Re: perl 5.36, C99, -Wdeclaration-after-statement -Wshadow=compatible-local

Andres Freund <andres(at)anarazel(dot)de> writes:
> The attached *prototype* patch is a slightly different spin on the idea of
> using -isystem: It adds a
> #pragma GCC system_header
> to plperl.h if supported by the compiler. That also avoids warnings from
> within plperl and subsidiary headers.

> I don't really have an opinion about whether using the pragma or -isystem is
> preferrable. I chose the pragma because it makes it easier to grep for headers
> where we chose to do this.

This seems like a reasonable answer. It feels quite a bit less magic
in the way that it suppresses warnings than -isystem, and also less
likely to have unexpected side-effects (I have a nasty feeling that
-isystem is more magic on macOS than elsewhere). So far it seems
like only the Perl headers have much of an issue, though I can
foresee Python coming along soon.

> In the compiler test, I chose to not check whether -Werror=unknown-pragmas is
> supported - it appears to be an old gcc flag, and the worst outcome is that
> HAVE_PRAGMA_SYSTEM_HEADER isn't defined.
> We could alternatively define HAVE_PRAGMA_SYSTEM_HEADER or such based on
> __GNUC__ being defined.

Hmm ... I guess the buildfarm would tell us whether that detection works
correctly on platforms where it matters. Let's keep it simple if we
can.

regards, tom lane