Ensure global categories include products in child categories

prefix_add_parents_to_permitted_cats.php

<?php
/**
 * Ensure global categories include products in child categories
 */
function prefix_add_parents_to_permitted_cats( $categories, $product_id, $global, $rule ) {

	// Iterate through each category
	// If it's got children, ensure they're added to the list
	if( $categories ) {
		foreach( $categories as $cat_id ) {
			$children = get_term_children( $cat_id, 'product_cat' );
			if( $children ) {
				$categories = array_merge( $categories, $children );
			}
		}
	}

	return $categories;

}
add_filter( 'pewc_filter_permitted_cats', 'prefix_add_parents_to_permitted_cats', 10, 4 );