in src/Assert.hack [680:691]
private static function sortArrayRecursive<Tk as arraykey>(
KeyedContainer<Tk, mixed> $arr,
): dict<arraykey, mixed> {
$out = dict[];
foreach ($arr as $k => $v) {
if ($v is KeyedContainer<_, _>) {
$v = self::sortArrayRecursive($v);
}
$out[$k as arraykey] = $v;
}
return $out;
}