Add Mentions section to user profile (fixes flarum/core#319)

extensions/mentions/src/Listener/AddFilterByMentions.php

@@ -0,0 +1,36 @@
+<?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\Mentions\Listener;
+
+use Flarum\Event\ConfigurePostsQuery;
+use Illuminate\Contracts\Events\Dispatcher;
+
+class AddFilterByMentions
+{
+    /**
+     * @param Dispatcher $events
+     */
+    public function subscribe(Dispatcher $events)
+    {
+        $events->listen(ConfigurePostsQuery::class, [$this, 'addFilter']);
+    }
+
+    /**
+     * @param ConfigurePostsQuery $event
+     */
+    public function addFilter(ConfigurePostsQuery $event)
+    {
+        if ($mentionedId = array_get($event->filter, 'mentioned')) {
+            $event->query->join('mentions_users', 'posts.id', '=', 'mentions_users.post_id')
+                ->where('mentions_users.mentions_id', '=', $mentionedId);
+        }
+    }
+}