test.hh

<?hh

interface ExceptionWithCode {
    public function getCode();
}

class Checkout_Exception extends Exception implements ExceptionWithCode {
    protected $data = [];
    
    public function __construct($msg = "", $code = 0, $data = []) {
        $this->data = $data;
        parent::__construct($msg, $code);
    }
}

class Foo {
    public function herp() {
	try {
	    $x = 1 + 1;
	} catch (ExceptionWithCode $e) {
	    throw new Checkout_Exception('hello', 42); 
	}
    }
}

Output:

test.hh:20:11,27: Invalid exception (Typing[4110])
  test.hh:20:11,27: This is an object of type Exception because it is used as an exception
  test.hh:20:11,27: It is incompatible with an object of type ExceptionWithCode