14086: Guest cart API ignoring cartId in url for some methods

Author: engcom-Charlie

app/code/Magento/Quote/Plugin/UpdateCartId.php

@@ -0,0 +1,49 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+
+declare(strict_types=1);
+
+namespace Magento\Quote\Plugin;
+
+use Magento\Framework\Webapi\Rest\Request as RestRequest;
+use Magento\Quote\Api\Data\CartItemInterface;
+use Magento\Quote\Api\GuestCartItemRepositoryInterface;
+
+/**
+ * Update cart id from request param
+ */
+class UpdateCartId
+{
+    /**
+     * @var RestRequest $request
+     */
+    private $request;
+
+    /**
+     * @param RestRequest $request
+     */
+    public function __construct(RestRequest $request)
+    {
+        $this->request = $request;
+    }
+
+    /**
+     * Update id from request if param cartId exist
+     *
+     * @param GuestCartItemRepositoryInterface $guestCartItemRepository
+     * @param CartItemInterface $cartItem
+     * @return void
+     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
+     */
+    public function beforeSave(
+        GuestCartItemRepositoryInterface $guestCartItemRepository,
+        CartItemInterface $cartItem
+    ): void {
+        if ($cartId = $this->request->getParam('cartId')) {
+            $cartItem->setQuoteId($cartId);
+        }
+    }
+}

app/code/Magento/Quote/etc/webapi_rest/di.xml

@@ -13,4 +13,7 @@
         <plugin name="accessControl" type="Magento\Quote\Model\QuoteRepository\Plugin\AccessChangeQuoteControl" />
         <plugin name="authorization" type="Magento\Quote\Model\QuoteRepository\Plugin\Authorization" />
     </type>
+    <type name="Magento\Quote\Api\GuestCartItemRepositoryInterface">
+        <plugin name="updateCartIdFromRequest" type="Magento\Quote\Plugin\UpdateCartId" />
+    </type>
 </config>

dev/tests/api-functional/testsuite/Magento/Quote/Api/GuestCartItemRepositoryTest.php

@@ -1,32 +1,41 @@
 <?php
 /**
- *
  * Copyright © Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
 namespace Magento\Quote\Api;
 
 use Magento\CatalogInventory\Api\StockRegistryInterface;
 use Magento\CatalogInventory\Model\Stock;
+use Magento\TestFramework\Helper\Bootstrap;
+use Magento\TestFramework\ObjectManager;
 use Magento\TestFramework\TestCase\WebapiAbstract;
 
+/**
+ * Test for Magento\Quote\Api\GuestCartItemRepositoryInterface.
+ */
 class GuestCartItemRepositoryTest extends WebapiAbstract
 {
-    const SERVICE_VERSION = 'V1';
-    const SERVICE_NAME = 'quoteGuestCartItemRepositoryV1';
-    const RESOURCE_PATH = '/V1/guest-carts/';
+    public const SERVICE_NAME = 'quoteGuestCartItemRepositoryV1';
+    private const SERVICE_VERSION = 'V1';
+    private const RESOURCE_PATH = '/V1/guest-carts/';
 
     /**
-     * @var \Magento\TestFramework\ObjectManager
+     * @var ObjectManager
      */
-    protected $objectManager;
+    private $objectManager;
 
+    /**
+     * @inheritdoc
+     */
     protected function setUp()
     {
-        $this->objectManager = \Magento\TestFramework\Helper\Bootstrap::getObjectManager();
+        $this->objectManager = Bootstrap::getObjectManager();
     }
 
     /**
+     * Test quote items
+     *
      * @magentoApiDataFixture Magento/Checkout/_files/quote_with_items_saved.php
      */
     public function testGetList()
@@ -112,12 +121,16 @@ public function testAddItem()
         ];
 
         $requestData = [
-            "cartItem" => [
-                "sku" => $productSku,
-                "qty" => 7,
-                "quote_id" => $cartId,
+            'cartItem' => [
+                'sku' => $productSku,
+                'qty' => 7,
             ],
         ];
+
+        if (TESTS_WEB_API_ADAPTER === self::ADAPTER_SOAP) {
+            $requestData['cartItem']['quote_id'] = $cartId;
+        }
+
         $this->_webApiCall($serviceInfo, $requestData);
         $this->assertTrue($quote->hasProductId(2));
         $this->assertEquals(7, $quote->getItemByProduct($product)->getQty());
@@ -205,20 +218,11 @@ public function testUpdateItem(array $stockData, string $errorMessage = null)
             ],
         ];
 
-        if (TESTS_WEB_API_ADAPTER == self::ADAPTER_SOAP) {
-            $requestData = [
-                "cartItem" => [
-                    "qty" => 5,
-                    "quote_id" => $cartId,
-                    "itemId" => $itemId,
-                ],
-            ];
-        } else {
-            $requestData = [
-                "cartItem" => [
-                    "qty" => 5,
-                    "quote_id" => $cartId,
-                ],
+        $requestData['cartItem']['qty'] = 5;
+        if (TESTS_WEB_API_ADAPTER === self::ADAPTER_SOAP) {
+            $requestData['cartItem'] += [
+                'quote_id' => $cartId,
+                'itemId' => $itemId,
             ];
         }
         if ($errorMessage) {