Make Webpacker the default JavaScript compiler for Rails 6 (#33079)

* Use Webpacker by default on new apps

* Stop including coffee-rails by default

* Drop using a js_compressor by default

* Drop extra test for coffeescript inclusion by default

* Stick with skip_javascript to signify skipping webpack

* Don't install a JS runtime by default any more

* app/javascript will be the new default directory for JS

* Make it clear that this is just for configuring the default Webpack framework setup now

* Start using the Webpack tag in the default layout

* Irrelevant test

* jQuery is long gone

* Stop having asset pipeline compile default application.js

* Add rails-ujs by default to the Webpack setup

* Add Active Storage JavaScript to application.js pack by default

* Consistent quoting

* Add Turbolinks to default pack

* Add Action Cable to default pack

Need some work on how to set the global consumer that channels will
work with. @javan?

* Require all channels by default and use a separate consumer stub

* Channel generator now targets Webpack style

* Update task docs to match new generator style

* Use uniform import style

* Drop the JS assets generator

It was barely helpful as it was. It’s no longer helpful in a Webpacked
world. Sayonara!

* Add app/javascript to the stats directories

* Simpler import style

Which match the other imports.

* Address test failures from dropping JS compilation (and compression)

* webpacker-default: Modify `AssetsGeneratorTest`

Before:

```
$ bin/test test/generators/assets_generator_test.rb
Run options: --seed 46201

F

Failure:
AssetsGeneratorTest#test_assets [/Users/ttanimichi/ghq/github.com/ttanimichi/rails/railties/test/generators/assets_generator_test.rb:12]:
Expected file "app/assets/javascripts/posts.js" to exist, but does not

bin/test /Users/ttanimichi/ghq/github.com/ttanimichi/rails/railties/test/generators/assets_generator_test.rb:10

.

Finished in 0.031343s, 63.8101 runs/s, 95.7152 assertions/s.
2 runs, 3 assertions, 1 failures, 0 errors, 0 skips
```

After:

```
$ bin/test test/generators/assets_generator_test.rb
Run options: --seed 43571

..

Finished in 0.030370s, 65.8545 runs/s, 65.8545 assertions/s.
2 runs, 2 assertions, 0 failures, 0 errors, 0 skips
```

* webpacker-default: Modify `ChannelGeneratorTest`

Before:

```
$ bin/test test/generators/channel_generator_test.rb
Run options: --seed 8986

.F

Failure:
ChannelGeneratorTest#test_channel_with_multiple_actions_is_created [/Users/ttanimichi/ghq/github.com/ttanimichi/rails/railties/test/generators/channel_generator_test.rb:43]:
Expected file "app/assets/javascripts/channels/chat.js" to exist, but does not

bin/test /Users/ttanimichi/ghq/github.com/ttanimichi/rails/railties/test/generators/channel_generator_test.rb:34

.F

Failure:
ChannelGeneratorTest#test_channel_is_created [/Users/ttanimichi/ghq/github.com/ttanimichi/rails/railties/test/generators/channel_generator_test.rb:29]:
Expected file "app/assets/javascripts/channels/chat.js" to exist, but does not

bin/test /Users/ttanimichi/ghq/github.com/ttanimichi/rails/railties/test/generators/channel_generator_test.rb:22

E

Error:
ChannelGeneratorTest#test_cable_js_is_created_if_not_present_already:
Errno::ENOENT: No such file or directory @ apply2files - /Users/ttanimichi/ghq/github.com/ttanimichi/rails/railties/test/fixtures/tmp/app/assets/javascripts/cable.js

bin/test /Users/ttanimichi/ghq/github.com/ttanimichi/rails/railties/test/generators/channel_generator_test.rb:60

F

Failure:
ChannelGeneratorTest#test_channel_suffix_is_not_duplicated [/Users/ttanimichi/ghq/github.com/ttanimichi/rails/railties/test/generators/channel_generator_test.rb:87]:
Expected file "app/assets/javascripts/channels/chat.js" to exist, but does not

bin/test /Users/ttanimichi/ghq/github.com/ttanimichi/rails/railties/test/generators/channel_generator_test.rb:80

F

Failure:
ChannelGeneratorTest#test_channel_on_revoke [/Users/ttanimichi/ghq/github.com/ttanimichi/rails/railties/test/generators/channel_generator_test.rb:77]:
Expected file "app/assets/javascripts/cable.js" to exist, but does not

bin/test /Users/ttanimichi/ghq/github.com/ttanimichi/rails/railties/test/generators/channel_generator_test.rb:68

Finished in 0.064384s, 108.7227 runs/s, 481.4861 assertions/s.
7 runs, 31 assertions, 4 failures, 1 errors, 0 skips
```

After:

```
$ bin/test test/generators/channel_generator_test.rb
Run options: --seed 44857

.......

Finished in 0.060243s, 116.1961 runs/s, 697.1764 assertions/s.
7 runs, 42 assertions, 0 failures, 0 errors, 0 skips
```

* Fix shared generator tests.

* webpacker-default: Modify `ControllerGeneratorTest`

The JS assets generator was dropped. ref. https://github.com/rails/rails/commit/46215b179483d3e4d264555f5a4952f43eb8142a

* Revert "Simpler import style". It's currently failing with an error of "TypeError: undefined is not an object (evaluating '__WEBPACK_IMPORTED_MODULE_2_activestorage___default.a.start')". Waiting for @javan to have a look.

This reverts commit 5d3ebb71059f635d3756cbda4ab9752027e09256.

