Dynamically (re)load Solidus core subscribers

Until now, adding subscribers to Spree::Event.subscribers was
developers' responsibility.

This commit aims at automating the task by making Rails load
subscriber files located in standard paths both in Solidus
core and in the store app during the Rails initialization
processs.
When each file is required, it's now also added to the
`Spree::Event.subscribers` list.

core/lib/spree/core/engine.rb

@@ -47,6 +47,7 @@ class Engine < ::Rails::Engine
       # Setup Event Subscribers
       initializer 'spree.core.initialize_subscribers' do |app|
         app.reloader.to_prepare do
+          Spree::Event.require_subscriber_files
           Spree::Event.subscribers.each(&:subscribe!)
         end
 

core/lib/spree/event.rb

@@ -26,6 +26,24 @@ def fire(event_name, opts = {})
       end
     end
 
+    # Loads all Solidus' core and application's event subscribers files.
+    #
+    # Files must be placed under the directory `app/subscribers` and their name
+    # must end with `_subscriber.rb`.
+    #
+    # Loading the files has the side effect of adding their module to the list
+    # in Spree::Event.subscribers.
+    def require_subscriber_files
+      pattern = "app/subscribers/**/*_subscriber.rb"
+      # Load Solidus subscribers
+      # rubocop:disable Rails/DynamicFindBy
+      solidus_core_dir = Gem::Specification.find_by_name('solidus_core').gem_dir
+      # rubocop:enable Rails/DynamicFindBy
+      Dir.glob(File.join(solidus_core_dir, pattern)) { |c| require_dependency(c.to_s) }
+      # Load application subscribers
+      Rails.root.glob(pattern) { |c| require_dependency(c.to_s) }
+    end
+
     # Subscribe to an event with the given name. The provided block is executed
     # every time the subscribed event is fired.
     #

core/lib/spree/event/configuration.rb

@@ -6,9 +6,7 @@ module Spree
   module Event
     class Configuration
       def subscribers
-        @subscribers ||= ::Spree::Core::ClassConstantizer::Set.new.tap do |set|
-          set << 'Spree::MailerSubscriber'
-        end
+        @subscribers ||= ::Spree::Core::ClassConstantizer::Set.new
       end
 
       attr_writer :adapter, :suffix

core/lib/spree/event/subscriber.rb

@@ -26,6 +26,8 @@ def self.included(base)
 
         base.mattr_accessor :event_actions
         base.event_actions = {}
+
+        Spree::Event.subscribers << base.name
       end
 
       # Declares a method name in the including module that can be subscribed/unsubscribed

core/spec/lib/spree/event_spec.rb

@@ -119,6 +119,8 @@
       allow(subscriber_name).to receive(:to_s).and_return(subscriber_name)
     end
 
+    after { described_class.subscribers.clear }
+
     it 'accepts the names of constants' do
       Spree::Config.events.subscribers << subscriber_name
 
@@ -133,4 +135,26 @@
       expect(described_class.subscribers.to_a).to eq([subscriber])
     end
   end
+
+  describe '.require_subscriber_files' do
+    let(:susbcribers_dir) { Rails.root.join("app", "subscribers", "spree") }
+
+    def create_foo_subscriber_file
+      FileUtils.mkdir_p(susbcribers_dir)
+      File.open File.join(susbcribers_dir, 'foo_subscriber.rb'), 'w' do |f|
+        f.puts "module Spree::FooSubscriber; include Spree::Event::Subscriber; end"
+      end
+    end
+
+    before { create_foo_subscriber_file }
+    after { FileUtils.rm_rf(susbcribers_dir) }
+
+    it 'requires subscriber files and loads them into Spree::Event.subscribers' do
+      expect do
+        described_class.require_subscriber_files
+      end.to change { described_class.subscribers.count }.by 1
+
+      expect(described_class.subscribers).to include Spree::FooSubscriber
+    end
+  end
 end