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/Compiler/JsCompiler.php

@@ -0,0 +1,84 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * (c) Toby Zerner <toby.zerner@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Flarum\Frontend\Compiler;
+
+use axy\sourcemap\SourceMap;
+use Flarum\Frontend\Compiler\Source\FileSource;
+
+class JsCompiler extends RevisionCompiler
+{
+    /**
+     * {@inheritdoc}
+     */
+    protected function save(string $file, array $sources): bool
+    {
+        $mapFile = $file.'.map';
+
+        $map = new SourceMap();
+        $map->file = $mapFile;
+        $output = [];
+        $line = 0;
+
+        // For each of the sources, get their content and add it to the
+        // output. For file sources, if a sourcemap is present, add it to
+        // the output sourcemap.
+        foreach ($sources as $source) {
+            $content = $source->getContent();
+
+            if ($source instanceof FileSource) {
+                $sourceMap = $source->getPath().'.map';
+
+                if (file_exists($sourceMap)) {
+                    $map->concat($sourceMap, $line);
+                }
+            }
+
+            $content = $this->format($content);
+            $output[] = $content;
+            $line += substr_count($content, "\n") + 1;
+        }
+
+        // Add a comment to the end of our file to point to the sourcemap
+        // we just constructed. We will then write the JS file, save the
+        // map to a temporary location, and then move it to the asset dir.
+        $output[] = '//# sourceMappingURL='.$this->assetsDir->url($mapFile);
+
+        $this->assetsDir->put($file, implode("\n", $output));
+
+        $mapTemp = tempnam(sys_get_temp_dir(), $mapFile);
+        $map->save($mapTemp);
+        $this->assetsDir->put($mapFile, file_get_contents($mapTemp));
+        @unlink($mapTemp);
+
+        return true;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function format(string $string): string
+    {
+        return preg_replace('~//# sourceMappingURL.*$~s', '', $string).";\n";
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function delete(string $file)
+    {
+        parent::delete($file);
+
+        if ($this->assetsDir->has($mapFile = $file.'.map')) {
+            $this->assetsDir->delete($mapFile);
+        }
+    }
+}