Clear DescendantsTracker on each request.

actionpack/lib/action_dispatch/middleware/callbacks.rb

@@ -8,7 +8,7 @@ module ActionDispatch
   class Callbacks
     include ActiveSupport::Callbacks
 
-    define_callbacks :call, :terminator => "result == false", :rescuable => true
+    define_callbacks :call, :rescuable => true
     define_callbacks :prepare, :scope => :name
 
     # Add a preparation callback. Preparation callbacks are run before every
@@ -37,12 +37,12 @@ def self.after(*args, &block)
 
     def initialize(app, prepare_each_request = false)
       @app, @prepare_each_request = app, prepare_each_request
-      run_callbacks(:prepare)
+      _run_prepare_callbacks
     end
 
     def call(env)
-      run_callbacks(:call) do
-        run_callbacks(:prepare) if @prepare_each_request
+      _run_call_callbacks do
+        _run_prepare_callbacks if @prepare_each_request
         @app.call(env)
       end
     end

activerecord/lib/active_record/railtie.rb

@@ -68,7 +68,6 @@ class Railtie < Rails::Railtie
       unless app.config.cache_classes
         ActiveSupport.on_load(:active_record) do
           ActionDispatch::Callbacks.after do
-            ActiveRecord::Base.reset_subclasses
             ActiveRecord::Base.clear_reloadable_connections!
           end
         end

railties/lib/rails/application/bootstrap.rb

 require "active_support/notifications"
+require "active_support/descendants_tracker"
 
 module Rails
   class Application
@@ -55,6 +56,7 @@ module Bootstrap
       initializer :set_clear_dependencies_hook do
         unless config.cache_classes
           ActionDispatch::Callbacks.after do
+            ActiveSupport::DescendantsTracker.clear
             ActiveSupport::Dependencies.clear
           end
         end

railties/test/application/initializers/load_path_test.rb

@@ -19,7 +19,7 @@ def setup
       assert $:.include?("#{app_path}/app/models")
     end
 
-    test "initializing an application adds lib path on inheritance hook" do
+    test "initializing an application allows to load code on lib path inside application class definitation" do
       app_file "lib/foo.rb", <<-RUBY
         module Foo; end
       RUBY

railties/test/application/model_initialization_test.rb → railties/test/application/loading_test.rb

 require 'isolation/abstract_unit'
 
-class PostTest < Test::Unit::TestCase
+class LoadingTest < Test::Unit::TestCase
   include ActiveSupport::Testing::Isolation
 
   def setup
@@ -8,14 +8,60 @@ def setup
     boot_rails
   end
 
-  def test_reload_should_reload_constants
+  def app
+    @app ||= Rails.application
+  end
+
+  def test_load_should_load_constants
     app_file "app/models/post.rb", <<-MODEL
       class Post < ActiveRecord::Base
         validates_acceptance_of :title, :accept => "omg"
       end
     MODEL
+  
+    require "#{rails_root}/config/environment"
+    setup_ar!
+  
+    p = Post.create(:title => 'omg')
+    assert_equal 1, Post.count
+    assert_equal 'omg', p.title
+    p = Post.first
+    assert_equal 'omg', p.title
+  end
+
+  def test_descendants_are_cleaned_on_each_request_without_cache_classes
+    add_to_config <<-RUBY
+      config.cache_classes = false
+    RUBY
+
+    app_file "app/models/post.rb", <<-MODEL
+      class Post < ActiveRecord::Base
+      end
+    MODEL
+
+    app_file 'config/routes.rb', <<-RUBY
+      AppTemplate::Application.routes.draw do |map|
+        match '/load',   :to => lambda { |env| [200, {}, Post.all] }
+        match '/unload', :to => lambda { |env| [200, {}, []] }
+      end
+    RUBY
+
+    require 'rack/test'
+    extend Rack::Test::Methods
 
     require "#{rails_root}/config/environment"
+    setup_ar!
+
+    assert_equal [], ActiveRecord::Base.descendants
+    get "/load"
+    assert_equal [Post], ActiveRecord::Base.descendants
+    get "/unload"
+    assert_equal [], ActiveRecord::Base.descendants
+  end
+
+  protected
+  
+  def setup_ar!
     ActiveRecord::Base.establish_connection(:adapter => "sqlite3", :database => ":memory:")
     ActiveRecord::Migration.verbose = false
     ActiveRecord::Schema.define(:version => 1) do
@@ -23,11 +69,5 @@ class Post < ActiveRecord::Base
         t.string :title
       end
     end
-
-    p = Post.create(:title => 'omg')
-    assert_equal 1, Post.count
-    assert_equal 'omg', p.title
-    p = Post.first
-    assert_equal 'omg', p.title
   end
 end

railties/test/application/rake_test.rb

@@ -9,7 +9,7 @@ def setup
       boot_rails
       FileUtils.rm_rf("#{app_path}/config/environments")
     end
-    
+
     def test_gems_tasks_are_loaded_first_than_application_ones
       app_file "lib/tasks/app.rake", <<-RUBY
         $task_loaded = Rake::Task.task_defined?("db:create:all")