Fix shipping total amount calculation for multishipping addresses

Author: ilnytskyi

app/code/Magento/OfflineShipping/Model/Carrier/Freeshipping.php

@@ -136,11 +136,10 @@ public function collectRates(RateRequest $request)
     protected function _updateFreeMethodQuote($request)
     {
         $freeShipping = false;
-        $items = $request->getAllItems();
-        $c = count($items);
-        for ($i = 0; $i < $c; $i++) {
-            if ($items[$i]->getProduct() instanceof \Magento\Catalog\Model\Product) {
-                if ($items[$i]->getFreeShipping()) {
+        $items = $request->getAllItems() ?: [];
+        foreach ($items as $item) {
+            if ($item->getProduct() instanceof \Magento\Catalog\Model\Product) {
+                if ($item->getFreeShipping()) {
                     $freeShipping = true;
                 } else {
                     return;

app/code/Magento/Tax/Model/Sales/Total/Quote/Shipping.php

@@ -38,6 +38,7 @@ public function collect(
             return $this;
         }
 
+        $shippingAddress = $shippingAssignment->getShipping()->getAddress();
         $quoteDetails = $this->prepareQuoteDetails($shippingAssignment, [$shippingDataObject]);
         $taxDetails = $this->taxCalculationService
             ->calculateTax($quoteDetails, $storeId);
@@ -48,10 +49,8 @@ public function collect(
             ->calculateTax($baseQuoteDetails, $storeId);
         $baseTaxDetailsItems = $baseTaxDetails->getItems()[self::ITEM_CODE_SHIPPING];
 
-        $quote->getShippingAddress()
-            ->setShippingAmount($taxDetailsItems->getRowTotal());
-        $quote->getShippingAddress()
-            ->setBaseShippingAmount($baseTaxDetailsItems->getRowTotal());
+        $shippingAddress->setShippingAmount($taxDetailsItems->getRowTotal());
+        $shippingAddress->setBaseShippingAmount($baseTaxDetailsItems->getRowTotal());
 
         $this->processShippingTaxInfo(
             $shippingAssignment,