* require webpacker in test app

* Add webpacker without making the build hang/timeout. (#33640)

* use yarn workspaces to allow for installing unreleased packages and only generate js/bootsnap when required

* no longer need to have webpacker in env templates as webpacker moved this config to yml file

* Fix rubocop violation

* Got the test passing for the running scaffold

* update expected lines of code

* update middleware tests to account for webpacker

* disable js in plugins be default to get the tests passing (#34009)

* clear codeclimate report issues

* Anything newer than currently released is good

* Use Webpacker development version during development of Rails

* Edge should get development webpacker as well

* Add changelog entry for Webpacker change

13 files changed, 86 insertions, 163 deletions

diff --git a/railties/test/application/assets_test.rb b/railties/test/application/assets_test.rb
index 4ca6d02b85..46ee0d670e 100644
--- a/railties/test/application/assets_test.rb
+++ b/railties/test/application/assets_test.rb
@@ -68,20 +68,6 @@ module ApplicationTests
       assert_equal 'a = "/assets/rails.png";', last_response.body.strip
     end
 
-    test "assets do not require compressors until it is used" do
-      app_file "app/assets/javascripts/demo.js.erb", "<%= :alert %>();"
-      add_to_env_config "production", "config.assets.compile = true"
-      add_to_env_config "production", "config.assets.precompile = []"
-
-      # Load app env
-      app "production"
-
-      assert_not defined?(Uglifier)
-      get "/assets/demo.js"
-      assert_match "alert()", last_response.body
-      assert defined?(Uglifier)
-    end
-
     test "precompile creates the file, gives it the original asset's content and run in production as default" do
       app_file "app/assets/config/manifest.js", "//= link_tree ../javascripts"
       app_file "app/assets/javascripts/application.js", "alert();"
@@ -443,13 +429,13 @@ module ApplicationTests
     end
 
     test "digested assets are not mistakenly removed" do
-      app_file "app/assets/application.js", "alert();"
+      app_file "app/assets/application.css", "div { font-weight: bold }"
       add_to_config "config.assets.compile = true"
 
       precompile!
 
-      files = Dir["#{app_path}/public/assets/application-*.js"]
-      assert_equal 1, files.length, "Expected digested application.js asset to be generated, but none found"
+      files = Dir["#{app_path}/public/assets/application-*.css"]
+      assert_equal 1, files.length, "Expected digested application.css asset to be generated, but none found"
     end
 
     test "digested assets are removed from configured path" do
diff --git a/railties/test/application/middleware_test.rb b/railties/test/application/middleware_test.rb
index 5efaf841d4..631f5bac7f 100644
--- a/railties/test/application/middleware_test.rb
+++ b/railties/test/application/middleware_test.rb
@@ -25,6 +25,7 @@ module ApplicationTests
       boot!
 
       assert_equal [
+        "Webpacker::DevServerProxy",
         "Rack::Sendfile",
         "ActionDispatch::Static",
         "ActionDispatch::Executor",
@@ -56,6 +57,7 @@ module ApplicationTests
       boot!
 
       assert_equal [
+        "Webpacker::DevServerProxy",
         "Rack::Sendfile",
         "ActionDispatch::Static",
         "ActionDispatch::Executor",
@@ -138,7 +140,7 @@ module ApplicationTests
       add_to_config "config.ssl_options = { redirect: { host: 'example.com' } }"
       boot!
 
-      assert_equal [{ redirect: { host: "example.com" } }], Rails.application.middleware.first.args
+      assert_equal [{ redirect: { host: "example.com" } }], Rails.application.middleware[1].args
     end
 
     test "removing Active Record omits its middleware" do
@@ -222,30 +224,31 @@ module ApplicationTests
     test "insert middleware after" do
       add_to_config "config.middleware.insert_after Rack::Sendfile, Rack::Config"
       boot!
-      assert_equal "Rack::Config", middleware.second
+      assert_equal "Rack::Config", middleware.third
     end
 
     test "unshift middleware" do
       add_to_config "config.middleware.unshift Rack::Config"
       boot!
-      assert_equal "Rack::Config", middleware.first
+      assert_equal "Rack::Config", middleware.second
     end
 
     test "Rails.cache does not respond to middleware" do
       add_to_config "config.cache_store = :memory_store"
       boot!
-      assert_equal "Rack::Runtime", middleware.fourth
+      assert_equal "Rack::Runtime", middleware.fifth
     end
 
     test "Rails.cache does respond to middleware" do
       boot!
-      assert_equal "Rack::Runtime", middleware.fifth
+      assert_equal "ActiveSupport::Cache::Strategy::LocalCache", middleware.fifth
+      assert_equal "Rack::Runtime", middleware[5]
     end
 
     test "insert middleware before" do
       add_to_config "config.middleware.insert_before Rack::Sendfile, Rack::Config"
       boot!
-      assert_equal "Rack::Config", middleware.first
+      assert_equal "Rack::Config", middleware.second
     end
 
     test "can't change middleware after it's built" do
diff --git a/railties/test/application/rake_test.rb b/railties/test/application/rake_test.rb
index 1522a2bbc5..a0cdae898b 100644
--- a/railties/test/application/rake_test.rb
+++ b/railties/test/application/rake_test.rb
@@ -118,7 +118,7 @@ module ApplicationTests
     end
 
     def test_code_statistics_sanity
-      assert_match "Code LOC: 25     Test LOC: 0     Code to Test Ratio: 1:0.0",
+      assert_match "Code LOC: 32     Test LOC: 0     Code to Test Ratio: 1:0.0",
         rails("stats")
     end
 
