I would find it extremely annoying if saving was blocked due to an error.
I'm not suggesting blocking saving. I'm suggesting blocking FTP Upload. I don't want to publish is there is an error.
And you can't rely on WeBuilder/RapidPHP matches a new version of i.e. PHP that might support a new syntax.
If I understand correctly, Rapid is using PHP -l (lint) to check syntax. To get syntax checking for PHP 7, I simply changed the path to the PHP executable to point to PHP 7.1.14. I did that with Rapid 2016. Therefore, syntax checking is not dependent on the version of Rapid.