Do not generate unused components contents in `app:update` task

Currently, `app:update` generates all contents regardless of the
component using in application.

For example, even if not using Action Cable, `app:update` will generate
a contents related to Action Cable. This is a little inconvenient.
This PR checks the existence of the component and does not generate
unnecessary contents.
Can not check all options in this way. However, it will be able to
prevent the generation of unnecessary files.

5 files changed, 60 insertions, 23 deletions

diff --git a/railties/CHANGELOG.md b/railties/CHANGELOG.md
index 761e2f4ded..5ea007bc33 100644
--- a/railties/CHANGELOG.md
+++ b/railties/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   Skip unused components when running `bin/rails app:update`.
+
+    If the initial app generation skipped Action Cable, Active Record etc.,
+    the update task honors those skips too.
+
+    *Yuji Yaginuma*
+
 *   Make Rails' test runner work better with minitest plugins.
 
     By demoting the Rails test runner to just another minitest plugin —
diff --git a/railties/lib/rails/app_updater.rb b/railties/lib/rails/app_updater.rb
new file mode 100644
index 0000000000..e53d1cf093
--- /dev/null
+++ b/railties/lib/rails/app_updater.rb
@@ -0,0 +1,31 @@
+require "rails/generators"
+require "rails/generators/rails/app/app_generator"
+
+module Rails
+  class AppUpdater # :nodoc:
+    class << self
+      def invoke_from_app_generator(method)
+        app_generator.send(method)
+      end
+
+      def app_generator
+        @app_generator ||= begin
+          gen = Rails::Generators::AppGenerator.new ["rails"], generator_options, destination_root: Rails.root
+          File.exist?(Rails.root.join("config", "application.rb")) ? gen.send(:app_const) : gen.send(:valid_const?)
+          gen
+        end
+      end
+
+      private
+        def generator_options
+          options = { api: !!Rails.application.config.api_only, update: true }
+          options[:skip_active_record] = !defined?(ActiveRecord::Railtie)
+          options[:skip_action_mailer] = !defined?(ActionMailer::Railtie)
+          options[:skip_action_cable]  = !defined?(ActionCable::Engine)
+          options[:skip_sprockets]     = !defined?(Sprockets::Railtie)
+          options[:skip_puma]          = !defined?(Puma)
+          options
+        end
+    end
+  end
+end
diff --git a/railties/lib/rails/generators/rails/app/app_generator.rb b/railties/lib/rails/generators/rails/app/app_generator.rb
index 7614e6304b..7a59f106e3 100644
--- a/railties/lib/rails/generators/rails/app/app_generator.rb
+++ b/railties/lib/rails/generators/rails/app/app_generator.rb
@@ -128,7 +128,7 @@ module Rails
         gsub_file "config/initializers/cookies_serializer.rb", /json(?!,)/, "marshal"
       end
 
-      unless action_cable_config_exist
+      if !options[:skip_action_cable] && !action_cable_config_exist
         template "config/cable.yml"
       end
 
diff --git a/railties/lib/rails/tasks/framework.rake b/railties/lib/rails/tasks/framework.rake
index f7e8f4f340..6c6e86d78d 100644
--- a/railties/lib/rails/tasks/framework.rake
+++ b/railties/lib/rails/tasks/framework.rake
@@ -36,38 +36,21 @@ namespace :app do
   end
 
   namespace :update do
-    class RailsUpdate
-      def self.invoke_from_app_generator(method)
-        app_generator.send(method)
-      end
-
-      def self.app_generator
-        @app_generator ||= begin
-          require_relative "../generators"
-          require_relative "../generators/rails/app/app_generator"
-          gen = Rails::Generators::AppGenerator.new ["rails"],
-                                                    { api: !!Rails.application.config.api_only, update: true },
-                                                    destination_root: Rails.root
-          File.exist?(Rails.root.join("config", "application.rb")) ?
-            gen.send(:app_const) : gen.send(:valid_const?)
-          gen
-        end
-      end
-    end
+    require_relative "../app_updater"
 
     # desc "Update config/boot.rb from your current rails install"
     task :configs do
-      RailsUpdate.invoke_from_app_generator :create_boot_file
-      RailsUpdate.invoke_from_app_generator :update_config_files
+      Rails::AppUpdater.invoke_from_app_generator :create_boot_file
+      Rails::AppUpdater.invoke_from_app_generator :update_config_files
     end
 
     # desc "Adds new executables to the application bin/ directory"
     task :bin do
-      RailsUpdate.invoke_from_app_generator :update_bin_files
+      Rails::AppUpdater.invoke_from_app_generator :update_bin_files
     end
 
     task :upgrade_guide_info do
-      RailsUpdate.invoke_from_app_generator :display_upgrade_guide_info
+      Rails::AppUpdater.invoke_from_app_generator :display_upgrade_guide_info
     end
   end
 end
diff --git a/railties/test/generators/app_generator_test.rb b/railties/test/generators/app_generator_test.rb
index 059c2692be..ffdee3a6b5 100644
--- a/railties/test/generators/app_generator_test.rb
+++ b/railties/test/generators/app_generator_test.rb
@@ -278,6 +278,22 @@ class AppGeneratorTest < Rails::Generators::TestCase
     end
   end
 
+  def test_app_update_does_not_generate_action_cable_contents_when_skip_action_cable_is_given
+    app_root = File.join(destination_root, "myapp")
+    run_generator [app_root, "--skip-action-cable"]
+
+    FileUtils.cd(app_root) do
+      # For avoid conflict file
+      FileUtils.rm("#{app_root}/config/secrets.yml")
+      quietly { system("bin/rails app:update") }
+    end
+
+    assert_no_file "#{app_root}/config/cable.yml"
+    assert_file "#{app_root}/config/environments/production.rb" do |content|
+      assert_no_match(/config\.action_cable/, content)
+    end
+  end
+
   def test_application_names_are_not_singularized
     run_generator [File.join(destination_root, "hats")]
     assert_file "hats/config/environment.rb", /Rails\.application\.initialize!/