Merge branch 'fix/79' into 'master'

Resolve "Fix PVE006-2, PVE012, PVE013-1-2-3-4"

Closes #79

See merge request aave-tech/protocol-v2!88

contracts/lendingpool/LendingPool.sol

@@ -262,15 +262,6 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
 
     ReserveLogic.InterestRateMode interestRateMode = ReserveLogic.InterestRateMode(rateMode);
 
-    //default to max amount
-    uint256 paybackAmount = interestRateMode == ReserveLogic.InterestRateMode.STABLE
-      ? stableDebt
-      : variableDebt;
-
-    if (amount < paybackAmount) {
-      paybackAmount = amount;
-    }
-
     ValidationLogic.validateRepay(
       reserve,
       amount,
@@ -280,6 +271,15 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
       variableDebt
     );
 
+    //default to max amount
+    uint256 paybackAmount = interestRateMode == ReserveLogic.InterestRateMode.STABLE
+      ? stableDebt
+      : variableDebt;
+
+    if (amount < paybackAmount) {
+      paybackAmount = amount;
+    }
+
     reserve.updateState();
 
     //burns an equivalent amount of debt tokens
@@ -356,9 +356,10 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
   }
 
   /**
-   * @dev rebalances the stable interest rate of a user if current liquidity rate > user stable rate.
-   * this is regulated by Aave to ensure that the protocol is not abused, and the user is paying a fair
-   * rate. Anyone can call this function.
+   * @dev rebalances the stable interest rate of a user. Users can be rebalanced if the following conditions are satisfied:
+   * 1. Usage ratio is above 95%
+   * 2. the current deposit APY is below REBALANCE_UP_THRESHOLD * maxVariableBorrowRate, which means that too much has been
+   *    borrowed at a stable rate and depositors are not earning enough.
    * @param asset the address of the reserve
    * @param user the address of the user to be rebalanced
    **/
@@ -373,7 +374,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
 
     uint256 stableBorrowBalance = IERC20(stableDebtToken).balanceOf(user);
 
-    //if the utilization rate is below 95%, no rebalances are needed
+    //if the usage ratio is below 95%, no rebalances are needed
     uint256 totalBorrows = stableDebtToken
       .totalSupply()
       .add(variableDebtToken.totalSupply())
@@ -417,7 +418,7 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
   /**
    * @dev allows depositors to enable or disable a specific deposit as collateral.
    * @param asset the address of the reserve
-   * @param useAsCollateral true if the user wants to user the deposit as collateral, false otherwise.
+   * @param useAsCollateral true if the user wants to use the deposit as collateral, false otherwise.
    **/
   function setUserUseReserveAsCollateral(address asset, bool useAsCollateral) external override {
     _whenNotPaused();

contracts/lendingpool/LendingPoolCollateralManager.sol

@@ -194,13 +194,6 @@ contract LendingPoolCollateralManager is VersionedInitializable, LendingPoolStor
     //update the principal reserve
     principalReserve.updateState();
 
-    principalReserve.updateInterestRates(
-      principal,
-      principalReserve.aTokenAddress,
-      vars.actualAmountToLiquidate,
-      0
-    );
-
     if (vars.userVariableDebt >= vars.actualAmountToLiquidate) {
       IVariableDebtToken(principalReserve.variableDebtTokenAddress).burn(
         user,
@@ -223,6 +216,13 @@ contract LendingPoolCollateralManager is VersionedInitializable, LendingPoolStor
       );
     }
 
+    principalReserve.updateInterestRates(
+      principal,
+      principalReserve.aTokenAddress,
+      vars.actualAmountToLiquidate,
+      0
+    );
+
     //if liquidator reclaims the aToken, he receives the equivalent atoken amount
     if (receiveAToken) {
       vars.collateralAtoken.transferOnLiquidation(user, msg.sender, vars.maxCollateralToLiquidate);
@@ -306,8 +306,8 @@ contract LendingPoolCollateralManager is VersionedInitializable, LendingPoolStor
       .principalCurrencyPrice
       .mul(purchaseAmount)
       .mul(10**vars.collateralDecimals)
-      .div(vars.collateralPrice.mul(10**vars.principalDecimals))
-      .percentMul(vars.liquidationBonus);
+      .percentMul(vars.liquidationBonus)
+      .div(vars.collateralPrice.mul(10**vars.principalDecimals));
 
     if (vars.maxAmountCollateralToLiquidate > userCollateralBalance) {
       collateralAmount = userCollateralBalance;

contracts/libraries/logic/GenericLogic.sol

@@ -25,7 +25,6 @@ library GenericLogic {
   using UserConfiguration for UserConfiguration.Map;
 
   uint256 public constant HEALTH_FACTOR_LIQUIDATION_THRESHOLD = 1 ether;
-  uint256 public constant HEALTH_FACTOR_CRITICAL_THRESHOLD = 0.98 ether;
 
   struct balanceDecreaseAllowedLocalVars {
     uint256 decimals;

contracts/tokenization/StableDebtToken.sol

@@ -196,8 +196,7 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
   /**
    * @dev Calculates the increase in balance since the last user interaction
    * @param user The address of the user for which the interest is being accumulated
-   * @return The previous principal balance, the new principal balance, the balance increase
-   * and the new user index
+   * @return The previous principal balance, the new principal balance and the balance increase
    **/
   function _calculateBalanceIncrease(address user)
     internal