The coupling of the breadcrumb to the menu_links and menu_router tables makes it very difficult for developers to present the desired breadcrumb and difficult for site builders to get an expected breadcrumb without writing code.
Drupal 8.x now implements a path based breadcrumb hierarchy similar to the Drupal 7.x contributed module Breadcrumbs by path
User interface changes
Some breadcrumbs will appear differently.
API changes
Entries in hook_menu() with only MENU_VISIBLE_IN_BREADCRUMB are not needed anymore.
menu_get_active_breadcrumb() is removed
PathBasedBreadcrumbBuilder replaces MenuLinkBreadcrumbBuilder as the default builder.
BookBreadcrumbBuilder is added to support book module hierarchy
hook_menu_breadcrumb_alter() is replaced by hook_system_breadcrumb_alter(), and is invoked from the BreadcrumbManager
menu_item_route_access() is not be used, instead the Drupal\Core\Access\AccessManager is used.
