Merge branch 'feat/101-first-borrowing-on-debt-tokens' into 'master'

Added return of is first borrowing on debt tokens mint()

Closes #101

See merge request aave-tech/protocol-v2!110

contracts/lendingpool/LendingPool.sol

@@ -888,34 +888,34 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
       oracle
     );
 
-    uint256 reserveId = reserve.id;
-    if (!userConfig.isBorrowing(reserveId)) {
-      userConfig.setBorrowing(reserveId, true);
-    }
-
     reserve.updateState();
 
     //caching the current stable borrow rate
     uint256 currentStableRate = 0;
-
+    
+    bool isFirstBorrowing = false;
     if (
       ReserveLogic.InterestRateMode(vars.interestRateMode) == ReserveLogic.InterestRateMode.STABLE
     ) {
       currentStableRate = reserve.currentStableBorrowRate;
 
-      IStableDebtToken(reserve.stableDebtTokenAddress).mint(
+      isFirstBorrowing = IStableDebtToken(reserve.stableDebtTokenAddress).mint(
         vars.onBehalfOf,
         vars.amount,
         currentStableRate
       );
     } else {
-      IVariableDebtToken(reserve.variableDebtTokenAddress).mint(
+      isFirstBorrowing = IVariableDebtToken(reserve.variableDebtTokenAddress).mint(
         vars.onBehalfOf,
         vars.amount,
         reserve.variableBorrowIndex
       );
     }
 
+    if (isFirstBorrowing) {
+      userConfig.setBorrowing(reserve.id, true);
+    }
+
     reserve.updateInterestRates(
       vars.asset,
       vars.aTokenAddress,

contracts/tokenization/StableDebtToken.sol

@@ -97,7 +97,7 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
     address user,
     uint256 amount,
     uint256 rate
-  ) external override onlyLendingPool {
+  ) external override onlyLendingPool returns(bool) {
     MintLocalVars memory vars;
 
     //cumulates the user debt
@@ -148,6 +148,8 @@ contract StableDebtToken is IStableDebtToken, DebtTokenBase {
       vars.newStableRate,
       vars.currentAvgStableRate
     );
+
+    return currentBalance == 0;
   }
 
   /**

contracts/tokenization/interfaces/IStableDebtToken.sol

@@ -62,7 +62,7 @@ interface IStableDebtToken {
     address user,
     uint256 amount,
     uint256 rate
-  ) external;
+  ) external returns(bool);
 
   /**
    * @dev burns debt of the target user.