[tz] Vanguard vs. "main" vs. rearguard
eggert at cs.ucla.edu
Mon Jun 7 17:01:02 UTC 2021
On 6/7/21 9:21 AM, Neil Fuller wrote:
> To fix this for future releases *safely*, I think downstream code like
> Android would need metadata at runtime (preferably mastered by TZDB) that
> indicates whether a zone ID is one of the ones that has flipped its
Surely it'd have to be more complicated than that, as a single Zone can
have negative DST some years, and positive DST other years. See
Africa/Windhoek, for example.
But perhaps I'm not understanding the problem correctly, as I don't see
why tzdb would need to maintain a separate set of data for this issue.
Android libraries could have a flag (or multiple versions, or however
Android folks like to do software changes) controlling whether an
application can tolerate negative DST. If the flag says "negative DST is
OK", the libraries can pass through data unscathed. If the flag says "I
don't want to see negative DST", then whenever the underlying data says
DST is negative, the Android library can swap standard and daylight time
and give the swapped info to the app. As I understand it, Android
libraries are already doing the latter; if so, all that needs to be
added is a flag so that they can do the former.
Anyway, I appreciate the info about why rearguard support will be needed
for quite some time.
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