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

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

quoted

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