https://gcc.gnu.org/bugzilla/show_bug.cgi?id=124539
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
We don't implement this:
If a continuation line subtracts N seconds from the UT offset after a
transition that would be interpreted to be later if using the continua‐
tion line's UT offset and rules, the “until” time of the previous zone
or continuation line is interpreted according to the continuation line's
UT offset and rules, and any rule that would otherwise take effect in
the next N seconds is instead assumed to take effect simultaneously.
For example:
# Rule NAME FROM TO - IN ON AT SAVE LETTER/S
Rule US 1967 2006 - Oct lastSun 2:00 0 S
Rule US 1967 1973 - Apr lastSun 2:00 1:00 D
# Zone NAME STDOFF RULES FORMAT [UNTIL]
Zone America/Menominee -5:00 - EST 1973 Apr 29 2:00
-6:00 US C%sT
Here, an incorrect reading would be there were two clock changes on
1973-04-29, the first from 02:00 EST (-05) to 01:00 CST (-06), and the
second an hour later from 02:00 CST (-06) to 03:00 CDT (-05). However,
zic interprets this more sensibly as a single transition from 02:00 CST
(-05) to 02:00 CDT (-05).
I think we use the incorrect reading.
