[tz] Wrong symlinks with BACKWARD=backward PACKRATDATA=backzone

[Paul Eggert]

On 2024-04-05 04:42, Benjamin Drung via tz wrote:
> Switching to TZDB's zic would be an option for the development release
> of Ubuntu, but not for the stable releases: We ship tzdata.zi in
> /usr/share/zoneinfo and we do not know if users rely on being able to
> use zic from glibc on that file.

Makes sense.

>> Come to think of it, glibc should do that too. I'll add that to my list
>> of things to do.
> 
> That would be great.

I committed that change to the glibc master repository and it should 
appear in the next glibc release. See 
<https://sourceware.org/git/?p=glibc.git;a=commit;h=1f94147a79fcb7211f1421b87383cad93986797f>.


> Attached the new version of the patch to avoid adding a new data format.

That patch would be problematic, as main.zi should reflect what's in the 
main files. That is, "cat africa antarctica ..." should output a copy of 
main.zi.

Let's take a step back for a minute. Today I read the bug report 
<https://bugs.launchpad.net/ubuntu/+source/tzdata/+bug/2003797> that 
caused Ubuntu to start using PACKRATLIST=zone.tab recently. This bug 
report doesn't mention user requests; instead, it seems to have been 
prompted by your impression that some Ubuntu users might be bothered by 
tzdata 2022b's changes to pre-1970 Europe/Oslo.

As you can guess, I doubt whether Ubuntu users care much about pre-1970 
computer-generated timestamps in Norway. If I'm wrong and some users do 
care, Ubuntu could instead move the packrat stuff to its tzdata-legacy 
package, or to a new tzdata-packrat package that contains the packrat 
info. This would simplify maintenance of main tzdata package, and would 
lessen the number of trivial differences between default Ubuntu and 
elsewhere.

Even if for some reason it's necessary to keep backzone's Europe/Oslo in 
Ubuntu's tzdata package, that doesn't mean Ubuntu tzdata needs all of 
backzone's entries. Instead, it could keep just the backzone entries 
that Ubuntu users actually need, and omit troublemaking entries like 
Africa/Asmara where the data are low quality and are surely wrong anyway 
(does anybody really think that the inhabitants of Asmara adjusted their 
clocks by 12 seconds on January 1, 1890 at midnight? I don't). Ubuntu 
could do that by creating a file packrat-ubuntu.tab containing lines 
like this:

   NO	+5955+01045	Europe/Oslo

i.e., just the subset of zone.tab that refers to backzone entries 
containing high-quality pre-1970 data that users actually need, and then 
building with:

   make PACKRATDATA=backzone PACKRATLIST=packrat-ubuntu.tab

Surely, though, it would be simpler and more reliable to eliminate the 
packrat stuff from the tzdata package, possibly moving it to 
tzdata-legacy or to a new tzdata-packrat package.