Re: [PATCH] t4212: handle systems with post-apocalyptic gmtime

From: Jeff King <peff@peff.net>
Date: Apr 1, 2014, 19:46 UTC
Message-ID: <20140401194606.GA20676@sigill.intra.peff.net>
In-Reply-To: <xmqqbnwk27it.fsf@gitster.dls.corp.google.com>

On Tue, Apr 01, 2014 at 12:07:22PM -0700, Junio C Hamano wrote:

Show 23 quoted lines

> Jeff King <peff@peff.net> writes:
> 
> > On Fri, Mar 28, 2014 at 12:30:02PM -0700, Junio C Hamano wrote:
> >
> >> Let's just deal with a simple known cases (like FreeBSD) in the real
> >> code that everybody exercises at runtime, and have the new test only
> >> check we do not segfault on a value we used to segfault upon seeing.
> >
> > OK. Here it is, with the other option as an "alt" patch for reference.
> >
> >   [1/2]: date: recognize bogus FreeBSD gmtime output
> >   [2/2]: t4212: loosen far-in-future test for AIX
> >   [2alt/2]: work around unreliable gmtime errors on AIX
> >
> > -Peff
> 
> Thanks.  2alt does not look too bad, but on the other hand, we are
> replacing a value that can produce the right result on correctly
> implemented gmtime with a completely bogus value only because we
> know there exists one broken implementation---which does not sound a
> very good trade-off, given that we would get a result that does not
> correspond to the input anyway with or without the change on the
> broken implementation.

One other option is to push _all_ callers through a git_gmtime() wrapper, and then use Makefile knobs to turn on specific quirks, like:

    struct tm *git_gmtime_r(const time_t *timep, struct tm *result)
    {
    #ifdef GMTIME_OVERFLOWS_32BIT
              if (*timep > 999999999999999)
                        return NULL;
    #endif

              ret = gmtime_r(timep, result);

    #ifdef GMTIME_ERROR_BLANK
              if (ret && !ret->tm_mday)
                        return NULL;
    #endif

              return ret;
    }

and then each platform can turn the knobs as appropriate.

-Peff