Avoid duplicate queries when running estimator taxation.

core/app/models/spree/stock/estimator.rb

@@ -31,14 +31,22 @@ def choose_default_shipping_rate(shipping_rates)
       end
 
       def calculate_shipping_rates(package)
+        tax_calculator_class = Spree::Config.shipping_rate_tax_calculator_class
+        tax_calculator = tax_calculator_class.new(package.shipment.order)
         shipping_methods(package).map do |shipping_method|
           cost = shipping_method.calculator.compute(package)
           if cost
             rate = shipping_method.shipping_rates.new(
               cost: cost,
               shipment: package.shipment
             )
-            Spree::Config.shipping_rate_taxer_class.new.tax(rate)
+            tax_calculator.calculate(rate).each do |tax|
+              rate.taxes.new(
+                amount: tax.amount,
+                tax_rate: tax.tax_rate
+              )
+            end
+            rate
           end
         end.compact
       end

core/app/models/spree/tax/shipping_rate_taxer.rb

@@ -8,7 +8,7 @@ class ShippingRateTaxer
       #   This parameter will be modified.
       # @return [Spree::ShippingRate] The shipping rate with associated tax objects
       def tax(shipping_rate)
-        taxes = Spree::Config.shipping_rate_tax_calculator_class.new(shipping_rate).calculate
+        taxes = Spree::Config.shipping_rate_tax_calculator_class.new(shipping_rate.order).calculate(shipping_rate)
         taxes.each do |tax|
           shipping_rate.taxes.build(
             amount: tax.amount,

core/app/models/spree/tax_calculator/shipping_rate.rb

@@ -21,15 +21,24 @@ class ShippingRate
       # @param [Spree::ShippingRate] shipping_rate the shipping rate to
       #   calculate taxes on
       # @return [Spree::TaxCalculator::ShippingRate]
-      def initialize(shipping_rate)
-        @shipping_rate = shipping_rate
+      def initialize(order)
+        if order.is_a?(::Spree::ShippingRate)
+          Spree::Deprecation.warn "passing a single shipping rate to Spree::TaxCalculator::ShippingRate is DEPRECATED. It now expects an order"
+          shipping_rate = order
+          @order = shipping_rate.order
+          @shipping_rate = shipping_rate
+        else
+          @order = order
+          @shipping_rate = nil
+        end
       end
 
       # Calculate taxes for a shipping rate.
       #
       # @return [Array<Spree::Tax::ItemTax>] the calculated taxes for the
       #   shipping rate
-      def calculate
+      def calculate(shipping_rate)
+        shipping_rate ||= @shipping_rate
         rates_for_item(shipping_rate).map do |rate|
           amount = rate.compute_amount(shipping_rate)
 

core/lib/spree/app_configuration.rb

@@ -287,8 +287,6 @@ def default_pricing_options
 
     class_name_attribute :shipping_rate_selector_class, default: 'Spree::Stock::ShippingRateSelector'
 
-    class_name_attribute :shipping_rate_taxer_class, default: 'Spree::Tax::ShippingRateTaxer'
-
     # Allows providing your own class for calculating taxes on a shipping rate.
     #
     # @!attribute [rw] shipping_rate_tax_calculator_class

core/spec/models/spree/stock/estimator_spec.rb

@@ -189,20 +189,19 @@ class Spree::Stock::TestSorter; end;
         end
 
         it 'uses the configured shipping rate taxer' do
-          class Spree::Tax::TestTaxer
-            def initialize
+          class Spree::Tax::TestTaxCalculator
+            def initialize(_order)
             end
 
-            def tax(_)
-              Spree::ShippingRate.new
+            def calculate(_shipping_rate)
+              [
+                Spree::Tax::ItemTax.new(label: "TAX", amount: 5)
+              ]
             end
           end
-          Spree::Config.shipping_rate_taxer_class = Spree::Tax::TestTaxer
-
-          shipping_rate = Spree::ShippingRate.new
-          allow(Spree::ShippingRate).to receive(:new).and_return(shipping_rate)
+          Spree::Config.shipping_rate_tax_calculator_class = Spree::Tax::TestTaxCalculator
 
-          expect(Spree::Tax::TestTaxer).to receive(:new).and_call_original
+          expect(Spree::Tax::TestTaxCalculator).to receive(:new).and_call_original
           subject.shipping_rates(package)
         end
       end