[tz] Why is "AEST" the abbreviation for Australia/Sydney in 1900?

[Florian Weimer]

* Paul Eggert:

> On 2024-05-02 01:10, Jonathan Wakely via tz wrote:
>
>> I mean glibc code such as:
>> https://sourceware.org/git/?p=glibc.git;a=blob;f=time/tzfile.c;h=41475399643913ac4eb78c7f84151692bc521984;hb=HEAD#l416
>> The comment says it's finding the offsets, but it seems to be finding
>> the abbreviations for the first two transitions, storing them in the
>> __tzname array.
>
> That code is present for a different reason. It's trying to support
> obsolescent (but POSIX-required) variables like tzname, which in
> general make no sense when TZif files are used. (The next POSIX draft
> tries to fix this, but it's messed up, and I haven't had time to
> interact with the POSIX committee to clean things up.)
>
> These obsolescent compatibility variables are not related to the
> question of what is the proper abbreviation to use for timestamps in
> 1908.

Unfortunately, __tzname is also used internally to ferry around
information, see __tz_compute and the way it uses that to set tm_zone.
We should not be doing that, but it's the code we currently have. 8-(

Thanks,
Florian