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

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

On Friday 18 May 2018 21:07:39 Greg Troxel wrote:
> Dave Tyson <dtyson%anduin.org.uk@localhost> writes:
> > 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.
> 
> First, you really need to remove all work/ directories before trying
> to build anything, especially after changing anything.  You might
> well not be having problems from stale work directories, but it's a
> common issue.
> 
> pkgsrc has a facility called "buildlink3".  The point is to create a
> directory of links to files that belong to packages that are declared
> as dependencies, as part of a scheme to hide files that are not
> explicitly recorded as dependencies.
> 
> Generally, packages have a line like:
> 
>   .include "../../x11/gtk2/buildlink3.mk"
> 
> which declares gtk2 as a manifest dependency.  This ensures that the
> package is installed, and creates symlinks to the .h files, the libs,
> and the pkgconfig file.
> 
> 
> For packages that can be from base or from pkgsrc, there is a
> "builtin.mk" that decides if the base system version can be used, or
> if it's necessary to use the pkgsrc version.  Either way, the
> headers/libs/pkgconfig files are provided by symlinks.
> 
> Then, the build uses the bl3 symlinks and tries to avoid using normal
> paths that pick up installed packages.  The point is to avoid having
> packages that are installed but not declared as manifest dependencies
> be visible to the build, so that packages are not different because
> some non-declared package happens to be installed.
> 
> So in the case of MesaLib, it may be that the manifest dependencies
> are not quite right.  It's fairly complicated, and I don't understand
> it well enough to say.  (I would expect that without the dri option,
> all kinds of dri would be hidden.)
> 
> In work/.buildlink, there will be logs of what was included.  You can
> read the bl3 and builtin.mk files and print variables with "make
> show-vars VARNAMES=USE_BUILTIN.foo" to figure out what choices were
> made.  No magic, just more details than normal people have the
> patience to understand.
> 
> If you do "make PKG_DEBUG_LEVEL=1", you'll get extra debug output that
> will explain many of the steps.  Or 2, if you can stand to read it.

Hi Greg, thanks for the explanation. I always clear out the work 
directory - have been burnt in the past. I'll take a look the the debug 
output and see if I can spot where the problem lies and if I can find a 
fix I will send-pr it.

Cheers,
Dave

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