Paul on Nostr: I generally start with -Wextra and then turn things off if I absolutely have to - ...

I generally start with -Wextra and then turn things off if I absolutely have to - sometimes via an indirect header with a pragma to turn it off just for a single library like GLib.

PHP is very similar to C, in that you can selectively turn off groups of warnings/errors. If a third party deprecates something that only affects your code if you've decided to turn deprecations into exceptions, so it's low impact.