diff -u b/core/modules/system/src/PathBasedBreadcrumbBuilder.php b/core/modules/system/src/PathBasedBreadcrumbBuilder.php
--- b/core/modules/system/src/PathBasedBreadcrumbBuilder.php
+++ b/core/modules/system/src/PathBasedBreadcrumbBuilder.php
@@ -144,7 +144,7 @@
     $exclude['user'] = TRUE;
     // Because this breadcrumb builder is entirely path-based, vary by the 'url'
     // cache context.
-    $breadcrumb->setCacheContexts(['url']);
+    $breadcrumb->setCacheContexts(['url.path']);
     while (count($path_elements) > 1) {
       array_pop($path_elements);
       // Copy the path elements for up-casting.
only in patch2:
unchanged:
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -39,6 +39,11 @@ services:
     arguments: ['@request_stack']
     tags:
       - { name: cache.context }
+  cache_context.url.path:
+    class: Drupal\Core\Cache\PathCacheContext
+    arguments: ['@request_stack']
+    tags:
+      - { name: cache.context }
   cache_context.url.query_args:
     class: Drupal\Core\Cache\QueryArgsCacheContext
     arguments: ['@request_stack']
only in patch2:
unchanged:
--- /dev/null
+++ b/core/lib/Drupal/Core/Cache/PathCacheContext.php
@@ -0,0 +1,35 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Cache\PathCacheContext.
+ */
+
+namespace Drupal\Core\Cache;
+
+/**
+ * Defines the PathCacheContext service, for "per URL path" caching.
+ *
+ * (This allows for caching generated relative URLs.)
+ *
+ * @see \Symfony\Component\HttpFoundation\Request::getBasePath()
+ * @see \Symfony\Component\HttpFoundation\Request::getPathInfo()
+ */
+class PathCacheContext extends RequestStackCacheContextBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getLabel() {
+    return t('Path');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getContext() {
+    $request = $this->requestStack->getCurrentRequest();
+    return $request->getBasePath() . $request->getPathInfo();
+  }
+
+}
only in patch2:
unchanged:
--- a/core/lib/Drupal/Core/Menu/menu.api.php
+++ b/core/lib/Drupal/Core/Menu/menu.api.php
@@ -533,12 +533,8 @@ function hook_contextual_links_plugins_alter(array &$contextual_links) {
 /**
  * Perform alterations to the breadcrumb built by the BreadcrumbManager.
  *
- * @param array $breadcrumb
- *   An array of breadcrumb link a tags, returned by the breadcrumb manager
- *   build method, for example
- *   @code
- *     array('<a href="/">Home</a>');
- *   @endcode
+ * @param \Drupal\Core\Breadcrumb\Breadcrumb $breadcrumb
+ *   A breadcrumb object returned by the breadcrumb manager build method.
  * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
  *   The current route match.
  * @param array $context
@@ -549,9 +545,9 @@ function hook_contextual_links_plugins_alter(array &$contextual_links) {
  *
  * @ingroup menu
  */
-function hook_system_breadcrumb_alter(array &$breadcrumb, \Drupal\Core\Routing\RouteMatchInterface $route_match, array $context) {
+function hook_system_breadcrumb_alter(Drupal\Core\Breadcrumb\Breadcrumb &$breadcrumb, \Drupal\Core\Routing\RouteMatchInterface $route_match, array $context) {
   // Add an item to the end of the breadcrumb.
-  $breadcrumb[] = Drupal::l(t('Text'), 'example_route_name');
+  $breadcrumb->addLink(Drupal::l(t('Text'), 'example_route_name'));
 }
 
 /**
only in patch2:
unchanged:
--- a/core/modules/menu_ui/menu_ui.module
+++ b/core/modules/menu_ui/menu_ui.module
@@ -486,14 +486,14 @@ function menu_ui_preprocess_block(&$variables) {
 /**
  * Implements hook_system_breadcrumb_alter().
  */
-function menu_ui_system_breadcrumb_alter(array &$breadcrumb, RouteMatchInterface $route_match, array $context) {
+function menu_ui_system_breadcrumb_alter(&$breadcrumb, RouteMatchInterface $route_match, array $context) {
   // Custom breadcrumb behavior for editing menu links, we append a link to
   // the menu in which the link is found.
   if (($route_match->getRouteName() == 'menu_ui.link_edit') && $menu_link = $route_match->getParameter('menu_link_plugin')) {
     if (($menu_link instanceof MenuLinkInterface)) {
       // Add a link to the menu admin screen.
       $menu = Menu::load($menu_link->getMenuName());
-      $breadcrumb[] = Link::createFromRoute($menu->label(), 'entity.menu.edit_form', array('menu' => $menu->id()));
+      $breadcrumb->addLink(Link::createFromRoute($menu->label(), 'entity.menu.edit_form', array('menu' => $menu->id())));
     }
   }
 }