Re: [ANNOUNCE] Git v2.9.1

From: Jeff King <peff@peff.net>
Date: Jul 12, 2016, 15:35 UTC
Message-ID: <20160712153520.GG613@sigill.intra.peff.net>
In-Reply-To: <CAPc5daWcb5bfgsxMP0vCrQ7gBdeYBgefzPNHztaaCKzqbCv2aQ@mail.gmail.com>

On Tue, Jul 12, 2016 at 08:25:51AM -0700, Junio C Hamano wrote:

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> On Tue, Jul 12, 2016 at 8:16 AM, Jeff King <peff@peff.net> wrote:
> >>
> >> But moving the internal time representation used in various fields
> >> like commit->date to time_t is likely to be a wrong thing to do,
> >> because the first problem with "unsigned long", i.e. "may not be
> >> wide enough", is not limited to "not wide enough to hold time_t".
> >> It also includes "it may not be wide enough to hold time somebody
> >> else recorded in existing objects".
> >
> > But that's a problem no matter what size we choose.
> 
> Yes, if somebody's time_t is larger than my intmax_t, the problem
> cannot be solved for me, if that timestamp is too far in the future or
> in the past.

I am less worried about their time_t and more about whatever crap they write in ascii into their objects. :)

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> But that is not the problem I am pointing out. I heard earlier in the
> thread that time_t on one system was 32-bit (was it Linux?) but I think
> they have "long long". Choosing time_t is strictly inferior choice when
> we already know that a platform with not-wide-enough time_t need to
> be supported, and a type that is wider than that is available.

I am not certain that there is a modern system with 32-bit time_t. We know there are systems with 32-bit unsigned long, and I think that is what produced the results people saw. I'd expect even 32-bit systems to use "int64_t" or similar for their time_t these days.

I'm also not convinced that we would be helping much to carry around a wider gittime_t. Most of the display code ends up touching a system time function one way or another, so I find it unlikely it would produce much better output.

It would help for simple cases like commit->date where we really do just parse it into a number and never do more with it. But...

> I was envisioning that we would have typedef <sometime> gittime_t
> with conversion helpers between it and time_t that allow us to do some
> range checks while at it.

I guess I am just willing to trust that time_t is basically that. And if your platform has a grossly undersized time_t, then too bad, we clamp everything it can't hold to 2038 or whatever, and hopefully your terrible platform dies out or gets a clue sometime in the next 20 years.

-Peff