There are several places in Drupal 8 that currently have code like the following:
<?php
/**
* Implements hook_custom_theme().
*
* @todo Add an event subscriber to the Ajax system to automatically set the
* base page theme for all Ajax requests, and then remove this one off.
*/
function edit_custom_theme() {
if (substr(current_path(), 0, 5) === 'edit/') {
return ajax_base_page_theme();
}
}
?>That's incorrect, since theme callback functions should be used instead. In addition to being ugly, the code is also error-prone since other hook_custom_theme() implementations might accidentally override it, plus the string-matching might accidentally match paths it doesn't intend to.
There's an issue at #1954892: Figure out how to deal with 'theme callback' that may wind up doing something to replace theme callbacks in Drupal 8 anyway. However, it's an easy patch to fix it here first, and that way the other issue can just do more of a find/replace on "theme callback" rather than dealing with these too, which if nothing else will make an eventual patch there easier to review.