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/RevisionCompiler.php

@@ -0,0 +1,276 @@
+<?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 Flarum\Frontend\Compiler\Source\SourceCollector;
+use Flarum\Frontend\Compiler\Source\SourceInterface;
+use Illuminate\Filesystem\FilesystemAdapter;
+
+class RevisionCompiler implements CompilerInterface
+{
+    const REV_MANIFEST = 'rev-manifest.json';
+
+    const EMPTY_REVISION = 'empty';
+
+    /**
+     * @var FilesystemAdapter
+     */
+    protected $assetsDir;
+
+    /**
+     * @var string
+     */
+    protected $filename;
+
+    /**
+     * @var callable[]
+     */
+    protected $sourcesCallbacks = [];
+
+    /**
+     * @param FilesystemAdapter $assetsDir
+     * @param string $filename
+     */
+    public function __construct(FilesystemAdapter $assetsDir, string $filename)
+    {
+        $this->assetsDir = $assetsDir;
+        $this->filename = $filename;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getFilename(): string
+    {
+        return $this->filename;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function setFilename(string $filename)
+    {
+        $this->filename = $filename;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function commit()
+    {
+        $sources = $this->getSources();
+
+        $oldRevision = $this->getRevision();
+
+        $newRevision = $this->calculateRevision($sources);
+
+        $oldFile = $oldRevision ? $this->getFilenameForRevision($oldRevision) : null;
+
+        if ($oldRevision !== $newRevision || ($oldFile && ! $this->assetsDir->has($oldFile))) {
+            $newFile = $this->getFilenameForRevision($newRevision);
+
+            if (! $this->save($newFile, $sources)) {
+                // If no file was written (because the sources were empty), we
+                // will set the revision to a special value so that we can tell
+                // that this file does not have a URL.
+                $newRevision = static::EMPTY_REVISION;
+            }
+
+            $this->putRevision($newRevision);
+
+            if ($oldFile) {
+                $this->delete($oldFile);
+            }
+        }
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function addSources(callable $callback)
+    {
+        $this->sourcesCallbacks[] = $callback;
+    }
+
+    /**
+     * @return SourceInterface[]
+     */
+    protected function getSources()
+    {
+        $sources = new SourceCollector;
+
+        foreach ($this->sourcesCallbacks as $callback) {
+            $callback($sources);
+        }
+
+        return $sources->getSources();
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getUrl(): ?string
+    {
+        $revision = $this->getRevision();
+
+        if (! $revision) {
+            $this->commit();
+
+            $revision = $this->getRevision();
+
+            if (! $revision) {
+                return null;
+            }
+        }
+
+        if ($revision === static::EMPTY_REVISION) {
+            return null;
+        }
+
+        $file = $this->getFilenameForRevision($revision);
+
+        return $this->assetsDir->url($file);
+    }
+
+    /**
+     * @param string $file
+     * @param SourceInterface[] $sources
+     * @return bool true if the file was written, false if there was nothing to write
+     */
+    protected function save(string $file, array $sources): bool
+    {
+        if ($content = $this->compile($sources)) {
+            $this->assetsDir->put($file, $content);
+
+            return true;
+        }
+
+        return false;
+    }
+
+    /**
+     * @param SourceInterface[] $sources
+     * @return string
+     */
+    protected function compile(array $sources): string
+    {
+        $output = '';
+
+        foreach ($sources as $source) {
+            $output .= $this->format($source->getContent());
+        }
+
+        return $output;
+    }
+
+    /**
+     * @param string $string
+     * @return string
+     */
+    protected function format(string $string): string
+    {
+        return $string;
+    }
+
+    /**
+     * Get the filename for the given revision.
+     *
+     * @param string $revision
+     * @return string
+     */
+    protected function getFilenameForRevision(string $revision): string
+    {
+        $ext = pathinfo($this->filename, PATHINFO_EXTENSION);
+
+        return substr_replace($this->filename, '-'.$revision, -strlen($ext) - 1, 0);
+    }
+
+    /**
+     * @return string|null
+     */
+    protected function getRevision(): ?string
+    {
+        if ($this->assetsDir->has(static::REV_MANIFEST)) {
+            $manifest = json_decode($this->assetsDir->read(static::REV_MANIFEST), true);
+
+            return array_get($manifest, $this->filename);
+        }
+
+        return null;
+    }
+
+    /**
+     * @param string|null $revision
+     */
+    protected function putRevision(?string $revision)
+    {
+        if ($this->assetsDir->has(static::REV_MANIFEST)) {
+            $manifest = json_decode($this->assetsDir->read(static::REV_MANIFEST), true);
+        } else {
+            $manifest = [];
+        }
+
+        if ($revision) {
+            $manifest[$this->filename] = $revision;
+        } else {
+            unset($manifest[$this->filename]);
+        }
+
+        $this->assetsDir->put(static::REV_MANIFEST, json_encode($manifest));
+    }
+
+    /**
+     * @param SourceInterface[] $sources
+     * @return string
+     */
+    protected function calculateRevision(array $sources): string
+    {
+        $cacheDifferentiator = [$this->getCacheDifferentiator()];
+
+        foreach ($sources as $source) {
+            $cacheDifferentiator[] = $source->getCacheDifferentiator();
+        }
+
+        return hash('crc32b', serialize($cacheDifferentiator));
+    }
+
+    /**
+     * @return mixed
+     */
+    protected function getCacheDifferentiator()
+    {
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function flush()
+    {
+        if ($revision = $this->getRevision()) {
+            $file = $this->getFilenameForRevision($revision);
+
+            $this->delete($file);
+
+            $this->putRevision(null);
+        }
+    }
+
+    /**
+     * @param string $file
+     */
+    protected function delete(string $file)
+    {
+        if ($this->assetsDir->has($file)) {
+            $this->assetsDir->delete($file);
+        }
+    }
+}