Reorganized initializers a bit to enable better hooks for common cases without the need for Railtie. Specifically, the following hooks were added:

* before_configuration: this hook is run immediately after the Application class 
  comes into existence, but before the user has added any configuration. This is
  the appropriate place to set configuration for your plugin
* before_initialize: This is run after all of the user's configuration has completed,
  but before any initializers have begun (in other words, it runs right after
  config/environments/{development,production,test}.rb)
* after_initialize: This is run after all of the initializers have run. It is an
  appropriate place for forking in a preforking setup

Each of these hooks may be used via ActiveSupport.on_load(name) { }. In all these cases, the context inside the block will be the Application object. This means that for simple cases, you can use these hooks without needing to create a Railtie.

8 files changed, 65 insertions, 39 deletions

diff --git a/railties/guides/source/initialization.textile b/railties/guides/source/initialization.textile
index 9ce27fa331..96d6998e1c 100644
--- a/railties/guides/source/initialization.textile
+++ b/railties/guides/source/initialization.textile
@@ -2379,7 +2379,6 @@ Now that we've referenced that class, it will be required for us. You'll notice
 * initialize_subscriber
 * set_clear_dependencies_hook
 * initialize_dependency_mechanism
-* bootstrap_load_path
 
 These are all defined using the +initializer+ method:
 
@@ -2930,7 +2929,6 @@ With +@@autoloads+ being
 * initialize_subscriber
 * set_clear_dependencies_hook
 * initialize_dependency_mechanism
-* bootstrap_load_path
 
 h4. Active Support Initializers
 
diff --git a/railties/lib/rails/application.rb b/railties/lib/rails/application.rb
index d39f9a2ae9..9e18dccf69 100644
--- a/railties/lib/rails/application.rb
+++ b/railties/lib/rails/application.rb
@@ -12,7 +12,7 @@ module Rails
   # points to it.
   #
   # In other words, Rails::Application is Singleton and whenever you are accessing
-  # Rails::Application.config or YourApplication::Application.config, you are actually 
+  # Rails::Application.config or YourApplication::Application.config, you are actually
   # accessing YourApplication::Application.instance.config.
   #
   # == Initialization
@@ -40,7 +40,7 @@ module Rails
   #
   # The Application is also responsible for building the middleware stack and setting up
   # both application and engines metals.
-  # 
+  #
   class Application < Engine
     autoload :Bootstrap,      'rails/application/bootstrap'
     autoload :Configurable,   'rails/application/configurable'
@@ -69,6 +69,8 @@ module Rails
         raise "You cannot have more than one Rails::Application" if Rails.application
         super
         Rails.application = base.instance
+
+        ActiveSupport.run_load_hooks(:before_configuration, base.instance)
       end
 
       def respond_to?(*args)
@@ -82,7 +84,7 @@ module Rails
       end
     end
 
-    delegate :metal_loader, :to => :config
+    delegate :middleware, :metal_loader, :to => :config
 
     def require_environment!
       environment = paths.config.environment.to_a.first
@@ -125,7 +127,7 @@ module Rails
     end
 
     def app
-      @app ||= middleware.build(routes)
+      @app ||= config.middleware.build(routes)
     end
 
     def call(env)
diff --git a/railties/lib/rails/application/bootstrap.rb b/railties/lib/rails/application/bootstrap.rb
index 022e1a91d8..e62eed8a87 100644
--- a/railties/lib/rails/application/bootstrap.rb
+++ b/railties/lib/rails/application/bootstrap.rb
@@ -10,7 +10,8 @@ module Rails
         require environment if environment
       end
 
-      initializer :load_all_active_support do
+      initializer :load_active_support do
+        require 'active_support/dependencies'
         require "active_support/all" unless config.active_support.bare
       end
 
@@ -18,7 +19,6 @@ module Rails
       # Used by Passenger to ensure everything's loaded before forking and
       # to avoid autoload race conditions in JRuby.
       initializer :preload_frameworks do
-        require 'active_support/dependencies'
         ActiveSupport::Autoload.eager_autoload! if config.preload_frameworks
       end
 
@@ -66,8 +66,8 @@ module Rails
         ActiveSupport::Dependencies.mechanism = config.cache_classes ? :require : :load
       end
 
-      initializer :bootstrap_load_path do
-        # This is just an initializer used as hook so all load paths are loaded together
+      initializer :bootstrap_hook do |app|
+        ActiveSupport.run_load_hooks(:before_initialize, app)
       end
     end
   end
diff --git a/railties/lib/rails/application/configuration.rb b/railties/lib/rails/application/configuration.rb
index 1ad77fdfec..cd77f1adaf 100644
--- a/railties/lib/rails/application/configuration.rb
+++ b/railties/lib/rails/application/configuration.rb
@@ -33,7 +33,7 @@ module Rails
       end
 
       def middleware
-        @middleware ||= default_middleware_stack
+        @middleware ||= app_middleware.merge_into(default_middleware_stack)
       end
 
       def metal_loader
diff --git a/railties/lib/rails/application/finisher.rb b/railties/lib/rails/application/finisher.rb
index 94507bb387..03bc270c81 100644
--- a/railties/lib/rails/application/finisher.rb
+++ b/railties/lib/rails/application/finisher.rb
@@ -35,10 +35,8 @@ module Rails
         app
       end
 