@@ -190,6 +190,7 @@ module ApplicationTests
       rails "generate", "model", "Cart"
       rails "generate", "scaffold", "LineItems", "product:references", "cart:belongs_to"
       with_rails_env("test") { rails("db:migrate") }
+      rails("webpacker:compile")
       output = rails("test")
 
       assert_match(/7 runs, 9 assertions, 0 failures, 0 errors/, output)
diff --git a/railties/test/engine/commands_test.rb b/railties/test/engine/commands_test.rb
index 48c93af80c..0e5167578d 100644
--- a/railties/test/engine/commands_test.rb
+++ b/railties/test/engine/commands_test.rb
@@ -24,7 +24,7 @@ class Rails::Engine::CommandsTest < ActiveSupport::TestCase
 
   def test_runner_command_work_inside_engine
     output = capture(:stdout) do
-      Dir.chdir(plugin_path) { system("bin/rails runner 'puts Rails.env'") }
+      Dir.chdir(plugin_path) { system({ "SKIP_REQUIRE_WEBPACKER" => "true" }, "bin/rails runner 'puts Rails.env'") }
     end
 
     assert_equal "test", output.strip
@@ -67,6 +67,7 @@ class Rails::Engine::CommandsTest < ActiveSupport::TestCase
 
     def spawn_command(command, fd)
       Process.spawn(
+        { "SKIP_REQUIRE_WEBPACKER" => "true" },
         "#{plugin_path}/bin/rails #{command}",
         in: fd, out: fd, err: fd
       )
diff --git a/railties/test/generators/api_app_generator_test.rb b/railties/test/generators/api_app_generator_test.rb
index c2540f4091..4f2894e71e 100644
--- a/railties/test/generators/api_app_generator_test.rb
+++ b/railties/test/generators/api_app_generator_test.rb
@@ -40,7 +40,6 @@ class ApiAppGeneratorTest < Rails::Generators::TestCase
     end
 
     assert_file "Gemfile" do |content|
-      assert_no_match(/gem 'coffee-rails'/, content)
       assert_no_match(/gem 'sass-rails'/, content)
       assert_no_match(/gem 'web-console'/, content)
       assert_no_match(/gem 'capybara'/, content)
diff --git a/railties/test/generators/app_generator_test.rb b/railties/test/generators/app_generator_test.rb
index 1169633244..48e8b7123f 100644
--- a/railties/test/generators/app_generator_test.rb
+++ b/railties/test/generators/app_generator_test.rb
@@ -13,10 +13,9 @@ DEFAULT_APP_FILES = %w(
   config.ru
   app/assets/config/manifest.js
   app/assets/images
-  app/assets/javascripts
-  app/assets/javascripts/application.js
-  app/assets/javascripts/cable.js
-  app/assets/javascripts/channels
+  app/javascript
+  app/javascript/channels
+  app/javascript/packs/application.js
   app/assets/stylesheets
   app/assets/stylesheets/application.css
   app/channels/application_cable/channel.rb
@@ -114,12 +113,12 @@ class AppGeneratorTest < Rails::Generators::TestCase
   end
 
   def test_assets
-    run_generator
+    run_generator [destination_root, "--no-skip-javascript"]
 
     assert_file("app/views/layouts/application.html.erb", /stylesheet_link_tag\s+'application', media: 'all', 'data-turbolinks-track': 'reload'/)
-    assert_file("app/views/layouts/application.html.erb", /javascript_include_tag\s+'application', 'data-turbolinks-track': 'reload'/)
+    assert_file("app/views/layouts/application.html.erb", /javascript_pack_tag\s+'application', 'data-turbolinks-track': 'reload'/)
     assert_file("app/assets/stylesheets/application.css")
-    assert_file("app/assets/javascripts/application.js")
+    assert_file("app/javascript/packs/application.js")
   end
 
   def test_application_job_file_present
@@ -215,7 +214,8 @@ class AppGeneratorTest < Rails::Generators::TestCase
 
   def test_new_application_load_defaults
     app_root = File.join(destination_root, "myfirstapp")
-    run_generator [app_root]
+    run_generator [app_root, "--no-skip-javascript"]
+
     output = nil
 
     assert_file "#{app_root}/config/application.rb", /\s+config\.load_defaults #{Rails::VERSION::STRING.to_f}/
@@ -559,7 +559,6 @@ class AppGeneratorTest < Rails::Generators::TestCase
     run_generator
 
     assert_gem "sass-rails"
-    assert_gem "uglifier"
   end
 
   def test_action_cable_redis_gems
@@ -601,24 +600,6 @@ class AppGeneratorTest < Rails::Generators::TestCase
     end
   end
 
-  def test_inclusion_of_javascript_runtime
-    run_generator
-    if defined?(JRUBY_VERSION)
-      assert_gem "therubyrhino"
-    elsif RUBY_PLATFORM =~ /mingw|mswin/
-      assert_gem "duktape"
-    else
-      assert_file "Gemfile", /# gem 'mini_racer', platforms: :ruby/
-    end
-  end
-
-  def test_rails_ujs_is_the_default_ujs_library
-    run_generator
-    assert_file "app/assets/javascripts/application.js" do |contents|
-      assert_match %r{^//= require rails-ujs}, contents
-    end
-  end
-
   def test_javascript_is_skipped_if_required
     run_generator [destination_root, "--skip-javascript"]
 
@@ -628,22 +609,6 @@ class AppGeneratorTest < Rails::Generators::TestCase
       assert_match(/stylesheet_link_tag\s+'application', media: 'all' %>/, contents)
       assert_no_match(/javascript_include_tag\s+'application' \%>/, contents)
     end
-
-    assert_no_gem "coffee-rails"
-    assert_no_gem "uglifier"
-
-    assert_file "config/environments/production.rb" do |content|
-      assert_no_match(/config\.assets\.js_compressor = :uglifier/, content)
-    end
-  end
-
-  def test_coffeescript_is_skipped_if_required
-    run_generator [destination_root, "--skip-coffee"]
-
-    assert_file "Gemfile" do |content|
-      assert_no_match(/coffee-rails/, content)
-      assert_match(/uglifier/, content)
-    end
   end
 
   def test_inclusion_of_jbuilder
@@ -819,22 +784,22 @@ class AppGeneratorTest < Rails::Generators::TestCase
     assert_no_gem "spring"
   end
 
