Bug report

PHPStan with PHP 8.1 shows an error when you use the default value for a read-only property in the constructor.

https://wiki.php.net/rfc/readonly_properties_v2

As the property has no default value, the assignment in the constructor is initializing, and thus legal. The constructor property promotion feature was specifically designed for forward-compatibility with readonly properties.

Code snippet that reproduces the problem

final class ErrorResponse
{
    public function __construct(public readonly string $message, public readonly array $parameters = [])
    {
    }
}

has error:

Readonly property cannot have a default value.

Expected output

No errors should be detected.