Ticket #36292: callback-rule.php

<?php

class WP_Rewrite_CallbackRule implements WP_Rewrite_RuleInterface {
        protected $callback;
        public function __construct( $callback ) {
                $this->callback = $callback;
        }

        public function should_parse_query() {
                return true;
        }

        public function get_query_vars( $matches ) {
                return call_user_func( $this->callback, $matches );
        }

        public function get_verbose_page_match() {
                return false;
        }
}

add_rewrite_rule( '/foo/', new WP_Rewrite_CallbackRule( function ( $matches ) {
        return [ 'args' ];
}));