MAGETWO-91639: Tax is added despite customer group changes

- Add recollect quote after customer group change

Author: stkorf

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

@@ -0,0 +1,61 @@
+<?php
+/**
+ * Copyright © Magento, Inc. All rights reserved.
+ * See COPYING.txt for license details.
+ */
+declare(strict_types=1);
+
+namespace Magento\Quote\Plugin;
+
+use Magento\Quote\Api\CartRepositoryInterface;
+use Magento\Customer\Model\ResourceModel\Customer as CustomerResource;
+use Magento\Customer\Model\Customer;
+
+/**
+ * Recollect quote totals after change customer group
+ */
+class RecollectOnGroupChange
+{
+    /**
+     * @var CartRepositoryInterface
+     */
+    private $cartRepository;
+
+    /**
+     * @param CartRepositoryInterface $cartRepository
+     */
+    public function __construct(
+        CartRepositoryInterface $cartRepository
+    ) {
+        $this->cartRepository = $cartRepository;
+    }
+
+    /**
+     * Recollect totals if customer group change
+     *
+     * @param CustomerResource $subject
+     * @param CustomerResource $result
+     * @param Customer $customer
+     * @return CustomerResource
+     *
+     * @SuppressWarnings(PHPMD.UnusedFormalParameter)
+     */
+    public function afterSave(CustomerResource $subject, CustomerResource $result, Customer $customer)
+    {
+        if ($customer->getOrigData('group_id') !== null
+            && $customer->getOrigData('group_id') != $customer->getGroupId()
+        ) {
+            try {
+                /** @var \Magento\Quote\Model\Quote $quote */
+                $quote = $this->cartRepository->getActiveForCustomer($customer->getId());
+                $quote->setCustomerGroupId($customer->getGroupId());
+                $quote->collectTotals();
+                $this->cartRepository->save($quote);
+            } catch (\Magento\Framework\Exception\NoSuchEntityException $e) {
+                //no active cart for customer
+            }
+        }
+
+        return $result;
+    }
+}

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

@@ -15,4 +15,7 @@
     <type name="Magento\Store\Api\StoreCookieManagerInterface">
         <plugin name="update_quote_store_after_switch_store_view" type="Magento\Quote\Plugin\UpdateQuoteStore"/>
     </type>
+    <type name="Magento\Customer\Model\ResourceModel\Customer">
+        <plugin name="cart_recollect_on_group_change" type="Magento\Quote\Plugin\RecollectOnGroupChange"/>
+    </type>
 </config>