Updated: tzcode, tzdata 2021b

Updated: tzcode, tzdata 2021b

[Cygwin]

The following packages have been upgraded in the Cygwin distribution:

* tzcode	2021b
* tzdata	2021b

The Time Zone Database (often called tz, tzdb, or zoneinfo) contains
data that represents the history of local time for many locations around
the world, and supports conversion of UTC time to local time at those
locations to allow display of those local times. It is updated
periodically to reflect changes made by political bodies to daylight
saving (summer time) rules, UTC offsets, and time zone boundaries.
The tzcode package provides the tzselect, zdump, and zic utilities.

For more information, see the announcement or below:

	https://mm.icann.org/pipermail/tz-announce/2021-January/000065.html


Release 2021b - 2021-09-24 16:23:00 -0700

  Briefly:
    Jordan now starts DST on February's last Thursday.
    Samoa no longer observes DST.
    Merge more location-based Zones whose timestamps agree since 1970.
    Move some backward-compatibility links to 'backward'.
    Rename Pacific/Enderbury to Pacific/Kanton.
    Correct many pre-1993 transitions in Malawi, Portugal, etc.
    zic now creates each output file or link atomically.
    zic -L no longer omits the POSIX TZ string in its output.
    zic fixes for truncation and leap second table expiration.
    zic now follows POSIX for TZ strings using all-year DST.
    Fix some localtime crashes and bugs in obscure cases.
    zdump -v now outputs more-useful boundary cases.
    tzfile.5 better matches a draft successor to RFC 8536.
    A new file SECURITY.

  This release is prompted by recent announcements by Jordan and Samoa.
  It incorporates many other changes that had accumulated since 2021a.
  However, it omits most proposed changes that merged all Zones
  agreeing since 1970, as concerns were raised about doing too many of
  these changes at once.  It does keeps some of these changes in the
  interest of making tzdb more equitable one step at a time; see
  "Merge more location-based Zones" below.

  Changes to future timestamps

    Jordan now starts DST on February's last Thursday.
    (Thanks to Steffen Thorsen.)

    Samoa no longer observes DST.  (Thanks to Geoffrey D. Bennett.)

  Changes to zone name

    Rename Pacific/Enderbury to Pacific/Kanton.  When we added
    Enderbury in 1993, we did not know that it is uninhabited and that
    Kanton (population two dozen) is the only inhabited location in
    that timezone.  The old name is now a backward-compatility link.

  Changes to past timestamps

    Correct many pre-1993 transitions, fixing entries originally
    derived from Shanks, Whitman, and Mundell.  The fixes include:
      - Barbados: standard time was introduced in 1911, not 1932; and
	DST was observed in 1942-1944
      - Cook Islands: In 1899 they switched from east to west of GMT,
	celebrating Christmas for two days.  They (and Niue) switched
	to standard time in 1952, not 1901.
      - Guyana: corrected LMT for Georgetown; the introduction of
	standard time in 1911, not 1915; and corrections to 1975 and
	1992 transitions
      - Kanton: uninhabited before 1937-08-31
      - Niue: only observed -11:20 from 1952 through 1964, then went to
        -11 instead of -11:30
      - Portugal: DST was observed in 1950
      - Tonga: corrected LMT; the introduction of standard time in 1945,
        not 1901; and corrections to the transition from +12:20 to +13
        in 1961, not 1941
    Additional fixes to entries in the 'backzone' file include:
      - Enderbury: inhabited only 1860/1885 and 1938-03-06/1942-02-09
      - The Gambia: 1933 and 1942 transitions
      - Malawi: several 1911 through 1925 transitions
      - Sierra Leone: several 1913 through 1941 transitions, and DST
	was NOT observed in 1957 through 1962
    (Thanks to P Chan, Michael Deckers, Alexander Krivenyshev and
    Alois Treindl.)

    Merge more location-based Zones whose timestamps agree since 1970,
    as pre-1970 timestamps are out of scope.  This is part of a
    process that has been ongoing since 2013.  This does not affect
    post-1970 timestamps, and timezone historians who build with 'make
    PACKRATDATA=backzone' should see no changes to pre-1970 timestamps.
    When merging, keep the most-populous location's data, and move
    data for other locations to 'backzone' with a backward
    link in 'backward'.  For example, move America/Creston data to
    'backzone' with a link in 'backward' from America/Phoenix because
    the two timezones' timestamps agree since 1970; this change
    affects some pre-1968 timestamps in America/Creston because
    Creston and Phoenix disagreed before 1968.  The affected Zones
    are Africa/Accra, America/Atikokan, America/Blanc-Sablon,
    America/Creston, America/Curacao, America/Nassau,
    America/Port_of_Spain, Antarctica/DumontDUrville, and
    Antarctica/Syowa.

  Changes to maintenance procedure

    The new file SECURITY covers how to report security-related bugs.

    Several backward-compatibility links have been moved to the
    'backward' file.  These links, which range from Africa/Addis_Ababa
    to Pacific/Saipan, are only for compatibility with now-obsolete
    guidelines suggesting an entry for every ISO 3166 code.
    The intercontinental convenience links Asia/Istanbul and
    Europe/Nicosia have also been moved to 'backward'.

