dont-force-structural-layouts.php

<?php
/**
 * Adds custom classes to the array of body classes.
 *
 * @param array $classes Classes for the body element.
 * @return array
 */
function prefix_body_classes( $classes ) {
	// Add class to the body if the sidebar has widgets.
	if ( is_active_sidebar( 'sidebar-1' ) && ! is_page() ) {
		$classes[] = 'has-sidebar';
	}

	return $classes;
}
add_filter( 'body_class', 'prefix_body_classes' );