A DESCRIPTION OF THE PROBLEM :
Starting in tzdb release 2022b, tzdata vanguard form has used "%z" in a Zone line's FORMAT column to indicate that the time zone abbreviation should be determined automatically from the time zone offset.

Also, starting in release 2022f, tzdata vanguard form uses a zone named "GMT", not "Etc/GMT", as the base for all the zones that stand for GMT.

TZUpdater should support these vanguard forms, as the mainline tzdata files will start using them soon. As far as I can tell, this is a new issue, not mentioned in earlier bug reports about TZUpdater and earlier vanguard forms.

The TZUpdater maintainers don't seem to have mentioned on the tz mailing list the status of TZUpdater and these uses of new features so I am filing this bug report as a heads-up.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
wget https://data.iana.org/time-zones/releases/tzdata2023c.tar.gz
wget https://data.iana.org/time-zones/releases/tzcode2023c.tar.gz
tar xf tzcode2023c.tar.gz
tar xf tzdata2023c.tar.gz
make vanguard.zi

Now, feed vanguard.zi as input to TZUpdater.


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
TZUpdater should work.
ACTUAL -
I don't use TZUpdater and so don't know what happens.
If TZUpdater already does the equivalent of "make rearguard.zi" it should be OK.

CUSTOMER SUBMITTED WORKAROUND :
make rearguard.zi

Feed rearguard.zi as input to TZUpdater.

FREQUENCY : always