MC-42813: Feature request: Cart qty update should be reverted back if the requested qty is not available

Author: Anna Bukatar

app/code/Magento/Checkout/Controller/Cart/UpdateItemQty.php

@@ -97,17 +97,23 @@ public function execute()
             $cartData = $this->quantityProcessor->process($cartData);
             $quote = $this->checkoutSession->getQuote();
 
+            $response = [];
             foreach ($cartData as $itemId => $itemInfo) {
                 $item = $quote->getItemById($itemId);
                 $qty = isset($itemInfo['qty']) ? (double) $itemInfo['qty'] : 0;
                 if ($item) {
-                    $this->updateItemQuantity($item, $qty);
+                    try {
+                        $this->updateItemQuantity($item, $qty);
+                    } catch (LocalizedException $e) {
+                        $response[] = [
+                            'error' => $e->getMessage(),
+                            'itemId' => $itemId
+                        ];
+                    }
                 }
             }
 
-            $this->jsonResponse();
-        } catch (LocalizedException $e) {
-            $this->jsonResponse($e->getMessage());
+            $this->jsonResponse(count($response)? json_encode($response) : '');
         } catch (\Exception $e) {
             $this->logger->critical($e->getMessage());
             $this->jsonResponse('Something went wrong while saving the page. Please refresh the page and try again.');

app/code/Magento/Checkout/Test/Mftf/Test/UpdateProductFromShoppingCartTest.xml

@@ -0,0 +1,51 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+ /**
+  * Copyright © Magento, Inc. All rights reserved.
+  * See COPYING.txt for license details.
+  */
+-->
+
+<tests xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xsi:noNamespaceSchemaLocation="urn:magento:mftf:Test/etc/testSchema.xsd">
+    <test name="UpdateProductFromShoppingCartTest">
+        <annotations>
+            <stories value="Shopping Cart"/>
+            <title value="Cart qty update should be reverted back if the requested qty is not available"/>
+            <description value="Update Product Qty on Shopping Cart when the requested qty is not available"/>
+            <severity value="MAJOR"/>
+            <testCaseId value="MC-42907"/>
+            <group value="shoppingCart"/>
+            <group value="mtf_migrated"/>
+        </annotations>
+
+        <before>
+            <!--Create product according to dataset.-->
+            <createData entity="simpleProductWithoutCategory" stepKey="createProduct"/>
+
+            <!--Add product to cart-->
+            <actionGroup ref="AddSimpleProductToCartActionGroup" stepKey="addToCartFromStorefrontProductPage">
+                <argument name="product" value="$$createProduct$$"/>
+            </actionGroup>
+        </before>
+
+        <after>
+            <!--Delete created data-->
+            <deleteData createDataKey="createProduct" stepKey="deleteProduct" />
+        </after>
+
+        <!--Go to cart page, update qty -->
+        <actionGroup ref="StorefrontCartPageOpenActionGroup" stepKey="goToCartPage"/>
+        <see userInput="Shopping Cart" stepKey="seeCartPageIsOpened"/>
+
+        <fillField selector="{{CheckoutCartProductSection.qty($$createProduct.sku$$)}}" userInput="1001" stepKey="updateProductQty"/>
+        <click selector="{{CheckoutCartProductSection.updateShoppingCartButton}}" stepKey="clickUpdateShoppingCart"/>
+        <waitForAjaxLoad stepKey="waitForAjaxLoad"/>
+        <click  selector=".modal-footer button[data-role='action']" stepKey="clickAlertMessage"/>
+        <grabValueFrom selector="{{CheckoutCartProductSection.qty($$createProduct.sku$$)}}" stepKey="grabQty"/>
+        <assertEquals stepKey="assertQty">
+            <actualResult type="const">$grabQty</actualResult>
+            <expectedResult type="const">1</expectedResult>
+        </assertEquals>
+    </test>
+</tests>

app/code/Magento/Checkout/view/frontend/templates/cart/item/default.phtml

@@ -109,6 +109,7 @@ $canApplyMsrp = $helper->isShowBeforeOrderConfirm($product) && $helper->isMinima
                                title="<?= $block->escapeHtmlAttr(__('Qty')) ?>"
                                class="input-text qty"
                                data-validate="{required:true,'validate-greater-than-zero':true}"
+                               data-item-qty="<?= $block->escapeHtmlAttr($block->getQty()) ?>"
                                data-role="cart-item-qty"/>
                     </label>
                 </div>

app/code/Magento/Checkout/view/frontend/web/js/action/update-shopping-cart.js

@@ -107,9 +107,26 @@ define([
          * Form validation failed.
          */
         onError: function (response) {
+            var that = this;
             if (response['error_message']) {
+                try {
+                    var responseData = JSON.parse(response['error_message']);
+                    $.each(responseData, function (index, data) {
+                        if (data['itemId'] !== undefined) {
+                            let elm = $('#cart-' + data['itemId'] + '-qty');
+                            elm.val(elm.attr('data-item-qty'));
+                        }
+                        response['error_message'] = data['error'];
+                    });
+                } catch (e) {}
                 alert({
-                    content: response['error_message']
+                    content: response['error_message'],
+                    actions: {
+                        /** @inheritdoc */
+                        always: function () {
+                            that.submitForm();
+                        }
+                    }
                 });
             } else {
                 this.submitForm();