Updated: tzdata/-posix/-right, tzcode 2026c - Time Zone Database and Utilities

[Cygwin tzcode/tzdata Maintainer]

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
summer daylight saving time rules, UTC offsets, and time zone boundaries.

Three data packages are available: base 'tzdata' is always installed;
optional 'tzdata-right' provides TAI-10s time in the 'right' subtree;
and optional 'tzdata-posix' provides the same zones and times as base
data in the 'posix' subtree, as an explicit distinction from 'right'.

To enable newlib CLOCK_TAI support, the base tzdata package now installs:

	/usr/share/zoneinfo/leap-seconds.list

with a symbolic link from the standard location:

	/etc/leap-seconds.list.

The tzcode package provides the tzselect, zdump, and zic utilities.

For more information, see the project home page:

	https://www.iana.org/time-zones

The following packages have been upgraded in the Cygwin distribution:

- tzcode	2026c	utilities
- tzdata	2026c	base zones tree
- tzdata-posix	2026c	posix zones subtree
- tzdata-right	2026c	TAI-10s right zones subtree

For more details on changes, see the announcement or below:

	https://lists.iana.org/hyperkitty/list/tz-announce@iana.org/2026/07/


2026-07-08	2026c

Briefly:

- Alberta moved to permanent -06 on 2026-06-18.
- Morocco moves to permanent +00 on 2026-09-20.
- More integer overflow bugs have been fixed in zic.

Changes to future timestamps

- Alberta’s 2026-03-08 spring forward was its last foreseeable clock
  change, as it moved to permanent -06 thereafter.
  Model this with its traditional abbreviation CST.
  Although the change to permanent -06 legally took place on 2026-06-18,
  temporarily model the change to occur on 2026-11-01 at 02:00 instead,
  for the same reason we introduced a similarly temporary hack for
  British Columbia in 2026b.

  Although another TZDB release will likely be needed soon because
  Northwest Territories will likely follow Alberta, the legal
  formalities have not yet taken place.

- Morocco plans to move back to permanent UTC, without daylight saving
  time transitions, on 2026-09-20 at 02:00.
  This also affects Western Sahara.

Changes to code

- zic no longer overflows integers when processing outlandish input like
    ‘Zone Ouch 0 - LMT 9223372036854775807’,
    ‘Zone Ouch 0 2562047788015215 LMT’,
    ‘Zone Ouch -2562047788015215:30:08 - LMT’, and
    ‘Zone Ouch -2562047788015215:30:08 - %%z’.
  This avoids undefined behavior in C.

- On platforms that have EFTYPE, tzalloc now fails with errno set to
  EFTYPE, not EINVAL, if it detects that the TZif file has an invalid
  format or is not a regular file.
  Formerly it did this only on NetBSD, and only when the file was not a
  regular file.

- Unprivileged programs no longer require TZif files to be regular files
  or reject relative names containing ".." components.
  This reverts to the more-permissive 2025b behavior, as the stricter
  behavior did not catch on in FreeBSD.

- zic now reports any failure to remove a temporary file when cleaning
  up after a previous failure.

Changes to commentary

- Northwest Territories is expected to move to permanent -06 prior to
  2026-11-01 02:00, when clocks would otherwise fall back.
  Model this with its traditional abbreviation CST.
  Unfortunately the change is not yet official, so it is currently
  present only as comments that can be uncommented as needed.

Changes to build procedure

- The undocumented ‘typecheck’ Makefile check rule has been removed.
  It stopped working in 2025a and evidently nobody noticed.
  The rule was superseded by ‘check_time_t_alternatives’ in 2013d.