Rely on a public contract between railties instead of accessing railtie methods directly.

actionpack/lib/abstract_controller/railties/routes_helpers.rb

@@ -5,8 +5,8 @@ module AbstractController
         Module.new do
           define_method(:inherited) do |klass|
             super(klass)
-            if namespace = klass.parents.detect {|m| m.respond_to?(:_railtie) }
-              klass.send(:include, namespace._railtie.routes.url_helpers)
+            if namespace = klass.parents.detect { |m| m.respond_to?(:railtie_routes_url_helpers) }
+              klass.send(:include, namespace.railtie_routes_url_helpers)
             else
               klass.send(:include, routes.url_helpers)
             end

actionpack/lib/action_controller/railties/paths.rb

@@ -6,13 +6,14 @@ module ActionController
           define_method(:inherited) do |klass|
             super(klass)
 
-            if namespace = klass.parents.detect {|m| m.respond_to?(:_railtie) }
-              paths = namespace._railtie.paths["app/helpers"].existent
+            if namespace = klass.parents.detect { |m| m.respond_to?(:railtie_helpers_paths) }
+              paths = namespace.railtie_helpers_paths
             else
-              paths = app.config.helpers_paths
+              paths = app.helpers_paths
             end
 
             klass.helpers_path = paths
+
             if klass.superclass == ActionController::Base && ActionController::Base.include_all_helpers
               klass.helper :all
             end

actionpack/test/activerecord/polymorphic_routes_test.rb

@@ -34,10 +34,8 @@ module Blog
     set_table_name 'projects'
   end
 
-  def self._railtie
-    o = Object.new
-    def o.railtie_name; "blog" end
-    o
+  def self.use_relative_model_naming?
+    true
   end
 end
 

actionpack/test/lib/controller/fake_models.rb

@@ -175,8 +175,8 @@ class HashBackedAuthor < Hash
 end
 
 module Blog
-  def self._railtie
-    self
+  def self.use_relative_model_naming?
+    true
   end
 
   class Post < Struct.new(:title, :id)

actionpack/test/template/form_helper_test.rb

@@ -740,7 +740,7 @@ class FormHelperTest < ActionView::TestCase
     assert_dom_equal expected, output_buffer
   end
 
-  def test_form_for_with_isolated_namespaced_model
+  def test_form_for_with_model_using_relative_model_naming
     form_for(@blog_post) do |f|
       concat f.text_field :title
       concat f.submit('Edit post')

activemodel/lib/active_model/naming.rb

@@ -13,18 +13,18 @@ module ActiveModel
     def initialize(klass, namespace = nil, name = nil)
       name ||= klass.name
       super(name)
-      @unnamespaced = self.sub(/^#{namespace.name}::/, '') if namespace
 
-      @klass = klass
-      @singular = _singularize(self).freeze
-      @plural = ActiveSupport::Inflector.pluralize(@singular).freeze
-      @element = ActiveSupport::Inflector.underscore(ActiveSupport::Inflector.demodulize(self)).freeze
-      @human = ActiveSupport::Inflector.humanize(@element).freeze
-      @collection = ActiveSupport::Inflector.tableize(self).freeze
+      @unnamespaced = self.sub(/^#{namespace.name}::/, '') if namespace
+      @klass        = klass
+      @singular     = _singularize(self).freeze
+      @plural       = ActiveSupport::Inflector.pluralize(@singular).freeze
+      @element      = ActiveSupport::Inflector.underscore(ActiveSupport::Inflector.demodulize(self)).freeze
+      @human        = ActiveSupport::Inflector.humanize(@element).freeze
+      @collection   = ActiveSupport::Inflector.tableize(self).freeze
       @partial_path = "#{@collection}/#{@element}".freeze
-      @param_key = (namespace ? _singularize(@unnamespaced) : @singular).freeze
-      @route_key = (namespace ? ActiveSupport::Inflector.pluralize(@param_key) : @plural).freeze
-      @i18n_key = self.underscore.to_sym
+      @param_key    = (namespace ? _singularize(@unnamespaced) : @singular).freeze
+      @route_key    = (namespace ? ActiveSupport::Inflector.pluralize(@param_key) : @plural).freeze
+      @i18n_key     = self.underscore.to_sym
     end
 
     # Transform the model name into a more humane format, using I18n. By default,
@@ -79,7 +79,9 @@ module ActiveModel
     # used to retrieve all kinds of naming-related information.
     def model_name
       @_model_name ||= begin
-        namespace = self.parents.detect { |n| n.respond_to?(:_railtie) }
+        namespace = self.parents.detect do |n|
+          n.respond_to?(:use_relative_model_naming?) && n.use_relative_model_naming?
+        end
         ActiveModel::Name.new(self, namespace)
       end
     end

activemodel/test/cases/naming_test.rb

@@ -74,10 +74,6 @@ class NamingWithNamespacedModelInIsolatedNamespaceTest < ActiveModel::TestCase
   def test_param_key
     assert_equal 'post', @model_name.param_key
   end
-
-  def test_recognizing_namespace
-    assert_equal 'Post', Blog::Post.model_name.instance_variable_get("@unnamespaced")
-  end
 end
 
 class NamingWithNamespacedModelInSharedNamespaceTest < ActiveModel::TestCase
@@ -160,6 +156,40 @@ class NamingWithSuppliedModelNameTest < ActiveModel::TestCase
   end
 end
 