-  def test_webpack_option
+  def test_skip_javascript_option
     command_check = -> command, *_ do
       @called ||= 0
       if command == "webpacker:install"
         @called += 1
-        assert_equal 1, @called, "webpacker:install expected to be called once, but was called #{@called} times."
+        assert_equal 0, @called, "webpacker:install expected not to be called once, but was called #{@called} times."
       end
     end
 
-    generator([destination_root], webpack: "webpack").stub(:rails_command, command_check) do
+    generator([destination_root], skip_javascript: true).stub(:rails_command, command_check) do
       generator.stub :bundle_command, nil do
         quietly { generator.invoke_all }
       end
     end
 
-    assert_gem "webpacker"
+    assert_no_gem "webpacker"
   end
 
   def test_webpack_option_with_js_framework
@@ -856,22 +821,24 @@ class AppGeneratorTest < Rails::Generators::TestCase
         quietly { generator.invoke_all }
       end
     end
+
+    assert_gem "webpacker"
   end
 
   def test_generator_if_skip_turbolinks_is_given
-    run_generator [destination_root, "--skip-turbolinks"]
+    run_generator [destination_root, "--skip-turbolinks", "--no-skip-javascript"]
 
     assert_no_gem "turbolinks"
     assert_file "app/views/layouts/application.html.erb" do |content|
       assert_no_match(/data-turbolinks-track/, content)
     end
-    assert_file "app/assets/javascripts/application.js" do |content|
+    assert_file "app/javascript/packs/application.js" do |content|
       assert_no_match(/turbolinks/, content)
     end
   end
 
   def test_bootsnap
-    run_generator
+    run_generator [destination_root, "--no-skip-bootsnap"]
 
     unless defined?(JRUBY_VERSION)
       assert_gem "bootsnap"
@@ -972,7 +939,7 @@ class AppGeneratorTest < Rails::Generators::TestCase
       template
     end
 
-    sequence = ["git init", "install", "binstubs bundler", "exec spring binstub --all", "echo ran after_bundle"]
+    sequence = ["git init", "install", "binstubs bundler", "exec spring binstub --all", "webpacker:install", "echo ran after_bundle"]
     @sequence_step ||= 0
     ensure_bundler_first = -> command, options = nil do
       assert_equal sequence[@sequence_step], command, "commands should be called in sequence #{sequence}"
@@ -989,7 +956,7 @@ class AppGeneratorTest < Rails::Generators::TestCase
       end
     end
 
-    assert_equal 5, @sequence_step
+    assert_equal 6, @sequence_step
   end
 
   def test_gitignore
diff --git a/railties/test/generators/assets_generator_test.rb b/railties/test/generators/assets_generator_test.rb
index 3cec41dbf8..83d2429acf 100644
--- a/railties/test/generators/assets_generator_test.rb
+++ b/railties/test/generators/assets_generator_test.rb
@@ -9,13 +9,11 @@ class AssetsGeneratorTest < Rails::Generators::TestCase
 
   def test_assets
     run_generator
-    assert_file "app/assets/javascripts/posts.js"
     assert_file "app/assets/stylesheets/posts.css"
   end
 
   def test_skipping_assets
-    run_generator ["posts", "--no-stylesheets", "--no-javascripts"]
-    assert_no_file "app/assets/javascripts/posts.js"
+    run_generator ["posts", "--no-stylesheets"]
     assert_no_file "app/assets/stylesheets/posts.css"
   end
 end
diff --git a/railties/test/generators/channel_generator_test.rb b/railties/test/generators/channel_generator_test.rb
index e543cc11b8..265d7c9618 100644
--- a/railties/test/generators/channel_generator_test.rb
+++ b/railties/test/generators/channel_generator_test.rb
@@ -26,8 +26,8 @@ class ChannelGeneratorTest < Rails::Generators::TestCase
       assert_match(/class ChatChannel < ApplicationCable::Channel/, channel)
     end
 
-    assert_file "app/assets/javascripts/channels/chat.js" do |channel|
-      assert_match(/App\.chat = App\.cable\.subscriptions\.create\("ChatChannel/, channel)
+    assert_file "app/javascript/channels/chat_channel.js" do |channel|
+      assert_match(/import consumer from "\.\/consumer"\s+consumer\.subscriptions\.create\("ChatChannel/, channel)
     end
   end
 
@@ -40,8 +40,8 @@ class ChannelGeneratorTest < Rails::Generators::TestCase
       assert_match(/def mute/, channel)
     end
 
-    assert_file "app/assets/javascripts/channels/chat.js" do |channel|
-      assert_match(/App\.chat = App\.cable\.subscriptions\.create\("ChatChannel/, channel)
+    assert_file "app/javascript/channels/chat_channel.js" do |channel|
+      assert_match(/import consumer from "\.\/consumer"\s+consumer\.subscriptions\.create\("ChatChannel/, channel)
       assert_match(/,\n\n  speak/, channel)
       assert_match(/,\n\n  mute: function\(\) \{\n    return this\.perform\('mute'\);\n  \}\n\}\);/, channel)
     end
@@ -54,15 +54,17 @@ class ChannelGeneratorTest < Rails::Generators::TestCase
       assert_match(/class ChatChannel < ApplicationCable::Channel/, channel)
     end
 
