diff --git a/phpBB/phpbb/storage/controller/attachment.php b/phpBB/phpbb/storage/controller/attachment.php
index 8cfae96905..11d254f24a 100644
--- a/phpBB/phpbb/storage/controller/attachment.php
+++ b/phpBB/phpbb/storage/controller/attachment.php
@@ -278,7 +278,7 @@ class attachment extends controller
 		$response->headers->set('Content-Disposition', $disposition);
 
 		// Set expires header for browser cache
-		$time = new \Datetime();
+		$time = new \DateTime();
 		$response->setExpires($time->modify('+1 year'));
 
 		return parent::handle($attachment['physical_filename']);
diff --git a/phpBB/phpbb/storage/controller/avatar.php b/phpBB/phpbb/storage/controller/avatar.php
index aaf347fd79..7055961230 100644
--- a/phpBB/phpbb/storage/controller/avatar.php
+++ b/phpBB/phpbb/storage/controller/avatar.php
@@ -107,7 +107,7 @@ class avatar extends controller
 
 		$response->headers->set('Content-Disposition', $disposition);
 
-		$time = new \Datetime();
+		$time = new \DateTime();
 		$response->setExpires($time->modify('+1 year'));
 
 		parent::prepare($response, $file);
diff --git a/phpBB/phpbb/storage/file_info.php b/phpBB/phpbb/storage/file_info.php
index b57faa42ed..2e93846838 100644
--- a/phpBB/phpbb/storage/file_info.php
+++ b/phpBB/phpbb/storage/file_info.php
@@ -43,7 +43,7 @@ class file_info
 	/**
 	 * Constructor
 	 *
-	 * @param \Symfony\Component\DependencyInjection\ContainerInterface $adapter
+	 * @param adapter_interface $adapter
 	 * @param string $path
 	 */
 	public function __construct(adapter_interface $adapter, $path)
diff --git a/phpBB/phpbb/storage/storage.php b/phpBB/phpbb/storage/storage.php
index 5689200569..671e9da1a3 100644
--- a/phpBB/phpbb/storage/storage.php
+++ b/phpBB/phpbb/storage/storage.php
@@ -403,7 +403,7 @@ class storage
 	 *
 	 * @param string	$path	The file
 	 *
-	 * @throws \phpbb\storage\exception\not_implemented	When the adapter doesnt implement the method
+	 * @throws \phpbb\storage\exception\exception	When the adapter doesnt implement the method
 	 *													When the file doesn't exist
 	 *
 	 * @return \phpbb\storage\file_info	Returns file_info object
diff --git a/phpBB/phpbb/template/template.php b/phpBB/phpbb/template/template.php
index 742dea8d3e..dcc530f37a 100644
--- a/phpBB/phpbb/template/template.php
+++ b/phpBB/phpbb/template/template.php
@@ -15,14 +15,6 @@ namespace phpbb\template;
 
 interface template
 {
-
-	/**
-	* Clear the cache
-	*
-	* @return \phpbb\template\template
-	*/
-	public function clear_cache();
-
 	/**
 	* Sets the template filenames for handles.
 	*
diff --git a/phpBB/phpbb/template/twig/extension.php b/phpBB/phpbb/template/twig/extension.php
index 6dc3bb2994..f745690089 100644
--- a/phpBB/phpbb/template/twig/extension.php
+++ b/phpBB/phpbb/template/twig/extension.php
@@ -53,7 +53,7 @@ class extension extends \Twig\Extension\AbstractExtension
 	/**
 	* Returns the token parser instance to add to the existing list.
 	*
-	* @return array An array of \Twig\TokenParser\AbstractTokenParser instances
+	* @return \Twig\TokenParser\TokenParserInterface[] An array of \Twig\TokenParser\AbstractTokenParser instances
 	*/
 	public function getTokenParsers()
 	{
@@ -69,7 +69,7 @@ class extension extends \Twig\Extension\AbstractExtension
 	/**
 	* Returns a list of filters to add to the existing list.
 	*
-	* @return array An array of filters
+	* @return \Twig\TwigFilter[] An array of filters
 	*/
 	public function getFilters()
 	{
@@ -85,7 +85,7 @@ class extension extends \Twig\Extension\AbstractExtension
 	/**
 	* Returns a list of global functions to add to the existing list.
 	*
-	* @return array An array of global functions
+	* @return \Twig\TwigFunction[] An array of global functions
 	*/
 	public function getFunctions()
 	{
@@ -100,7 +100,7 @@ class extension extends \Twig\Extension\AbstractExtension
 	/**
 	* Returns a list of operators to add to the existing list.
 	*
-	* @return array An array of operators
+	* @return array[] An array of operators
 	*/
 	public function getOperators()
 	{
diff --git a/phpBB/phpbb/template/twig/extension/avatar.php b/phpBB/phpbb/template/twig/extension/avatar.php
index d8b27fed9f..fb7ec92655 100644
--- a/phpBB/phpbb/template/twig/extension/avatar.php
+++ b/phpBB/phpbb/template/twig/extension/avatar.php
@@ -30,9 +30,9 @@ class avatar extends AbstractExtension
 	/**
 	 * Returns a list of global functions to add to the existing list.
 	 *
-	 * @return array An array of global functions
+	 * @return \Twig\TwigFunction[] An array of global functions
 	 */
-	public function getFunctions()
+	public function getFunctions(): array
 	{
 		return array(
 			new \Twig\TwigFunction('avatar', array($this, 'get_avatar')),
diff --git a/phpBB/phpbb/template/twig/extension/config.php b/phpBB/phpbb/template/twig/extension/config.php
index a7f1189d27..ebb4f0c3ca 100644
--- a/phpBB/phpbb/template/twig/extension/config.php
+++ b/phpBB/phpbb/template/twig/extension/config.php
@@ -43,9 +43,9 @@ class config extends AbstractExtension
 	/**
 	 * Returns a list of global functions to add to the existing list.
 	 *
-	 * @return array An array of global functions
+	 * @return \Twig\TwigFunction[] An array of global functions
 	 */
-	public function getFunctions()
+	public function getFunctions(): array
 	{
 		return array(
 			new \Twig\TwigFunction('config', array($this, 'get_config')),
diff --git a/phpBB/phpbb/template/twig/extension/routing.php b/phpBB/phpbb/template/twig/extension/routing.php
index 9c404e55d3..3073675d0c 100644
--- a/phpBB/phpbb/template/twig/extension/routing.php
+++ b/phpBB/phpbb/template/twig/extension/routing.php
@@ -22,7 +22,7 @@ use Twig\TwigFunction;
 
