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

3 files changed, 73 insertions, 4 deletions

diff --git a/activestorage/test/dummy/app/assets/config/manifest.js b/activestorage/test/dummy/app/assets/config/manifest.js
index a8adebe722..bb109908b2 100644
--- a/activestorage/test/dummy/app/assets/config/manifest.js
+++ b/activestorage/test/dummy/app/assets/config/manifest.js
@@ -1,5 +1,3 @@
 
 //= link_tree ../images
-//= link_directory ../javascripts .js
 //= link_directory ../stylesheets .css
-//= link active_storage_manifest.js
diff --git a/activestorage/test/dummy/config/environments/production.rb b/activestorage/test/dummy/config/environments/production.rb
index 34ac3bc561..be7f5b80d4 100644
--- a/activestorage/test/dummy/config/environments/production.rb
+++ b/activestorage/test/dummy/config/environments/production.rb
@@ -25,8 +25,7 @@ Rails.application.configure do
   # Apache or NGINX already handles this.
   config.public_file_server.enabled = ENV["RAILS_SERVE_STATIC_FILES"].present?
 
-  # Compress JavaScripts and CSS.
-  config.assets.js_compressor = :uglifier
+  # Compress CSS using a preprocessor.
   # config.assets.css_compressor = :sass
 
   # Do not fallback to assets pipeline if a precompiled asset is missed.
diff --git a/activestorage/test/dummy/config/webpacker.yml b/activestorage/test/dummy/config/webpacker.yml
new file mode 100644
index 0000000000..c1515a2e95
--- /dev/null
+++ b/activestorage/test/dummy/config/webpacker.yml
@@ -0,0 +1,72 @@
+# Note: You must restart bin/webpack-dev-server for changes to take effect
+
+default: &default
+  source_path: app/javascript
+  source_entry_path: packs
+  public_output_path: packs
+  cache_path: tmp/cache/webpacker
+  check_yarn_integrity: false
+
+  # Additional paths webpack should lookup modules
+  # ['app/assets', 'engine/foo/app/assets']
+  resolved_paths: []
+
+  # Reload manifest.json on all requests so we reload latest compiled packs
+  cache_manifest: false
+
+  extensions:
+    - .js
+    - .sass
+    - .scss
+    - .css
+    - .module.sass
+    - .module.scss
+    - .module.css
+    - .png
+    - .svg
+    - .gif
+    - .jpeg
+    - .jpg
+
+development:
+  <<: *default
+  compile: true
+
+  # Verifies that versions and hashed value of the package contents in the project's package.json
+  check_yarn_integrity: true
+
+  # Reference: https://webpack.js.org/configuration/dev-server/
+  dev_server:
+    https: false
+    host: localhost
+    port: 3035
+    public: localhost:3035
+    hmr: false
+    # Inline should be set to true if using HMR
+    inline: true
+    overlay: true
+    compress: true
+    disable_host_check: true
+    use_local_ip: false
+    quiet: false
+    headers:
+      'Access-Control-Allow-Origin': '*'
+    watch_options:
+      ignored: /node_modules/
+
+
+test:
+  <<: *default
+  compile: true
+
+  # Compile test packs to a separate directory
+  public_output_path: packs-test
+
+production:
+  <<: *default
+
+  # Production depends on precompilation of packs prior to booting for performance.
+  compile: false
+
+  # Cache manifest.json for performance
+  cache_manifest: true