By catch on
Change record status: 
Published (View all published change records)
Project: 
Drupal core
Introduced in branch: 
9.3.x
Introduced in version: 
9.3.0-alpha1
Issue links: 
https://www.drupal.org/node/3160307
Description: 

The signature of ThemeManagerInterface::getActiveTheme() has been updated to the following:

public function getActiveTheme(RouteMatchInterface $route_match = NULL) {

The lack of this parameter was an oversight when the interface was originally committed, and the sole core implementation (ThemeManager::getActiveTheme() has this parameter.

Impacts: 
Module developers
Themers