diff -u b/core/lib/Drupal/Core/Url.php b/core/lib/Drupal/Core/Url.php
--- b/core/lib/Drupal/Core/Url.php
+++ b/core/lib/Drupal/Core/Url.php
@@ -112,7 +112,7 @@
    * code more self-documenting.
    *
    * @param string $route_name
-   *   The name of the route
+   *   The name of the route.
    * @param array $route_parameters
    *   (optional) An associative array of parameter names and values.
    * @param array $options
@@ -124,7 +124,7 @@
    * @todo Update this documentation for non-routed URIs in
    *   https://www.drupal.org/node/2346787
    */
-  public function __construct($route_name, $route_parameters = [], $options = []) {
+  public function __construct($route_name, array $route_parameters = [], array $options = []) {
     $this->routeName = $route_name;
     $this->routeParameters = $route_parameters;
     $this->options = $options;
@@ -138,7 +138,7 @@
    * path (like robots.txt) use Url::fromUri() with the base: scheme.
    *
    * @param string $route_name
-   *   The name of the route
+   *   The name of the route.
    * @param array $route_parameters
    *   (optional) An associative array of route parameter names and values.
    * @param array $options
@@ -150,7 +150,7 @@
    * @see \Drupal\Core\Url::fromUserInput()
    * @see \Drupal\Core\Url::fromUri()
    */
-  public static function fromRoute($route_name, $route_parameters = [], $options = []) {
+  public static function fromRoute($route_name, array $route_parameters = [], array $options = []) {
     return new static($route_name, $route_parameters, $options);
   }
 
@@ -207,7 +207,7 @@
    *   Thrown when the user input does not begin with one of the following
    *   characters: '/', '?', or '#'.
    */
-  public static function fromUserInput($user_input, $options = []) {
+  public static function fromUserInput($user_input, array $options = []) {
     // Ensuring one of these initial characters also enforces that what is
     // passed is a relative URI reference rather than an absolute URI,
     // because these are URI reserved characters that a scheme name may not
@@ -275,7 +275,7 @@
    * @see \Drupal\Core\Url::fromRoute()
    * @see \Drupal\Core\Url::fromUserInput()
    */
-  public static function fromUri($uri, $options = []) {
+  public static function fromUri($uri, array $options = []) {
     // parse_url() incorrectly parses base:number/... as hostname:port/...
     // and not the scheme. Prevent that by prefixing the path with a slash.
     if (preg_match('/^base:\d/', $uri)) {
@@ -322,7 +322,7 @@
       $url = static::fromRouteUri($uri_parts, $uri_options, $uri);
     }
     elseif (in_array($uri_parts['scheme'], stream_get_wrappers())) {
-      $url = static::fromRouteUri($uri_parts, $uri_options, $uri);
+      $url = static::fromStreamWrapper($uri_parts, $uri_options, $uri);
     }
     else {
       $url = new static($uri, [], $options);
@@ -514,11 +514,11 @@
   }
 
   /**
-   * Creates a URL
+   * Creates a URL.
    */
   protected static function fromStreamWrapper($uri_parts, $uri_options, $uri) {
   }
-  
+
   /**
    * Generates a URI string that represents the data in the Url object.
    *
@@ -606,7 +606,7 @@
    * @throws \UnexpectedValueException.
    *   If this is a URI with no corresponding route.
    */
-  public function setRouteParameters($parameters) {
+  public function setRouteParameters(array $parameters) {
     if ($this->unrouted) {
       throw new \UnexpectedValueException('External URLs do not have route parameters.');
     }
@@ -674,7 +674,7 @@
    *
    * @return $this
    */
-  public function setOptions($options) {
+  public function setOptions(array $options) {
     $this->options = $options;
     return $this;
   }
@@ -708,7 +708,7 @@
    *
    * @return $this
    */
-  public function mergeOptions($options) {
+  public function mergeOptions(array $options) {
     $this->options = NestedArray::mergeDeep($this->options, $options);
     return $this;
   }