-    assert_no_file "app/assets/javascripts/channels/chat.js"
+    assert_no_file "app/javascript/channels/chat_channel.js"
   end
 
   def test_cable_js_is_created_if_not_present_already
     run_generator ["chat"]
-    FileUtils.rm("#{destination_root}/app/assets/javascripts/cable.js")
+    FileUtils.rm("#{destination_root}/app/javascript/channels/index.js")
+    FileUtils.rm("#{destination_root}/app/javascript/channels/consumer.js")
     run_generator ["camp"]
 
-    assert_file "app/assets/javascripts/cable.js"
+    assert_file "app/javascript/channels/index.js"
+    assert_file "app/javascript/channels/consumer.js"
   end
 
   def test_channel_on_revoke
@@ -74,7 +76,8 @@ class ChannelGeneratorTest < Rails::Generators::TestCase
 
     assert_file "app/channels/application_cable/channel.rb"
     assert_file "app/channels/application_cable/connection.rb"
-    assert_file "app/assets/javascripts/cable.js"
+    assert_file "app/javascript/channels/index.js"
+    assert_file "app/javascript/channels/consumer.js"
   end
 
   def test_channel_suffix_is_not_duplicated
@@ -84,6 +87,6 @@ class ChannelGeneratorTest < Rails::Generators::TestCase
     assert_file "app/channels/chat_channel.rb"
 
     assert_no_file "app/assets/javascripts/channels/chat_channel.js"
-    assert_file "app/assets/javascripts/channels/chat.js"
+    assert_file "app/javascript/channels/chat_channel.js"
   end
 end
diff --git a/railties/test/generators/controller_generator_test.rb b/railties/test/generators/controller_generator_test.rb
index 021004c9b8..adef56255a 100644
--- a/railties/test/generators/controller_generator_test.rb
+++ b/railties/test/generators/controller_generator_test.rb
@@ -39,13 +39,11 @@ class ControllerGeneratorTest < Rails::Generators::TestCase
 
   def test_invokes_assets
     run_generator
-    assert_file "app/assets/javascripts/account.js"
     assert_file "app/assets/stylesheets/account.css"
   end
 
   def test_does_not_invoke_assets_if_required
     run_generator ["account", "--skip-assets"]
-    assert_no_file "app/assets/javascripts/account.js"
     assert_no_file "app/assets/stylesheets/account.css"
   end
 
@@ -133,7 +131,6 @@ class ControllerGeneratorTest < Rails::Generators::TestCase
     assert_file "app/helpers/account_helper.rb"
 
     assert_no_file "app/assets/javascripts/account_controller.js"
-    assert_file "app/assets/javascripts/account.js"
 
     assert_no_file "app/assets/stylesheets/account_controller.css"
     assert_file "app/assets/stylesheets/account.css"
diff --git a/railties/test/generators/plugin_generator_test.rb b/railties/test/generators/plugin_generator_test.rb
index 468a9c9e89..66286fc554 100644
--- a/railties/test/generators/plugin_generator_test.rb
+++ b/railties/test/generators/plugin_generator_test.rb
@@ -140,10 +140,6 @@ class PluginGeneratorTest < Rails::Generators::TestCase
     run_generator
 
     assert_file "test/dummy/app/assets/stylesheets/application.css"
-
-    assert_file "test/dummy/app/assets/javascripts/application.js" do |contents|
-      assert_no_match(/jquery/, contents)
-    end
   end
 
   def test_ensure_that_plugin_options_are_not_passed_to_app_generator
@@ -210,28 +206,10 @@ class PluginGeneratorTest < Rails::Generators::TestCase
     assert_no_file "#{destination_root}/Gemfile.lock"
   end
 
-  def test_skipping_javascripts_without_mountable_option
-    run_generator
-    assert_no_file "app/assets/javascripts/bukkits/application.js"
-  end
-
-  def test_javascripts_generation
-    run_generator [destination_root, "--mountable"]
-    assert_file "app/assets/javascripts/bukkits/application.js" do |content|
-      assert_match "//= require rails-ujs", content
-      assert_match "//= require activestorage", content
-      assert_match "//= require_tree .", content
-    end
-    assert_file "app/views/layouts/bukkits/application.html.erb" do |content|
-      assert_match "javascript_include_tag", content
-    end
-  end
-
-  def test_skip_javascripts
+  def test_skip_javascript
     run_generator [destination_root, "--skip-javascript", "--mountable"]
-    assert_no_file "app/assets/javascripts/bukkits/application.js"
     assert_file "app/views/layouts/bukkits/application.html.erb" do |content|
-      assert_no_match "javascript_include_tag", content
+      assert_no_match "javascript_pack_tag", content
     end
   end
 
@@ -264,7 +242,6 @@ class PluginGeneratorTest < Rails::Generators::TestCase
 
   def test_creating_engine_in_full_mode
     run_generator [destination_root, "--full"]
-    assert_file "app/assets/javascripts/bukkits"
     assert_file "app/assets/stylesheets/bukkits"
     assert_file "app/assets/images/bukkits"
     assert_file "app/models"
@@ -280,7 +257,7 @@ class PluginGeneratorTest < Rails::Generators::TestCase
 
   def test_creating_engine_with_hyphenated_name_in_full_mode
     run_generator [File.join(destination_root, "hyphenated-name"), "--full"]
-    assert_file "hyphenated-name/app/assets/javascripts/hyphenated/name"
+    assert_no_file "hyphenated-name/app/assets/javascripts/hyphenated/name"
     assert_file "hyphenated-name/app/assets/stylesheets/hyphenated/name"
     assert_file "hyphenated-name/app/assets/images/hyphenated/name"
     assert_file "hyphenated-name/app/models"
@@ -297,7 +274,7 @@ class PluginGeneratorTest < Rails::Generators::TestCase
 
