[tz] Version identification (was Re: Downstream use of 2021c)

[Tom Lane]

Guy Harris <gharris at sonic.net> writes:
> On Oct 7, 2021, at 10:00 AM, Tom Lane via tz <tz at iana.org> wrote:
>> I'm envisioning that there could be a text file at the top level,
>> say /usr/share/zoneinfo/version in typical layouts, containing
>> "2021a" or the appropriate string.  This'd make it a lot easier
>> to diagnose what you've got in a particular installation.

> $ cat /usr/share/zoneinfo/+VERSION
> 2021a

Interesting ... and in fact, Apple's labeling it in another way too,
because I see this on my Mac laptop:

$ ls -l /usr/share/zoneinfo/
lrwxr-xr-x  1 root  wheel  38 Sep 13 19:15 /usr/share/zoneinfo/ -> /var/db/timezone/tz/2021a.1.0/zoneinfo

But that pretty much just begs the point, which is that there's
no *standard* cross-platform way to get this info.  On my RHEL
workstation, I don't see any identification info except the
first line of tzdata.zi, which isn't a standard inclusion either.
(Of course, I can consult the RPM package database to find out the
version of the tzdata package ... still more platform dependency.)

My point isn't whether it's possible to figure this out on any
given platform, but that tzdata itself ought to define a standard
way to find it out.  And I do not agree with Paul's opinion that
"include tzdata.zi" is a good enough answer; lots of platforms
won't care to expend the disk space to do it that way.

(But, in view of Apple having already done it like that, maybe
there's something to be said for using +VERSION as the file name.)

			regards, tom lane