Merge pull request #713 from neutron-org/fix/negative_lo_withdraw

Fix: Add case to handle negative withdraw amounts

x/dex/keeper/integration_cancellimitorder_test.go

@@ -212,6 +212,24 @@ func (s *DexTestSuite) TestCancelPartiallyFilled() {
 	s.Assert().False(found)
 }
 
+func (s *DexTestSuite) TestCancelWithdrawThenCancel() {
+	s.fundAliceBalances(10, 0)
+	s.fundBobBalances(0, 20)
+
+	// GIVEN alice limit sells 10 TokenA
+	trancheKey := s.aliceLimitSells("TokenA", -6931, 10)
+	// Bob swaps some TokenB for 5 TokenA
+	s.bobLimitSellsWithMaxOut("TokenB", 7000, 20, 5)
+
+	// WHEN alice withdraws
+	s.aliceWithdrawsLimitSell(trancheKey)
+	s.assertAliceBalancesInt(sdkmath.ZeroInt(), sdkmath.NewInt(9999181))
+
+	// THEN Alice cancel still works
+	s.aliceCancelsLimitSell(trancheKey)
+	s.assertAliceBalancesInt(sdkmath.NewInt(4999999), sdkmath.NewInt(9999181))
+}
+
 func (s *DexTestSuite) TestCancelPartiallyFilledWithdrawFails() {
 	s.fundAliceBalances(50, 0)
 	s.fundBobBalances(0, 10)

x/dex/types/limit_order_tranche.go

@@ -147,6 +147,11 @@ func (t *LimitOrderTranche) CalcWithdrawAmount(trancheUser *LimitOrderTrancheUse
 	ratioFilled := t.RatioFilled()
 	maxAllowedToWithdraw := ratioFilled.MulInt(trancheUser.SharesOwned)
 	sharesToWithdrawDec := maxAllowedToWithdraw.Sub(math_utils.NewPrecDecFromInt(trancheUser.SharesWithdrawn))
+
+	// Given rounding it is possible for sharesToWithdrawn > maxAllowedToWithdraw. In this case we just exit.
+	if !sharesToWithdrawDec.IsPositive() {
+		return math.ZeroInt(), math.ZeroInt()
+	}
 	amountOutTokenOutDec := sharesToWithdrawDec.Quo(t.PriceTakerToMaker)
 
 	// Round shares withdrawn up and amountOut down to ensure math favors dex