  Changes to code

    zic now creates each output file or link atomically,
    possibly by creating a temporary file and then renaming it.
    This avoids races where a TZ setting would temporarily stop
    working while zic was installing a replacement file or link.

    zic -L no longer omits the POSIX TZ string in its output.
    Starting with 2020a, zic -L truncated its output according to the
    "Expires" directive or "#expires" comment in the leapseconds file.
    The resulting TZif files omitted daylight saving transitions after
    the leap second table expired, which led to far less-accurate
    predictions of times after the expiry.  Although future timestamps
    cannot be converted accurately in the presence of leap seconds, it
    is more accurate to convert near-future timestamps with a few
    seconds error than with an hour error, so zic -L no longer
    truncates output in this way.

    Instead, when zic -L is given the "Expires" directive, it now
    outputs the expiration by appending a no-change entry to the leap
    second table.  Although this should work well with most TZif
    readers, it does not conform to Internet RFC 8536 and some pickier
    clients (including tzdb 2017c through 2021a) reject it, so
    "Expires" directives are currently disabled by default.  To enable
    them, set the EXPIRES_LINE Makefile variable.  If a TZif file uses
    this new feature it is marked with a new TZif version number 4,
    a format intended to be documented in a successor to RFC 8536.

    zic -L LEAPFILE -r @LO no longer generates an invalid TZif file
    that omits leap second information for the range LO..B when LO
    falls between two leap seconds A and B.  Instead, it generates a
    TZif version 4 file that represents the previously-missing
    information.

    The TZif reader now allows the leap second table to begin with a
    correction other than -1 or +1, and to contain adjacent
    transitions with equal corrections.  This supports TZif version 4.

    The TZif reader now lets leap seconds occur less than 28 days
    apart.  This supports possible future TZif extensions.

    Fix bug that caused 'localtime' etc. to crash when TZ was
    set to a all-year DST string like "EST5EDT4,0/0,J365/25" that does
    not conform to POSIX but does conform to Internet RFC 8536.

    Fix another bug that caused 'localtime' etc. to crash when TZ was
    set to a POSIX-conforming but unusual TZ string like
    "EST5EDT4,0/0,J365/0", where almost all the year is DST.

    Fix yet another bug that caused 'localtime' etc. to mishandle slim
    TZif files containing leap seconds after the last explicit
    transition in the table, or when handling far-future timestamps
    in slim TZif files lacking leap seconds.

    Fix localtime misbehavior involving positive leap seconds.
    This change affects only behavior for "right" system time,
    which contains leap seconds, and only if the UT offset is
    not a multiple of 60 seconds when a positive leap second occurs.
    (No such timezone exists in tzdb, luckily.)  Without the fix,
    the timestamp was ambiguous during a positive leap second.
    With the fix, any seconds occurring after a positive leap second
    and within the same localtime minute are counted through 60, not
    through 59; their UT offset (tm_gmtoff) is the same as before.
    Here is how the fix affects timestamps in a timezone with UT
    offset +01:23:45 (5025 seconds) and with a positive leap second at
    1972-06-30 23:59:60 UTC (78796800):

	time_t    without the fix      with the fix
	78796800  1972-07-01 01:23:45  1972-07-01 01:23:45 (leap second)
	78796801  1972-07-01 01:23:45  1972-07-01 01:23:46
	...
	78796815  1972-07-01 01:23:59  1972-07-01 01:23:60
	78796816  1972-07-01 01:24:00  1972-07-01 01:24:00

    Fix an unlikely bug that caused 'localtime' etc. to misbehave if
    civil time changes a few seconds before time_t wraps around, when
    leap seconds are enabled.

    Fix bug in zic -r; in some cases, the dummy time type after the
    last time transition disagreed with the TZ string, contrary to
    Internet RFC 8563 section 3.3.

    Fix a bug with 'zic -r @X' when X is a negative leap second that
    has a nonnegative correction.  Without the fix, the output file
    was truncated so that X appeared to be a positive leap second.
    Fix a similar, even-less-likely bug when truncating at a positive
    leap second that has a nonpositive correction.

    zic -r now reports an error if given rolling leap seconds, as this
    usage has never generally worked and is evidently unused.

    zic now generates a POSIX-conforming TZ string for TZif files
    where all-year DST is predicted for the indefinite future.
    For example, for all-year Eastern Daylight Time, zic now generates
    "XXX3EDT4,0/0,J365/23" where it previously generated
    "EST5EDT,0/0,J365/25" or "".  (Thanks to Michael Deckers for
    noting the possibility of POSIX conformance.)

    zic.c no longer requires sys/wait.h (thanks to spazmodius for
    noting it wasn't needed).

    When reading slim TZif files, zdump no longer mishandles leap
    seconds on the rare platforms where time_t counts leap seconds,
    fixing a bug introduced in 2014g.

    zdump -v now outputs timestamps at boundaries of what localtime
    and gmtime can represent, instead of the less-useful timestamps
    one day after the minimum and one day before the maximum.
    (Thanks to Arthur David Olson for prototype code, and to Manuela
    Friedrich for debugging help.)

    zdump's -c and -t options are now consistently inclusive for the
    lower time bound and exclusive for the upper.  Formerly they were
    inconsistent.  (Confusion noted by Martin Burnicki.)

  Changes to build procedure

    You can now compile with -DHAVE_MALLOC_ERRNO=0 to port to
    non-POSIX hosts where malloc doesn't set errno.
    (Problem reported by Jan Engelhardt.)

  Changes to documentation

    tzfile.5 better matches a draft successor to RFC 8536
    <https://datatracker.ietf.org/doc/draft-murchison-rfc8536bis/01/>.