CFTimeZone: resolve GMT offset names

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;

Tests/CFTimeZone/gmt.m

@@ -0,0 +1,43 @@
+#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.");
+  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);
+  return 0;
+}