ACP2E-3403: Cart Price Rules Miscalculating Discount

Author: aplapana

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

@@ -188,10 +188,10 @@ public function collect(
         $items = $this->calculator->sortItemsByPriority($items, $address);
         $itemsToApplyRules = $items;
         $rules = $this->calculator->getRules($address);
-        $totalDiscount = [];
         $address->setBaseDiscountAmount(0);
         /** @var Rule $rule */
         foreach ($rules as $rule) {
+            $ruleTotalDiscount = 0;
             /** @var Item $item */
             foreach ($itemsToApplyRules as $key => $item) {
                 if ($item->getNoDiscount() || !$this->calculator->canApplyDiscount($item) || $item->getParentItem()) {
@@ -221,14 +221,14 @@ public function collect(
                     unset($itemsToApplyRules[$key]);
                 }
 
-                if (($children = $item->getChildren()) && $item->isChildrenCalculated()) {
-                    foreach ($children as $child) {
-                        $totalDiscount[$child->getId()] = $child->getBaseDiscountAmount();
+                if ($item->getChildren() && $item->isChildrenCalculated()) {
+                    foreach ($item->getChildren() as $child) {
+                        $ruleTotalDiscount += $child->getBaseDiscountAmount();
                     }
                 }
-                $totalDiscount[$item->getId()] = $item->getBaseDiscountAmount();
+                $ruleTotalDiscount += $item->getBaseDiscountAmount();
             }
-            $address->setBaseDiscountAmount(array_sum(array_values($totalDiscount)));
+            $address->setBaseDiscountAmount($ruleTotalDiscount);
         }
         $this->calculator->initTotals($items, $address);
         foreach ($items as $item) {