Clone product before adding to cart

This prevents undesired behavior when adding multiple variants of the same SKU
to the cart in a single request. Without cloning the product when adding to,
the product object set with the quote item is a referenced object. When adding
a n+1 cart item with same sku, but different options multiple cart items are
referencing the same instance of a product object. This causes
Item::representProduct to ignore custom option and variant differences.

Fixes magento/graphql-ce#854

Author: pmclain

app/code/Magento/QuoteGraphQl/Model/Cart/AddSimpleProductToCart.php

@@ -55,7 +55,7 @@ public function execute(Quote $cart, array $cartItemData): void
         $sku = $this->extractSku($cartItemData);
 
         try {
-            $product = $this->productRepository->get($sku);
+            $product = clone $this->productRepository->get($sku);
         } catch (NoSuchEntityException $e) {
             throw new GraphQlNoSuchEntityException(__('Could not find a product with SKU "%sku"', ['sku' => $sku]));
         }

dev/tests/api-functional/testsuite/Magento/GraphQl/ConfigurableProduct/AddConfigurableProductToCartTest.php

@@ -67,6 +67,78 @@ public function testAddConfigurableProductToCart()
         self::assertArrayHasKey('value_label', $option);
     }
 
+    /**
+     * @magentoApiDataFixture Magento/ConfigurableProduct/_files/product_configurable.php
+     * @magentoApiDataFixture Magento/Checkout/_files/active_quote.php
+     */
+    public function testAddMultipleConfigurableProductToCart()
+    {
+        $searchResponse = $this->graphQlQuery($this->getFetchProductQuery('configurable'));
+        $product = current($searchResponse['products']['items']);
+
+        $quantityOne = 1;
+        $quantityTwo = 2;
+        $maskedQuoteId = $this->getMaskedQuoteIdByReservedOrderId->execute('test_order_1');
+        $parentSku = $product['sku'];
+        $skuOne = 'simple_10';
+        $skuTwo = 'simple_20';
+        $valueIdOne = $product['configurable_options'][0]['values'][0]['value_index'];
+
+        $query = <<<QUERY
+mutation {
+  addConfigurableProductsToCart(input:{
+    cart_id:"{$maskedQuoteId}"
+    cart_items:[
+      {
+        parent_sku:"{$parentSku}"
+        data:{
+          sku:"{$skuOne}"
+          quantity:{$quantityOne}
+        }
+      }
+      {
+        parent_sku:"{$parentSku}"
+        data:{
+          sku:"{$skuTwo}"
+          quantity:{$quantityTwo}
+        }
+      }
+    ]
+  }) {
+    cart {
+      items {
+        id
+        quantity
+        product {
+          sku
+        }
+        ... on ConfigurableCartItem {
+          configurable_options {
+            option_label
+            value_label
+            value_id
+          }
+        }
+      }
+    }
+  }
+}
+QUERY;
+
+        $response = $this->graphQlMutation($query);
+
+        $cartItems = $response['addConfigurableProductsToCart']['cart']['items'];
+        self::assertCount(2, $cartItems);
+
+        foreach ($cartItems as $cartItem) {
+            if ($cartItem['configurable_options'][0]['value_id'] === $valueIdOne) {
+                self::assertEquals($quantityOne, $cartItem['quantity']);
+            } else {
+                self::assertEquals($quantityTwo, $cartItem['quantity']);
+            }
+        }
+    }
+
     /**
      * @magentoApiDataFixture Magento/ConfigurableProduct/_files/product_configurable_sku.php
      * @magentoApiDataFixture Magento/Checkout/_files/active_quote.php