Merge branch 'master' into feat/18

contracts/flashloan/interfaces/IFlashLoanReceiver.sol

@@ -13,5 +13,5 @@ interface IFlashLoanReceiver {
     uint256 amount,
     uint256 fee,
     bytes calldata params
-  ) external;
+  ) external returns (bool);
 }

contracts/lendingpool/LendingPool.sol

@@ -579,7 +579,10 @@ contract LendingPool is VersionedInitializable, ILendingPool, LendingPoolStorage
     IAToken(vars.aTokenAddress).transferUnderlyingTo(receiverAddress, amount);
 
     //execute action of the receiver
-    vars.receiver.executeOperation(asset, amount, vars.premium, params);
+    require(
+      vars.receiver.executeOperation(asset, amount, vars.premium, params),
+      Errors.INVALID_FLASH_LOAN_EXECUTOR_RETURN
+    );
 
     vars.amountPlusPremium = amount.add(vars.premium);
 

contracts/lendingpool/LendingPoolCollateralManager.sol

@@ -239,12 +239,15 @@ contract LendingPoolCollateralManager is VersionedInitializable, LendingPoolStor
         principalReserve.variableBorrowIndex
       );
     } else {
-      IVariableDebtToken(principalReserve.variableDebtTokenAddress).burn(
-        user,
-        vars.userVariableDebt,
-        principalReserve.variableBorrowIndex
-      );
-
+      //if the user does not have variable debt, no need to try to burn variable
+      //debt tokens
+      if (vars.userVariableDebt > 0) {
+        IVariableDebtToken(principalReserve.variableDebtTokenAddress).burn(
+          user,
+          vars.userVariableDebt,
+          principalReserve.variableBorrowIndex
+        );
+      }
       IStableDebtToken(principalReserve.stableDebtTokenAddress).burn(
         user,
         vars.actualAmountToLiquidate.sub(vars.userVariableDebt)

contracts/libraries/helpers/Errors.sol

@@ -44,11 +44,14 @@ library Errors {
   string public constant FAILED_COLLATERAL_SWAP = '55';
   string public constant INVALID_EQUAL_ASSETS_TO_SWAP = '56';
   string public constant NO_MORE_RESERVES_ALLOWED = '59';
+  string public constant INVALID_FLASH_LOAN_EXECUTOR_RETURN = '60';
 
-  // require error messages - aToken
+  // require error messages - aToken - DebtTokens
   string public constant CALLER_MUST_BE_LENDING_POOL = '28'; // 'The caller of this function must be a lending pool'
   string public constant CANNOT_GIVE_ALLOWANCE_TO_HIMSELF = '30'; // 'User cannot give allowance to himself'
   string public constant TRANSFER_AMOUNT_NOT_GT_0 = '31'; // 'Transferred amount needs to be greater than zero'
+  string public constant INVALID_MINT_AMOUNT = '53'; //invalid amount to mint
+  string public constant INVALID_BURN_AMOUNT = '54'; //invalid amount to burn
 
   // require error messages - ReserveLogic
   string public constant RESERVE_ALREADY_INITIALIZED = '34'; // 'Reserve has already been initialized'

contracts/mocks/flashloan/MockFlashLoanReceiver.sol

@@ -20,6 +20,7 @@ contract MockFlashLoanReceiver is FlashLoanReceiverBase {
 
   bool _failExecution;
   uint256 _amountToApprove;
+  bool _simulateEOA;
 
   constructor(ILendingPoolAddressesProvider provider) public FlashLoanReceiverBase(provider) {}
 
@@ -31,16 +32,25 @@ contract MockFlashLoanReceiver is FlashLoanReceiverBase {
     _amountToApprove = amountToApprove;
   }
 
+  function setSimulateEOA(bool flag) public {
+    _simulateEOA = flag;
+  }
+
   function amountToApprove() public view returns (uint256) {
     return _amountToApprove;
   }
 
+  function simulateEOA() public view returns (bool) {
+    return _simulateEOA;
+  }
+
   function executeOperation(
     address reserve,
     uint256 amount,
     uint256 fee,
     bytes memory params
-  ) public override {
+  ) public override returns (bool) {
+    params;
     //mint to this contract the specific amount
     MintableERC20 token = MintableERC20(reserve);
 
@@ -51,7 +61,7 @@ contract MockFlashLoanReceiver is FlashLoanReceiverBase {
 
     if (_failExecution) {
       emit ExecutedWithFail(reserve, amount, fee);
-      return;
+      return !_simulateEOA;
     }
 
     //execution does not fail - mint tokens and return them to the _destination
@@ -62,5 +72,7 @@ contract MockFlashLoanReceiver is FlashLoanReceiverBase {
     IERC20(reserve).approve(_addressesProvider.getLendingPool(), amountToReturn);
 
     emit ExecutedWithSuccess(reserve, amount, fee);
+
+    return true;
   }
 }

contracts/tokenization/AToken.sol

@@ -101,7 +101,9 @@ contract AToken is VersionedInitializable, IncentivizedERC20, IAToken {
     uint256 amount,
     uint256 index
   ) external override onlyLendingPool {
-    _burn(user, amount.rayDiv(index));
+    uint256 amountScaled = amount.rayDiv(index);
+    require(amountScaled != 0, Errors.INVALID_BURN_AMOUNT);
+    _burn(user, amountScaled);
 