   def test_creating_engine_with_hyphenated_and_underscored_name_in_full_mode
     run_generator [File.join(destination_root, "my_hyphenated-name"), "--full"]
-    assert_file "my_hyphenated-name/app/assets/javascripts/my_hyphenated/name"
+    assert_no_file "my_hyphenated-name/app/assets/javascripts/my_hyphenated/name"
     assert_file "my_hyphenated-name/app/assets/stylesheets/my_hyphenated/name"
     assert_file "my_hyphenated-name/app/assets/images/my_hyphenated/name"
     assert_file "my_hyphenated-name/app/models"
@@ -318,7 +295,7 @@ class PluginGeneratorTest < Rails::Generators::TestCase
 
   def test_create_mountable_application_with_mountable_option
     run_generator [destination_root, "--mountable"]
-    assert_file "app/assets/javascripts/bukkits"
+    assert_no_file "app/assets/javascripts/bukkits"
     assert_file "app/assets/stylesheets/bukkits"
     assert_file "app/assets/images/bukkits"
     assert_file "config/routes.rb", /Bukkits::Engine\.routes\.draw do/
@@ -334,7 +311,7 @@ class PluginGeneratorTest < Rails::Generators::TestCase
       assert_match "<%= csrf_meta_tags %>", contents
       assert_match "<%= csp_meta_tag %>", contents
       assert_match(/stylesheet_link_tag\s+['"]bukkits\/application['"]/, contents)
-      assert_match(/javascript_include_tag\s+['"]bukkits\/application['"]/, contents)
+      assert_no_match(/javascript_include_tag\s+['"]bukkits\/application['"]/, contents)
       assert_match "<%= yield %>", contents
     end
     assert_file "test/test_helper.rb" do |content|
@@ -348,7 +325,7 @@ class PluginGeneratorTest < Rails::Generators::TestCase
 
   def test_create_mountable_application_with_mountable_option_and_hypenated_name
     run_generator [File.join(destination_root, "hyphenated-name"), "--mountable"]
-    assert_file "hyphenated-name/app/assets/javascripts/hyphenated/name"
+    assert_no_file "hyphenated-name/app/assets/javascripts/hyphenated/name"
     assert_file "hyphenated-name/app/assets/stylesheets/hyphenated/name"
     assert_file "hyphenated-name/app/assets/images/hyphenated/name"
     assert_file "hyphenated-name/config/routes.rb",                                          /Hyphenated::Name::Engine\.routes\.draw do/
@@ -364,13 +341,13 @@ class PluginGeneratorTest < Rails::Generators::TestCase
     assert_file "hyphenated-name/app/views/layouts/hyphenated/name/application.html.erb" do |contents|
       assert_match "<title>Hyphenated name</title>", contents
       assert_match(/stylesheet_link_tag\s+['"]hyphenated\/name\/application['"]/, contents)
-      assert_match(/javascript_include_tag\s+['"]hyphenated\/name\/application['"]/, contents)
+      assert_no_match(/javascript_include_tag\s+['"]hyphenated\/name\/application['"]/, contents)
     end
   end
 
   def test_create_mountable_application_with_mountable_option_and_hypenated_and_underscored_name
     run_generator [File.join(destination_root, "my_hyphenated-name"), "--mountable"]
-    assert_file "my_hyphenated-name/app/assets/javascripts/my_hyphenated/name"
+    assert_no_file "my_hyphenated-name/app/assets/javascripts/my_hyphenated/name"
     assert_file "my_hyphenated-name/app/assets/stylesheets/my_hyphenated/name"
     assert_file "my_hyphenated-name/app/assets/images/my_hyphenated/name"
     assert_file "my_hyphenated-name/config/routes.rb",                                             /MyHyphenated::Name::Engine\.routes\.draw do/
@@ -386,13 +363,13 @@ class PluginGeneratorTest < Rails::Generators::TestCase
     assert_file "my_hyphenated-name/app/views/layouts/my_hyphenated/name/application.html.erb" do |contents|
       assert_match "<title>My hyphenated name</title>", contents
       assert_match(/stylesheet_link_tag\s+['"]my_hyphenated\/name\/application['"]/, contents)
-      assert_match(/javascript_include_tag\s+['"]my_hyphenated\/name\/application['"]/, contents)
+      assert_no_match(/javascript_include_tag\s+['"]my_hyphenated\/name\/application['"]/, contents)
     end
   end
 
   def test_create_mountable_application_with_mountable_option_and_multiple_hypenates_in_name
     run_generator [File.join(destination_root, "deep-hyphenated-name"), "--mountable"]
-    assert_file "deep-hyphenated-name/app/assets/javascripts/deep/hyphenated/name"
+    assert_no_file "deep-hyphenated-name/app/assets/javascripts/deep/hyphenated/name"
     assert_file "deep-hyphenated-name/app/assets/stylesheets/deep/hyphenated/name"
     assert_file "deep-hyphenated-name/app/assets/images/deep/hyphenated/name"
     assert_file "deep-hyphenated-name/config/routes.rb",                                               /Deep::Hyphenated::Name::Engine\.routes\.draw do/
@@ -408,7 +385,7 @@ class PluginGeneratorTest < Rails::Generators::TestCase
     assert_file "deep-hyphenated-name/app/views/layouts/deep/hyphenated/name/application.html.erb" do |contents|
       assert_match "<title>Deep hyphenated name</title>", contents
       assert_match(/stylesheet_link_tag\s+['"]deep\/hyphenated\/name\/application['"]/, contents)
-      assert_match(/javascript_include_tag\s+['"]deep\/hyphenated\/name\/application['"]/, contents)
+      assert_no_match(/javascript_include_tag\s+['"]deep\/hyphenated\/name\/application['"]/, contents)
     end
   end
 
diff --git a/railties/test/generators/scaffold_generator_test.rb b/railties/test/generators/scaffold_generator_test.rb
index 94aab15aa9..21b5013484 100644
--- a/railties/test/generators/scaffold_generator_test.rb
+++ b/railties/test/generators/scaffold_generator_test.rb
@@ -93,7 +93,6 @@ class ScaffoldGeneratorTest < Rails::Generators::TestCase
 
