I wrote:
I also pointed out America/Argentina/San_Luis. It turns out that zic is deliberately declining to fill the POSIX-TZ field, because of the DSTness of the last observation. This is the same reason why it left that field empty in Africa/Cairo, once it had made the mistake about which observation came last. I have a plan for improving this situation, which I'll address in a separate patch.
Attached patch changes this behaviour. In the case where 400 years of explicit observations are being generated due to inability to express the extension rule in the POSIX-TZ field, if there are actually no observations being generated then a redundant observation is added on the end. This provides an explicit endpoint for the explicit observations. Code that claims no knowledge after the final transition, like my Perl module, are OK for 400 years. Code that tries to repeat the last 400 years has some clue as to which 400 years to repeat. I extended the existing exception for the case where the source lists explicit transitions up to 2037. The code recognises this as indicating that the behaviour after 2037 is not expressed in the zone source, rather than being an explicit list of transitions that actually ends in 2037. The code declines to fill the POSIX-TZ field in this case. I made it also decline to add the redundant observation 400 years later. When this is applied on top of my previous patch, the only tzfile affected by this change is America/Argentina/San_Luis. I reviewed all the tzfiles that have their POSIX-TZ field empty. I believe all the remaining ones have a good excuse. Specifically (excluding links): America/Santiago Antarctica/Palmer Pacific/Easter "Chile" rules, transitions on Sun>=9, can't be expressed in POSIX-TZ America/Godthab "EU" rules, transitions at 01:00 UT which would be 22:00 or 23:00 of previous day in local time, can't be expresssed in POSIX-TZ Asia/Amman "Jordan" rules, transition at 24:00 local time, can't be expressed in POSIX-TZ Asia/Jerusalem "Zion" rules, real rule inexpressible in source, transitions listed explicitly up to 2037 Asia/Tehran "Iran" rules, real rule inexpressible in source, transitions listed explicitly up to 2037 -zefram