From 4f7e59ee213c6bca82ee049fda1db8ffaec6ea83 Mon Sep 17 00:00:00 2001
From: Todd White <todd.white@thalion.global>
Date: Wed, 22 Jul 2026 10:16:18 -0400
Subject: [PATCH 1/2] CFTimeZone: resolve GMT offset names

CFTimeZoneCreateWithName looked for a zone file for every name, so a GMT
offset such as GMT+05:00 (which has no file) returned NULL.  In particular a
calendar whose time zone was created from a GMT offset could not be copied
back, since CFCalendarCopyTimeZone recreates the zone from its name.  Parse a
GMT offset name and build the zone from the offset directly.
---
 Source/CFTimeZone.c    | 24 +++++++++++++++++++++++-
 Tests/CFTimeZone/gmt.m | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+), 1 deletion(-)
 create mode 100644 Tests/CFTimeZone/gmt.m

diff --git a/Source/CFTimeZone.c b/Source/CFTimeZone.c
index da8a104..6d52eb8 100644
--- a/Source/CFTimeZone.c
+++ b/Source/CFTimeZone.c
@@ -328,7 +328,29 @@ CFTimeZoneCreateWithName (CFAllocatorRef alloc, CFStringRef name,
   CFURLRef path;
   CFDataRef data;
   CFTimeZoneRef new;
-  
+  char cname[16];
+
+  /* A GMT offset such as GMT+05:00 has no zone file; build it directly. */
+  if (CFStringGetCString (name, cname, sizeof (cname), kCFStringEncodingASCII)
+      && strncmp (cname, "GMT", 3) == 0
+      && (cname[3] == '+' || cname[3] == '-'))
+    {
+      int sign = (cname[3] == '-') ? -1 : 1;
+      const char *p = cname + 4;
+      int hh = 0;
+      int mm = 0;
+
+      while (*p >= '0' && *p <= '9')
+        hh = hh * 10 + (*p++ - '0');
+      if (*p == ':')
+        ++p;
+      while (*p >= '0' && *p <= '9')
+        mm = mm * 10 + (*p++ - '0');
+
+      return CFTimeZoneCreateWithTimeIntervalFromGMT (alloc,
+        sign * (hh * 3600 + mm * 60));
+    }
+
   if (tryAbbrev)
     {
       CFDictionaryRef abbrevs;
diff --git a/Tests/CFTimeZone/gmt.m b/Tests/CFTimeZone/gmt.m
new file mode 100644
index 0000000..bfbe29c
--- /dev/null
+++ b/Tests/CFTimeZone/gmt.m
@@ -0,0 +1,35 @@
+#include "CoreFoundation/CFTimeZone.h"
+#include "CoreFoundation/CFCalendar.h"
+#include "../CFTesting.h"
+
+/* CFTimeZoneCreateWithName resolves GMT and UTC offset names, so a calendar
+   whose time zone is a GMT offset can be copied back. */
+
+int main (void)
+{
+  CFTimeZoneRef z0 = CFTimeZoneCreateWithTimeIntervalFromGMT (NULL, 0.0);
+  CFTimeZoneRef tz;
+  CFCalendarRef cal;
+
+  tz = CFTimeZoneCreateWithName (NULL, CFSTR ("GMT"), true);
+  PASS_CF (tz != NULL && CFTimeZoneGetSecondsFromGMT (tz, 0.0) == 0,
+    "GMT resolves to a zero offset.");
+
+  tz = CFTimeZoneCreateWithName (NULL, CFSTR ("UTC"), true);
+  PASS_CF (tz != NULL && CFTimeZoneGetSecondsFromGMT (tz, 0.0) == 0,
+    "UTC resolves to a zero offset.");
+
+  tz = CFTimeZoneCreateWithName (NULL, CFSTR ("GMT-05:00"), true);
+  PASS_CF (tz != NULL && CFTimeZoneGetSecondsFromGMT (tz, 0.0) == -18000,
+    "GMT-05:00 resolves to minus 18000 seconds.");
+
+  cal = CFCalendarCreateWithIdentifier (NULL, kCFGregorianCalendar);
+  CFCalendarSetTimeZone (cal, z0);
+  tz = CFCalendarCopyTimeZone (cal);
+  PASS_CF (tz != NULL && CFTimeZoneGetSecondsFromGMT (tz, 0.0) == 0,
+    "A calendar's GMT time zone can be copied back.");
+
+  CFRelease (cal);
+  CFRelease (z0);
+  return 0;
+}

From df61052312f6b5633dbb9a38bde993151633f17a Mon Sep 17 00:00:00 2001
From: Todd White <todd.white@thalion.global>
Date: Thu, 23 Jul 2026 08:48:21 -0400
Subject: [PATCH 2/2] Tests: release each resolved time zone in the GMT-name
 test

---
 Tests/CFTimeZone/gmt.m | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Tests/CFTimeZone/gmt.m b/Tests/CFTimeZone/gmt.m
index bfbe29c..988497e 100644
--- a/Tests/CFTimeZone/gmt.m
+++ b/Tests/CFTimeZone/gmt.m
@@ -14,20 +14,28 @@ int main (void)
   tz = CFTimeZoneCreateWithName (NULL, CFSTR ("GMT"), true);
   PASS_CF (tz != NULL && CFTimeZoneGetSecondsFromGMT (tz, 0.0) == 0,
     "GMT resolves to a zero offset.");
+  if (tz != NULL)
+    CFRelease (tz);
 
   tz = CFTimeZoneCreateWithName (NULL, CFSTR ("UTC"), true);
   PASS_CF (tz != NULL && CFTimeZoneGetSecondsFromGMT (tz, 0.0) == 0,
     "UTC resolves to a zero offset.");
+  if (tz != NULL)
+    CFRelease (tz);
 
   tz = CFTimeZoneCreateWithName (NULL, CFSTR ("GMT-05:00"), true);
   PASS_CF (tz != NULL && CFTimeZoneGetSecondsFromGMT (tz, 0.0) == -18000,
     "GMT-05:00 resolves to minus 18000 seconds.");
+  if (tz != NULL)
+    CFRelease (tz);
 
   cal = CFCalendarCreateWithIdentifier (NULL, kCFGregorianCalendar);
   CFCalendarSetTimeZone (cal, z0);
   tz = CFCalendarCopyTimeZone (cal);
   PASS_CF (tz != NULL && CFTimeZoneGetSecondsFromGMT (tz, 0.0) == 0,
     "A calendar's GMT time zone can be copied back.");
+  if (tz != NULL)
+    CFRelease (tz);
 
   CFRelease (cal);
   CFRelease (z0);