Add message when you have no routes defined.

Print a message in both `rake routes` and at GET "/rails/info/routes"
that lets you know you have no routes defined, as well as linking to the
Rails Guide on the topic.

actionpack/CHANGELOG.md

@@ -1,5 +1,11 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Add a message when you have no routes defined to both `rake routes` and
+    GET "/rails/info/routes" that lets you know you have none defined and links
+    to the Rails Guide on the topic.
+
+    *Steve Klabnik*
+
 *   Change `image_alt` method to replace underscores/hyphens to spaces in filenames.
 
     Previously, underscored filenames became `alt="A_long_file_name_with_underscores"`

actionpack/lib/action_dispatch/routing/inspector.rb

@@ -91,6 +91,11 @@ def format(formatter, filter = nil)
 
         routes = collect_routes(routes_to_display)
 
+        if routes.none?
+          formatter.no_routes
+          return formatter.result
+        end
+
         formatter.header routes
         formatter.section routes
 
@@ -161,6 +166,16 @@ def header(routes)
         @buffer << draw_header(routes)
       end
 
+      def no_routes
+        @buffer << <<-MESSAGE
+You don't have any routes defined!
+
+Please add some routes in config/routes.rb.
+
+For more information about routes, see the Rails Guide: http://guides.rubyonrails.org/routing.html .
+MESSAGE
+      end
+
       private
         def draw_section(routes)
           name_width, verb_width, path_width = widths(routes)
@@ -197,6 +212,16 @@ def section(routes)
         @buffer << @view.render(partial: "routes/route", collection: routes)
       end
 
+      def no_routes
+        @buffer << <<-MESSAGE
+<p>You don't have any routes defined!</p>
+<ul>
+<li>Please add some routes in config/routes.rb.</li>
+<li>For more information about routes, please <a href="http://guides.rubyonrails.org/routing.html">see the Rails Guide</a>.</li>
+</ul>
+MESSAGE
+      end
+
       def result
         @view.raw @view.render(layout: "routes/table") {
           @view.raw @buffer.join("\n")

railties/test/application/rake_test.rb

@@ -143,6 +143,21 @@ def test_rake_routes_calls_the_route_inspector
       assert_equal "cart GET /cart(.:format) cart#show\n", Dir.chdir(app_path){ `rake routes` }
     end
 
+    def test_rake_routes_displays_message_when_no_routes_are_defined
+      app_file "config/routes.rb", <<-RUBY
+        AppTemplate::Application.routes.draw do
+        end
+      RUBY
+
+      assert_equal <<-MESSAGE, Dir.chdir(app_path){ `rake routes` }
+You don't have any routes defined!
+
+Please add some routes in config/routes.rb.
+
+For more information about routes, see the Rails Guide: http://guides.rubyonrails.org/routing.html .
+MESSAGE
+    end
+
     def test_logger_is_flushed_when_exiting_production_rake_tasks
       add_to_config <<-RUBY
         rake_tasks do