Re: Setting TZDIR (was Re: A single reference to installed non-binaries)

[Leo Famulari <leo@famulari.name>]

On Tue, Aug 17, 2021 at 08:49:27PM +0200, Edouard Klein wrote:
> It does, thanks, but I'm in a bit of a pickle there because this
> packagge needs, for reasons outside of my control, to be deployable on
> a multitude of host (non-GuixSD) linux distributions, and as a docker
> container. In those cases, I can't expect the timezone data to be up to
> date or to be there at all.
> 
> Even if I list tzdata as a dependency, the host system's TZDIR will not
> point to it.

You wouldn't list tzdata as a dependency at all. It's the responsibility
of the host operating system to provide the correct and current time
zone database, and applications should look it up at run-time via TZDIR.

If you are deploying to systems without a time zone database, then you
could indeed consider "baking" the reference into your package while
building, or consider if you need to care about having correct local
time at all.

> I understand that if I regularly guix pull and guix package -u, then the
> tzdata package will be kept up to date. Is that correct ?

Yes. But, installed packages should not need to be rebuilt to display
the correct time. To elaborate, if you hardcode a store reference to
tzdata in your package definitions, then old generations of installed
packages will eventually display incorrect local time, because time
zones are frequently changed by local governments. And that failure mode
is not okay for packages included in GNU Guix.

This is one of the rare cases in Guix packaging where dynamic lookup of
dependencies is preferred.