[tz] draft of change summary for next tz release

Andy Heninger aheninger at google.com
Tue Sep 17 22:43:24 UTC 2013

Can I suggest that we split this into two updates, the first containing
only the Fiji change, and the second with everything else?

The Fiji change will need to roll into our production systems quickly. The
raft of other changes have a non-negligible chance of causing a glitch or
two as they moves through our internal tooling, so it would be nice to
decouple the two.


  -- Andy Heninger

On Tue, Sep 17, 2013 at 2:38 PM, Paul Eggert <eggert at cs.ucla.edu> wrote:

> On 09/12/13 08:39, Tim Parenti wrote:
> > it would be quite prudent to summarize specifically what changes
> > are (and are not) made by this changeset
> Yes, although I normally write a change summary when preparing a
> release and publish it as part of the release announcement, the
> proposed change is large enough that it'd be helpful to circulate
> a draft of the change summary now.  Here is a draft for the
> current set of proposed changes, which is:
> https://github.com/eggert/tz/compare/8f10e5c...738ad89
>   Changes affecting near-future time stamps
>     This year Fiji will start DST on October 27, not October 20.
>     (Thanks to David Wheeler for the heads-up.)  For now, guess that
>     Fiji will continue to spring forward the Sunday before the fourth
>     Monday in October.
>   Changes affecting current and future time zone abbreviations
>     Use WIB/WITA/WIT rather than WIT/CIT/EIT for alphabetic Indonesian
>     time zone abbreviations since 1932.  (Thanks to George Ziegler,
>     Priyadi Iman Nurcahyo, Zakaria, Jason Grimes, Martin Pitt, and
>     Benny Lin.)  This affects Asia/Dili, Asia/Jakarta, Asia/Jayapura,
>     Asia/Makassar, and Asia/Pontianak.
>     Use ART (UTC-3, standard time), rather than WARST (also UTC-3, but
>     daylight saving time) for San Luis, Argentina since 2009.
>   Changes affecting Godthab time stamps after 2037 if version mismatch
>     Allow POSIX-like TZ strings where the transition time's hour can
>     range from -167 through 167, instead of the POSIX-required 0
>     through 24.  E.g., TZ='FJT-12FJST,M10.3.1/146,M1.3.4/75' for the
>     new Fiji rules.  This is a more-compact way to represent
>     far-future time stamps for America/Godthab, America/Santiago,
>     Antarctica/Palmer, Asia/Gaza, Asia/Hebron, Asia/Jerusalem,
>     Pacific/Easter, and Pacific/Fiji.  Other zones are unaffected by
>     this change.  (Derived from a suggestion by Arthur David Olson.)
>     Allow POSIX-like TZ strings where daylight saving time is in
>     effect all year.  E.g., TZ='WART4WARST,J1/0,J365/25' for Western
>     Argentina Summer Time all year.  This supports a more-compact way
>     to represent the 2013d data for America/Argentina/San_Luis.
>     Because of the change for San Luis noted above this change does not
>     affect the current data.  (Thanks to Andrew Main (Zefram) for
>     suggestions that improved this change.)
>     Where these two TZ changes take effect, there is a minor extension
>     to the tz file format in that it allows new values for the
>     embedded TZ-format string, and the tz file format version number
>     has therefore been increased from 2 to 3 as a precaution.
>     Version-2-based client code should continue to work as before for
>     all time stamps before 2038.  Existing version-2-based client code
>     (tzcode, GNU/Linux, Solaris) has been tested on version-3-format
>     files, and typically works in practice even for time stamps after
>     2037; the only known exception is America/Godthab.
>   Changes affecting time stamps before 1970
>     Pacific/Johnston is now a link to Pacific/Honolulu.  This corrects
>     some errors before 1947.
>     Some zones have been turned into links, when they differ from
>     existing zones only in older data that was likely invented or that
>     differs only in LMT or transition from LMT.  These changes affect
>     only time stamps before 1943.  The affected zones are:
>     Africa/Juba, America/Anguilla, America/Aruba, America/Dominica,
>     America/Grenada, America/Guadeloupe, America/Marigot,
>     America/Montserrat, America/St_Barthelemy, America/St_Kitts,
>     America/St_Lucia, America/St_Thomas, America/St_Vincent,
>     America/Tortola, and Europe/Vaduz.
>     Change Kingston Mean Time from -5:07:12 to -5:07:11.  This affects
>     America/Cayman, America/Jamaica and America/Grand_Turk time stamps
>     from 1890 to 1912.
>     Change the UT offset of Bern Mean Time from 0:29:44 to 0:29:46.
>     This affects Europe/Zurich time stamps from 1853 to 1894.  (Thanks
>     to Alois Treindl).
>     Change the date of the circa-1850 Zurich transition from 1849-09-12
>     to 1853-07-16, overriding Shanks with data from Messerli about
>     postal and telegraph time in Switzerland.
>   Changes affecting time zone abbreviations before 1970
>     For Asia/Jakarta, use BMT (not JMT) for mean time from 1923 to 1932,
>     as Jakarta was called Batavia back then.
>   Changes affecting API
>     The 'zic' command now outputs a dummy transition when far-future
>     data can't be summarized using a TZ string, and uses a 402-year
>     window rather than a 400-year window.  For the current data, this
>     affects only the Asia/Tehran file.  It does not affect any of the
>     time stamps that this file represents, so zdump outputs the same
>     information as before.  (Thanks to Andrew Main (Zefram).)
