Add routes --unused option to detect extraneous routes.

Routes take a long time to draw. Over time, a Rails app can become slow
to boot simply because of how many routes it has. This script can be
used to detect routes that are drawn, but aren't actually valid.
Removing routes this script detects can help speed up your app and
remove dead code.

Example:

```
> bin/rails routes --unused

Found 2 unused routes:

Prefix Verb URI Pattern    Controller#Action
   one GET  /one(.:format) action#one
   two GET  /two(.:format) action#two
```

actionpack/lib/action_dispatch/journey/routes.rb

@@ -9,8 +9,8 @@ module ActionDispatch
 
       attr_reader :routes, :custom_routes, :anchored_routes
 
-      def initialize
-        @routes             = []
+      def initialize(routes = [])
+        @routes             = routes
         @ast                = nil
         @anchored_routes    = []
         @custom_routes      = []

actionpack/lib/action_dispatch/routing/inspector.rb

@@ -237,6 +237,27 @@ module ActionDispatch
             "--[ Route #{index} ]".ljust(@width, "-")
           end
       end
+
+      class Unused < Sheet
+        def header(routes)
+          @buffer << <<~MSG
+            Found #{routes.count} unused #{"route".pluralize(routes.count)}:
+          MSG
+
+          super
+        end
+
+        def no_routes(routes, filter)
+          @buffer <<
+            if filter.none?
+              "No unused routes found."
+            elsif filter.key?(:controller)
+              "No unused routes found for this controller."
+            elsif filter.key?(:grep)
+              "No unused routes found for this grep pattern."
+            end
+        end
+      end
     end
 
     class HtmlTableFormatter

railties/CHANGELOG.md

@@ -1,3 +1,19 @@
+*   Add `routes --unused` option to detect extraneous routes.
+
+    Example:
+
+    ```
+    > bin/rails rails --unused
+
+    Found 2 unused routes:
+
+    Prefix Verb URI Pattern    Controller#Action
+       one GET  /one(.:format) action#one
+       two GET  /two(.:format) action#two
+    ```
+
+    *Gannon McGibbon*
+
 *   Add `--parent` option to controller generator to specify parent class of job.
 
     Example:

railties/lib/rails/commands/routes/routes_command.rb

@@ -8,6 +8,15 @@ module Rails
       class_option :controller, aliases: "-c", desc: "Filter by a specific controller, e.g. PostsController or Admin::PostsController."
       class_option :grep, aliases: "-g", desc: "Grep routes by a specific pattern."
       class_option :expanded, type: :boolean, aliases: "-E", desc: "Print routes expanded vertically with parts explained."
+      class_option :unused, type: :boolean, aliases: "-u", desc: "Print unused routes."
+
+      def invoke_command(*)
+        if options.key?("unused")
+          Rails::Command.invoke "unused_routes", ARGV
+        else
+          super
+        end
+      end
 
       def perform(*)
         require_application_and_environment!

railties/lib/rails/commands/unused_routes/unused_routes_command.rb

@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+require "rails/commands/routes/routes_command"
+
+module Rails
+  module Command
+    class UnusedRoutesCommand < Rails::Command::Base # :nodoc:
+      hide_command!
+      class_option :controller, aliases: "-c", desc: "Filter by a specific controller, e.g. PostsController or Admin::PostsController."
+      class_option :grep, aliases: "-g", desc: "Grep routes by a specific pattern."
+
+      class RouteInfo
+        def initialize(route)
+          requirements = route.requirements
+          @controller_name = requirements[:controller]
+          @action_name = requirements[:action]
+          @controller_class = (@controller_name.to_s.camelize + "Controller").safe_constantize
+        end
+
+        def unused?
+          controller_class_missing? || (action_missing? && template_missing?)
+        end
+
+        private
+          def view_path(root)
+            File.join(root.path, @controller_name, @action_name)
+          end
+
+          def controller_class_missing?
+            @controller_name && @controller_class.nil?
+          end
+
+          def template_missing?
+            @controller_class && @controller_class.try(:view_paths).to_a.flat_map { |path| Dir["#{view_path(path)}.*"] }.none?
+          end
+
+          def action_missing?
+            @controller_class && @controller_class.instance_methods.exclude?(@action_name.to_sym)
+          end
+      end
+
+      def perform(*)
+        require_application_and_environment!
+        require "action_dispatch/routing/inspector"
+
+        say(inspector.format(formatter, routes_filter))
+
+        exit(1) if routes.any?
+      end
+
+      private
+        def inspector
+          ActionDispatch::Routing::RoutesInspector.new(routes)
+        end
+
+        def routes
+          @routes ||= begin
+            routes = Rails.application.routes.routes.select do |route|
+              RouteInfo.new(route).unused?
+            end
+
+            ActionDispatch::Journey::Routes.new(routes)
+          end
+        end
+
+        def formatter
+          ActionDispatch::Routing::ConsoleFormatter::Unused.new
+        end
+
+        def routes_filter
+          options.symbolize_keys.slice(:controller, :grep)
+        end
+    end
+  end
+end

