Brazil rule issue

Gustavo De Nardin gustavodn at
Wed Dec 10 04:50:02 UTC 2008

2008/12/8 Robert Elz <kre at>:
>    Date:        Mon, 8 Dec 2008 02:55:34 -0200
>    From:        "Gustavo De Nardin" <gustavodn at>
>    Message-ID:  <50af0a260812072055x338351c8saadc4b8805261761 at>
> I can't believe this discussion is still going on, or for that
> matter, ever started.

I don't read this list daily, I replied when I read the rest of the thread.

> Aside from the perfectly normal small group of messages that started
> this Subject header, the rest of this thread started with a quote
> from one of the messages that was on topic (explaining how the tz
> rule files work) that included ...
> olsona at said:
>  | The cases are specified through 2038 (the maximum year associated with a
>  | signed, 32-bit time_t value). After that (through year "max") the rules say
>  | that DST ends the third Sunday of February every year; this is wrong by a
>  | week in some cases but is better than nothing.
> to which you responded ...
> gustavodn at said:
>  | Just a note.. personally I don't think a knowingly wrong rule is "better than
>  | nothing",
> Did you actually read what ado said?  The "this is wrong" (that is,
> we expect now to have invalid data) applies to the years 2039 and beyond.
> What's more, the error is only sometimes, even after 2039, other years
> (as we understand the rules now) tzdata is going to be correct.

Yes, finally we have a consistent and predictable rule instead of per
year decrees. My point was about the previous years, and (obviously
not a matter for Brazil anytime soon now) about the practice of making
the current year rule be valid for all unknown future years.

> But do you seriously believe that Brazil (of all places - perhaps the
> country in the world that has the hardest possible summer time decisions
> to make) is going to keep the rules that we believe are true now for the
> next 20 years, without changing them???

It doesn't matter. The previous decrees were for the current year,
they specifically said "from dd/mm/yyyy to DD/MM/YYYY", but the rules
were written as valid for the current and future years, so the rules
were wrong. The arguments that say "it's better to have the rule valid
for future years" are also wrong, as every year the DST changes here
brings discussions about dropping the DST entirely (and some states do
so on their own decision I believe), so maybe in the future we don't
have it at all (sure, very unlikely, but  ...). The new decree is for
the current and future years, so writing a rule for the current and
future years is the right thing now.

(Sorry for cutting the rest, but it was a bit longish and besides my
point, per above.)

I'm OK if the consensus here is to make per-year decrees valid for the
future as a "guess", and even more so because this shouldn't affect
Brazil "anymore" now ;], but the given arguments don't cut it to me,
compared to the griefs that behavior actually caused (specially when
previous year's rule started too much before current year's decree was
stated for people to talk about DST and remember it should be fixed
before causing problems).


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