Past times can be one hour off because of DST mismatch

[barefootcoder]

I think I can explain this most easily with a demonstration, using faketime (from the package of the same name):

[cibola:~/proj/date-easy] date +%z
-0700
[cibola:~/proj/date-easy] faketime 12/31/1969 date +%z
-0800
[cibola:~/proj/date-easy] perl -MTime::ParseDate -le 'print parsedate("1969/12/31 16:00:00")'
-3600

The proper answer, in my particular timezone, is 0.

This problem appears to be happening because this particular example fires tz_local_offset (in Time::Timezone), which doesn't account for any discrepancy in DST between the past and present. tz_offset, for instance, specifically checks for the $dst flag of the time in question to see if it should account for DST in choosing the right timezone. But tz_local_offset doesn't bother, since there's only a single timezone.

However, even though there's no difference geographically, there's a difference temporally. Currently we're in DST where I am, but the time being parsed was not in DST at that point in time. So the offset being used is actually one hour off.

I don't see a quick fix here, although I note that Date::Parse gets it right, so perhaps they have some code worth stealing. But I think it's just a matter of comparing the DST flag for the passed in time vs the current time and adjusting appropriately if they don't match.

Or perhaps you can see a more elegant solution. :-)

[barefootcoder]

So, if I were to submit a patch attempting to fix this issue, is that something that you would consider merging?

[muir]

Yes

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On Fri, Dec 7, 2018 at 3:07 PM Buddy Burden ***@***.***> wrote: So, if I were to submit a patch attempting to fix this issue, is that something that you would consider merging? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#8 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AATWFaILFqztCJONgtBUS2Jf82V_5ujiks5u2vSlgaJpZM4IH9og> .