railties/test/commands/routes_test.rb

@@ -251,7 +251,7 @@ rails_conductor_inbound_email_incinerate POST /rails/conductor/action_mailbox/:i
       URI               | /rails/conductor/action_mailbox/inbound_emails(.:format)
       Controller#Action | rails/conductor/action_mailbox/inbound_emails#index
       --[ Route 9 ]--------------
-      Prefix            | 
+      Prefix            |#{" "}
       Verb              | POST
       URI               | /rails/conductor/action_mailbox/inbound_emails(.:format)
       Controller#Action | rails/conductor/action_mailbox/inbound_emails#create
@@ -296,7 +296,7 @@ rails_conductor_inbound_email_incinerate POST /rails/conductor/action_mailbox/:i
       URI               | /rails/active_storage/blobs/proxy/:signed_id/*filename(.:format)
       Controller#Action | active_storage/blobs/proxy#show
       --[ Route 18 ]-------------
-      Prefix            | 
+      Prefix            |#{" "}
       Verb              | GET
       URI               | /rails/active_storage/blobs/:signed_id/*filename(.:format)
       Controller#Action | active_storage/blobs/redirect#show
@@ -311,7 +311,7 @@ rails_conductor_inbound_email_incinerate POST /rails/conductor/action_mailbox/:i
       URI               | /rails/active_storage/representations/proxy/:signed_blob_id/:variation_key/*filename(.:format)
       Controller#Action | active_storage/representations/proxy#show
       --[ Route 21 ]-------------
-      Prefix            | 
+      Prefix            |#{" "}
       Verb              | GET
       URI               | /rails/active_storage/representations/:signed_blob_id/:variation_key/*filename(.:format)
       Controller#Action | active_storage/representations/redirect#show
@@ -334,6 +334,17 @@ rails_conductor_inbound_email_incinerate POST /rails/conductor/action_mailbox/:i
     # rubocop:enable Layout/TrailingWhitespace
   end
 
+  test "rails routes with unused option" do
+    app_file "config/routes.rb", <<-RUBY
+      Rails.application.routes.draw do
+      end
+    RUBY
+
+    output = run_routes_command([ "--unused" ])
+
+    assert_equal(output, "No unused routes found.\n")
+  end
+
   private
     def run_routes_command(args = [])
       rails "routes", args

