[bug-diffutils] bug#51228: Incorrect timezone in unified diff on Solaris?

[Vladimir Marek]

Hi,

I believe that this is bug in diffutils, but I am not entirely sure. The
problem manifested itself while testing patchutils on Solaris. One of
the tests was failing. Upon closer inspection the filterdiff (aka
lsdiff) decides whether a give chunk is creating (or deleting) a file
based on timestamp the chunk is having. It compares whether the timezone
recorded equals to current timezone.

https://github.com/twaugh/patchutils/blob/master/src/filterdiff.c#L156

On Solaris patchutils correctly detect that there is no
struct tm ->  tm_gmtoff (HAVE_TM_GMTOFF). On line 1417 of nstrftime.c

 1415 #if HAVE_TM_GMTOFF
 1416             diff = tp->tm_gmtoff;
 1417 #else
 1418             if (!tz)
 1419               diff = 0;
 1420             else

And since there is zero tz specified in context.c

if (! (tm && nstrftime (buf, sizeof buf, time_format, tm, 0, nsec)))
                                                         ^^^

The resulting chunk has zero timezone offset (on Solaris). Like here:

$ TZ=EST+5 gdiff -urN dir.orig dir
diff -urN dir.orig/a dir/a
--- dir.orig/a  1969-12-31 19:00:00.000000000 +0000  <------ this file is 
missing
+++ dir/a       2021-10-14 12:24:20.785102347 +0000

On Linux and after my fix on Solaris the result is

--- dir.orig/a  1969-12-31 19:00:00.000000000 -0500

I am not entirely sure where is nstrftime.c coming from, so I'm
reporting the issue here. I am also attaching patch I plan to use on
Solaris. The patch and additional test works for me on diffutils 3.8 on
both Linux and Solaris.

Thanks for diffutils, I believe it's the most important tool for release
engineer :)

Cheers
-- 
        Vlad

timezone.patch
Description: Text document