Check negative totals after full discount #10790

Author: ilnytskyi

app/code/Magento/SalesRule/Model/Utility.php

@@ -189,6 +189,8 @@ public function deltaRoundingFix(
     ) {
         $discountAmount = $discountData->getAmount();
         $baseDiscountAmount = $discountData->getBaseAmount();
+        $rowTotalInclTax = $item->getRowTotalInclTax();
+        $baseRowTotalInclTax = $item->getBaseRowTotalInclTax();
 
         //TODO Seems \Magento\Quote\Model\Quote\Item\AbstractItem::getDiscountPercent() returns float value
         //that can not be used as array index
@@ -205,6 +207,23 @@ public function deltaRoundingFix(
                 - $this->priceCurrency->round($baseDiscountAmount);
         }
 
+        /**
+         * When we have 100% discount check if totals will not be negative
+         */
+
+        if ($percentKey == 100) {
+            $discountDelta = $rowTotalInclTax - $discountAmount;
+            $baseDiscountDelta = $baseRowTotalInclTax - $baseDiscountAmount;
+
+            if ($discountDelta < 0) {
+                $discountAmount += $discountDelta;
+            }
+
+            if ($baseDiscountDelta < 0) {
+                $baseDiscountAmount += $baseDiscountDelta;
+            }
+        }
+
         $discountData->setAmount($this->priceCurrency->round($discountAmount));
         $discountData->setBaseAmount($this->priceCurrency->round($baseDiscountAmount));
 

app/code/Magento/Tax/Model/Calculation/AbstractAggregateCalculator.php

@@ -154,12 +154,6 @@ protected function calculateWithTaxNotInPrice(QuoteDetailsItemInterface $item, $
             $priceInclTax = $this->calculationTool->round($priceInclTax);
         }
 
-        $pricePerItemInclTax = $rowTotalInclTax / $quantity;
-
-        if (($pricePerItemInclTax - $priceInclTax) < 0) {
-            $priceInclTax = $pricePerItemInclTax;
-        }
-
         return $this->taxDetailsItemDataObjectFactory->create()
             ->setCode($item->getCode())
             ->setType($item->getType())