railties/test/commands/unused_routes_test.rb

@@ -0,0 +1,154 @@
+# frozen_string_literal: true
+
+require "isolation/abstract_unit"
+require "rails/command"
+require "rails/commands/routes/routes_command"
+require "io/console/size"
+
+class Rails::Command::UnusedRoutesTest < ActiveSupport::TestCase
+  setup :build_app
+  teardown :teardown_app
+
+  test "no results" do
+    app_file "config/routes.rb", <<-RUBY
+      Rails.application.routes.draw do
+      end
+    RUBY
+
+    assert_equal <<~OUTPUT, run_unused_routes_command
+      No unused routes found.
+    OUTPUT
+  end
+
+  test "no controller" do
+    app_file "config/routes.rb", <<-RUBY
+      Rails.application.routes.draw do
+        get "/", to: "my#index", as: :my_route
+      end
+    RUBY
+
+    assert_equal <<~OUTPUT, run_unused_routes_command(allow_failure: true)
+      Found 1 unused route:
+
+        Prefix Verb URI Pattern Controller#Action
+      my_route GET  /           my#index
+    OUTPUT
+  end
+
+  test "no action" do
+    app_file "app/controllers/my_controller.rb", <<-RUBY
+      class MyController < ActionController::Base
+      end
+    RUBY
+
+    app_file "config/routes.rb", <<-RUBY
+      Rails.application.routes.draw do
+        get "/", to: "my#index", as: :my_route
+      end
+    RUBY
+
+    assert_equal <<~OUTPUT, run_unused_routes_command(allow_failure: true)
+      Found 1 unused route:
+
+        Prefix Verb URI Pattern Controller#Action
+      my_route GET  /           my#index
+    OUTPUT
+  end
+
+  test "implicit render" do
+    app_file "app/controllers/my_controller.rb", <<-RUBY
+      class MyController < ActionController::Base
+      end
+    RUBY
+
+    app_file "app/views/my/index.html.erb", <<-HTML
+      <h1>Hello world</h1>
+    HTML
+
+    app_file "config/routes.rb", <<-RUBY
+      Rails.application.routes.draw do
+        get "/", to: "my#index", as: :my_route
+      end
+    RUBY
+
+    assert_equal <<~OUTPUT, run_unused_routes_command
+      No unused routes found.
+    OUTPUT
+  end
+
+  test "multiple unused routes" do
+    app_file "config/routes.rb", <<-RUBY
+      Rails.application.routes.draw do
+        get "/one", to: "action#one"
+        get "/two", to: "action#two"
+      end
+    RUBY
+
+    assert_equal <<~OUTPUT, run_unused_routes_command(allow_failure: true)
+      Found 2 unused routes:
+
+      Prefix Verb URI Pattern    Controller#Action
+         one GET  /one(.:format) action#one
+         two GET  /two(.:format) action#two
+    OUTPUT
+  end
+
+  test "filter by grep" do
+    app_file "config/routes.rb", <<-RUBY
+      Rails.application.routes.draw do
+        get "/one", to: "posts#one"
+        get "/two", to: "users#two"
+      end
+    RUBY
+
+    assert_equal <<~OUTPUT, run_unused_routes_command(["-g", "one"], allow_failure: true)
+      Found 1 unused route:
+
+      Prefix Verb URI Pattern    Controller#Action
+         one GET  /one(.:format) posts#one
+    OUTPUT
+  end
+
+  test "filter by grep no results" do
+    app_file "config/routes.rb", <<-RUBY
+      Rails.application.routes.draw do
+      end
+    RUBY
+
+    assert_equal <<~OUTPUT, run_unused_routes_command(["-g", "one"])
+      No unused routes found for this grep pattern.
+    OUTPUT
+  end
+
+  test "filter by controller" do
+    app_file "config/routes.rb", <<-RUBY
+      Rails.application.routes.draw do
+        get "/one", to: "posts#one"
+        get "/two", to: "users#two"
+      end
+    RUBY
+
+    assert_equal <<~OUTPUT, run_unused_routes_command(["-c", "posts"], allow_failure: true)
+      Found 1 unused route:
+
+      Prefix Verb URI Pattern    Controller#Action
+         one GET  /one(.:format) posts#one
+    OUTPUT
+  end
+
+  test "filter by controller no results" do
+    app_file "config/routes.rb", <<-RUBY
+      Rails.application.routes.draw do
+      end
+    RUBY
+
+    assert_equal <<~OUTPUT, run_unused_routes_command(["-c", "posts"])
+      No unused routes found for this controller.
+    OUTPUT
+  end
+
+  private
+    def run_unused_routes_command(args = [], allow_failure: false)
+      rails "unused_routes", args, allow_failure: allow_failure
+    end
+end