2023a release of tz code and data available

22 Mar 2023

      The 2023a release of the tz code and data is available.

This release contains the following changes:

   Briefly:
     Egypt now uses DST again, from April through October.
     This year Morocco springs forward April 23, not April 30.
     Palestine delays the start of DST this year.
     Much of Greenland still uses DST from 2024 on.
     America/Yellowknife now links to America/Edmonton.
     tzselect can now use current time to help infer timezone.
     The code now defaults to C99 or later.
     Fix use of C23 attributes.

   Changes to future timestamps

     Starting in 2023, Egypt will observe DST from April's last Friday
     through October's last Thursday.  (Thanks to Ahmad ElDardiry.)
     Assume the transition times are 00:00 and 24:00, respectively.

     In 2023 Morocco's spring-forward transition after Ramadan
     will occur April 23, not April 30.  (Thanks to Milamber.)
     Adjust predictions for future years accordingly.  This affects
     predictions for 2023, 2031, 2038, and later years.

     This year Palestine will delay its spring forward from
     March 25 to April 29 due to Ramadan.  (Thanks to Heba Hamad.)
     Make guesses for future Ramadans too.

     Much of Greenland, represented by America/Nuuk, will continue to
     observe DST using European Union rules.  When combined with
     Greenland's decision not to change the clocks in fall 2023,
     America/Nuuk therefore changes from -03/-02 to -02/-01 effective
     2023-10-29 at 01:00 UTC.  (Thanks to Thomas M. Steenholdt.)
     This change from 2022g doesn't affect timestamps until 2024-03-30,
     and doesn't affect tm_isdst until 2023-03-25.

   Changes to past timestamps

     America/Yellowknife has changed from a Zone to a backward
     compatibility Link, as it no longer differs from America/Edmonton
     since 1970.  (Thanks to Almaz Mingaleev.)  This affects some
     pre-1948 timestamps.  The old data are now in 'backzone'.

   Changes to past time zone abbreviations

     When observing Moscow time, Europe/Kirov and Europe/Volgograd now
     use the abbreviations MSK/MSD instead of numeric abbreviations,
     for consistency with other timezones observing Moscow time.

   Changes to code

     You can now tell tzselect local time, to simplify later choices.
     Select the 'time' option in its first prompt.

     You can now compile with -DTZNAME_MAXIMUM=N to limit time zone
     abbreviations to N bytes (default 255).  The reference runtime
     library now rejects POSIX-style TZ strings that contain longer
     abbreviations, treating them as UTC.  Previously the limit was
     platform dependent and abbreviations were silently truncated to
     16 bytes even when the limit was greater than 16.

     The code by default is now designed for C99 or later.  To build in
     a C89 environment, compile with -DPORT_TO_C89.  To support C89
     callers of the tzcode library, compile with -DSUPPORT_C89.  The
     two new macros are transitional aids planned to be removed in a
     future version, when C99 or later will be required.

     The code now builds again on pre-C99 platforms, if you compile
     with -DPORT_TO_C89.  This fixes a bug introduced in 2022f.

     On C23-compatible platforms tzcode no longer uses syntax like
     'static [[noreturn]] void usage(void);'.  Instead, it uses
     '[[noreturn]] static void usage(void);' as strict C23 requires.
     (Problem reported by Houge Langley.)

     The code's functions now constrain their arguments with the C
     'restrict' keyword consistently with their documentation.
     This may allow future optimizations.

     zdump again builds standalone with ckdadd and without setenv,
     fixing a bug introduced in 2022g.  (Problem reported by panic.)

     leapseconds.awk can now process a leap seconds file that never
     expires; this might be useful if leap seconds are discontinued.

   Changes to commentary

     tz-link.html has a new section "Coordinating with governments and
     distributors".  (Thanks to Neil Fuller for some of the text.)

     To improve tzselect diagnostics, zone1970.tab's comments column is
     now limited to countries that have multiple timezones.

     Note that leap seconds are planned to be discontinued by 2035.

Here are links to the release files:

   https://www.iana.org/time-zones/repository/releases/tzcode2023a.tar.gz
   https://www.iana.org/time-zones/repository/releases/tzdata2023a.tar.gz
   https://www.iana.org/time-zones/repository/releases/tzdb-2023a.tar.lz

The following convenience links are also available, although they may 
point to the previous release until the relevant caches are refreshed:

   https://www.iana.org/time-zones/repository/tzcode-latest.tar.gz
   https://www.iana.org/time-zones/repository/tzdata-latest.tar.gz
   https://www.iana.org/time-zones/repository/tzdb-latest.tar.lz

Links are also available via plain HTTP, and via FTP from 
ftp://ftp.iana.org/tz/releases with the same basenames as above.

Each release file has a GPG signature, which can be retrieved by 
appending ".asc" to the above URLs. Copies of these signatures are 
appended to this message.

This release corresponds to commit 
f24b84a13556c12441dd55c323f9a8fd3b6fbbee dated 2023-03-22 12:39:33 -0700 
and tagged '2023a' in the development GitHub repository at 
<https://github.com/eggert/tz>.

Here are the SHA-512 checksums for the release files:

d45fc677a0a32ae807bf421faceff675565ee15e3ff42d3a4121df10e1f7855ac16b27fbc28bd365f93c57f40c5bdf19cde88546f7090cfab7676cac0a5516a4 
  tzcode2023a.tar.gz
10aadd6eba50f63f427399281065ba34cb474f6a854f8dc7a6f4f1343b1474a05f22b69b1e113ea67bb5f3f479253610a16b89d9dfa157bf0fde4c69aa3d6493 
  tzdata2023a.tar.gz
8e959f6cad84e9481ed5a6efcc8d7126d41fadfdc860715fea87fb15f7dcfdbc4c9d49828df2945ee9304dbdd3370c5b5048c62637bdd4f4962830ba101008bd 
  tzdb-2023a.tar.lz

Here are GPG digital signatures for the release files:

Paul Eggert

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