What should the following code return?

$promise = async(static function (): int {
    try {
        await(React\Promise\Timer\sleep(2));
    } catch (Exception $e) {
        return 1;
    }

    return 2;
})();

$promise->cancel();

var_dump(await($promise));

At the moment, the code would print 1. The same cancellation logic is triggered for fibers (#20) and coroutines (#13). Accordingly, this affects Async v3 and Async v4.

Perhaps we should reject the entire promise? (See also reactphp/promise#56 for discussion about cancellation semantics in Promise v3).