Hi Yoshito, On Fri, 2023-05-19 at 21:20 +0000, Yoshito Umaoka via tz wrote:
Dear all, I was looking at some Unicode ICU test failure on Ubuntu related to time zone. ICU utilizes TZ database including backward file. In backward file, Europe/Tiraspol is defined as a link of Europe/Chisinau. So the actual rule is coming from Europe/Chisinau as below (2023c) # Zone NAME STDOFF RULES FORMAT [UNTIL] Zone Europe/Chisinau 1:55:20 - LMT 1880 1:55 - CMT 1918 Feb 15 # Chisinau MT 1:44:24 - BMT 1931 Jul 24 # Bucharest MT 2:00 Romania EE%sT 1940 Aug 15 2:00 1:00 EEST 1941 Jul 17 1:00 C-Eur CE%sT 1944 Aug 24 3:00 Russia MSK/MSD 1990 May 6 2:00 2:00 Russia EE%sT 1992 2:00 E-Eur EE%sT 1997 # See Romania commentary for the guessed 1997 transition to EU rules. 2:00 Moldova EE%sT I found behavior of Europe/Tiraspol is different on Ubuntu. When I set Europe/Tiraspol as the system time zone, the default offset set to timezone variable becomes -10800 (3 hour ahead of UTC). However, Europe/Chisinau above shows it should be -7200 (2 hour ahead of UTC) at this moment. (POSIX timezone variable should store “standard offset”, not counting daylight adjustment). On Ubuntu, when I set Europe/Tiraspol as system time zone, -10800 is set to timezone variable. However, when I set Europe/Chisinau, it changes to -7200. Then I realized Ubuntu is using backzone file, which contains different rule. In backzone file, Europe/Tiraspol is defined as below (2023c) # Moldova / Transnistria Zone Europe/Tiraspol 1:58:32 - LMT 1880 1:55 - CMT 1918 Feb 15 # Chisinau MT 1:44:24 - BMT 1931 Jul 24 # Bucharest MT 2:00 Romania EE%sT 1940 Aug 15 2:00 1:00 EEST 1941 Jul 17 1:00 C-Eur CE%sT 1944 Aug 24 3:00 Russia MSK/MSD 1991 Mar 31 2:00 2:00 Russia EE%sT 1992 Jan 19 2:00 3:00 Russia MSK/MSD I understand backzone was created for preserving zone definition of some locations which only differs pre-1970 date, and these data might not be reliable. In reality, I think most of TZ database consumer still rely on either backward or backzone for backward compatibility. I think it’s problematic if these two files produce different results today. I guess the zone definition in backzone file might be outdated, and Tiraspol is actually UTC+2/+3.
We (or better only blame me) enabled using backzone in Ubuntu recently (see https://launchpad.net/bugs/2003797), but noticed that this changes Europe/Tiraspol and some other timezones for post-1970 dates (see https://launchpad.net/bugs/2017999). So we are building tzdata with PACKRATLIST=zone.tab now to fix that. Please follow https://launchpad.net/bugs/2017999 for details and progress. -- Benjamin Drung Debian & Ubuntu Developer