Convert ActionCable javascript to ES2015 modules with modern build environment

We've replaced the sprockets `//= require` directives with ES2015
imports. As a result, the ActionCable javascript can now be compiled
with rollup (like ActiveStorage already is).

- Rename action_cable/index.js.erb -> action_cable/index.js

- Add rake task to generate a javascript module of the ActionCable::INTERNAL ruby hash

  This will allow us to get rid of ERB from the actioncable javascript,
  since it is only used to interpolate ActionCable::INTERNAL.to_json.

- Import INTERNAL directly in ActionCable Connection module

  This is necessary to remove a load-order dependency conflict in the
  rollup-compiled build. Using ActionCable.INTERNAL would result in a
  runtime error:
  ```
  TypeError: Cannot read property 'INTERNAL' of undefined
  ```
  because ActionCable.INTERNAL is not set before the Connection module
  is executed.

  All other ActionCable.* references are executed inside of the body of a
  function, so there is no load-order dependency there.

- Add eslint and eslint-plugin-import devDependencies to actioncable

  These will be used to add a linting setup to actioncable like the one
  in activestorage.

- Add .eslintrc to actioncable

  This lint configuration was copied from activestorage

- Add lint script to actioncable

  This is the same as the lint script in activestorage

- Add babel-core, babel-plugin-external-helpers, and babel-preset-env devDependencies to actioncable

  These will be used to add ES2015 transpilation support to actioncable
  like we have in activestorage.

- Add .babelrc to actioncable

  This configuration was copied from activestorage

- Enable loose mode in ActionCable's babel config

  This generates a smaller bundle when compiled

- Add rollup devDependencies to actioncable

  These will be used to add a modern build pipeline to actioncable like
  the one in activestorage.

- Add rollup config to actioncable

  This is essentially the same as the rollup config from activestorage

- Add prebuild and build scripts to actioncable package

  These scripts were copied from activestorage

- Invoke code generation task as part of actioncable's prebuild script

  This will guarantee that the action_cable/internal.js module is
  available at build time (which is important, because two other modules
  now depend on it).

- Update actioncable package to reference the rollup-compiled files

  Now that we have a fully functional rollup pipeline in actioncable, we
  can use the compiled output in our npm package.

- Remove build section from ActionCable blade config

  Now that rollup is responsible for building ActionCable, we can remove
  that responsibility from Blade.

- Remove assets:compile and assets:verify tasks from ActionCable

  Now that we've added a compiled ActionCable bundle to version control,
  we don't need to compile and verify it at publish-time.

  (We're following the pattern set in ActiveStorage.)

- Include compiled ActionCable javascript bundle in published gem

  This is necessary to maintain support for depending on the ActionCable
  javascript through the Sprockets asset pipeline.

- Add compiled ActionCable bundle to version control

  This mirrors what we do in ActiveStorage, and allows ActionCable to
  continue to be consumed via the sprockets-based asset pipeline when
  using a git source instead of a published version of the gem.

1 files changed, 7 insertions, 36 deletions

diff --git a/actioncable/Rakefile b/actioncable/Rakefile
index fb75d14363..52c86eb5d7 100644
--- a/actioncable/Rakefile
+++ b/actioncable/Rakefile
@@ -7,7 +7,7 @@ require "action_cable"
 
 task default: :test
 
-task package: %w( assets:compile assets:verify )
+task :package
 
 Rake::TestTask.new do |t|
   t.libs << "test"
@@ -35,42 +35,13 @@ namespace :test do
 end
 
 namespace :assets do
-  desc "Compile Action Cable assets"
-  task :compile do
-    require "blade"
-    require "sprockets"
-    require "sprockets/export"
-    Blade.build
-  end
-
-  desc "Verify compiled Action Cable assets"
-  task :verify do
-    file = "lib/assets/compiled/action_cable.js"
-    pathname = Pathname.new("#{__dir__}/#{file}")
-
-    print "[verify] #{file} exists "
-    if pathname.exist?
-      puts "[OK]"
-    else
-      $stderr.puts "[FAIL]"
-      fail
-    end
+  desc "Generate ActionCable::INTERNAL JS module"
+  task :codegen do
+    require "json"
+    require "action_cable"
 
-    print "[verify] #{file} is a UMD module "
-    if /module\.exports.*define\.amd/m.match?(pathname.read)
-      puts "[OK]"
-    else
-      $stderr.puts "[FAIL]"
-      fail
-    end
-
-    print "[verify] #{__dir__} can be required as a module "
-    _, stderr, status = Open3.capture3("node", "--print", "window = {}; require('#{__dir__}');")
-    if status.success?
-      puts "[OK]"
-    else
-      $stderr.puts "[FAIL]\n#{stderr}"
-      fail
+    File.open(File.join(__dir__, "app/javascript/action_cable/internal.js").to_s, "w+") do |file|
+      file.write("export default #{JSON.generate(ActionCable::INTERNAL)}")
     end
   end
 end