+class NamingUsingRelativeModelNameTest < ActiveModel::TestCase
+  def setup
+    @model_name = Blog::Post.model_name
+  end
+
+  def test_singular
+    assert_equal 'blog_post', @model_name.singular
+  end
+
+  def test_plural
+    assert_equal 'blog_posts', @model_name.plural
+  end
+
+  def test_element
+    assert_equal 'post', @model_name.element
+  end
+
+  def test_collection
+    assert_equal 'blog/posts', @model_name.collection
+  end
+
+  def test_human
+    assert_equal 'Post', @model_name.human
+  end
+
+  def test_route_key
+    assert_equal 'posts', @model_name.route_key
+  end
+
+  def test_param_key
+    assert_equal 'post', @model_name.param_key
+  end
+end
+
 class NamingHelpersTest < Test::Unit::TestCase
   def setup
     @klass  = Contact

activemodel/test/models/blog_post.rb

@@ -1,10 +1,6 @@
 module Blog
-  def self._railtie
-    Object.new
-  end
-
-  def self.table_name_prefix
-    "blog_"
+  def self.use_relative_model_naming?
+    true
   end
 
   class Post

railties/lib/rails/application.rb

@@ -141,6 +141,10 @@ module Rails
       self
     end
 
+    def helpers_paths
+      config.helpers_paths
+    end
+
   protected
 
     alias :build_middleware_stack :app

railties/lib/rails/engine.rb

@@ -371,20 +371,28 @@ module Rails
         self.routes.default_scope = { :module => ActiveSupport::Inflector.underscore(mod.name) }
         self.isolated = true
 
-        unless mod.respond_to?(:_railtie)
-          name = engine_name
-          _railtie = self
+        unless mod.respond_to?(:railtie_namespace)
+          name, railtie = engine_name, self
+
           mod.singleton_class.instance_eval do
-            define_method(:_railtie) do
-              _railtie
-            end
+            define_method(:railtie_namespace) { railtie }
 
             unless mod.respond_to?(:table_name_prefix)
-              define_method(:table_name_prefix) do
-                "#{name}_"
-              end
+              define_method(:table_name_prefix) { "#{name}_" }
             end
-         end
+
+            unless mod.respond_to?(:use_relative_model_naming?)
+              class_eval "def use_relative_model_naming?; true; end", __FILE__, __LINE__
+            end
+
+            unless mod.respond_to?(:railtie_helpers_paths)
+              define_method(:railtie_helpers_paths) { railtie.helpers_paths }
+            end
+
+            unless mod.respond_to?(:railtie_routes_url_helpers)
+              define_method(:railtie_routes_url_helpers) { railtie.routes_url_helpers }
+            end
+          end
         end
       end
 
@@ -429,13 +437,6 @@ module Rails
     def helpers
       @helpers ||= begin
         helpers = Module.new
-
-        helpers_paths = if config.respond_to?(:helpers_paths)
-          config.helpers_paths
-        else
-          paths["app/helpers"].existent
-        end
-
         all = ActionController::Base.all_helpers_from_path(helpers_paths)
         ActionController::Base.modules_for_helpers(all).each do |mod|
           helpers.send(:include, mod)
@@ -444,6 +445,14 @@ module Rails
       end
     end
 
+    def helpers_paths
+      paths["app/helpers"].existent
+    end
+
+    def routes_url_helpers
+      routes.url_helpers
+    end
+
     def app
       @app ||= begin
         config.middleware = config.middleware.merge_into(default_middleware_stack)

railties/lib/rails/railtie.rb

@@ -196,7 +196,7 @@ module Rails
     end
 
     def railtie_namespace
-      @railtie_namespace ||= self.class.parents.detect { |n| n.respond_to?(:_railtie) }
+      @railtie_namespace ||= self.class.parents.detect { |n| n.respond_to?(:railtie_namespace) }
     end
   end
 end

railties/test/railties/engine_test.rb

@@ -323,7 +323,7 @@ module RailtiesTest
 
       assert_equal "bukkits_", Bukkits.table_name_prefix
       assert_equal "bukkits", Bukkits::Engine.engine_name
-      assert_equal Bukkits._railtie, Bukkits::Engine
+      assert_equal Bukkits.railtie_namespace, Bukkits::Engine
       assert ::Bukkits::MyMailer.method_defined?(:foo_path)
       assert !::Bukkits::MyMailer.method_defined?(:bar_path)
 
@@ -467,7 +467,7 @@ module RailtiesTest
       assert_nil Rails.application.load_seed
     end
 
-    test "using namespace more than once on one module should not overwrite _railtie method" do
+    test "using namespace more than once on one module should not overwrite railtie_namespace method" do
       @plugin.write "lib/bukkits.rb", <<-RUBY
         module AppTemplate
           class Engine < ::Rails::Engine
@@ -484,7 +484,7 @@ module RailtiesTest
 
       boot_rails
 
-      assert_equal AppTemplate._railtie, AppTemplate::Engine
+      assert_equal AppTemplate.railtie_namespace, AppTemplate::Engine
     end
 
     test "properly reload routes" do