adds --skip-listen to the application generator [closes #23590]

railties/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   The application generator supports `--skip-listen` to opt-out of features
+    that depend on the listen gem. As of this writing they are the evented file
+    system monitor and the async plugin for spring.
+
 *   The Gemfiles of new applications include spring-watcher-listen on Linux and
     Mac OS X (unless --skip-spring).
 

railties/lib/rails/generators/app_base.rb

@@ -63,6 +63,9 @@ module Rails
         class_option :skip_spring,        type: :boolean, default: false,
                                           desc: "Don't install Spring application preloader"
 
+        class_option :skip_listen,        type: :boolean, default: false,
+                                          desc: "Don't generate configuration that depends on the listen gem"
+
         class_option :skip_javascript,    type: :boolean, aliases: '-J', default: false,
                                           desc: 'Skip JavaScript files'
 
@@ -390,6 +393,10 @@ module Rails
         !options[:skip_spring] && !options.dev? && Process.respond_to?(:fork) && !RUBY_PLATFORM.include?("cygwin")
       end
 
+      def depend_on_listen?
+        !options[:skip_listen] && os_supports_listen_out_of_the_box?
+      end
+
       def os_supports_listen_out_of_the_box?
         RbConfig::CONFIG['host_os'] =~ /darwin|linux/
       end

railties/lib/rails/generators/rails/app/templates/Gemfile

@@ -38,13 +38,13 @@ group :development do
   gem 'web-console', '~> 3.0'
   <%- end -%>
 <%- end -%>
-<% if  os_supports_listen_out_of_the_box? -%>
+<% if  depend_on_listen? -%>
   gem 'listen', '~> 3.0.5'
 <% end  -%>
 <% if  spring_install? -%>
   # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
   gem 'spring'
-<% if  os_supports_listen_out_of_the_box? -%>
+<% if  depend_on_listen? -%>
   gem 'spring-watcher-listen', '~> 2.0.0'
 <% end  -%>
 <% end  -%>

railties/lib/rails/generators/rails/app/templates/config/environments/development.rb.tt

@@ -58,5 +58,5 @@ Rails.application.configure do
 
   # Use an evented file watcher to asynchronously detect changes in source code,
   # routes, locales, etc. This feature depends on the listen gem.
-  <%= '# ' unless os_supports_listen_out_of_the_box? %>config.file_watcher = ActiveSupport::EventedFileUpdateChecker
+  <%= '# ' unless depend_on_listen? %>config.file_watcher = ActiveSupport::EventedFileUpdateChecker
 end

railties/test/generators/app_generator_test.rb

@@ -479,18 +479,20 @@ class AppGeneratorTest < Rails::Generators::TestCase
     end
   end
 
-  def test_inclusion_of_listen_related_gems
+  def test_inclusion_of_listen_related_configuration_by_default
     run_generator
     if RbConfig::CONFIG['host_os'] =~ /darwin|linux/
-      assert_gem 'listen'
+      assert_listen_related_configuration
-      assert_gem 'spring-watcher-listen'
     else
-      assert_file 'Gemfile' do |content|
+      assert_no_listen_related_configuration
-        assert_no_match(/listen/, content)
-      end
     end
   end
 
+  def test_non_inclusion_of_listen_related_configuration_if_skip_listen
+    run_generator [destination_root, '--skip-listen']
+    assert_no_listen_related_configuration
+  end
+
   def test_evented_file_update_checker_config
     run_generator
     assert_file 'config/environments/development.rb' do |content|
@@ -759,4 +761,23 @@ class AppGeneratorTest < Rails::Generators::TestCase
       assert_file "Gemfile", /^\s*gem\s+["']#{gem}["']$*/
     end
   end
+
+  def assert_listen_related_configuration
+    assert_gem 'listen'
+    assert_gem 'spring-watcher-listen'
+
+    assert_file 'config/environments/development.rb' do |content|
+      assert_match(/^\s*config.file_watcher = ActiveSupport::EventedFileUpdateChecker/, content)
+    end
+  end
+
+  def assert_no_listen_related_configuration
+    assert_file 'Gemfile' do |content|
+      assert_no_match(/listen/, content)
+    end
+
+    assert_file 'config/environments/development.rb' do |content|
+      assert_match(/^\s*# config.file_watcher = ActiveSupport::EventedFileUpdateChecker/, content)
+    end
+  end
 end

railties/test/isolation/abstract_unit.rb

@@ -154,8 +154,6 @@ module TestHelpers
         config.action_controller.allow_forgery_protection = false
         config.log_level = :info
       RUBY
-
-      remove_from_env_config('development', 'config.file_watcher.*')
     end
 
     def teardown_app
@@ -328,7 +326,6 @@ class ActiveSupport::TestCase
   include ActiveSupport::Testing::Stream
 
   self.test_order = :sorted
-
 end
 
 # Create a scope and build a fixture rails app
@@ -342,7 +339,7 @@ Module.new do
   environment = File.expand_path('../../../../load_paths', __FILE__)
   require_environment = "-r #{environment}"
 
-  `#{Gem.ruby} #{require_environment} #{RAILS_FRAMEWORK_ROOT}/railties/exe/rails new #{app_template_path} --skip-gemfile --no-rc`
+  `#{Gem.ruby} #{require_environment} #{RAILS_FRAMEWORK_ROOT}/railties/exe/rails new #{app_template_path} --skip-gemfile --skip-listen --no-rc`
   File.open("#{app_template_path}/config/boot.rb", 'w') do |f|
     f.puts "require '#{environment}'"
     f.puts "require 'rails/all'"