How to detect if $this is used in Closure?

class Cl {
    public function makeClosureWithoutThisUsed() {
        return function () {
            echo 'x';
        };
    }

    public function makeClosureWithThisUsed() {
        return function () {
            $this->x = 'dummy';
            echo 'x';
        };
    }
}

$cl = new Cl();
$fxWithoutThis = $cl->makeClosureWithoutThisUsed();
$fxWithThis = $cl->makeClosureWithThisUsed();

\Closure::bind($fxWithoutThis, null); // no $this used, no warning
\Closure::bind($fxWithThis, null); // $this used, warning emitted

$doesUseThis = function (\Closure $fx): bool {
    // how to check if $fx uses $this?
};

var_dump($doesUseThis($fxWithoutThis)); // should print false
var_dump($doesUseThis($fxWithThis)); // should print true

When Closure is not declared as static (static function () {...}) it can be made effectively static by rebounding it to null using Closure::bind.

However, if there is an use of $this inside, it will emit a warning like:

Warning: Cannot unbind $this of closure using $this in /in/7fX2Y on line 19

Is there is a better way (using reflection etc.) to detect if $this is used than catching the php warning?