Allow to display engine's routes when running `rake routes ENGINES=true`

railties/CHANGELOG.md

 ## Rails 3.2.0 (unreleased) ##
 
-*   Allow to change the loading order of railties with `config.railties_order=`. Example:
+*   Added displaying of mounted engine's routes with `rake routes ENGINES=true`. *Piotr Sarnacki*
 
-    config.railties_order = [Blog::Engine, :main_app, :all]
+*   Allow to change the loading order of railties with `config.railties_order=`. *Piotr Sarnacki*
+
+    Example:
+        config.railties_order = [Blog::Engine, :main_app, :all]
 
 *   Scaffold returns 204 No Content for API requests without content. This makes scaffold work with jQuery out of the box. *José Valim*
 

railties/lib/rails/application/route_inspector.rb

@@ -4,12 +4,23 @@ class Application
     # This class is just used for displaying route information when someone
     # executes `rake routes`.  People should not use this class.
     class RouteInspector # :nodoc:
+      def initialize
+        @engines = ActiveSupport::OrderedHash.new
+      end
+
       def format all_routes, filter = nil
         if filter
           all_routes = all_routes.select{ |route| route.defaults[:controller] == filter }
         end
 
-        routes = all_routes.collect do |route|
+        routes = collect_routes(all_routes)
+
+        formatted_routes(routes) +
+          formatted_routes_for_engines
+      end
+
+      def collect_routes(routes)
+        routes = routes.collect do |route|
           route_reqs = route.requirements
 
           rack_app = route.app unless route.app.class.name.to_s =~ /^ActionDispatch::Routing/
@@ -25,12 +36,32 @@ def format all_routes, filter = nil
 
           verb = route.verb.source.gsub(/[$^]/, '')
 
-          {:name => route.name.to_s, :verb => verb, :path => route.path.spec.to_s, :reqs => reqs}
+          collect_engine_routes(reqs, rack_app)
+
+          {:name => route.name.to_s, :verb => verb, :path => route.path.spec.to_s, :reqs => reqs }
         end
 
         # Skip the route if it's internal info route
-        routes.reject! { |r| r[:path] =~ %r{/rails/info/properties|^/assets} }
+        routes.reject { |r| r[:path] =~ %r{/rails/info/properties|^/assets} }
+      end
+
+      def collect_engine_routes(name, rack_app)
+        return unless rack_app && ENV["ENGINES"] && rack_app.respond_to?(:routes)
+        return if @engines[name]
+
+        routes = rack_app.routes
+        if routes.is_a?(ActionDispatch::Routing::RouteSet)
+          @engines[name] = collect_routes(routes.routes)
+        end
+      end
+
+      def formatted_routes_for_engines
+        @engines.map do |name, routes|
+          ["\nRoutes for #{name}:"] + formatted_routes(routes)
+        end.flatten
+      end
 
+      def formatted_routes(routes)
         name_width = routes.map{ |r| r[:name].length }.max
         verb_width = routes.map{ |r| r[:verb].length }.max
         path_width = routes.map{ |r| r[:path].length }.max

railties/lib/rails/tasks/routes.rake

-desc 'Print out all defined routes in match order, with names. Target specific controller with CONTROLLER=x.'
+desc 'Print out all defined routes in match order, with names. Target specific controller with CONTROLLER=x. Include engine\'s routes with ENGINES=true'
 task :routes => :environment do
   Rails.application.reload_routes!
   all_routes = Rails.application.routes.routes

railties/test/application/route_inspect_test.rb

 require 'test/unit'
 require 'rails/application/route_inspector'
 require 'action_controller'
+require 'rails/engine'
 
 module ApplicationTests
   class RouteInspectTest < Test::Unit::TestCase
@@ -9,6 +10,35 @@ def setup
       @inspector = Rails::Application::RouteInspector.new
     end
 
+    def test_displaying_routes_for_engines
+      ENV["ENGINES"] = "true"
+
+      engine = Class.new(Rails::Engine) do
+        def self.to_s
+          "Blog::Engine"
+        end
+      end
+      engine.routes.draw do
+        get '/cart', :to => 'cart#show'
+      end
+
+      @set.draw do
+        get '/custom/assets', :to => 'custom_assets#show'
+        mount engine => "/blog", :as => "blog"
+      end
+
+      output = @inspector.format @set.routes
+      expected = [
+        "custom_assets GET /custom/assets(.:format) custom_assets#show",
+        "         blog     /blog                    Blog::Engine",
+        "\nRoutes for Blog::Engine:",
+        "cart GET /cart(.:format) cart#show"
+      ]
+      assert_equal expected, output
+    ensure
+      ENV["ENGINES"] = nil
+    end
+
     def test_cart_inspect
       @set.draw do
         get '/cart', :to => 'cart#show'