[tz] Swiss time selectable for Germany

[Paul Eggert]

On 2023-01-08 12:46, Guy Harris via tz wrote:
> Presumably updating glibc with a new tzdb release involves 1) updating libc's tzdb-reading code to support any new tzif features (and fix any bugs that we fixed, if they're also in their code, as well as picking up features they think reasonable) and 2) picking up new versions of the rest of the code and data.

Nowadays glibc does (1) but only part of (2). Glibc no longer syncs from 
tzdata (it has a copy of an old version, but just for testing; it's not 
meant for use). Instead, GNU/Linux distros put tzdata into a separate 
package, so that data can be updated quickly and independently of the C 
library. tzcode's executables are also typically put into a separate 
package, so at least three packages are involved: one for the C library, 
one for the tzcode executables, and one for tzdata. On Ubuntu these 
packages are called "libc6", "libc-bin", and "tzdata".

Glibc copies of tzcode source files like tzselect.ksh and zic.c are 
byte-for-byte identical with tzcode. In other words, there isn't a fork 
like there is currently with NetBSD (something I'd like to see fixed).

That being said, the GNU C library's copies of tzcode were last synced 
from tzdb 2020a, so they're due for a refresh, whenever I or someone 
else gets around to doing that.