generate config/spring.rb in new applications [closes #18874]

railties/CHANGELOG.md

+*   The application generator writes a new file `config/spring.rb`, which tells
+    Spring to watch additional common files.
+
+    *Xavier Noria*
+
 *   The tasks in the rails task namespace is deprecated in favor of app namespace.
     (e.g. `rails:update` and `rails:template` tasks is renamed to `app:update` and `app:template`.)
 

railties/lib/rails/generators/rails/app/app_generator.rb

@@ -80,6 +80,7 @@ def config
         template "secrets.yml"
         template "cable.yml" unless options[:skip_action_cable]
         template "puma.rb"   unless options[:skip_puma]
+        template "spring.rb" if spring_install?
 
         directory "environments"
         directory "initializers"

railties/lib/rails/generators/rails/app/templates/config/spring.rb

+%w(
+  .ruby-version
+  .rbenv-vars
+  tmp/restart.txt
+  tmp/caching-dev.txt
+).each { |path| Spring.watch(path) }

railties/test/generators/app_generator_test.rb

@@ -28,6 +28,7 @@
   config/locales
   config/cable.yml
   config/puma.rb
+  config/spring.rb
   db
   lib
   lib/tasks
@@ -681,6 +682,7 @@ def test_spring_no_fork
   def test_skip_spring
     run_generator [destination_root, "--skip-spring"]
 
+    assert_no_file 'config/spring.rb'
     assert_file "Gemfile" do |content|
       assert_no_match(/spring/, content)
     end