wp-includes/class-wp-customize-widgets.php:560Determines whether the widgets panel is active, based on whether there are sidebars registered.
bool public function is_panel_active() { global $wp_registered_sidebars; return ! empty( $wp_registered_sidebars ); }Introduced in 4.4.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-customize-widgets.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.