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

[Jonathan Wakely]

On Thu, 2 May 2024 at 08:18, Florian Weimer wrote:
>
> * Jonathan Wakely via tz:
>
> > And that matches what glibc does: it finds the earliest transition
> > with SAVE of zero, and uses that LETTER for the period before the
> > first transition.
>
> Do you mean zic instead of glibc?  I don't think we have a .zi parser in
> glibc proper.  We mostly bundle zic for historic reasons.

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.

There's similar logic here:
https://sourceware.org/git/?p=glibc.git;a=blob;f=time/tzfile.c;h=41475399643913ac4eb78c7f84151692bc521984;hb=HEAD#l596

When I ran `TZ=Australia/Sydney date -d 1900-01-01` under gdb that
seemed to be the code that decided on AEST, but maybe I got confused.