Make SimpleCoordinator inventory_units keyword arg

core/app/models/spree/exchange.rb

@@ -22,7 +22,10 @@ def display_amount
 
     def perform!
       begin
-        shipments = Spree::Config.stock.coordinator_class.new(@order, @reimbursement_objects.map(&:build_exchange_inventory_unit)).shipments
+        shipments = Spree::Config.stock.coordinator_class.new(
+          @order,
+          inventory_units: @reimbursement_objects.map(&:build_exchange_inventory_unit)
+        ).shipments
       rescue Spree::Order::InsufficientStock
         raise UnableToCreateShipments.new("Could not generate shipments for all items. Out of stock?")
       end

core/app/models/spree/order.rb

@@ -513,9 +513,9 @@ def create_proposed_shipments
     end
 
     def create_shipments_for_line_item(line_item)
-      units = Spree::Config.stock.inventory_unit_builder_class.new(self).missing_units_for_line_item(line_item)
+      inventory_units = Spree::Config.stock.inventory_unit_builder_class.new(self).missing_units_for_line_item(line_item)
 
-      Spree::Config.stock.coordinator_class.new(self, units).shipments.each do |shipment|
+      Spree::Config.stock.coordinator_class.new(self, inventory_units:).shipments.each do |shipment|
         shipments << shipment
       end
     end

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

@@ -27,7 +27,14 @@ class SimpleCoordinator
         :filtered_stock_locations, :inventory_units_by_variant, :desired,
         :availability, :allocator, :packages
 
-      def initialize(order, inventory_units = nil)
+      def initialize(order, inventory_units_deprecated = nil, inventory_units: nil)
+        if inventory_units_deprecated
+          Spree.deprecator.warn "Using the `inventory_units` positional " \
+            "argument is deprecated in favor of using the keyword argument. "
+
+          inventory_units ||= inventory_units_deprecated
+        end
+
         @order = order
         @inventory_units =
           inventory_units || Spree::Config.stock.inventory_unit_builder_class.new(order).units