Encode the query of a URL with RFC3986.

encode_query.php

<?php
function encode_query(string $url): string {
    if ($query = parse_url($url, PHP_URL_QUERY)) {
        [$path] = explode($query, $url, 2);
        parse_str($query, $data);
        $query = http_build_query($data, "", NULL, PHP_QUERY_RFC3986);
        if ($fragment = parse_url($url, PHP_URL_FRAGMENT)) {
            $fragment = '#'.rawurlencode($fragment);
        }
        return join([$path, $query, $fragment]);
    }
    return $url;
}

// TEST
$url = 'http://username:password@hostname:9090/path?z=3,&arg[]=value d#anchor q';
echo encode_query($url);
http://username:password@hostname:9090/path?z=3%2C&arg%5B0%5D=value%20d#anchor%20q