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

From: Jeff King <peff@peff.net>
Date: Mar 26, 2014, 19:33 UTC
Message-ID: <20140326193359.GA14105@sigill.intra.peff.net>
In-Reply-To: <20140326192536.GA13989@sigill.intra.peff.net>

On Wed, Mar 26, 2014 at 03:25:36PM -0400, Jeff King wrote:

Show 24 quoted lines

> > The primary thing you wanted to achieve by the "gmtime gave us NULL,
> > let's substitute it with an arbitrary value to avoid dereferencing
> > the NULL" change was *not* that we see that same arbitrary value
> > comes out of the system, but that we do not die by attempting to
> > reference the NULL, I think.  Not dying is the primary thing we want
> > to (and we already do) test, no?
> 
> I think there are really two separate behaviors we are testing here (and
> in the surrounding tests):
> 
>   1. Don't segfault if gmtime returns NULL.
> 
>   2. Whenever we cannot process a date (either because gmtime fails, or
>      because we fail before even getting the value to gmtime),
>      consistently return the sentinel date (so the reader can easily
>      know it's bogus).
> 
> Having the test be particular about its output helped us find a case
> where FreeBSD did not trigger (1), but did trigger (2), by returning a
> blanked "struct tm".
> 
> I'm open to the argument that (2) is not worth worrying about that much
> if it is a hassle to test. But I don't think it is that much hassle
> (yet, anyway).

That being said, is the AIX value actually right? I did not look closely at first, but just assumed that it was vaguely right. But:

  999999999999999999 / (86400 * 365)

is something like 31 billion years in the future, not 160 million. A real date calculation will have a few tweaks (leap years, etc), but that is orders of magnitude off.

So I am not sure that AIX is not actually just giving us utter crap. In that case, the test is not wrong; it's pickiness is actually finding a real problem. But I am not sure it is a problem worth solving. I do not want to get into heuristics deciding whether a particular platform's gmtime output is crap or not. That pushes this into the realm of "it's not worth testing", and we should stick to just testing that we did not segfault.

-Peff