AC-7901: Can't create credit memo - free shipping related

Author: glo17680

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

@@ -136,8 +136,14 @@ public function collect(Creditmemo $creditmemo)
 
             if ($shippingDelta > $creditmemo->getBaseShippingAmount() ||
                 $this->isShippingIncludeTaxWithTaxAfterDiscount($order->getStoreId())) {
-                $part = $creditmemo->getShippingAmount() / $orderShippingAmount;
-                $basePart = $creditmemo->getBaseShippingAmount() / $baseOrderShippingAmount;
+                $part = $creditmemo->getShippingAmount();
+                if ($orderShippingAmount > 0) {
+                    $part = $creditmemo->getShippingAmount() / $orderShippingAmount;
+                }
+                $basePart = $creditmemo->getBaseShippingAmount();
+                if ($baseOrderShippingAmount > 0) {
+                    $basePart = $creditmemo->getBaseShippingAmount() / $baseOrderShippingAmount;
+                }
                 $shippingTaxAmount = $order->getShippingTaxAmount() * $part;
                 $baseShippingTaxAmount = $order->getBaseShippingTaxAmount() * $basePart;
                 $shippingDiscountTaxCompensationAmount = $order->getShippingDiscountTaxCompensationAmount() * $part;

app/code/Magento/Sales/Test/Unit/Model/Order/Creditmemo/Total/TaxTest.php

@@ -806,6 +806,67 @@ public function collectDataProvider()
             ],
         ];
 
+        // scenario 8: 1 items, 1 invoiced, shipping covered by cart rule
+        // shipping amount is 0 i.e., free shipping
+        $result['creditmemo_with_discount_for_entire_shipping_all_prices_including_tax_free_shipping'] = [
+            'order_data' => [
+                'data_fields' => [
+                    'shipping_tax_amount' => 0,
+                    'base_shipping_tax_amount' => 0,
+                    'shipping_discount_tax_compensation_amount' => 1.36,
+                    'base_shipping_discount_tax_compensation_amount' => 1.36,
+                    'tax_amount' => 1.22,
+                    'base_tax_amount' => 1.22,
+                    'tax_invoiced' => 1.22,
+                    'base_tax_invoiced' => 1.22,
+                    'shipping_amount' => 0,
+                    'shipping_discount_amount' => 15,
+                    'base_shipping_amount' => 13.64,
+                    'discount_tax_compensation_invoiced' => 1.73,
+                    'base_discount_tax_compensation_invoiced' => 1.73
+                ],
+            ],
+            'creditmemo_data' => [
+                'items' => [
+                    'item_1' => [
+                        'order_item' => [
+                            'qty_invoiced' => 1,
+                            'tax_invoiced' => 1.22,
+                            'base_tax_invoiced' => 1.22,
+                            'discount_tax_compensation_amount' => 1.73,
+                            'base_discount_tax_compensation_amount' => 1.73,
+                            'discount_tax_compensation_invoiced' => 1.73,
+                            'base_discount_tax_compensation_invoiced' => 1.73
+                        ],
+                        'is_last' => true,
+                        'qty' => 1,
+                    ],
+                ],
+                'is_last' => true,
+                'data_fields' => [
+                    'shipping_amount' => 0,
+                    'base_shipping_amount' => 0,
+                    'grand_total' => 10.45,
+                    'base_grand_total' => 10.45,
+                    'tax_amount' => 0,
+                    'base_tax_amount' => 0
+                ],
+            ],
+            'expected_results' => [
+                'creditmemo_items' => [
+                    'item_1' => [
+                        'tax_amount' => 1.22,
+                        'base_tax_amount' => 1.22,
+                    ],
+                ],
+                'creditmemo_data' => [
+                    'grand_total' => 13.4,
+                    'base_grand_total' => 13.4,
+                    'tax_amount' => 1.22,
+                    'base_tax_amount' => 1.22,
+                ],
+            ],
+        ];
         return $result;
     }