-      initializer :after_initialize do
-        config.after_initialize_blocks.each do |block|
-          block.call(self)
-        end
+      initializer :finisher_hook do |app|
+        ActiveSupport.run_load_hooks(:after_initialize, app)
       end
 
       # Disable dependency loading during request cycle
diff --git a/railties/lib/rails/engine.rb b/railties/lib/rails/engine.rb
index ab0ead65a9..652bd40ee4 100644
--- a/railties/lib/rails/engine.rb
+++ b/railties/lib/rails/engine.rb
@@ -45,7 +45,7 @@ module Rails
   #       app.middleware.use MyEngine::Middleware
   #     end
   #   end
-  # 
+  #
   # == Paths
   #
   # Since Rails 3.0, both your Application and Engines do not have hardcoded paths.
@@ -125,7 +125,7 @@ module Rails
       end
     end
 
-    delegate :middleware, :paths, :root, :to => :config
+    delegate :paths, :root, :to => :config
 
     def load_tasks
       super
@@ -133,7 +133,7 @@ module Rails
     end
 
     # Add configured load paths to ruby load paths and remove duplicates.
-    initializer :set_load_path, :before => :bootstrap_load_path do
+    initializer :set_load_path, :before => :bootstrap_hook do
       config.load_paths.reverse_each do |path|
         $LOAD_PATH.unshift(path) if File.directory?(path)
       end
@@ -142,7 +142,10 @@ module Rails
 
     # Set the paths from which Rails will automatically load source files,
     # and the load_once paths.
-    initializer :set_autoload_paths, :before => :bootstrap_load_path do |app|
+    #
+    # This needs to be an initializer, since it needs to run once
+    # per engine and get the engine as a block parameter
+    initializer :set_autoload_paths, :before => :bootstrap_hook do |app|
       ActiveSupport::Dependencies.load_paths.unshift(*config.load_paths)
 
       if reloadable?(app)
@@ -200,7 +203,9 @@ module Rails
       end
     end
 
-    initializer :load_app_classes do |app|
+    # This needs to be an initializer, since it needs to run once
+    # per engine and get the engine as a block parameter
+    initializer :load_app_classes, :before => :finisher_hook do |app|
       next if $rails_rake_task
 
       if app.config.cache_classes
diff --git a/railties/lib/rails/railtie/configuration.rb b/railties/lib/rails/railtie/configuration.rb
index 16eccaccc4..f57d82a3d8 100644
--- a/railties/lib/rails/railtie/configuration.rb
+++ b/railties/lib/rails/railtie/configuration.rb
@@ -3,10 +3,50 @@ require 'rails/configuration'
 module Rails
   class Railtie
     class Configuration
+      class MiddlewareStackProxy
+        def initialize
+          @operations = []
+        end
+
+        def insert_before(*args, &block)
+          @operations << [:insert_before, args, block]
+        end
+
+        alias insert insert_before
+
+        def insert_after(*args, &block)
+          @operations << [:insert_after, args, block]
+        end
+
+        def swap(*args, &block)
+          @operations << [:swap, args, block]
+        end
+
+        def use(*args, &block)
+          @operations << [:use, args, block]
+        end
+
+        def merge_into(other)
+          @operations.each do |operation, args, block|
+            other.send(operation, *args, &block)
+          end
+          other
+        end
+      end
+
       def initialize
         @@options ||= {}
       end
 
+      # This allows you to modify the application's middlewares from Engines.
+      #
+      # All operations you run on the app_middleware will be replayed on the
+      # application once it is defined and the default_middlewares are
+      # created
+      def app_middleware
+        @@app_middleware ||= MiddlewareStackProxy.new
+      end
+
       # Holds generators configuration:
       #
       #   config.generators do |g|
@@ -28,12 +68,8 @@ module Rails
         end
       end
 
-      def after_initialize_blocks
-        @@after_initialize_blocks ||= []
-      end
-
-      def after_initialize(&blk)
-        after_initialize_blocks << blk if blk
+      def after_initialize(&block)
+        ActiveSupport.on_load(:after_initialize, :yield => true, &block)
       end
 
       def to_prepare_blocks
diff --git a/railties/test/application/initializers/initializers_test.rb b/railties/test/application/initializers/initializers_test.rb
index 2e6a707175..eca42dada6 100644
--- a/railties/test/application/initializers/initializers_test.rb
+++ b/railties/test/application/initializers/initializers_test.rb
@@ -28,19 +28,6 @@ module ApplicationTests
       assert_equal "congratulations", $test_after_initialize_block2
     end
 
-    test "after_initialize block works correctly when no block is passed" do
-      add_to_config <<-RUBY
-        config.root = "#{app_path}"
-        config.after_initialize { $test_after_initialize_block1 = "success" }
-        config.after_initialize # don't pass a block, this is what we're testing!
-        config.after_initialize { $test_after_initialize_block2 = "congratulations" }
-      RUBY
-      require "#{app_path}/config/environment"
-
-      assert_equal "success", $test_after_initialize_block1
-      assert_equal "congratulations", $test_after_initialize_block2
-    end
-
     test "after_initialize runs after frameworks have been initialized" do
       $activerecord_configurations = nil
       add_to_config <<-RUBY