Re: tzcode resync

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

On Apr 29 02:05, Mark Geisert wrote:
> On Wed, 29 Apr 2020, Corinna Vinschen wrote:
> > On Apr 29 00:03, Mark Geisert wrote:
> > > On Mon, 27 Apr 2020, Corinna Vinschen wrote:
> > > > On Apr 24 17:19, Yaakov Selkowitz wrote:
> > > > > Our winsup/cygwin/localtime.cc is a mashup of a very old version of
> > > > > upstream tzcode's private.h, tzfile.h, and localtime.c with Cygwin-
> > > > > specific patches for getting the timezone from windows as a fallback,
> > > > > as well as handling API compatibility with pre-tm_gmtoff binaries.
> > > > > 
> > > > > The upstream tzcode/tzdata have introduced database changes which
> > > > > cannot be read by old code.  Currently, I am building tzdata in the old
> > > > > ("rearguard") format to keep compatibility, but at this point we're
> > > > > *way* behind upstream and we really should update our code.  Given how
> > > > > long it's been though, it's going to be a bit of work.
> > > > [...]
> > > I can take this on.  I've looked at the current NetBSD code diffed against
> > > the version we use: there's a fair amount of prototype rejiggering and
> > > recoding of localized areas.  New code too, of course.  I've done this kind
> > > of thing before and this project seems doable to me.
> > 
> > Sounds good to me.  I started with this yesterday but didn't make a lot
> > of progress, see below.  I'd be happy if you like to take over.
> 
> Yes, please :-).
> [...]
> > [...]
> > Cygwin has a builtin binary representation of the file "posixrules" in
> > tz_posixrules.h.  Since 2000.  And unchanged since 2000!
> > 
> > This binary representation is used as posixrules data if the posixrules
> > file doesn't exist or is unreadable.  I have a vague feeling that this
> > data is hopelessly outdated and, probably, the format changed as well.
> > 
> > So I assume the data in tz_posixrules.h needs either an update, or
> > we drop the inline data entirely.
> > 
> > Dropping this inline data shouldn't be much of a problem, right?
> > Cygwin installations shouldn't need it and 3PPs can easily provide
> > a posixrules file, I guess...
> > 
> > Mark, Yaakov, what's your stance in terms of this posixrules data?
> 
> I think this is an example of the very thing Yaakov mentioned in the quotes
> above.  Both this internal backup of posixrules and the usual posixrules
> file in /usr/share/zoneinfo are written in the obsolete Version 0 format.
> The current localtime code can only read this version.
> 
> When localtime.cc gets updated, it can read Version 2 (there was no Version
> 1 as far as I can tell).  Yaakov will generate V.2 formatted zone files at
> that point.
> 
> I can't see a reason to keep this internal backup copy, regardless of which
> Version it is.  But if we do need it, we can generate a V.2 version of it
> once localtime.cc is able to read it.

Yeah, I guess that's the way to go.  The idea of all this was trying to
make sure a lone Cygwin with an executable would function outside of a
full installation.  That's also the reason we have builtin locale data.
How much sense does this make these days...?  I don't know.  It's just
a safety net for border scenarios.


Corinna

-- 
Corinna Vinschen
Cygwin Maintainer