Resolve DIV/0 unstaking in a burn epoch with no burn (#748)

* created unit test which reproduces div/0 error upon unstake

* add FIXME comment

* ported tests to RC4

* brute-force zero checks (#745)

* removed FIXME which was fixed

src/RewardsManager.sol

@@ -525,7 +525,7 @@ contract RewardsManager is IRewardsManager, ReentrancyGuard {
  ) = _getPoolAccumulators(ajnaPool_, nextEpoch_, epoch_);
 
  // calculate rewards earned
- newRewards_ = Maths.wmul(
+ newRewards_ = totalInterestEarnedInPeriod == 0 ? 0 : Maths.wmul(
  REWARD_FACTOR,
  Maths.wdiv(
  Maths.wmul(interestEarned_, totalBurnedInPeriod),
@@ -783,7 +783,7 @@ contract RewardsManager is IRewardsManager, ReentrancyGuard {
  (, , , uint256 bucketDeposit, ) = IPool(pool_).bucketInfo(bucketIndex_);
 
  uint256 burnFactor = Maths.wmul(totalBurned_, bucketDeposit);
- uint256 interestFactor = Maths.wdiv(
+ uint256 interestFactor = interestEarned_ == 0 ? 0 : Maths.wdiv(
  Maths.WAD - Maths.wdiv(prevBucketExchangeRate, curBucketExchangeRate),
  interestEarned_
  );

tests/forge/unit/Rewards/RewardsManager.t.sol

@@ -177,6 +177,123 @@ contract RewardsManagerTest is RewardsHelperContract {
  });
  }
 
+ function testUnstakeTokenAfterBurnNoInterest() external {
+ skip(10);
+ ERC20Pool pool = ERC20Pool(address(_pool));
+
+ // deposit into a high and low bucket
+ deal(address(_quoteOne), _minterOne, 400 * 1e18);
+ changePrank(_minterOne);
+ _quoteOne.approve(address(_pool), type(uint256).max);
+ _pool.addQuoteToken(200 * 1e18, 2_000, type(uint256).max);
+ _pool.addQuoteToken(200 * 1e18, 4_000, type(uint256).max);
+ skip(1 hours);
+
+ // draw debt between the buckets
+ uint256 borrowAmount = 100 * 1e18;
+ uint256 limitIndex = 3_000;
+ assertGt(_pool.depositSize(), borrowAmount);
+ (
+ uint256 collateralToPledge
+ ) = _createTestBorrower(address(_pool), _borrower, borrowAmount, limitIndex);
+ pool.drawDebt(_borrower, borrowAmount, limitIndex, collateralToPledge);
+ skip(3 days);
+ (,,, uint256 htpIndex,,) = _poolUtils.poolPricesInfo(address(_pool));
+ assertLt(htpIndex, 4_000);
+
+ // mint LP NFT and memorialize position for only the bucket which did not earn interest
+ (uint256 lpBalance, ) = _pool.lenderInfo(4000, _minterOne);
+ assertGt(lpBalance, 0);
+ uint256[] memory indexes = new uint256[](1);
+ indexes[0] = 4_000;
+ uint256[] memory lpBalances = new uint256[](1);
+ lpBalances[0] = lpBalance;
+ changePrank(_minterOne);
+ _pool.increaseLPAllowance(address(_positionManager), indexes, lpBalances);
+ IPositionManagerOwnerActions.MintParams memory mintParams = IPositionManagerOwnerActions.MintParams(
+ _minterOne, address(_pool), keccak256("ERC20_NON_SUBSET_HASH"));
+ uint256 tokenId = _positionManager.mint(mintParams);
+ IPositionManagerOwnerActions.MemorializePositionsParams memory memorializeParams = IPositionManagerOwnerActions.MemorializePositionsParams(
+ tokenId, indexes
+ );
+ _positionManager.memorializePositions(memorializeParams);
+ _registerLender(address(_positionManager), indexes);
+ skip(4 days);
+
+ // stake rewards
+ _stakeToken(address(_pool), _minterOne, tokenId);
+ skip(7 days);
+
+ // repay debt to accumulate some reserves
+ changePrank(_borrower);
+ pool.repayDebt(_borrower, type(uint256).max, collateralToPledge, _borrower, MAX_FENWICK_INDEX);
+ skip(2 hours);
+
+ // burn
+ changePrank(_bidder);
+ pool.kickReserveAuction();
+ skip(11 hours);
+ _ajnaToken.approve(address(_pool), type(uint256).max);
+ (,, uint256 curClaimableReservesRemaining,,) = _poolUtils.poolReservesInfo(address(_pool));
+ _pool.takeReserves(curClaimableReservesRemaining);
+
+ // unstake with no interest earned
+ changePrank(_minterOne);
+ vm.expectEmit(true, true, true, true);
+ emit Unstake(_minterOne, address(_pool), tokenId);
+ _rewardsManager.unstake(tokenId);
+ assertEq(PositionManager(address(_positionManager)).ownerOf(tokenId), _minterOne);
+ }
+
+ function testUnstakeNoBurn() external {
+ skip(10);
+ ERC20Pool pool = ERC20Pool(address(_pool));
+
+ // deposit into some buckets and mint an NFT
+ uint256[] memory indexes = new uint256[](3);
+ indexes[0] = 2000;
+ indexes[1] = 2500;
+ indexes[2] = 3000;
+ uint256 tokenId = _mintAndMemorializePositionNFT({
+ indexes: indexes,
+ minter: _minterOne,
+ mintAmount: 1_000 * 1e18,
+ pool: address(_pool)
+ });
+
+ // draw debt
+ uint256 borrowAmount = 1_500 * 1e18;
+ uint256 limitIndex = 2_500;
+ assertEq(_pool.depositIndex(borrowAmount), limitIndex);
+ assertGt(_pool.depositSize(), borrowAmount);
+ (
+ uint256 collateralToPledge
+ ) = _createTestBorrower(address(_pool), _borrower, borrowAmount, limitIndex);
+ pool.drawDebt(_borrower, borrowAmount, limitIndex, collateralToPledge);
+ skip(3 days);
+
+ // stake rewards
+ _stakeToken(address(_pool), _minterOne, tokenId);
+ skip(7 days);
+
+ // repay debt to accumulate some reserves
+ changePrank(_borrower);
+ pool.repayDebt(_borrower, type(uint256).max, collateralToPledge, _borrower, MAX_FENWICK_INDEX);
+ skip(2 hours);
+
+ // start auction, but no burn
+ changePrank(_bidder);
+ pool.kickReserveAuction();
+ skip(11 hours);
+
+ // unstake
+ changePrank(_minterOne);
+ vm.expectEmit(true, true, true, true);
+ emit Unstake(_minterOne, address(_pool), tokenId);
+ _rewardsManager.unstake(tokenId);
+ assertEq(PositionManager(address(_positionManager)).ownerOf(tokenId), _minterOne);
+ }
+
  function testUpdateExchangeRatesAndClaimRewards() external {
  skip(10);