chrono-tz v0.10.0: 2024b

TZDB version 2024b (2024-09-05).

Changes

• Make OffsetName::abbreviation return an Option.
  This reflects that numeric values such as +11 are no longer encoded in the upstream TZDB as abbreviations (#185).

TZDB 2024b

The 2024b release of the tz code and data is available.

This release is prompted by the accumulated weight of many non-urgent changes to both code and data. It changes one timestamp abbreviation, for the long-obsolete System V setting TZ='MET'; see below. Otherwise, the timestamps affected by this release all predate April 2008, so you can skip this release if your application uses only tzdata and does not use older timestamps.

This release contains the following changes:

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.