     # Assets
     assert_file "app/assets/stylesheets/scaffold.css"
-    assert_file "app/assets/javascripts/product_lines.js"
     assert_file "app/assets/stylesheets/product_lines.css"
   end
 
@@ -166,7 +165,6 @@ class ScaffoldGeneratorTest < Rails::Generators::TestCase
 
     # Assets
     assert_no_file "app/assets/stylesheets/scaffold.css"
-    assert_no_file "app/assets/javascripts/product_lines.js"
     assert_no_file "app/assets/stylesheets/product_lines.css"
   end
 
@@ -222,7 +220,6 @@ class ScaffoldGeneratorTest < Rails::Generators::TestCase
 
     # Assets
     assert_file "app/assets/stylesheets/scaffold.css", /:visited/
-    assert_no_file "app/assets/javascripts/product_lines.js"
     assert_no_file "app/assets/stylesheets/product_lines.css"
   end
 
@@ -299,7 +296,6 @@ class ScaffoldGeneratorTest < Rails::Generators::TestCase
 
     # Assets
     assert_file "app/assets/stylesheets/scaffold.css", /:visited/
-    assert_file "app/assets/javascripts/admin/roles.js"
     assert_file "app/assets/stylesheets/admin/roles.css"
   end
 
@@ -335,7 +331,6 @@ class ScaffoldGeneratorTest < Rails::Generators::TestCase
 
     # Assets
     assert_file "app/assets/stylesheets/scaffold.css"
-    assert_no_file "app/assets/javascripts/admin/roles.js"
     assert_no_file "app/assets/stylesheets/admin/roles.css"
   end
 
@@ -380,28 +375,24 @@ class ScaffoldGeneratorTest < Rails::Generators::TestCase
   def test_scaffold_generator_no_assets_with_switch_no_assets
     run_generator [ "posts", "--no-assets" ]
     assert_no_file "app/assets/stylesheets/scaffold.css"
-    assert_no_file "app/assets/javascripts/posts.js"
     assert_no_file "app/assets/stylesheets/posts.css"
   end
 
   def test_scaffold_generator_no_assets_with_switch_assets_false
     run_generator [ "posts", "--assets=false" ]
     assert_no_file "app/assets/stylesheets/scaffold.css"
-    assert_no_file "app/assets/javascripts/posts.js"
     assert_no_file "app/assets/stylesheets/posts.css"
   end
 
   def test_scaffold_generator_no_scaffold_stylesheet_with_switch_no_scaffold_stylesheet
     run_generator [ "posts", "--no-scaffold-stylesheet" ]
     assert_no_file "app/assets/stylesheets/scaffold.css"
-    assert_file "app/assets/javascripts/posts.js"
     assert_file "app/assets/stylesheets/posts.css"
   end
 
   def test_scaffold_generator_no_scaffold_stylesheet_with_switch_scaffold_stylesheet_false
     run_generator [ "posts", "--scaffold-stylesheet=false" ]
     assert_no_file "app/assets/stylesheets/scaffold.css"
-    assert_file "app/assets/javascripts/posts.js"
     assert_file "app/assets/stylesheets/posts.css"
   end
 
@@ -429,17 +420,9 @@ class ScaffoldGeneratorTest < Rails::Generators::TestCase
   def test_scaffold_generator_no_stylesheets
     run_generator [ "posts", "--no-stylesheets" ]
     assert_no_file "app/assets/stylesheets/scaffold.css"
-    assert_file "app/assets/javascripts/posts.js"
     assert_no_file "app/assets/stylesheets/posts.css"
   end
 
-  def test_scaffold_generator_no_javascripts
-    run_generator [ "posts", "--no-javascripts" ]
-    assert_file "app/assets/stylesheets/scaffold.css"
-    assert_no_file "app/assets/javascripts/posts.js"
-    assert_file "app/assets/stylesheets/posts.css"
-  end
-
   def test_scaffold_generator_outputs_error_message_on_missing_attribute_type
     run_generator ["post", "title", "body:text", "author"]
 
@@ -630,7 +613,6 @@ class ScaffoldGeneratorTest < Rails::Generators::TestCase
 
       assert File.exist?("app/helpers/bukkits/users_helper.rb")
 
-      assert File.exist?("app/assets/javascripts/bukkits/users.js")
       assert File.exist?("app/assets/stylesheets/bukkits/users.css")
     end
   end
@@ -660,7 +642,6 @@ class ScaffoldGeneratorTest < Rails::Generators::TestCase
 
       assert_not File.exist?("app/helpers/bukkits/users_helper.rb")
 
