Better error message when running `rake routes` with CONTROLLER arg:

- `CONTROLLER` argument can now be supplied in different ways (Rails::WelcomeController, Rails::Welcome, rails/welcome)
- If `CONTROLLER` argument was supplied but it does not exist, will warn the user that this controller does not exist
- If `CONTROLLER` argument was supplied and no routes could be found matching this filter, will warn the user that no routes were found matching the supplied filter
- If no routes were defined in the config/routes.rb file, will warn the user with the original message

3 files changed, 64 insertions, 7 deletions

diff --git a/actionpack/CHANGELOG.md b/actionpack/CHANGELOG.md
index 0a5da2a94e..a732622b00 100644
--- a/actionpack/CHANGELOG.md
+++ b/actionpack/CHANGELOG.md
@@ -1,3 +1,11 @@
+*   More explicit error message when running `rake routes`. `CONTROLLER` argument
+    can now be supplied in different ways:
+    `Rails::WelcomeController`, `Rails::Welcome`, `rails/welcome`
+
+    Fixes #22918
+
+    *Edouard Chin*
+
 *   Allow `ActionController::Parameters` instances as an argument to URL
     helper methods. An `ArguemntError` will be raised if the passed parameters
     are not secure.
diff --git a/actionpack/lib/action_dispatch/routing/inspector.rb b/actionpack/lib/action_dispatch/routing/inspector.rb
index f3a5268d2e..69e6dd5215 100644
--- a/actionpack/lib/action_dispatch/routing/inspector.rb
+++ b/actionpack/lib/action_dispatch/routing/inspector.rb
@@ -65,7 +65,7 @@ module ActionDispatch
         routes = collect_routes(routes_to_display)
 
         if routes.none?
-          formatter.no_routes
+          formatter.no_routes(collect_routes(@routes), filter)
           return formatter.result
         end
 
@@ -84,7 +84,8 @@ module ActionDispatch
 
       def filter_routes(filter)
         if filter
-          @routes.select { |route| route.defaults[:controller] == filter }
+          filter_name = filter.underscore.sub(/_controller$/, '')
+          @routes.select { |route| route.defaults[:controller] == filter_name }
         else
           @routes
         end
@@ -136,17 +137,27 @@ module ActionDispatch
         @buffer << draw_header(routes)
       end
 
-      def no_routes
-        @buffer << <<-MESSAGE.strip_heredoc
+      def no_routes(routes, filter)
+        @buffer <<
+        if routes.none?
+          <<-MESSAGE.strip_heredoc
           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
+        elsif missing_controller?(filter)
+          "The controller #{filter} does not exist!"
+        else
+          "No routes were found for this controller"
+        end
+        @buffer << "For more information about routes, see the Rails guide: http://guides.rubyonrails.org/routing.html."
       end
 
       private
+        def missing_controller?(controller_name)
+          [ controller_name.camelize, "#{controller_name.camelize}Controller" ].none?(&:safe_constantize)
+        end
+
         def draw_section(routes)
           header_lengths = ['Prefix', 'Verb', 'URI Pattern'].map(&:length)
           name_width, verb_width, path_width = widths(routes).zip(header_lengths).map(&:max)
@@ -187,7 +198,7 @@ module ActionDispatch
       def header(routes)
       end
 
-      def no_routes
+      def no_routes(*)
         @buffer << <<-MESSAGE.strip_heredoc
           <p>You don't have any routes defined!</p>
           <ul>
diff --git a/actionpack/test/dispatch/routing/inspector_test.rb b/actionpack/test/dispatch/routing/inspector_test.rb
index a17d07c40b..7382c267c7 100644
--- a/actionpack/test/dispatch/routing/inspector_test.rb
+++ b/actionpack/test/dispatch/routing/inspector_test.rb
@@ -7,6 +7,9 @@ class MountedRackApp
   end
 end
 
+class Rails::DummyController
+end
+
 module ActionDispatch
   module Routing
     class RoutesInspectorTest < ActiveSupport::TestCase
@@ -331,6 +334,41 @@ module ActionDispatch
           "  cart GET  /cart(.:format) cart#show"
         ], output
       end
+
+      def test_routes_with_undefined_filter
+        output = draw(:filter => 'Rails::MissingController') do
+          get 'photos/:id' => 'photos#show', :id => /[A-Z]\d{5}/
+        end
+
+        assert_equal [
+          "The controller Rails::MissingController does not exist!",
+          "For more information about routes, see the Rails guide: http://guides.rubyonrails.org/routing.html."
+        ], output
+      end
+
+      def test_no_routes_matched_filter
+        output = draw(:filter => 'rails/dummy') do
+          get 'photos/:id' => 'photos#show', :id => /[A-Z]\d{5}/
+        end
+
+        assert_equal [
+          "No routes were found for this controller",
+          "For more information about routes, see the Rails guide: http://guides.rubyonrails.org/routing.html."
+        ], output
+      end
+
+      def test_no_routes_were_defined
+        output = draw(:filter => 'Rails::DummyController') { }
+
+        assert_equal [
+          "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."
+        ], output
+      end
+
     end
   end
 end