WP_ADMIN_DIR not set properly

[perochak]

In file
wp-includes/theme.php
on lines 1759 and 1772, there should be constant WP_ADMIN_DIR rather then wp_admin.

Line 1759

<?php
require_once( ABSPATH .'wp-admin/custom-header.php' );

Which should be

<?php
require_once( ABSPATH . WP_ADMIN_DIR.'/custom-header.php' );

Same is true for line 1772

[perochak]

Same issue found in wp-admin/admin.php on line 82 and on number of points in wp-admin/includes/admin.php, wp-admin/includes/template.php and other files.

Seems that WP_ADMIN_DIR is not properly used where required.

[pento]

Thank you for the feature request, @perochak!

Per #7194, the wp-admin directory is not intended to be customisable, it's hard-coded in over 1000 places across the WordPress codebase.

WP_ADMIN_DIR is not used in the WordPress codebase, it was just the suggested name for a constant to contain the directory name.