Frontend refactor (#1471)

Refactor Frontend + Asset code

- Use Laravel's Filesystem component for asset IO, meaning theoretically
  assets should be storable on S3 etc.

- More reliable checking for asset recompilation when debug mode is on,
  so you don't have to constantly delete the compiled assets to force
  a recompile. Should also fix issues with locale JS files being
  recompiled with the same name and cached.

- Remove JavaScript minification, because it will be done by Webpack
  (exception is for the TextFormatter JS).

- Add support for JS sourcemaps.

- Separate frontend view and assets completely. This is an important
  distinction because frontend assets are compiled independent of a
  request, whereas putting together a view depends on a request.

- Bind frontend view/asset factory instances to the container (in
  service providers) rather than subclassing. Asset and content
  populators can be added to these factories – these are simply objects
  that populate the asset compilers or the view with information.

- Add RouteHandlerFactory functions that make it easy to hook up a
  frontend controller with a frontend instance ± some content.

- Remove the need for "nojs"

- Fix cache:clear command

- Recompile assets when settings/enabled extensions change

src/Frontend/FrontendServiceProvider.php

@@ -12,14 +12,73 @@
 namespace Flarum\Frontend;
 
 use Flarum\Foundation\AbstractServiceProvider;
+use Flarum\Http\UrlGenerator;
+use Illuminate\Contracts\View\Factory as ViewFactory;
 
 class FrontendServiceProvider extends AbstractServiceProvider
 {
+    public function register()
+    {
+        // Yo dawg, I heard you like factories, so I made you a factory to
+        // create your factory. We expose a couple of factory functions that
+        // will create frontend factories and configure them with some default
+        // settings common to both the forum and admin frontends.
+
+        $this->app->singleton('flarum.frontend.assets.defaults', function () {
+            return function (string $name) {
+                $assets = new CompilerFactory(
+                    $name,
+                    $this->app->make('filesystem')->disk('flarum-assets'),
+                    $this->app->storagePath()
+                );
+
+                $assets->setLessImportDirs([
+                    $this->app->basePath().'/vendor/components/font-awesome/less' => ''
+                ]);
+
+                $assets->add(function () use ($name) {
+                    $translations = $this->app->make(Asset\Translations::class);
+                    $translations->setFilter(function (string $id) use ($name) {
+                        return preg_match('/^.+(?:\.|::)(?:'.$name.'|lib)\./', $id);
+                    });
+
+                    return [
+                        new Asset\CoreAssets($name),
+                        $this->app->make(Asset\LessVariables::class),
+                        $translations,
+                        $this->app->make(Asset\LocaleAssets::class)
+                    ];
+                });
+
+                return $assets;
+            };
+        });
+
+        $this->app->singleton('flarum.frontend.view.defaults', function () {
+            return function (string $name) {
+                $view = $this->app->make(HtmlDocumentFactory::class);
+
+                $view->setCommitAssets($this->app->inDebugMode());
+
+                $view->add(new Content\Layout('flarum::frontend.'.$name));
+                $view->add($this->app->make(Content\CorePayload::class));
+                $view->add($this->app->make(Content\Meta::class));
+
+                return $view;
+            };
+        });
+    }
+
     /**
      * {@inheritdoc}
      */
     public function boot()
     {
         $this->loadViewsFrom(__DIR__.'/../../views', 'flarum');
+
+        $this->app->make(ViewFactory::class)->share([
+            'translator' => $this->app->make('translator'),
+            'url' => $this->app->make(UrlGenerator::class)
+        ]);
     }
 }