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perl: call timegm and timelocal with 4-digit year

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Amazingly, timegm(gmtime(0)) is only 0 before 2020 because perl's
timegm deviates from GNU timegm(3) in how it handles years.

man Time::Local says

 Whenever possible, use an absolute four digit year instead.

with a detailed explanation about ambiguity of 2-digit years above that.

Even though this ambiguity is error-prone with >50% of users getting it
wrong, it has been like this for 20+ years, so we just use 4-digit years
everywhere to be on the safe side.

We add some extra logic to cvsimport because it allows 2-digit year
input and interpreting an 18 as 1918 can be avoided easily and safely.

Signed-off-by: Bernhard M. Wiedemann <bwiedemann@suse.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Bernhard M. Wiedemann
2018-02-23 18:20:45 +01:00
committed by Junio C Hamano
parent ffa9524972
commit a40e06ee33
4 changed files with 8 additions and 4 deletions
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4
perl/Git.pm
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@ -534,7 +534,9 @@ If TIME is not supplied, the current local time is used.
sub get_tz_offset {
# some systems don't handle or mishandle %z, so be creative.
my $t = shift || time;
my $gm = timegm(localtime($t));
my @t = localtime($t);
$t[5] += 1900;
my $gm = timegm(@t);
my $sign = qw( + + - )[ $gm <=> $t ];
return sprintf("%s%02d%02d", $sign, (gmtime(abs($t - $gm)))[2,1]);
}