 class routing extends AbstractExtension
 {
-	/** @var \phpbb\controller\helper */
+	/** @var \phpbb\routing\helper */
 	protected $helper;
 
 	/**
diff --git a/phpBB/phpbb/template/twig/extension/username.php b/phpBB/phpbb/template/twig/extension/username.php
index 83cbebe29a..bf99907232 100644
--- a/phpBB/phpbb/template/twig/extension/username.php
+++ b/phpBB/phpbb/template/twig/extension/username.php
@@ -28,14 +28,12 @@ class username extends AbstractExtension
 	}
 
 	/**
-	 * Returns a list of global functions to add to the existing list.
-	 *
-	 * @return array An array of global functions
+	 * {@inheritDoc}
 	 */
 	public function getFunctions()
 	{
 		return array(
-			new \Twig\TwigFunction('username', array($this, 'get_username')),
+			new \Twig\TwigFunction('username', [$this, 'get_username']),
 		);
 	}
 
diff --git a/phpBB/phpbb/template/twig/node/event.php b/phpBB/phpbb/template/twig/node/event.php
index 76bfc6d127..4eddcbcf38 100644
--- a/phpBB/phpbb/template/twig/node/event.php
+++ b/phpBB/phpbb/template/twig/node/event.php
@@ -21,7 +21,7 @@ class event extends \Twig\Node\Node
 	*/
 	protected $listener_directory = 'event/';
 
-	/** @var \Twig\Environment */
+	/** @var \phpbb\template\twig\environment */
 	protected $environment;
 
 	public function __construct(\Twig\Node\Expression\AbstractExpression $expr, \phpbb\template\twig\environment $environment, $lineno, $tag = null)
diff --git a/phpBB/phpbb/template/twig/tokenparser/defineparser.php b/phpBB/phpbb/template/twig/tokenparser/defineparser.php
index ac98dce421..a8c83c42bc 100644
--- a/phpBB/phpbb/template/twig/tokenparser/defineparser.php
+++ b/phpBB/phpbb/template/twig/tokenparser/defineparser.php
@@ -23,7 +23,7 @@ class defineparser extends \Twig\TokenParser\AbstractTokenParser
 	*
 	* @return \Twig\Node\Node A Twig\Node instance
 	* @throws \Twig\Error\SyntaxError
-	* @throws \phpbb\template\twig\node\definenode
+	* @returns \phpbb\template\twig\node\definenode
 	*/
 	public function parse(\Twig\Token $token)
 	{
diff --git a/phpBB/phpbb/template/twig/twig.php b/phpBB/phpbb/template/twig/twig.php
index 6f442401ff..1259618175 100644
--- a/phpBB/phpbb/template/twig/twig.php
+++ b/phpBB/phpbb/template/twig/twig.php
@@ -92,27 +92,14 @@ class twig extends \phpbb\template\base
 		}
 
 		// Add admin namespace
-		if ($this->path_helper->get_adm_relative_path() !== null && is_dir($this->phpbb_root_path . $this->path_helper->get_adm_relative_path() . 'style/'))
+		if ($this->path_helper->get_adm_relative_path() !== null
+			&& is_dir($this->phpbb_root_path . $this->path_helper->get_adm_relative_path() . 'style/')
+			&& $this->loader instanceof \Twig\Loader\FilesystemLoader)
 		{
 			$this->loader->setPaths($this->phpbb_root_path . $this->path_helper->get_adm_relative_path() . 'style/', 'admin');
 		}
 	}
 
-	/**
-	* Clear the cache
-	*
-	* @return \phpbb\template\template
-	*/
-	public function clear_cache()
-	{
-		if (is_dir($this->cachepath))
-		{
-			$this->twig->clearCacheFiles();
-		}
-
-		return $this;
-	}
-
 	/**
 	* Get the style tree of the style preferred by the current user
 	*