-isystem in pc(5) (was: Packaging liba2i, a new library I wrote, for Gentoo)

[Alejandro Colomar]

[CC += libbsd, Guillem]

Hi Sam,

On Wed, Feb 07, 2024 at 03:01:14AM +0100, Alejandro Colomar wrote:
> > 
> > * pkgconfig: The pkgconfig file looks wrong
> >   (https://www.alejandro-colomar.es/src/alx/alx/lib/liba2i.git/tree/share/pkgconfig/liba2i-uninstalled.pc#n13):
> >   I don't think you should be injecting things into -isystem like that,
> 
> Hmm, I thought this was normal.  Otherwise, programs would get warnings
> from included libraries, no?
> 
> But after your comment, I looked at my system, and indeed you seem to be
> right:
> 
> 	$ grep -hr Cflags /usr/share/pkgconfig/ \
> 	| grep -o -- '-I[^ /]*' \
> 	| sort \
> 	| uniq -c;
> 	     31 -I${includedir}
> 	$ grep -hr Cflags /usr/lib/x86_64-linux-gnu/pkgconfig/ \
> 	| grep -o -- '-I[^ /]*' \
> 	| sort \
> 	| uniq -c;
> 	      4 -I
> 	      1 -I${OpenEXR_includedir}
> 	      3 -I${includearchdir}
> 	    154 -I${includedir}
> 	      1 -I${libdir}
> 	      2 -I${prefix}
> 	      1 -I${sdkdir}

I have seen again the first pc(5) file that I saw in my life, from which
I learnt to write my libraries.  It was libbsd, which I started using
long ago.  It uses -isystem.  That's probably why I always used
-isystem.  Is it problematic?

	$ pkgconf --cflags libbsd-overlay
	-isystem /usr/include/bsd -DLIBBSD_OVERLAY

I've always thought it would be the right choice, as you don't want to
inject warnings in other projects.  But majority seems to be with '-I',
as I learnt recently.

	$ grep -hr Cflags /usr/lib/x86_64-linux-gnu/pkgconfig/ \
	| grep -o -- '-isystem' \
	| sort \
	| uniq -c;
	      7 -isystem


Have a lovely day!
Alex

-- 
<https://www.alejandro-colomar.es/>
Looking for a remote C programming job at the moment.
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