Use host data from /usr/share/zoneinfo on Unix

[ijackson]

Hi.

chrono-tz contains the Olson TZ data (at least, AFAICT, it does on crates.io, although it's not in git). No doubt this is good for Windows where the OS does not provide sensible timezone data.

But on Unix, the OS provides the Olson TZ database directly, generally in /usr/share/zoneinfo. OS updates update it. On Unix it is not right that Rust programs should end up with the timezone data embedded into the program, because if governments change the clocks (which they have been known to do at very short notice) this should be handled by an OS update, not by having to give everyone rebuilt Rust binaries.

So it seems to me that on Unix, chrono-tz should (by default at least) only use data from the OS installed timezone database. Would you be amenable to something like this? It seems to me that the default behaviour should be controlled by a feature flag.

I think implementing this needs an impl of TimeZone for &[parse_zoneinfo::ZoneInfo], or something along those lines.

[quodlibetor]

Yes, I would like this to be supported.

Right now you should be able to use the tzfile crate, although I'm not sure how mature it is.

[ijackson]

Yes, I would like this to be supported.

Right now you should be able to use the tzfile crate, although I'm not sure how mature it is.

Thanks for the reference! I hadn't found that crate, so pointing me at that is super-useful to me since I my program doesn't run on Windows anyway...

In this Issue I think I am saying, therefore, that chrono-tz should use tzfile (by default) on Unix.