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, 58 insertions, 0 deletions

diff --git a/actioncable/app/javascript/action_cable/index.js b/actioncable/app/javascript/action_cable/index.js
new file mode 100644
index 0000000000..eb0c4844df
--- /dev/null
+++ b/actioncable/app/javascript/action_cable/index.js
@@ -0,0 +1,58 @@
+import Connection from "./connection"
+import ConnectionMonitor from "./connection_monitor"
+import Consumer from "./consumer"
+import INTERNAL from "./internal"
+import Subscription from "./subscription"
+import Subscriptions from "./subscriptions"
+
+export default {
+  Connection,
+  ConnectionMonitor,
+  Consumer,
+  INTERNAL,
+  Subscription,
+  Subscriptions,
+  WebSocket: window.WebSocket,
+  logger: window.console,
+
+  createConsumer(url) {
+    if (url == null) {
+      const urlConfig = this.getConfig("url")
+      url = (urlConfig ? urlConfig : this.INTERNAL.default_mount_path)
+    }
+    return new Consumer(this.createWebSocketURL(url))
+  },
+
+  getConfig(name) {
+    const element = document.head.querySelector(`meta[name='action-cable-${name}']`)
+    return (element ? element.getAttribute("content") : undefined)
+  },
+
+  createWebSocketURL(url) {
+    if (url && !/^wss?:/i.test(url)) {
+      const a = document.createElement("a")
+      a.href = url
+      // Fix populating Location properties in IE. Otherwise, protocol will be blank.
+      a.href = a.href
+      a.protocol = a.protocol.replace("http", "ws")
+      return a.href
+    } else {
+      return url
+    }
+  },
+
+  startDebugging() {
+    this.debugging = true
+  },
+
+  stopDebugging() {
+    this.debugging = null
+  },
+
+  log(...messages) {
+    if (this.debugging) {
+      messages.push(Date.now())
+      this.logger.log("[ActionCable]", ...messages)
+    }
+  }
+}