perl: call timegm and timelocal with 4-digit year

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>

1 files changed, 3 insertions, 1 deletions

diff --git a/git-cvsimport.perl b/git-cvsimport.perl
index 2d8df83172..b31613cb8a 100755
--- a/git-cvsimport.perl
+++ b/git-cvsimport.perl
@@ -601,7 +601,9 @@ sub pdate($) {
 	my ($d) = @_;
 	m#(\d{2,4})/(\d\d)/(\d\d)\s(\d\d):(\d\d)(?::(\d\d))?#
 		or die "Unparseable date: $d\n";
-	my $y=$1; $y-=1900 if $y>1900;
+	my $y=$1;
+	$y+=100 if $y<70;
+	$y+=1900 if $y<1000;
 	return timegm($6||0,$5,$4,$3,$2-1,$y);
 }