[ticket/12847] Allow the extensions to say if they can be enabled

PHPBB3-12847

phpBB/phpbb/extension/base.php

@@ -40,6 +40,7 @@ class base implements \phpbb\extension\extension_interface
 	*
 	* @param ContainerInterface $container Container object
 	* @param \phpbb\finder $extension_finder
+	* @param \phpbb\db\migrator $migrator
 	* @param string $extension_name Name of this extension (from ext.manager)
 	* @param string $extension_path Relative path to this extension
 	*/
@@ -53,6 +54,14 @@ class base implements \phpbb\extension\extension_interface
 		$this->extension_path = $extension_path;
 	}
 
+	/**
+	* {@inheritdoc}
+	*/
+	public function is_enableable()
+	{
+		return true;
+	}
+
 	/**
 	* Single enable step that installs any included migrations
 	*

phpBB/phpbb/extension/extension_interface.php

@@ -19,6 +19,13 @@ namespace phpbb\extension;
 */
 interface extension_interface
 {
+	/**
+	* Indicate whether or not the extension can be enabled.
+	*
+	* @return bool
+	*/
+	public function is_enableable();
+
 	/**
 	* enable_step is executed on enabling an extension until it returns false.
 	*

phpBB/phpbb/extension/manager.php

@@ -177,6 +177,12 @@ class manager
 		$old_state = (isset($this->extensions[$name]['ext_state'])) ? unserialize($this->extensions[$name]['ext_state']) : false;
 
 		$extension = $this->get_extension($name);
+
+		if (!$extension->is_enableable())
+		{
+			return false;
+		}
+
 		$state = $extension->enable_step($old_state);
 
 		$active = ($state === false);