pkg-config and cached *.pc files under the work directory

[Dave Tyson <dtyson%anduin.org.uk@localhost>]

I have been trying to understand why when building MesaLib with the llvm 
and dri options it fails to find dri3proto yet finds dri2proto without 
any problem. (as per thread in pkgsrc-users) 

Both config files exist in /usr/X11R7/lib/pkgconfig and so I was baffled 
why the configure script failed to find several packages.

A bit of grovelling in the internals of the package build process shows 
that pkg-config actually uses a local copy of the package configuration 
files in:

/usr/pkgsrc/graphics/MesaLib/work/.buildlink/lib/pkgconfig

and there is no surprise that this has an entry for dri2proto.pc, but 
none for dri3proto.pc (and a few other required config files)!

The question is what guides the package install process in deciding 
which files to copy into the above directory from the source files in 
the base and elsewhere. The pkgsrc guide seems to be silent on this 
area. 

I can see there are some references to *.pc files in some of the .mk 
files but it seems far from obvious what decides which files to copy in. 
If I can manage to get the relevant pc files added in then I might stand 
a fighting chance of moving forward...

Could a pkgsrc expert please enlighten me?

Cheers,
Dave

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