hook_menu() has been removed from Drupal 8.
Documentation
Files Affected
confirm_form() is now \Drupal\Core\Form\ConfirmFormBase
Documentation
Files Affected
drupal_add_tabledrag() is now the #tabledrag property of a render array.
Documentation
Files Affected
drupal_goto() has been removed.
Documentation
Files Affected
drupal_render() has been removed.
Files Affected
element_children() is now a method of the Element class.
Documentation
Files Affected
entity_extract_ids() replaced by methods of EntityInterface
Documentation
Files Affected
node_load() has been removed.
Documentation
Files Affected
user_load() has been removed.
Documentation
Files Affected
taxonomy_term_load() has been removed.
Documentation
Files Affected
taxonomy_term_load_multiple() has been removed.
Documentation
Files Affected
The Field API CRUD functions have been removed.
Documentation
Files Affected
drupal_get_form() has moved into the FormBuilder service.
Documentation
Files Affected
form_error() is now a method of FormStateInterface.
Documentation
Files Affected
form_set_error() is now a method of FormStateInterface.
Documentation
Files Affected
form_set_value() is now a method of FormStateInterface.
Documentation
Files Affected
menu_link_get_preferred() has been removed.
Documentation
Files Affected
menu_set_active_trail() has been removed.
Documentation
Files Affected
menu_get_item() has been removed.
Documentation
Files Affected
menu_parent_options() has been replaced by menu.link_tree service.
Documentation
Files Affected
menu_tree_set_path() has been replaced by menu.link_tree service.
Documentation
Files Affected
theme() has been renamed to _theme(), and should never be called directly.
Documentation
Files Affected
The core token API is now a service.
Documentation
Files Affected
The core token API is now a service.
Documentation
Files Affected
drupal_strtolower() has been moved into the Unicode utility class.
Documentation
Files Affected
url() has been removed.
Documentation
Files Affected
variable_del() has been removed.
Documentation
Files Affected
variable_get() has been removed.
Documentation
Files Affected
Many common functions, shared variables, and constants have been renamed.
Documentation
Static permissions are now defined in MODULE.permissions.yml.
Documentation
Files Affected

This issue can be fixed automatically.

Default configuration is deleted automatically.
Files Affected
Module info files' core key must have a value of 8.x.
Documentation
Files Affected
Info files must contain a type key.
Documentation
Files Affected
Many common dependencies have moved into core.
Documentation
Files Affected
Modules no longer declare classes in their info file.
Documentation
Files Affected
Module info files' configure key must be a route name, not a path.
Documentation
Files Affected
Automated web tests must be in a PSR-4 namespace, and unit tests must be converted to PHPUnit.
Documentation