From 2bdf366e820066124545b54ef126fca7e9c4c597 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?K=C5=8Dan?= <koan.bot@atoomic.org>
Date: Thu, 7 May 2026 07:21:24 -0600
Subject: [PATCH] fix: format_z loses sign for negative sub-hour timezone
 offsets

int($o / 3600) truncates -1800 to 0, so sprintf("%+03d", 0) produces
"+00" instead of "-00". Affects any negative offset under one hour
(e.g. -0030, -0015, -0045).

Fix: extract sign from original offset before taking abs(), then
format with explicit sign character.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
---
 lib/Date/Format/Generic.pm |  4 +++-
 t/format-z-sign.t          | 22 ++++++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 t/format-z-sign.t

diff --git a/lib/Date/Format/Generic.pm b/lib/Date/Format/Generic.pm
index b3b8bdf..1f7c496 100644
--- a/lib/Date/Format/Generic.pm
+++ b/lib/Date/Format/Generic.pm
@@ -207,7 +207,9 @@ sub format_Z {
 sub format_z {
  my $t = $_[0]->[9];
  my $o = defined $tzname ? tz_offset($tzname, $t) : tz_offset(undef,$t);
- sprintf("%+03d%02d", int($o / 3600), int(abs($o) % 3600) / 60);
+ my $sign = $o < 0 ? '-' : '+';
+ my $abs  = abs($o);
+ sprintf("%s%02d%02d", $sign, int($abs / 3600), int($abs % 3600) / 60);
 }
 
 sub format_c { &format_x . " " . &format_X }
diff --git a/t/format-z-sign.t b/t/format-z-sign.t
new file mode 100644
index 0000000..9c4b6ac
--- /dev/null
+++ b/t/format-z-sign.t
@@ -0,0 +1,22 @@
+use strict;
+use warnings;
+use Test::More tests => 6;
+use Date::Format qw(time2str);
+
+# Regression: format_z lost the sign for negative sub-hour timezone offsets
+# because int(-1800/3600) truncates to 0, and sprintf("%+03d",...) renders
+# 0 as "+00" instead of "-00".
+
+my $epoch = 946684800; # 2000-01-01 00:00:00 UTC
+
+# Negative sub-hour offsets (the bug)
+is(time2str("%z", $epoch, "-0030"), "-0030", "%z preserves sign for -0030");
+is(time2str("%z", $epoch, "-0015"), "-0015", "%z preserves sign for -0015");
+is(time2str("%z", $epoch, "-0045"), "-0045", "%z preserves sign for -0045");
+
+# Positive sub-hour offsets (control)
+is(time2str("%z", $epoch, "+0030"), "+0030", "%z correct for +0030");
+is(time2str("%z", $epoch, "+0545"), "+0545", "%z correct for +0545 (Nepal)");
+
+# Zero offset
+is(time2str("%z", $epoch, "+0000"), "+0000", "%z correct for UTC");