ACP2E-3403: Cart Price Rules Miscalculating Discount

Author: aplapana

app/code/Magento/Quote/Model/Quote/Item/AbstractItem.php

@@ -678,9 +678,7 @@ public function getTotalDiscountAmount()
             foreach ($children as $child) {
                 $totalDiscountAmount += $child->getDiscountAmount();
             }
-        } else {
-            $totalDiscountAmount = $this->getDiscountAmount();
         }
-        return $totalDiscountAmount;
+        return $totalDiscountAmount + $this->getDiscountAmount();
     }
 }

app/code/Magento/SalesRule/Model/Quote/Discount.php

@@ -221,15 +221,12 @@ public function collect(
                     unset($itemsToApplyRules[$key]);
                 }
 
-                if ($item->getChildren() && $item->isChildrenCalculated()) {
-                    $childTotal = 0;
-                    foreach ($item->getChildren() as $child) {
-                        $childTotal += $child->getBaseDiscountAmount();
+                if (($children = $item->getChildren()) && $item->isChildrenCalculated()) {
+                    foreach ($children as $child) {
+                        $totalDiscount[$child->getId()] = $child->getBaseDiscountAmount();
                     }
-                    $totalDiscount[$item->getId()] = $childTotal;
-                } else {
-                    $totalDiscount[$item->getId()] = $item->getBaseDiscountAmount();
                 }
+                $totalDiscount[$item->getId()] = $item->getBaseDiscountAmount();
             }
             $address->setBaseDiscountAmount(array_sum(array_values($totalDiscount)));
         }

app/code/Magento/SalesRule/Model/Rule/Action/Discount/CartFixed.php

@@ -141,6 +141,9 @@ public function calculate($rule, $item, $qty)
             $baseDiscountAmount = min($baseItemPrice * $qty, $baseDiscountAmount);
             if ($ruleItemsCount <= 1) {
                 $this->deltaPriceRound->reset($discountType);
+                if ($baseDiscountAmount > $availableDiscountAmount) {
+                    $baseDiscountAmount = $availableDiscountAmount;
+                }
             } else {
                 $this->validator->decrementRuleItemTotalsCount($rule->getId());
             }