[tz] TZDB use cases
Michael H Deckers
michael.h.deckers at googlemail.com
Tue Oct 5 13:49:38 UTC 2021
On 2021-10-04 01:45, Paul Eggert commented on my remark:
>> it is not even true that the two time scales
>> always agree after 1970, although most people seem to believe
> If there are counterexamples please suggest fixes, preferably in 'git
> format-patch' form. Although 'backzone' is documented to be less
> reliable, we're certainly open to fixes from the community.
Before proposing premature fixes, I think it is appropriate
to first agree and then specify what the backzone file should
The backzone file says:
# This file contains data outside the normal scope of the tz
# in that its zones do not differ from normal tz zones after 1970.
If this were intended to mean that
# The timezones in this file agree after 1970 with tz zones
# in other files.
then America/Ensenada must not occur in backzone. But the text does
not say that, and America/Ensenada occurs in backzone; so we do
not know what, if anything at all, is wrong here.
The backzone file also says:
# ... Many of
# the zones were formerly in other source files, but were
# replaced by links as their data entries were questionable
# differed from other zones only in pre-1970 timestamps.
What is the purpose of keeping "questionable" versions of a timezone
when we have a better version? If we know an error, it should be
corrected -- but I do not see any purpose in keeping the incorrect
version in backzone.
And if we do not know where the errors are, then the timezone is in good
company: except for a few carefully researched cases, we are never sure
whether we have listed all transitions, or whether all transitions are
correct. No need to keep it in backzone either.
So the stuff about "questionable" data entries should disappear from
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