On 3/25/22 15:36, Michael H Deckers via tz wrote:
• The fact that two timezones agree since 1970 is not represented independently from the data of each timezone.
Yes, and more generally the problem is that the zic input format does not allow one Zone to say something like "before 1966 I was like this other Zone", or "between 1922 and 1945 I was like this other Zone". This problem is not limited to data in the "backzone" file. To fix this more general problem, we could change the zic input format and change the data accordingly. (This has already been proposed, but has not been implemented.) Or we could have some sort of prepass over the data.Or we could do both. I doubt whether it'd be worth the hassle of trying to fix it only for "backzone".
The file backzone is an integral part of the tzdb data, not just a container for additional data of lesser quality.
Here I'm afraid I'll have to disagree. "backzone" contains a considerable amount data of lesser quality. (Some of the lack of quality is that we don't record or even know how low the quality is.) I don't have time to maintain "backzone" well and I doubt whether anyone else does either. This need to limit the maintenance burden (much of it political, and some behind the scenes) is not something always appreciated by users. That doesn't make it any less real.
Thus we should get rid of Zone data for Argentina/Rosario etc (or else update them); keeping data that are known to be wrong is not only useless, it is an invitation for consequential errors.
Feel free to propose changes to "backzone" along these lines. Please send them in "git format-patch" form. If there's no objection it wouldn't be much work to install them.
• The fact that two timezones agree since 1970 has nothing to do with the fact that some timezones have changed their names, with the old names being kept as Links to the new names. Currently, however, Links representing one or both facts are kept in the same file backward,
Yes, that's a problem and should be fixed. Much of it is a relic of last year's controversy, which ended up with only nine zones being moved to "backward" instead of the thirty-odd that I originally proposed, under the idea the original proposal was too big a change to install all at once. It's time to move the rest of the zones (or at least, move nine more), and once the move is done we can attack the problem of categorizing Link lines better than they're categorized now, with the goal of making it easier for people like Stephen Colebourne to maintain downstream versions that use a different approach.