#38811: Leverage pre-collected rates when determining cheapest shipping

Author: Tomasito665

app/code/Magento/InstantPurchase/Model/ShippingMethodChoose/CheapestMethodDeferredChooser.php

@@ -20,10 +20,7 @@ class CheapestMethodDeferredChooser implements DeferredShippingMethodChooserInte
      */
     public function choose(Address $address)
     {
-        $address->setCollectShippingRates(true);
-        $address->collectShippingRates();
-        $shippingRates = $address->getAllShippingRates();
-
+        $shippingRates = $this->getShippingRates($address);
         if (empty($shippingRates)) {
             return null;
         }
@@ -32,6 +29,22 @@ public function choose(Address $address)
         return $cheapestRate->getCode();
     }
 
+    /**
+     * Retrieves previously collected shipping rates or computes new ones.
+     *
+     * @param Address $address
+     * @return Rate[]
+     */
+    private function getShippingRates(Address $address) : array {
+        if (!empty($shippingRates = $address->getAllShippingRates())) {
+            // Favour previously collected rates over recomputing.
+            return $shippingRates;
+        }
+        $address->setCollectShippingRates(true);
+        $address->collectShippingRates();
+        return $address->getAllShippingRates();
+    }
+
     /**
      * Selects shipping price with minimal price.
      *