Re: pgsql: Fix for globals.c- c.h must come first

On 2018-06-19 14:09:15 -0400, Tom Lane wrote:
> Bruce Momjian <bruce@momjian.us> writes:
> > On Sat, May 19, 2018 at 01:20:47AM +0000, Stephen Frost wrote:
> >> Commit da9b580 mistakenly put a system header before postgres.h (which
> >> includes c.h).  That can cause portability issues and broke (at least)
> >> builds with older Windows compilers.
> 
> > I assume there is no way to add defined and checks to globals.c and c.h
> > to cause a compile error when this happens.
> 
> Hm.  You could imagine adding something like
> 
> #ifdef some-relevant-macro
> #error include ordering problem, c.h must come before system headers
> #endif
> 
> near the head of c.h.  But I'm not sure how we'd get full coverage.
> The case presumably would only occur for off-the-beaten-path headers
> (this particular mistake was <sys/stat.h>), and there are lots of those.

If we were ok with doing this in a very platform specific manner, we
probably could make the dependency fairly generic. I.e. glibc IIRC will
pretty much always end up including features.h, so we could check for
that (#ifdef _FEATURES_H).  I'd suspect other C libraries have similar
things.

Greetings,

Andres Freund