[Bug #21144] Win32: Use Windows time zone ID if TZ is not set

If the TZ environment variable is not set, the time zone names
retrieved from the system are localized for UI display and may vary
across editions and language packs for the same time zone.
Use the time zone IDs that are invariant across environments instead.

hash.c

@@ -5016,7 +5016,7 @@ env_name(volatile VALUE *s)
 static VALUE env_aset(VALUE nm, VALUE val);
 
 static void
-reset_by_modified_env(const char *nam)
+reset_by_modified_env(const char *nam, const char *val)
 {
     /*
      * ENV['TZ'] = nil has a special meaning.
@@ -5025,7 +5025,7 @@ reset_by_modified_env(const char *nam)
      * This hack might works only on Linux glibc.
      */
     if (ENVMATCH(nam, TZ_ENV)) {
-        ruby_reset_timezone();
+        ruby_reset_timezone(val);
     }
 }
 
@@ -5033,7 +5033,7 @@ static VALUE
 env_delete(VALUE name)
 {
     const char *nam = env_name(name);
-    reset_by_modified_env(nam);
+    reset_by_modified_env(nam, NULL);
     VALUE val = getenv_with_lock(nam);
 
     if (!NIL_P(val)) {
@@ -5439,7 +5439,7 @@ env_aset(VALUE nm, VALUE val)
     get_env_ptr(value, val);
 
     ruby_setenv(name, value);
-    reset_by_modified_env(name);
+    reset_by_modified_env(name, value);
     return val;
 }
 

internal/time.h

@@ -28,7 +28,10 @@ struct timeval rb_time_timeval(VALUE);
 RUBY_SYMBOL_EXPORT_BEGIN
 /* time.c (export) */
 void ruby_reset_leap_second_info(void);
-void ruby_reset_timezone(void);
+#ifdef RBIMPL_ATTR_DEPRECATED_INTERNAL_ONLY
+RBIMPL_ATTR_DEPRECATED_INTERNAL_ONLY()
+#endif
+void ruby_reset_timezone(const char *);
 RUBY_SYMBOL_EXPORT_END
 
 #endif /* INTERNAL_TIME_H */

time.c

@@ -45,6 +45,10 @@
 #include "ruby/util.h"
 #include "timev.h"
 
+#if defined(_WIN32)
+# include "timezoneapi.h" /* DYNAMIC_TIME_ZONE_INFORMATION */
+#endif
+
 #include "builtin.h"
 
 static ID id_submicro, id_nano_num, id_nano_den, id_offset, id_zone;
@@ -703,10 +707,51 @@ static VALUE tm_from_time(VALUE klass, VALUE time);
 
 bool ruby_tz_uptodate_p;
 
+#ifdef _WIN32
+enum {tzkey_max = numberof(((DYNAMIC_TIME_ZONE_INFORMATION *)NULL)->TimeZoneKeyName)};
+static struct {
+    char use_tzkey;
+    char name[tzkey_max * 4 + 1];
+} w32_tz;
+
+static char *
+get_tzname(int dst)
+{
+    if (w32_tz.use_tzkey) {
+        if (w32_tz.name[0]) {
+            return w32_tz.name;
+        }
+        else {
+            /*
+             * Use GetDynamicTimeZoneInformation::TimeZoneKeyName, Windows
+             * time zone ID, which is not localized because it is the key
+             * for "Dynamic DST" keys under the "Time Zones" registry.
+             * Available since Windows Vista and Windows Server 2008.
+             */
+            DYNAMIC_TIME_ZONE_INFORMATION tzi;
+            WCHAR *const wtzkey = tzi.TimeZoneKeyName;
+            DWORD tzret = GetDynamicTimeZoneInformation(&tzi);
+            if (tzret != TIME_ZONE_ID_INVALID && *wtzkey) {
+                int wlen = (int)wcsnlen(wtzkey, tzkey_max);
+                int clen = WideCharToMultiByte(CP_UTF8, 0, wtzkey, wlen,
+                                               w32_tz.name, sizeof(w32_tz.name) - 1,
+                                               NULL, NULL);
+                w32_tz.name[clen] = '\0';
+                return w32_tz.name;
+            }
+        }
+    }
+    return _tzname[_daylight && dst];
+}
+#endif
+
 void
-ruby_reset_timezone(void)
+ruby_reset_timezone(const char *val)
 {
     ruby_tz_uptodate_p = false;
+#ifdef _WIN32
+    w32_tz.use_tzkey = !val || !*val;
+#endif
     ruby_reset_leap_second_info();
 }
 
@@ -1653,11 +1698,9 @@ localtime_with_gmtoff_zone(const time_t *t, struct tm *result, long *gmtoff, VAL
         if (zone) {
 #if defined(HAVE_TM_ZONE)
             *zone = zone_str(tm.tm_zone);
+#elif defined(_WIN32)
+            *zone = zone_str(get_tzname(tm.tm_isdst));
 #elif defined(HAVE_TZNAME) && defined(HAVE_DAYLIGHT)
-# if defined(RUBY_MSVCRT_VERSION) && RUBY_MSVCRT_VERSION >= 140
-#  define tzname _tzname
-#  define daylight _daylight
-# endif
             /* this needs tzset or localtime, instead of localtime_r */
             *zone = zone_str(tzname[daylight && tm.tm_isdst]);
 #else
@@ -5863,6 +5906,10 @@ rb_time_zone_abbreviation(VALUE zone, VALUE time)
 void
 Init_Time(void)
 {
+#ifdef _WIN32
+    ruby_reset_timezone(getenv("TZ"));
+#endif
+
     id_submicro = rb_intern_const("submicro");
     id_nano_num = rb_intern_const("nano_num");
     id_nano_den = rb_intern_const("nano_den");