pkg-config

[Regina Obe]

> The big question is: do correct installs of all supported geos versions
> install pkg-config?   My pkgsrc install of geos certainly does but I'm
> on the latest release.  If you can tell someone with geos  and without a
.pc that
> their packaging/install is broken and they should fix it, and feel ok
about that,
> then yes this is good.
>
I presume you mean current?
For PostGIS 3.5+, we dropped support for all GEOS < 3.8 
Sadly it looks like GEOS 3.8 (or at least my setup) does not install a
pkgconfig, but GEOS 3.9 on does.

However, we just EOL'd GEOS 3.8 https://libgeos.org/usage/download/  so in
theory we can have another
motion to drop GEOS 3.8 as well in PostGIS 3.5.  That would I think clear up
some extra baggage we have left for 3.8.

So as it stands we still need to support geos-config, and we really should
anyway for another release, with a note saying
"Change your build script cause this is a legacy way of doing it".  Similar
to the message we had thrown up about proj when we enabled the pkg support
for proj.
 
> If there are non-broken geos installs that are missing a .pc, then I think
you need
> 
> >   if (pkg-config found) AND pkg-config --modversion geos
> >     use pkg-config
> >   elseif (geos-config on path)
> >     use geos-config
> >   else
> >     error cannot find geos

Greg is that pseudo code or you can pass that --modversion geos to pkg and
it will detect if your pkg has it?
That will deal with my concern, of having missed putting GEOS in my pkg
path.