Source

File: wp-includes/Requests/Transport/cURL.php

protected static function format_get($url, $data) {
		if (!empty($data)) {
			$url_parts = parse_url($url);
			if (empty($url_parts['query'])) {
				$query = $url_parts['query'] = '';
			}
			else {
				$query = $url_parts['query'];
			}

			$query .= '&' . http_build_query($data, null, '&');
			$query = trim($query, '&');

			if (empty($url_parts['query'])) {
				$url .= '?' . $query;
			}
			else {
				$url = str_replace($url_parts['query'], $query, $url);
			}
		}
		return $url;
	}