Add config.file_watcher so developers can provide their own watchers (for instance, hooking on fsevents).

railties/guides/source/configuring.textile

@@ -82,6 +82,8 @@ NOTE. The +config.asset_path+ configuration is ignored if the asset pipeline is
 
 * +config.encoding+ sets up the application-wide encoding. Defaults to UTF-8.
 
+* +config.file_watcher+ the class used to detect file updates in the filesystem when +config.reload_classes_only_on_change+ is true. Must conform to +ActiveSupport::FileUpdateChecker+ API.
+
 * +config.filter_parameters+ used for filtering out the parameters that you don't want shown in the logs, such as passwords or credit card numbers.
 
 * +config.force_ssl+ forces all requests to be under HTTPS protocol by using +Rack::SSL+ middleware.
@@ -98,7 +100,7 @@ NOTE. The +config.asset_path+ configuration is ignored if the asset pipeline is
 
 * +config.preload_frameworks+ enables or disables preloading all frameworks at startup. Enabled by +config.threadsafe!+. Defaults to +nil+, so is disabled.
 
-* +config.reload_classes_only_on_change+ enables or disables reloading of classes only when tracked files change. By default tracks everything on autoload paths and is set to true.
+* +config.reload_classes_only_on_change+ enables or disables reloading of classes only when tracked files change. By default tracks everything on autoload paths and is set to true. If +config.cache_classes+ is true, this option is ignored.
 
 * +config.reload_plugins+ enables or disables plugin reloading. Defaults to false.
 

railties/lib/rails/application.rb

@@ -1,5 +1,4 @@
 require 'active_support/core_ext/hash/reverse_merge'
-require 'active_support/file_update_checker'
 require 'fileutils'
 require 'rails/plugin'
 require 'rails/engine'
@@ -135,7 +134,7 @@ module Rails
       end
 
       if config.reload_classes_only_on_change
-        reloader = ActiveSupport::FileUpdateChecker.new(watchable_args, true, &callback)
+        reloader = config.file_watcher.new(watchable_args, true, &callback)
         self.reloaders << reloader
         # We need to set a to_prepare callback regardless of the reloader result, i.e.
         # models should be reloaded if any of the reloaders (i18n, routes) were updated.

railties/lib/rails/application/configuration.rb

@@ -1,5 +1,6 @@
 require 'active_support/core_ext/string/encoding'
 require 'active_support/core_ext/kernel/reporting'
+require 'active_support/file_update_checker'
 require 'rails/engine/configuration'
 
 module Rails
@@ -7,8 +8,8 @@ module Rails
     class Configuration < ::Rails::Engine::Configuration
       attr_accessor :allow_concurrency, :asset_host, :asset_path, :assets,
                     :cache_classes, :cache_store, :consider_all_requests_local,
-                    :dependency_loading, :filter_parameters, :force_ssl, :helpers_paths,
-                    :logger, :log_tags, :preload_frameworks,
+                    :dependency_loading, :file_watcher, :filter_parameters,
+                    :force_ssl, :helpers_paths, :logger, :log_tags, :preload_frameworks,
                     :railties_order, :relative_url_root, :reload_plugins, :secret_token,
                     :serve_static_assets, :ssl_options, :static_cache_control, :session_options,
                     :time_zone, :reload_classes_only_on_change, :whiny_nils
@@ -38,6 +39,7 @@ module Rails
         @railties_order                = [:all]
         @relative_url_root             = ENV["RAILS_RELATIVE_URL_ROOT"]
         @reload_classes_only_on_change = true
+        @file_watcher                  = ActiveSupport::FileUpdateChecker
 
         @assets = ActiveSupport::OrderedOptions.new
         @assets.enabled                  = false

railties/test/application/loading_test.rb

@@ -16,7 +16,7 @@ class LoadingTest < Test::Unit::TestCase
     @app ||= Rails.application
   end
 
-  def test_constants_in_app_are_autoloaded
+  test "constants in app are autoloaded" do
     app_file "app/models/post.rb", <<-MODEL
       class Post < ActiveRecord::Base
         validates_acceptance_of :title, :accept => "omg"
@@ -33,7 +33,7 @@ class LoadingTest < Test::Unit::TestCase
     assert_equal 'omg', p.title
   end
 
-  def test_models_without_table_do_not_panic_on_scope_definitions_when_loaded
+  test "models without table do not panic on scope definitions when loaded" do
     app_file "app/models/user.rb", <<-MODEL
       class User < ActiveRecord::Base
         default_scope where(:published => true)
@@ -63,7 +63,7 @@ class LoadingTest < Test::Unit::TestCase
     assert ::AppTemplate::Application.config.loaded
   end
 
-  def test_descendants_are_cleaned_on_each_request_without_cache_classes
+  test "descendants are cleaned on each request without cache classes" do
     add_to_config <<-RUBY
       config.cache_classes = false
       config.reload_classes_only_on_change = false
@@ -99,6 +99,82 @@ class LoadingTest < Test::Unit::TestCase
     assert_raise(RuntimeError) { ::AppTemplate::Application.initialize! }
   end
 
+  test "reload constants on development" do
+    add_to_config <<-RUBY
+      config.cache_classes = false
+    RUBY
+
+    app_file 'config/routes.rb', <<-RUBY
+      AppTemplate::Application.routes.draw do
+        match '/c', :to => lambda { |env| [200, {"Content-Type" => "text/plain"}, [User.counter.to_s]] }
+      end
+    RUBY
+
+    app_file "app/models/user.rb", <<-MODEL
+      class User
+        def self.counter; 1; end
+      end
+    MODEL
+
+    require 'rack/test'
+    extend Rack::Test::Methods
+
+    require "#{rails_root}/config/environment"
+    sleep(1)
+
+    get "/c"
+    assert_equal "1", last_response.body
+
+    app_file "app/models/user.rb", <<-MODEL
+      class User
+        def self.counter; 2; end
+      end
+    MODEL
+
+    get "/c"
+    assert_equal "2", last_response.body
+  end
+
+  test "does not reload constants on development if custom file watcher always returns false" do
+    add_to_config <<-RUBY
+      config.cache_classes = false
+      config.file_watcher = Class.new do
+        def initialize(*); end
+        def updated?; false; end
+      end
+    RUBY
+
+    app_file 'config/routes.rb', <<-RUBY
+      AppTemplate::Application.routes.draw do
+        match '/c', :to => lambda { |env| [200, {"Content-Type" => "text/plain"}, [User.counter.to_s]] }
+      end
+    RUBY
+
+    app_file "app/models/user.rb", <<-MODEL
+      class User
+        def self.counter; 1; end
+      end
+    MODEL
+
+    require 'rack/test'
+    extend Rack::Test::Methods
+
+    require "#{rails_root}/config/environment"
+    sleep(1)
+
+    get "/c"
+    assert_equal "1", last_response.body
+
+    app_file "app/models/user.rb", <<-MODEL
+      class User
+        def self.counter; 2; end
+      end
+    MODEL
+
+    get "/c"
+    assert_equal "1", last_response.body
+  end
+
   protected
 
   def setup_ar!