pkg-config

[Regina Obe]

> I do not understand the need for new postgis to support old geos.
> People are either drinking the LTS koolaid and should be happy with old
> everything, or they should be relatively up-to-date.  My personal rule is
that
> when Foo N is released on date D, it should be happy with any version of
any
> dependency, as long as that version is at least the version that was
generally
> recommended for all uses on D - 2years.
> 
That's nice in theory but at least in my reality, some people want a really
new PostGIS
and will stick with LTS from 2 years ago which ships with an old GEOS.
Sure they'd like a new GEOS especially if it has improvements they are
looking to take advantage of,
but OS upgrades are scary and database upgrades are scary too (why we
support like 4-5 versions of PostgreSQL on each PostGIS version)

I still see a lot of GEOS 3.9s out there of people who really want a PostGIS
3.5 badly.
GEOS 3.8 is kinda where I feel the fuzzy zone is.  I know two people who'll
be a bit upset if we drop support for GEOS 3.8
in PostGIS 3.5.

But you can't make everyone happy.

I'd like to hit the 75% mark and my gut feeling says the 75% mark is
somewhere around GEOS 3.8, but one can argue
how much new functionality we'll have in PostGIS 3.5 that will be off limits
to GEOS 3.8 to make it not worthwhile for a GEOS 3.8 user
to be using a newer PostGIS given that PostGIS 3.4 we've probably got at
least another 3 years of support on that.

> That is not pseudocode; it's real.  It is -modversion instead of -version
because
> you want to probe geos and its version, not find out the version of
pkg-config.
> An example of really running it, and with a bad package name that is not
found.
> 
>   $ pkg-config --modversion geos
>   3.12.1
>   $ pkg-config --modversion geoos
>   Package geoos was not found in the pkg-config search path.
>   Perhaps you should add the directory containing `geoos.pc'
>   to the PKG_CONFIG_PATH environment variable
>   Package 'geoos', required by 'virtual:world', not found

Nice