Add Spree::Config.tax_adjuster extension point

To allow easier customization of tax calculation in extensions or
applications.

CHANGELOG.md

@@ -1,5 +1,10 @@
 ## Solidus 2.1.0 (master, unreleased)
 
+* Added Spree::Config.tax_adjuster_class
+
+ To allow easier customization of tax calculation in extensions or
+ applications.
+
 * Remove `is_default` boolean from `Spree::Price` model
 
  This boolean used to mean "the price to be used". With the new
@@ -19,7 +24,7 @@
 * Removals
 
  * Removed deprecated method `Spree::TaxRate.adjust` (not to be confused with
- Spree::TaxRate#adjust) in favor of `Spree::Tax::OrderAdjuster`.
+ Spree::TaxRate#adjust) in favor of `Spree::Config.tax_adjuster_class`.
 
  https://github.com/solidusio/solidus/pull/1462
 

core/app/models/spree/app_configuration.rb

@@ -371,6 +371,16 @@ def add_payment_sources_to_wallet_class
  @add_payment_sources_to_wallet_class ||= Spree::Wallet::AddPaymentSourcesToWallet
  end
 
+ # Allows providing your own class for calculating taxes on an order.
+ #
+ # @!attribute [rw] tax_adjuster_class
+ # @return [Class] a class with the same public interfaces as
+ # Spree::Tax::OrderAdjuster
+ attr_writer :tax_adjuster_class
+ def tax_adjuster_class
+ @tax_adjuster_class ||= Spree::Tax::OrderAdjuster
+ end
+
  def static_model_preferences
  @static_model_preferences ||= Spree::Preferences::StaticModelPreferences.new
  end

core/app/models/spree/order.rb

@@ -350,7 +350,7 @@ def line_item_options_match(line_item, options)
  # include taxes then price adjustments are created instead.
  # @deprecated This now happens during #update!
  def create_tax_charge!
- Spree::Tax::OrderAdjuster.new(self).adjust!
+ Spree::Config.tax_adjuster_class.new(self).adjust!
  end
  deprecate create_tax_charge!: :update!, deprecator: Spree::Deprecation
 

core/app/models/spree/order_updater.rb

@@ -197,7 +197,7 @@ def update_order_promotions
  end
 
  def update_taxes
- Spree::Tax::OrderAdjuster.new(order).adjust!
+ Spree::Config.tax_adjuster_class.new(order).adjust!
 
  [*line_items, *shipments].each do |item|
  tax_adjustments = item.adjustments.select(&:tax?)

core/spec/models/spree/order_updater_spec.rb

@@ -298,6 +298,23 @@ def create_adjustment(label, amount)
  }.from(1).to(2)
  end
  end
+
+ context 'with a custom tax_adjuster_class' do
+ let(:custom_adjuster_class) { double }
+ let(:custom_adjuster_instance) { double }
+
+ before do
+ order # generate this first so we can expect it
+ Spree::Config.tax_adjuster_class = custom_adjuster_class
+ end
+
+ it 'uses the configured class' do
+ expect(custom_adjuster_class).to receive(:new).with(order).at_least(:once).and_return(custom_adjuster_instance)
+ expect(custom_adjuster_instance).to receive(:adjust!).at_least(:once)
+
+ order.update!
+ end
+ end
  end
  end