Re: tzcode resync

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

Hi Mark,

On Apr 29 00:03, Mark Geisert wrote:
> Hi folks,
> 
> 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.
> > 
> > When I updated localtime.cc back in 2012, I tried to keep it in a format
> > which allows further updates from the NetBSD version later on.
> > 
> > The last localtime.c update in NetBSD is from 2019.  That should be
> > sufficient, shouldn't it?
> > 
> > The upstream localtime.c diff from version 1.72 to current 1.122 is
> > 3K lines of code, so it's still a lot of work, probably...
> 
> 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.

> I assume I can bring the current NetBSD code directly into Cygwin?  In a
> legal sense, I mean.

Yes, that's perfectly fine, given the BSD license.

> Code-wise I see what Yaakov's suggested and it seems
> like a great way to go.

Yesterday eve I was already looking into this and given how NetBSD
is still under CVS control, I decided trying to pull our localtime.cc
up from 1.72 to 1.122 version by version, just to be really careful.

I managed to get up to 1.83 and stumbled over a big problem in terms
of TZ data format.

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?


> The other question I have is, once I believe I've got it incorporated into
> Cygwin, what can I use to test that it's operating correctly?

Uhm... Yaakov?


Thanks,
Corinna

-- 
Corinna Vinschen
Cygwin Maintainer