     //transfers the underlying to the target
     IERC20(UNDERLYING_ASSET_ADDRESS).safeTransfer(receiverOfUnderlying, amount);
@@ -116,22 +118,39 @@ contract AToken is VersionedInitializable, IncentivizedERC20, IAToken {
    * only lending pools can call this function
    * @param user the address receiving the minted tokens
    * @param amount the amount of tokens to mint
+   * @param index the the last index of the reserve
    */
   function mint(
     address user,
     uint256 amount,
     uint256 index
   ) external override onlyLendingPool {
-    //mint an equivalent amount of tokens to cover the new deposit
-    _mint(user, amount.rayDiv(index));
+    uint256 amountScaled = amount.rayDiv(index);
+    require(amountScaled != 0, Errors.INVALID_MINT_AMOUNT);
+    _mint(user, amountScaled);
 
     //transfer event to track balances
     emit Transfer(address(0), user, amount);
     emit Mint(user, amount, index);
   }
 
+  /**
+   * @dev mints aTokens to reserve treasury
+   * only lending pools can call this function
+   * @param amount the amount of tokens to mint to the treasury
+   * @param index the the last index of the reserve
+   */
   function mintToTreasury(uint256 amount, uint256 index) external override onlyLendingPool {
-    _mint(RESERVE_TREASURY_ADDRESS, amount.div(index));
+    if (amount == 0) {
+      return;
+    }
+
+    //compared to the normal mint, we don't check for rounding errors.
+    //the amount to mint can easily be very small since is a fraction of the interest
+    //accrued. in that case, the treasury will experience a (very small) loss, but it
+    //wont cause potentially valid transactions to fail.
+
+    _mint(RESERVE_TREASURY_ADDRESS, amount.rayDiv(index));
 
     //transfer event to track balances
     emit Transfer(address(0), RESERVE_TREASURY_ADDRESS, amount);

contracts/tokenization/VariableDebtToken.sol

@@ -7,6 +7,7 @@ import {SafeMath} from '@openzeppelin/contracts/math/SafeMath.sol';
 import {DebtTokenBase} from './base/DebtTokenBase.sol';
 import {WadRayMath} from '../libraries/math/WadRayMath.sol';
 import {IVariableDebtToken} from './interfaces/IVariableDebtToken.sol';
+import {Errors} from '../libraries/helpers/Errors.sol';
 
 /**
  * @title contract VariableDebtToken
@@ -59,7 +60,10 @@ contract VariableDebtToken is DebtTokenBase, IVariableDebtToken {
     uint256 amount,
     uint256 index
   ) external override onlyLendingPool {
-    _mint(user, amount.rayDiv(index));
+    uint256 amountScaled = amount.rayDiv(index);
+    require(amountScaled != 0, Errors.INVALID_MINT_AMOUNT);
+
+    _mint(user, amountScaled);
 
     emit Transfer(address(0), user, amount);
     emit Mint(user, amount, index);
@@ -75,7 +79,10 @@ contract VariableDebtToken is DebtTokenBase, IVariableDebtToken {
     uint256 amount,
     uint256 index
   ) external override onlyLendingPool {
-    _burn(user, amount.rayDiv(index));
+    uint256 amountScaled = amount.rayDiv(index);
+    require(amountScaled != 0, Errors.INVALID_BURN_AMOUNT);
+
+    _burn(user, amountScaled);
 
     emit Transfer(user, address(0), amount);
     emit Burn(user, amount, index);

helpers/types.ts

@@ -90,6 +90,7 @@ export enum ProtocolErrors {
   REQUESTED_AMOUNT_TOO_SMALL = '25', // 'The requested amount is too small for a FlashLoan.'
   INCONSISTENT_PROTOCOL_ACTUAL_BALANCE = '26', // 'The actual balance of the protocol is inconsistent'
   CALLER_NOT_LENDING_POOL_CONFIGURATOR = '27', // 'The actual balance of the protocol is inconsistent'
+  INVALID_FLASH_LOAN_EXECUTOR_RETURN = '60', // The flash loan received returned 0 (EOA)
 
   // require error messages - aToken
   CALLER_MUST_BE_LENDING_POOL = '28', // 'The caller of this function must be a lending pool'

test/flashloan.spec.ts

@@ -24,6 +24,7 @@ makeSuite('LendingPool FlashLoan function', (testEnv: TestEnv) => {
     INVALID_FLASHLOAN_MODE,
     SAFEERC20_LOWLEVEL_CALL,
     IS_PAUSED,
+    INVALID_FLASH_LOAN_EXECUTOR_RETURN,
   } = ProtocolErrors;
 
   before(async () => {
@@ -116,9 +117,30 @@ makeSuite('LendingPool FlashLoan function', (testEnv: TestEnv) => {
     ).to.be.revertedWith(TRANSFER_AMOUNT_EXCEEDS_BALANCE);
   });
 
+  it('Takes WETH flashloan, simulating a receiver as EOA (revert expected)', async () => {
+    const {pool, weth, users} = testEnv;
+    const caller = users[1];
+    await _mockFlashLoanReceiver.setFailExecutionTransfer(true);
+    await _mockFlashLoanReceiver.setSimulateEOA(true);
+
+    await expect(
+      pool
+        .connect(caller.signer)
+        .flashLoan(
+          _mockFlashLoanReceiver.address,
+          weth.address,
+          ethers.utils.parseEther('0.8'),
+          0,
+          '0x10',
+          '0'
+        )
+    ).to.be.revertedWith(INVALID_FLASH_LOAN_EXECUTOR_RETURN);
+  });
+
   it('Takes a WETH flashloan with an invalid mode. (revert expected)', async () => {
     const {pool, weth, users} = testEnv;
     const caller = users[1];
+    await _mockFlashLoanReceiver.setSimulateEOA(false);
     await _mockFlashLoanReceiver.setFailExecutionTransfer(true);
 
     await expect(