>     The 'date' command has a new '-r' option, which lets you specify
>     the integer time to display, a la FreeBSD.
>     The 'tzselect' command has two new options '-c' and '-n', which lets
> you
>     select a zone based on latitude and longitude.
>     The 'zic' command's '-v' option now warns about constructs that
>     require the new version-3 binary file format.  (Thanks to Arthur
>     David Olson for the suggestion.)
>     Support for floating-point time_t has been removed.
>     It was always dicey, and POSIX no longer requires it.
>     (Thanks to Eric Blake for suggesting to the POSIX committee to
>     remove it, and thanks to Alan Barrett, Clive D.W. Feather, Andy
>     Heninger, Arthur David Olson, and Alois Treindl, for reporting
>     bugs and elucidating some of the corners of the old floating-point
>     implementation.)
>     The signatures of 'offtime', 'timeoff', and 'gtime' have been
>     changed back to the old practice of using 'long' to represent UT
>     offsets.  This had been inadvertently and mistakenly changed to
>     'int_fast32_t'.  (Thanks to Christos Zoulos.)
>     The code avoids undefined behavior on integer overflow in some
>     more places, including gmtime, localtime, mktime and zdump.
>   Changes affecting the zdump utility
>     zdump now outputs "UT" when referring to Universal Time, not "UTC".
>     "UTC" does not make sense for time stamps that predate the introduction
>     of UTC, whereas "UT", a more-generic term, does.  (Thanks to Steve
> Allen
>     for clarifying UT vs UTC.)
>   Data changes affecting behavior of tzselect and similar programs
>     Country code BQ is now called the more-common name "Caribbean
> Netherlands"
>     rather than the more-official "Bonaire, St Eustatius & Saba".
>     Remove from zone.tab the names America/Montreal, America/Shiprock,
>     and Antarctica/South_Pole, as they are equivalent to existing
>     same-country-code zones for post-1970 time stamps.  The data for
>     these names are unchanged, so the names continue to work as before.
>   Changes affecting code internals
>     zic -c now runs way faster on 64-bit hosts when given large numbers.
>     zic now uses vfprintf to allocating and freeing some memory.
>     tzselect now computes the list of continents from the data,
>     rather than have it hard-coded.
>     Minor changes pacify GCC 4.7.3 and GCC 4.8.1.
>   Changes affecting the build procedure
>     The 'leapseconds' file is now generated automatically from a
>     new file 'leap-seconds.list', which is a copy of
>     <ftp://time.nist.gov/pub/leap-seconds.list>.
>     A new source file 'leapseconds.awk' implements this.
>     The goal is simplification of the future maintenance of 'leapseconds'.
>     When building the 'posix' or 'right' subdirectories, if the
>     subdirectory would be a copy of the default subdirectory, it is
>     now made a symbolic link if that is supported.  This saves about
>     2 MB of file system space.
>     The links America/Shiprock and Antarctica/South_Pole have been
>     moved to the 'backward' file.  This affects only nondefault builds
>     that omit 'backward'.
>   Changes affecting version-control only
>     .gitignore now ignores 'date'.
>   Changes affecting documentation and commentary
>     Changes to the 'tzfile' man page
>       It now mentions that the binary file format may be extended in
>       future versions by appending data.
>       It now refers to the 'zdump' and 'zic' man pages.
>     Changes to the 'zic' man page
>       It lists conditions that elicit a warning with '-v'.
>       It says that the behavior is unspecified when duplicate names
>       are given, or if the source of one link is the target of another.
>       Its examples are updated to match the latest data.
>       The definition of white space has been clarified slightly.
>       (Thanks to Michael Deckers.)
>     Changes to the 'Theory' file
>       There is a new section about the accuracy of the tz database,
>       describing the many ways that errors can creep in, and
>       explaining why so many of the pre-1970 time stamps are wrong or
>       misleading (thanks to Steve Allen, Lester Caine, and Garrett
>       Wollman for discussions that contributed to this).
>       The 'Theory' file describes LMT better (this follows a
>       suggestion by Guy Harris).
>       It refers to the 2013 edition of POSIX rather than the 2004 edition.
>       It's mentioned that excluding 'backward' should not affect the
>       other data, and it suggests at least one zone.tab name per
>       inhabited country (thanks to Stephen Colebourne).
>       Some longstanding restrictions on names are documented, e.g.,
>       'America/New_York' precludes 'America/New_York/Bronx'.
>       It gives more reasons for the 1970 cutoff.
>       It now mentions which time_t variants are supported, such as
>       signed integer time_t.  (Thanks to Paul Goyette for reporting
>       typos in an experimental version of this change.)
>       (Thanks to Philip Newton for correcting typos in these changes.)
>     Documentation and commentary is more careful to distinguish UT in
>     general from UTC in particular.  (Thanks to Steve Allen.)
>     Add a better source for the Zurich 1894 transition.
>     (Thanks to Pierre-Yves Berger.)
>     Update shapefile citations in tz-link.htm.  (Thanks to Guy Harris.)
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