Only reload Active Admin if active admin files have changed

This is a HUGE performance increase in development mode. Before this
Active Admin was reloading on every single request to the servers
(assets included). Now we only reload the Active Admin files if
something in the AA load paths has changed.

Author: gregbell

features/support/env.rb

@@ -9,18 +9,24 @@
 require File.expand_path('../../../spec/support/detect_rails_version', __FILE__)
 ENV["RAILS"] = detect_rails_version
 
+ENV["RAILS_ENV"] ||= "cucumber"
+ENV['RAILS_ROOT'] = File.expand_path("../../../spec/rails/rails-#{ENV["RAILS"]}", __FILE__)
+
+
 require 'rubygems'
 require "bundler"
 Bundler.setup
 
-ENV["RAILS_ENV"] ||= "cucumber"
-ENV['RAILS_ROOT'] = File.expand_path("../../../spec/rails/rails-#{ENV["RAILS"]}", __FILE__)
-
 # Create the test app if it doesn't exists
 unless File.exists?(ENV['RAILS_ROOT'])
   system 'rake setup'
 end
 
+# Ensure the Active Admin load path is happy
+require 'rails'
+require 'active_admin'
+ActiveAdmin.application.load_paths = [ENV['RAILS_ROOT'] + "/app/admin"]
+
 require ENV['RAILS_ROOT'] + '/config/environment'
 
 # Setup autoloading of ActiveAdmin and the load path

lib/active_admin/application.rb

@@ -211,7 +211,7 @@ def remove_active_admin_load_paths_from_rails_autoload_and_eager_load
     end
 
     def attach_reloader
-      ActiveAdmin::Reloader.new(Rails.version).attach!
+      ActiveAdmin::Reloader.new(self, Rails.version).attach!
     end
 
 

lib/active_admin/reloader.rb

@@ -6,16 +6,21 @@ class Reloader
     # @param [String] rails_version
     #   The version of Rails we're using. We use this to switch between
     #   the correcr Rails reloader class.
-    def initialize(rails_version)
+    def initialize(app, rails_version)
+      @app = app
       @rails_version = rails_version.to_s
     end
 
     # Attach to Rails and perform the reload on each request.
     def attach!
-      reloader_class.to_prepare do
+      file_update_checker = ActiveSupport::FileUpdateChecker.new(@app.load_paths) do
         ActiveAdmin.application.unload!
         Rails.application.reload_routes!
       end
+
+      reloader_class.to_prepare do
+        file_update_checker.execute_if_updated
+      end
     end
 
     def reloader_class

spec/unit/reloader_spec.rb

@@ -4,25 +4,33 @@
 begin
   ActionDispatch::Reloader
 rescue
-  module ActionDispatch; module Reloader; end; end
+  module ActionDispatch; module Reloader; def self.to_prepare; end; end; end
 end
 
 begin
   ActionDispatch::Callbacks
 rescue
-  module ActionDispatch; module Callbacks; end; end
+  module ActionDispatch; module Callbacks; def self.to_prepare; end; end; end
 end
 
 
 describe ActiveAdmin::Reloader do
 
+  let(:mock_app){ mock(:load_paths => []) }
+
   it "should use ActionDispatch::Reloader if rails 3.1" do
-    reloader = ActiveAdmin::Reloader.new '3.1.0'
+    reloader = ActiveAdmin::Reloader.new mock_app, '3.1.0'
     reloader.reloader_class.should == ActionDispatch::Reloader
   end
 
   it "should use ActionDispatch::Callbacks if rails 3.0" do
-    reloader = ActiveAdmin::Reloader.new '3.0.0'
+    reloader = ActiveAdmin::Reloader.new mock_app, '3.0.0'
     reloader.reloader_class.should == ActionDispatch::Callbacks
   end
+
+  it "should initialize a new file update checker" do
+    ActiveSupport::FileUpdateChecker.should_receive(:new).with(mock_app.load_paths).and_return(mock(:execute_if_updated => true))
+    ActiveAdmin::Reloader.new(mock_app, '3.1.0').attach!
+  end
+
 end