Version 2024.2

Upstream version 2024b released 2024-09-04T19:27:47+00:00

Briefly:

Improve historical data for Mexico, Mongolia, and Portugal. System V names are
now obsolescent. The main data form now uses %z. The code now conforms to RFC
8536 for early timestamps. Support POSIX.1-2024, which removes asctime_r and
ctime_r. Assume POSIX.2-1992 or later for shell scripts. SUPPORT_C89 now
defaults to 1.

Changes to past timestamps

Asia/Choibalsan is now an alias for Asia/Ulaanbaatar rather than being a
separate Zone with differing behavior before April 2008. This seems better given
our wildly conflicting information about Mongolia's time zone history. (Thanks
to Heitor David Pinto.)

Historical transitions for Mexico have been updated based on official Mexican
decrees. The affected timestamps occur during the years 1921-1927, 1931, 1945,
1949-1970, and 1981-1997. The affected zones are America/Bahia_Banderas,
America/Cancun, America/Chihuahua, America/Ciudad_Juarez, America/Hermosillo,
America/Mazatlan, America/Merida, America/Mexico_City, America/Monterrey,
America/Ojinaga, and America/Tijuana. (Thanks to Heitor David Pinto.)

Historical transitions for Portugal, represented by Europe/Lisbon,
Atlantic/Azores, and Atlantic/Madeira, have been updated based on a close
reading of old Portuguese legislation, replacing previous data mainly
originating from Whitman and Shanks & Pottenger. These changes affect a few
transitions in 1917-1921, 1924, and 1940 throughout these regions by a few hours
or days, and various timestamps between 1977 and 1993 depending on the region.
In particular, the Azores and Madeira did not observe DST from 1977 to 1981.
Additionally, the adoption of standard zonal time in former Portuguese colonies
have been adjusted: Africa/Maputo in 1909, and Asia/Dili by 22 minutes at the
start of 1912. (Thanks to Tim Parenti.)

Changes to past tm_isdst flags

The period from 1966-04-03 through 1966-10-02 in Portugal is now modeled as DST,
to more closely reflect how contemporaneous changes in law entered into force.

Changes to data

Names present only for compatibility with UNIX System V (last released in the
1990s) have been moved to 'backward'. These names, which for post-1970
timestamps mostly just duplicate data of geographical names, were confusing
downstream uses. Names moved to 'backward' are now links to geographical names.
This affects behavior for TZ='EET' for some pre-1981 timestamps, for TZ='CET'
for some pre-1947 timestamps, and for TZ='WET' for some pre-1996 timestamps.
Also, TZ='MET' now behaves like TZ='CET' and so uses the abbreviation "CET"
rather than "MET". Those needing the previous TZDB behavior, which does not
match any real-world clocks, can find the old entries in 'backzone'. (Problem
reported by Justin Grant.)

The main source files' time zone abbreviations now use %z, supported by zic
since release 2015f and used in vanguard form since release 2022b. For example,
America/Sao_Paulo now contains the zone continuation line "-3:00 Brazil %z",
which is less error prone than the old "-3:00 Brazil -03/-02". This does not
change the represented data: the generated TZif files are unchanged. Rearguard
form still avoids %z, to support obsolescent parsers.

Asia/Almaty has been removed from zonenow.tab as it now agrees with
Asia/Tashkent for future timestamps, due to Kazakhstan's 2024-02-29 time zone
change. Similarly, America/Scoresbysund has been removed, as it now agrees with
America/Nuuk due to its 2024-03-31 time zone change.

Changes to documentation

The documentation now reflects POSIX.1-2024.

Changes to commentary

Commentary about historical transitions in Portugal and her former colonies has
been expanded with links to many relevant legislation. (Thanks to Tim Parenti.)