Add routes --unused option to detect extraneous routes.

actionpack/lib/action_dispatch/journey/routes.rb

@@ -9,8 +9,8 @@ class Routes # :nodoc:
 
       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 @@ def route_header(index:)
             "--[ 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 @@ class RoutesCommand < Base # :nodoc:
       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 @@ class Rails::Command::RoutesTest < ActiveSupport::TestCase
       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 @@ class Rails::Command::RoutesTest < ActiveSupport::TestCase
       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 @@ class Rails::Command::RoutesTest < ActiveSupport::TestCase
       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 @@ class Rails::Command::RoutesTest < ActiveSupport::TestCase
     # 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