[Nix-dev] should libc depend on tzdata

[Mihaly Barasz]

Hello,

Lately I've been paying more attention to the time zone handling in
Nix and I realized something that strikes me as weird. I've been
bumping into this before, but didn't pay much attention. The issue is
the following:

To get proper time zone handling in Nix/NixOS you _have to_ have the
TZDIR environment variable set.

This is in stark contrast with "traditional" linux distributions,
where libc has the location of "system time zone database" compiled
in, and you only need to set TZDIR if you want to use a different one.

And, this does cause random issues once in a while: eg., the
environment variable is not set by cron on NixOS, so stuff isn't
working from cron if you change your TZ...

This also seems contrary to Nix' spirit that the dependencies should
be explicit... So, I'd like to raise the following question:

Shouldn't libc depend explicitly on tzdata and use it as its `zonedir`?

This might turn out not completely trivial technically, I didn't
finish testing it yet. But, I didn't get into roadblocks yet. And, if
this is done, there are potential simplification opportunities; most
importantly: we don't need to set up TZDIR in all the random places.
:)

Opinions?

Mihaly