ACP2E-3498: Incorrect discount value when multiple cart price rules are applied simultaneously with discounted/special priced products

Author: aplapana

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

@@ -13,6 +13,7 @@
 use Magento\SalesRule\Model\DeltaPriceRound;
 use Magento\SalesRule\Model\Rule;
 use Magento\SalesRule\Model\Validator;
+use Magento\Quote\Model\Quote\Item;
 
 /**
  * Calculates discount for cart item if fixed discount applied on whole cart.
@@ -79,10 +80,11 @@ public function calculate($rule, $item, $qty)
         $discountData = $this->discountFactory->create();
 
         $ruleTotals = $this->validator->getRuleItemTotalsInfo($rule->getId());
-        if (is_null($rule->getExistingDiscounts())) {
+        if ($rule->getExistingDiscounts() === null) {
             $existingRuleDiscount = 0;
+            /** @var Item $ruleItem */
             foreach ($ruleTotals['affected_items'] as $ruleItem) {
-                $existingRuleDiscount += $ruleItem->getBaseDiscountAmount() * $qty;
+                $existingRuleDiscount += $ruleItem->getBaseDiscountAmount();
             }
             $rule->setExistingDiscounts($existingRuleDiscount);
         }

app/code/Magento/SalesRule/Test/Unit/Model/Rule/Action/Discount/CartFixedTest.php

@@ -185,7 +185,6 @@ public function testCalculate(array $shipping, array $ruleDetails): void
             ->willReturn(true);
         $cartExtensionMock = $this->getMockBuilder(CartExtensionInterface::class)
             ->disableOriginalConstructor()
-            ->addMethods(['getShippingAssignments'])
             ->getMockForAbstractClass();
         $this->quote->expects($this->any())->method('getCartFixedRules')->will($this->returnValue([]));
         $store = $this->createMock(Store::class);
@@ -279,7 +278,8 @@ public static function dataProviderActions()
                     'items_count' => 1,
                     'rounded_amount' => 0.0,
                     'discounted_amount' => 10.0,
-                    'cart_rules' => 0.0
+                    'cart_rules' => 0.0,
+                    'affected_items' => []
                 ]
             ],
             'regular shipping with two items and single shipping' => [
@@ -294,7 +294,8 @@ public static function dataProviderActions()
                     'items_count' => 2,
                     'rounded_amount' => 0.0,
                     'discounted_amount' => 10.0,
-                    'cart_rules' => 0.0
+                    'cart_rules' => 0.0,
+                    'affected_items' => []
                 ]
             ],
             'regular shipping with two items and multiple shipping' => [
@@ -309,7 +310,8 @@ public static function dataProviderActions()
                     'items_count' => 2,
                     'rounded_amount' => 0.0,
                     'discounted_amount' => 10.0,
-                    'cart_rules' => 0.0
+                    'cart_rules' => 0.0,
+                    'affected_items' => []
                 ]
             ]
 

app/code/Magento/SalesRule/Test/Unit/Model/ValidatorTest.php

@@ -461,6 +461,7 @@ public function testInitTotalsCanApplyDiscount(): void
         $this->assertArrayHasKey('items_price', $this->model->getRuleItemTotalsInfo($rule->getId()));
         $this->assertArrayHasKey('base_items_price', $this->model->getRuleItemTotalsInfo($rule->getId()));
         $this->assertArrayHasKey('items_count', $this->model->getRuleItemTotalsInfo($rule->getId()));
+        $this->assertArrayHasKey('affected_items', $this->model->getRuleItemTotalsInfo($rule->getId()));
         $this->assertEquals(1, $this->model->getRuleItemTotalsInfo($rule->getId())['items_count']);
     }
 

dev/tests/integration/testsuite/Magento/SalesRule/Model/Rule/Action/Discount/CartFixedTest.php

@@ -526,11 +526,11 @@ public static function discountByPercentDataProvider()
             ],
             [
                 'percentDiscount' => 15.5,
-                'expectedDiscounts' => ['simple1' => 3.66, 'simple2' => 9.75, 'totalDiscount' => -13.41]
+                'expectedDiscounts' => ['simple1' => 3.65, 'simple2' => 9.76, 'totalDiscount' => -13.41]
             ],
             [
                 'percentDiscount' => 50,
-                'expectedDiscounts' => ['simple1' => 5.73, 'simple2' => 15.26, 'totalDiscount' => -20.99]
+                'expectedDiscounts' => ['simple1' => 5.72, 'simple2' => 15.27, 'totalDiscount' => -20.99]
             ],
             [
                 'percentDiscount' => 100,