Add ClassConstantizer

This class is responsible for holding as set of references to classes
(by their name). This is done instead of just having the classes to
avoid loading the classes too early as well as to allow code reloading
of these classes.

core/lib/spree/core.rb

@@ -63,6 +63,7 @@ class DestroyWithOrdersError < StandardError; end
 
 require 'spree/core/version'
 
+require 'spree/core/class_constantizer'
 require 'spree/core/environment_extension'
 require 'spree/core/environment/calculators'
 require 'spree/core/environment'

core/lib/spree/core/class_constantizer.rb

@@ -0,0 +1,31 @@
+module Spree
+  module Core
+    module ClassConstantizer
+      class Set
+        include Enumerable
+
+        def initialize
+          @collection = ::Set.new
+        end
+
+        def <<(klass)
+          @collection << klass.to_s
+        end
+
+        def concat(klasses)
+          klasses.each do |klass|
+            self << klass
+          end
+        end
+
+        delegate :clear, :empty?, to: :@collection
+
+        def each
+          @collection.each do |klass|
+            yield klass.constantize
+          end
+        end
+      end
+    end
+  end
+end

core/lib/spree/core/engine.rb

@@ -54,7 +54,6 @@ class Engine < ::Rails::Engine
       # We need to define promotions rules here so extensions and existing apps
       # can add their custom classes on their initializer files
       initializer 'spree.promo.environment', before: :load_config_initializers do |app|
-        app.config.spree.add_class('promotions')
         app.config.spree.promotions = Spree::Promo::Environment.new
         app.config.spree.promotions.rules = []
       end

core/lib/spree/core/environment.rb

@@ -3,12 +3,15 @@ module Core
     class Environment
       include EnvironmentExtension
 
-      attr_accessor :calculators, :payment_methods, :preferences,
-                    :stock_splitters
+      add_class_set :payment_methods
+      add_class_set :stock_splitters
+
+      attr_accessor :calculators, :preferences, :promotions
 
       def initialize
         @calculators = Calculators.new
         @preferences = Spree::AppConfiguration.new
+        @promotions = Spree::Promo::Environment.new
       end
     end
   end

core/lib/spree/core/environment/calculators.rb

@@ -4,7 +4,8 @@ class Environment
       class Calculators
         include EnvironmentExtension
 
-        attr_accessor :shipping_methods, :tax_rates
+        add_class_set :shipping_methods
+        add_class_set :tax_rates
       end
     end
   end

core/lib/spree/core/environment_extension.rb

@@ -1,24 +1,28 @@
+require 'spree/core/class_constantizer'
+
 module Spree
   module Core
     module EnvironmentExtension
       extend ActiveSupport::Concern
 
-      def add_class(name)
-        instance_variable_set "@#{name}", Set.new
-
-        create_method( "#{name}=".to_sym ) { |val|
-          instance_variable_set( "@" + name, val)
-        }
+      class_methods do
+        def add_class_set(name)
+          define_method(name) do
+            set = instance_variable_get("@#{name}")
+            send("#{name}=", []) unless set
+            set
+          end
 
-        create_method(name.to_sym) do
-          instance_variable_get( "@" + name )
+          define_method("#{name}=") do |klasses|
+            set = ClassConstantizer::Set.new
+            set.concat(klasses)
+            instance_variable_set("@#{name}", set)
+          end
         end
       end
 
-      private
-
-      def create_method(name, &block)
-        self.class.send(:define_method, name, &block)
+      def add_class(name)
+        singleton_class.send(:add_class_set, name)
       end
     end
   end

core/lib/spree/promo/environment.rb

@@ -3,7 +3,8 @@ module Promo
     class Environment
       include Core::EnvironmentExtension
 
-      attr_accessor :rules, :actions
+      add_class_set :rules
+      add_class_set :actions
     end
   end
 end

core/spec/lib/spree/core/class_constantizer_spec.rb

@@ -0,0 +1,68 @@
+require 'spec_helper'
+
+module ClassConstantizerTest
+  ClassA = Class.new
+  ClassB = Class.new
+
+  def self.reload
+    [:ClassA, :ClassB].each do |klass|
+      remove_const(klass)
+      const_set(klass, Class.new)
+    end
+  end
+end
+
+describe Spree::Core::ClassConstantizer::Set do
+  let(:set) { described_class.new }
+
+  describe "#concat" do
+    it "can add one item" do
+      set.concat(['ClassConstantizerTest::ClassA'])
+      expect(set).to include(ClassConstantizerTest::ClassA)
+    end
+
+    it "can add two items" do
+      set.concat(['ClassConstantizerTest::ClassA', ClassConstantizerTest::ClassB])
+      expect(set).to include(ClassConstantizerTest::ClassA)
+      expect(set).to include(ClassConstantizerTest::ClassB)
+    end
+  end
+
+  describe "<<" do
+    it "can add by string" do
+      set << "ClassConstantizerTest::ClassA"
+      expect(set).to include(ClassConstantizerTest::ClassA)
+    end
+
+    it "can add by class" do
+      set << ClassConstantizerTest::ClassA
+      expect(set).to include(ClassConstantizerTest::ClassA)
+    end
+
+    describe "class redefinition" do
+      shared_examples "working code reloading" do
+        it "works with a class" do
+          original = ClassConstantizerTest::ClassA
+
+          ClassConstantizerTest.reload
+
+          # Sanity check
+          expect(original).not_to eq(ClassConstantizerTest::ClassA)
+
+          expect(set).to include(ClassConstantizerTest::ClassA)
+          expect(set).to_not include(original)
+        end
+      end
+
+      context "with a class" do
+        before { set << ClassConstantizerTest::ClassA }
+        it_should_behave_like "working code reloading"
+      end
+
+      context "with a string" do
+        before { set << "ClassConstantizerTest::ClassA" }
+        it_should_behave_like "working code reloading"
+      end
+    end
+  end
+end