By andypost on
Change record status: 
Draft (View all draft change records)
Project: 
Drupal core
Introduced in branch: 
8.0.x
Issue links: 
https://www.drupal.org/node/2231853
Description: 

Theme keys maintenance_page & install_page are removed in favour of page template variants page--maintenance and page--maintenance--install

Template name changes.
maintenance_page => page--maintenance
install_page => page--maintenance--install
maintenance_page__offline => page__maintenance__offline

preprocess functions moved to system module
template_preprocess_maintenance_page() => system_preprocess_page__maintenance()
template_preprocess_install_page => system_preprocess_page__maintenance__install()

Hook implementations should be renamed
HOOK_preprocess_maintenance_page() to HOOK_preprocess_page__maintenance()
HOOK_preprocess_install_page() to HOOK_preprocess_page__maintenance__install()

Impacts: 
Module developers
Themers