Align rearguard metazone variant overrides with CLDR #6896
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We only need rearguard semantics while zone is in a metazone, and in fact with the current CLDR overrides we can only have overrides while a zone is in a metazone. Casablanca has not been in a metazone since TZDB started modeling it as negative DST. |
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Not sure what you mean by "CLDR is agnostic to the guardedness of Casablanca".
Because "we've always done it this way" is not a convincing argument and I'm trying to get a way from rearguard. |
CLDR does not define the offsets for Casablanca post-2018 and therefore it is not the decision-maker. We are the decision-maker in ICU4X.
It's a very convincing argument. We are trying to get to CLDRguard, and until CLDRguard defines this behavior, we shouldn't proactively adopt something else. |
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Could we make UTS 35 say "the DST semantics are those of TZDB Rearguard except where there are overrides"? |
No. We don't have access to rearguard during datagen, we had hardcoded this before but that is not a long term solution. Outside a metazone it does not matter. |
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If it doesn't matter at all for anything (I guess with no Specific Location there isn't any case where it is used), then can we remove this data from TimezonePeriodsV1? |
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We could, however there is some value knowing that Casblanca can be +1 or +0, without judging which one is standard time. We also wouldn't be improving data size, as the offsets need to be there for metazone periods and making this variably-typed is only going to increase size. |
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If I were making this change, I would have introduced a condition like "if DST offset < 0, then flip standard/daylight to make the DST offset > 0". I think it is harmful to change this time zone to vanguard, even if we aren't using the DST bit for anything at this moment in time. I also do not wish to see this PR used as precedent for introducing negative DST in Casablanca or any other CLDR time zone. With that understanding, I'll unblock the PR.
Not vanguard, main. The default TZDB variant that many other systems are also using. |
Follow-up #6893