diff --git a/core/includes/common.inc b/core/includes/common.inc
index cbac8af..3ebc4df 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -1942,11 +1942,7 @@ function url($path = NULL, array $options = array()) {
  *   Boolean TRUE or FALSE, where TRUE indicates an external path.
  */
 function url_is_external($path) {
-  $colonpos = strpos($path, ':');
-  // Avoid calling drupal_strip_dangerous_protocols() if there is any
-  // slash (/), hash (#) or question_mark (?) before the colon (:)
-  // occurrence - if any - as this would clearly mean it is not a URL.
-  return $colonpos !== FALSE && !preg_match('![/?#]!', substr($path, 0, $colonpos)) && drupal_strip_dangerous_protocols($path) == $path;
+  return drupal_container()->get('router.generator')->urlIsExternal($path);
 }
 
 /**
@@ -2035,10 +2031,7 @@ function l($text, $path, array $options = array()) {
   // query parameters of the link equal those of the current request, since the
   // same request with different query parameters may yield a different page
   // (e.g., pagers).
-  $is_active = ($path == current_path() || ($path == '<front>' && drupal_is_front_page()));
-  $is_active = $is_active && (empty($options['language']) || $options['language']->langcode == language(LANGUAGE_TYPE_URL)->langcode);
-  $is_active = $is_active && (drupal_container()->get('request')->query->all() == $options['query']);
-  if ($is_active) {
+  if (drupal_container()->get('router.generator')->urlIsActive($path, $options)) {
     $options['attributes']['class'][] = 'active';
   }
 
diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 0edb028..10f248a 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1691,7 +1691,11 @@ function theme_status_messages($variables) {
  * @see l()
  */
 function theme_link($variables) {
-  return '<a href="' . check_plain(url($variables['path'], $variables['options'])) . '"' . new Attribute($variables['options']['attributes']) . '>' . ($variables['options']['html'] ? $variables['text'] : check_plain($variables['text'])) . '</a>';
+  $attributes = new Attribute($variables['options']['attributes']);
+  if (drupal_container()->get('router.generator')->urlIsActive($path, $options)) {
+    $attributes['class'][] = 'active';
+  }
+  return '<a href="' . check_plain(url($variables['path'], $variables['options'])) . '"' . $attributes . '>' . ($variables['options']['html'] ? $variables['text'] : check_plain($variables['text'])) . '</a>';
 }
 
 /**
diff --git a/core/lib/Drupal/Core/Routing/UrlGenerator.php b/core/lib/Drupal/Core/Routing/UrlGenerator.php
index 518c02d..aa545d9 100644
--- a/core/lib/Drupal/Core/Routing/UrlGenerator.php
+++ b/core/lib/Drupal/Core/Routing/UrlGenerator.php
@@ -92,9 +92,9 @@ public function generateFromPath($path = NULL, $options = array()) {
     if (!isset($options['external'])) {
       // Return an external link if $path contains an allowed absolute URL. Only
       // call the slow drupal_strip_dangerous_protocols() if $path contains a ':'
-      // before any / ? or #. Note: we could use url_is_external($path) here, but
-      // that would require another function call, and performance inside url() is
-      // critical.
+      // before any / ? or #. Note: we could use $this->urlIsExternal($path) here,
+      // but that would require another function call, and performance inside
+      // url() is critical.
       $colonpos = strpos($path, ':');
       $options['external'] = ($colonpos !== FALSE && !preg_match('![/?#]!', substr($path, 0, $colonpos)) && $this->stripDisallowedProtocols($path) == $path);
     }
@@ -165,6 +165,41 @@ public function generateFromPath($path = NULL, $options = array()) {
   }
 
   /**
+   * Returns TRUE if the given path, language and query match those of the current request.
+   */
+  public function urlIsActive($path = NULL, $options = array()) {
+    // A path is only active if it corresponds to the current path, the
+    // language of the path is equal to the current language, and if the
+    // query parameters of the url equal those of the current request, since the
+    // same request with different query parameters may yield a different page
+    // (e.g., pagers).
+    // @todo Figure out how to deal with urlIsActive() calls when there is no request.
+    if ($this->request) {
+      $path_query = $this->request->query->all();
+      $path_match = ($path == $this->request->getPathInfo() || ($path == '<front>' && drupal_is_front_page()));
+      $lang_match = (empty($options['language']) || $options['language']->langcode == language(LANGUAGE_TYPE_URL)->langcode);
+      $query_match = (empty($options['query']) && empty($path_query)) || ($options['query'] == $path_query);
+
+      return $path_match && $lang_match && $query_match;
+    }
+    else {
+      return FALSE;
+    }
+  }
+
+  /**
+   * Returns TRUE if path points to an external URL.
+   */
+  public function urlIsExternal($path) {
+    // Link is external if $path contains an allowed absolute URL. Only
+    // call the slow drupal_strip_dangerous_protocols() if $path contains a ':'
+    // before any / ? or #.
+    $colonpos = strpos($path, ':');
+
+    return ($colonpos !== FALSE && !preg_match('![/?#]!', substr($path, 0, $colonpos)) && $this->stripDisallowedProtocols($path) == $path);
+  }
+
+  /**
    * Implements \Drupal\Core\Routing\PathBasedGeneratorInterface::stripDisallowedProtocols().
    */
   public function stripDisallowedProtocols($uri) {