Switch core to use Spree::Config.environment

This is clearer and more direct than going through the rails
environment, as we're setting and retrieving settings we directly
control.

core/app/models/concerns/spree/calculated_adjustments.rb

@@ -22,7 +22,7 @@ def model_name_without_spree_namespace
       end
 
       def spree_calculators
-        Rails.application.config.spree.calculators
+        Spree::Config.environment.calculators
       end
     end
 

core/app/models/spree/calculator.rb

@@ -29,7 +29,7 @@ def self.description
     def self.calculators
       Spree::Deprecation.warn("Calling .calculators is deprecated. Please access through Rails.application.config.spree.calculators")
 
-      Rails.application.config.spree.calculators
+      Spree::Config.environment.calculators
     end
 
     def to_s

core/app/models/spree/payment_method.rb

@@ -58,7 +58,7 @@ class << self
       def providers
         Spree::Deprecation.warn 'Spree::PaymentMethod.providers is deprecated and will be deleted in Solidus 3.0. ' \
           'Please use Rails.application.config.spree.payment_methods instead'
-        Rails.application.config.spree.payment_methods
+        Spree::Config.environment.payment_methods
       end
 
       def available(display_on = nil, store: nil)

core/app/models/spree/promotion_action.rb

@@ -9,7 +9,7 @@ class PromotionAction < Spree::Base
     belongs_to :promotion, class_name: 'Spree::Promotion', inverse_of: :promotion_actions
 
     scope :of_type, ->(t) { where(type: Array.wrap(t).map(&:to_s)) }
-    scope :shipping, -> { of_type(Rails.application.config.spree.promotions.shipping_actions.to_a) }
+    scope :shipping, -> { of_type(Spree::Config.environment.promotions.shipping_actions.to_a) }
 
     # Updates the state of the order or performs some other action depending on
     # the subclass options will contain the payload from the event that

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

@@ -10,7 +10,7 @@ module Stock
     #   * Combine allocated and on hand inventory into a single shipment per-location
     #
     # After allocation, splitters are run on each Package (as configured in
-    # Rails.application.config.spree.stock_splitters)
+    # Spree::Config.environment.stock_splitters)
     #
     # Finally, shipping rates are calculated using the class configured as
     # Spree::Config.stock.estimator_class.
@@ -20,7 +20,7 @@ class SimpleCoordinator
       def initialize(order, inventory_units = nil)
         @order = order
         @inventory_units = inventory_units || InventoryUnitBuilder.new(order).units
-        @splitters = Rails.application.config.spree.stock_splitters
+        @splitters = Spree::Config.environment.stock_splitters
         @stock_locations = Spree::StockLocation.active
 
         @inventory_units_by_variant = @inventory_units.group_by(&:variant)

core/lib/spree/testing_support/preferences.rb

@@ -11,6 +11,7 @@ module Preferences
       def reset_spree_preferences(&config_block)
         Spree::Config.instance_variables.each { |iv| Spree::Config.remove_instance_variable(iv) }
         Spree::Config.preference_store = Spree::Config.default_preferences
+        Rails.application.config.spree = Spree::Config.environment
 
         configure_spree_preferences(&config_block) if block_given?
       end

core/spec/models/spree/promotion_handler/shipping_spec.rb

@@ -74,16 +74,11 @@ module PromotionHandler
         before do
           stub_const('CustomShippingAction', custom_klass)
 
-          @old_shipping_actions = Rails.application.config.spree.promotions.shipping_actions
-          Rails.application.config.spree.promotions.shipping_actions = ['CustomShippingAction']
+          Spree::Config.environment.promotions.shipping_actions = ['CustomShippingAction']
 
           order.order_promotions.create!(promotion: promotion, promotion_code: promotion.codes.first)
         end
 
-        after do
-          Rails.application.config.spree.promotions.shipping_actions = @old_shipping_actions
-        end
-
         let(:action) { custom_klass.new }
         let(:custom_klass) { Class.new(Spree::Promotion::Actions::FreeShipping) }
         let(:promotion) { create(:promotion, code: 'customshipping', promotion_actions: [action]) }