Add Service Provider Extender (#2437)

src/Extend/ServiceProvider.php

@@ -0,0 +1,40 @@
+<?php
+
+/*
+ * This file is part of Flarum.
+ *
+ * For detailed copyright and license information, please view the
+ * LICENSE file that was distributed with this source code.
+ */
+
+namespace Flarum\Extend;
+
+use Flarum\Extension\Extension;
+use Illuminate\Contracts\Container\Container;
+
+class ServiceProvider implements ExtenderInterface
+{
+    private $providers = [];
+
+    /**
+     * Register a service provider.
+     *
+     * @param string $serviceProviderClass The ::class attribute of the service provider class.
+     * @return self
+     */
+    public function register(string $serviceProviderClass)
+    {
+        $this->providers[] = $serviceProviderClass;
+
+        return $this;
+    }
+
+    public function extend(Container $container, Extension $extension = null)
+    {
+        $app = $container->make('flarum');
+
+        foreach ($this->providers as $provider) {
+            $app->register($provider);
+        }
+    }
+}