-      assert_not File.exist?("app/assets/javascripts/bukkits/users.js")
       assert_not File.exist?("app/assets/stylesheets/bukkits/users.css")
     end
   end
diff --git a/railties/test/generators/shared_generator_tests.rb b/railties/test/generators/shared_generator_tests.rb
index 5a1257e5c1..521f775553 100644
--- a/railties/test/generators/shared_generator_tests.rb
+++ b/railties/test/generators/shared_generator_tests.rb
@@ -27,7 +27,7 @@ module SharedGeneratorTests
   end
 
   def test_skeleton_is_created
-    run_generator
+    run_generator [destination_root, "--no-skip-javascript"]
 
     default_files.each { |path| assert_file path }
   end
@@ -196,10 +196,12 @@ module SharedGeneratorTests
   end
 
   def test_generator_for_active_storage
-    run_generator
+    run_generator [destination_root, "--no-skip-javascript"]
 
-    assert_file "#{application_path}/app/assets/javascripts/application.js" do |content|
-      assert_match(/^\/\/= require activestorage/, content)
+    unless generator_class.name == "Rails::Generators::PluginGenerator"
+      assert_file "#{application_path}/app/javascript/packs/application.js" do |content|
+        assert_match(/^import \* as ActiveStorage from "activestorage"\nActiveStorage.start\(\)/, content)
+      end
     end
 
     assert_file "#{application_path}/config/environments/development.rb" do |content|
@@ -224,11 +226,11 @@ module SharedGeneratorTests
   end
 
   def test_generator_if_skip_active_storage_is_given
-    run_generator [destination_root, "--skip-active-storage"]
+    run_generator [destination_root, "--skip-active-storage", "--no-skip-javascript"]
 
     assert_file "#{application_path}/config/application.rb", /#\s+require\s+["']active_storage\/engine["']/
 
-    assert_file "#{application_path}/app/assets/javascripts/application.js" do |content|
+    assert_file "#{application_path}/app/javascript/packs/application.js" do |content|
       assert_no_match(/^\/\/= require activestorage/, content)
     end
 
@@ -254,12 +256,12 @@ module SharedGeneratorTests
   end
 
   def test_generator_does_not_generate_active_storage_contents_if_skip_active_record_is_given
-    run_generator [destination_root, "--skip-active-record"]
+    run_generator [destination_root, "--skip-active-record", "--no-skip-javascript"]
 
     assert_file "#{application_path}/config/application.rb", /#\s+require\s+["']active_storage\/engine["']/
 
-    assert_file "#{application_path}/app/assets/javascripts/application.js" do |content|
-      assert_no_match(/^\/\/= require activestorage/, content)
+    assert_file "#{application_path}/app/javascript/packs/application.js" do |content|
+      assert_no_match(/^import * as ActiveStorage from "activestorage"\nActiveStorage.start()/, content)
     end
 
     assert_file "#{application_path}/config/environments/development.rb" do |content|
@@ -320,8 +322,6 @@ module SharedGeneratorTests
 
     assert_file "Gemfile" do |content|
       assert_no_match(/sass-rails/, content)
-      assert_no_match(/uglifier/, content)
-      assert_no_match(/coffee-rails/, content)
     end
 
     assert_file "#{application_path}/config/environments/development.rb" do |content|
@@ -330,7 +330,6 @@ module SharedGeneratorTests
 
     assert_file "#{application_path}/config/environments/production.rb" do |content|
       assert_no_match(/config\.assets\.digest/, content)
-      assert_no_match(/config\.assets\.js_compressor/, content)
       assert_no_match(/config\.assets\.css_compressor/, content)
       assert_no_match(/config\.assets\.compile/, content)
     end
diff --git a/railties/test/isolation/abstract_unit.rb b/railties/test/isolation/abstract_unit.rb
index 2a8c6d8f97..e44f21380e 100644
--- a/railties/test/isolation/abstract_unit.rb
+++ b/railties/test/isolation/abstract_unit.rb
@@ -30,11 +30,11 @@ require "rails/secrets"
 module TestHelpers
   module Paths
     def app_template_path
-      File.join Dir.tmpdir, "app_template"
+      File.join RAILS_FRAMEWORK_ROOT, "tmp/templates/app_template"
     end
 
     def tmp_path(*args)
-      @tmp_path ||= File.realpath(Dir.mktmpdir)
+      @tmp_path ||= File.realpath(Dir.mktmpdir(nil, File.join(RAILS_FRAMEWORK_ROOT, "tmp")))
       File.join(@tmp_path, *args)
     end
 
@@ -469,17 +469,28 @@ Module.new do
 
   # Build a rails app
   FileUtils.rm_rf(app_template_path)
-  FileUtils.mkdir(app_template_path)
+  FileUtils.mkdir_p(app_template_path)
+
+  Dir.chdir "#{RAILS_FRAMEWORK_ROOT}/actionview" do
+    `yarn build`
+  end
 
   `#{Gem.ruby} #{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 'rails/all'"
   end
 
+  Dir.chdir(app_template_path) { `yarn add https://github.com/rails/webpacker.git` } # Use the latest version.
+
+  # Manually install `webpack` as bin symlinks are not created for subdependencies
+  # in workspaces. See https://github.com/yarnpkg/yarn/issues/4964
+  Dir.chdir(app_template_path) { `yarn add webpack@4.17.1 --tilde` }
+  Dir.chdir(app_template_path) { `yarn add webpack-cli` }
+
   # Fake 'Bundler.require' -- we run using the repo's Gemfile, not an
   # app-specific one: we don't want to require every gem that lists.
   contents = File.read("#{app_template_path}/config/application.rb")
-  contents.sub!(/^Bundler\.require.*/, "%w(turbolinks).each { |r| require r }")
+  contents.sub!(/^Bundler\.require.*/, "%w(turbolinks webpacker).each { |r| require r }")
   File.write("#{app_template_path}/config/application.rb", contents)
 
   require "rails"