserve": "DAI",
             "amount": "100",
+            "borrowRateMode": "stable",
+            "user": "1",
+            "timeTravel": "365"
+          },
+          "expected": "success"
+        },
+        {
+          "name": "rebalanceStableBorrowRate",
+          "args": {
+            "reserve": "DAI",
+            "user": "0",
+            "target": "1"
+          },
+          "expected": "revert",
+          "revertMessage": "Interest rate rebalance conditions were not met"
+        }
+      ]
+    },
+    {
+      "description": "User 2 deposits ETH and borrows the remaining DAI, causing the stable rates to rise (usage ratio = 94%). User 0 tries to rebalance user 1 (revert expected)",
+      "actions": [
+        {
+          "name": "mint",
+          "args": {
+            "reserve": "WETH",
+            "amount": "5",
+            "user": "2"
+          },
+          "expected": "success"
+        },
+        {
+          "name": "approve",
+          "args": {
+            "reserve": "WETH",
+            "user": "2"
+          },
+          "expected": "success"
+        },
+        {
+          "name": "deposit",
+          "args": {
+            "reserve": "WETH",
+
+            "amount": "5",
+            "user": "2"
+          },
+          "expected": "success"
+        },
+        {
+          "name": "borrow",
+          "args": {
+            "reserve": "DAI",
+            "amount": "190",
             "borrowRateMode": "variable",
             "user": "2"
           },
@@ -174,40 +228,13 @@
       ]
     },
     {
-      "description": "User 2 borrows more DAI, causing the liquidity rate to rise above user 1 stable borrow rate User 0 rebalances user 1",
+      "description": "User 2 borrows the remaining DAI (usage ratio = 100%). User 0 rebalances user 1",
       "actions": [
-        {
-          "name": "mint",
-          "args": {
-            "reserve": "WETH",
-            "amount": "3",
-            "user": "2"
-          },
-          "expected": "success"
-        },
-        {
-          "name": "approve",
-          "args": {
-            "reserve": "WETH",
-            "user": "2"
-          },
-          "expected": "success"
-        },
-        {
-          "name": "deposit",
-          "args": {
-            "reserve": "WETH",
-
-            "amount": "3",
-            "user": "2"
-          },
-          "expected": "success"
-        },
         {
           "name": "borrow",
           "args": {
             "reserve": "DAI",
-            "amount": "700",
+            "amount": "60",
             "borrowRateMode": "variable",
             "user": "2"
           },