ACP2E-1313: Refund shipping issue with discounted order (Apply Discount On Prices = Including tax)

Author: o-iegorov

app/code/Magento/Sales/Model/Order/Creditmemo/Total/Shipping.php

@@ -7,6 +7,7 @@
 
 use Magento\Framework\Pricing\PriceCurrencyInterface;
 use Magento\Tax\Model\Calculation as TaxCalculation;
+use Magento\Sales\Model\Order;
 
 /**
  * Order creditmemo shipping total calculation model
@@ -115,25 +116,26 @@ public function collect(\Magento\Sales\Model\Order\Creditmemo $creditmemo)
     /**
      * Checks if shipping provided incl tax, tax applied after discount, and discount applied on shipping excl tax
      *
-     * @param \Magento\Sales\Model\Order $order
+     * @param Order $order
      * @return bool
      */
-    private function isShippingIncludeTaxWithTaxAfterDiscountOnExcl($order): bool
+    private function isShippingIncludeTaxWithTaxAfterDiscount(Order $order): bool
     {
-        return $this->getTaxConfig()->getCalculationSequence($order->getStoreId())
-            === TaxCalculation::CALC_TAX_AFTER_DISCOUNT_ON_EXCL &&
-            $this->isSuppliedShippingAmountInclTax($order);
+        $calculationSequence = $this->getTaxConfig()->getCalculationSequence($order->getStoreId());
+        return ($calculationSequence === TaxCalculation::CALC_TAX_AFTER_DISCOUNT_ON_EXCL
+            || $calculationSequence === TaxCalculation::CALC_TAX_AFTER_DISCOUNT_ON_INCL)
+            && $this->isSuppliedShippingAmountInclTax($order);
     }
 
     /**
      * Get allowed shipping amount to refund based on tax settings
      *
-     * @param \Magento\Sales\Model\Order $order
+     * @param Order $order
      * @return float
      */
-    private function getAllowedAmountInclTax(\Magento\Sales\Model\Order $order): float
+    private function getAllowedAmountInclTax(Order $order): float
     {
-        if ($this->isShippingIncludeTaxWithTaxAfterDiscountOnExcl($order)) {
+        if ($this->isShippingIncludeTaxWithTaxAfterDiscount($order)) {
             $result = $order->getShippingInclTax();
             foreach ($order->getCreditmemosCollection() as $creditmemo) {
                 $result -= $creditmemo->getShippingInclTax();
@@ -155,7 +157,7 @@ private function getAllowedAmountInclTax(\Magento\Sales\Model\Order $order): flo
     private function getBaseAllowedAmountInclTax(\Magento\Sales\Model\Order $order): float
     {
         $result = $order->getBaseShippingInclTax();
-        if ($this->isShippingIncludeTaxWithTaxAfterDiscountOnExcl($order)) {
+        if ($this->isShippingIncludeTaxWithTaxAfterDiscount($order)) {
             foreach ($order->getCreditmemosCollection() as $creditmemo) {
                 $result -= $creditmemo->getBaseShippingInclTax();
             }

app/code/Magento/Sales/Model/Order/Creditmemo/Total/Tax.php

@@ -5,13 +5,13 @@
  */
 namespace Magento\Sales\Model\Order\Creditmemo\Total;
 
+use Magento\Framework\App\ObjectManager;
 use Magento\Sales\Api\Data\CreditmemoInterface;
 use Magento\Sales\Model\Order\Creditmemo;
 use Magento\Sales\Model\Order\Invoice;
 use Magento\Sales\Model\ResourceModel\Order\Invoice as ResourceInvoice;
-use Magento\Tax\Model\Config as TaxConfig;
 use Magento\Tax\Model\Calculation as TaxCalculation;
-use Magento\Framework\App\ObjectManager;
+use Magento\Tax\Model\Config as TaxConfig;
 
 /**
  * Collects credit memo taxes.
@@ -135,7 +135,7 @@ public function collect(Creditmemo $creditmemo)
             $shippingDelta = $baseOrderShippingAmount - $baseOrderShippingRefundedAmount;
 
             if ($shippingDelta > $creditmemo->getBaseShippingAmount() ||
-                $this->isShippingIncludeTaxWithTaxAfterDiscountOnExcl($order->getStoreId())) {
+                $this->isShippingIncludeTaxWithTaxAfterDiscount($order->getStoreId())) {
                 $part = $creditmemo->getShippingAmount() / $orderShippingAmount;
                 $basePart = $creditmemo->getBaseShippingAmount() / $baseOrderShippingAmount;
                 $shippingTaxAmount = $order->getShippingTaxAmount() * $part;
@@ -213,10 +213,12 @@ public function collect(Creditmemo $creditmemo)
      * @param int|null $storeId
      * @return bool
      */
-    private function isShippingIncludeTaxWithTaxAfterDiscountOnExcl(?int $storeId): bool
+    private function isShippingIncludeTaxWithTaxAfterDiscount(?int $storeId): bool
     {
-        return $this->taxConfig->getCalculationSequence($storeId) === TaxCalculation::CALC_TAX_AFTER_DISCOUNT_ON_EXCL &&
-            $this->taxConfig->displaySalesShippingInclTax($storeId);
+        $calculationSequence = $this->taxConfig->getCalculationSequence($storeId);
+        return ($calculationSequence === TaxCalculation::CALC_TAX_AFTER_DISCOUNT_ON_EXCL
+            || $calculationSequence === TaxCalculation::CALC_TAX_AFTER_DISCOUNT_ON_INCL)
+            && $this->taxConfig->displaySalesShippingInclTax($storeId);
     }
 
     /**