Fix Windows time zone name extraction. Update API docs

runtime/vm/os_win.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_OS_WINDOWS)
 
 #include "vm/os.h"
 
 #include <malloc.h>  // NOLINT
@@ skipping 16 matching lines @@
 
 
 intptr_t OS::ProcessId() {
   return static_cast<intptr_t>(GetCurrentProcessId());
 }
 
 
 // As a side-effect sets the globals _timezone, _daylight and _tzname.
 static bool LocalTime(int64_t seconds_since_epoch, tm* tm_result) {
   time_t seconds = static_cast<time_t>(seconds_since_epoch);
-  if (seconds != seconds_since_epoch) return false;
+  if (seconds != seconds_since_epoch) {
+    return false;
+  }
   // localtime_s implicitly sets _timezone, _daylight and _tzname.
   errno_t error_code = localtime_s(tm_result, &seconds);
   return error_code == 0;
 }
 
 
 static int GetDaylightSavingBiasInSeconds() {
   TIME_ZONE_INFORMATION zone_information;
   memset(&zone_information, 0, sizeof(zone_information));
   if (GetTimeZoneInformation(&zone_information) == TIME_ZONE_ID_INVALID) {
     // By default the daylight saving offset is an hour.
     return -60 * 60;
   } else {
     return static_cast<int>(zone_information.DaylightBias * 60);
   }
 }
 
 
 const char* OS::GetTimeZoneName(int64_t seconds_since_epoch) {
-  tm decomposed;
-  // LocalTime will set _tzname.
-  bool succeeded = LocalTime(seconds_since_epoch, &decomposed);
-  if (succeeded) {
-    int inDaylightSavingsTime = decomposed.tm_isdst;
-    ASSERT(inDaylightSavingsTime == 0 || inDaylightSavingsTime == 1);
-    return _tzname[inDaylightSavingsTime];
-  } else {
-    // Return an empty string like V8 does.
-    return "";
+  TIME_ZONE_INFORMATION zone_information;
+  memset(&zone_information, 0, sizeof(zone_information));
+
+  // Initialize and grab the time zone data.
+  _tzset();
+  if (GetTimeZoneInformation(&zone_information) == TIME_ZONE_ID_INVALID) {
+    // If we can't get the time zone data, fallback on PDT.

[siva, 2016/06/14 20:07:06]

fallback on PST ?

In the past looks like we were returning "" why did you change that?

[zra, 2016/06/14 20:42:18]

I didn't notice that on other platforms we also return "" on failure. I've
changed back to return "".

+    return "Pacific Standard Time";
   }
+
+  // Grab the local time to see if we are in daylight savings time.
+  tm local_time;
+  bool daylight_savings = false;
+  if (LocalTime(seconds_since_epoch, &local_time)) {
+    daylight_savings = (local_time.tm_isdst == 1);
+  }
+
+  // Convert the wchar string to a null-terminated utf8 string.
+  wchar_t* wchar_name = daylight_savings
+                      ? zone_information.DaylightName
+                      : zone_information.StandardName;
+  intptr_t utf8_len = WideCharToMultiByte(
+      CP_UTF8, 0, wchar_name, -1, NULL, 0, NULL, NULL);
+  char* name = Thread::Current()->zone()->Alloc<char>(utf8_len + 1);
+  WideCharToMultiByte(
+      CP_UTF8, 0, wchar_name, -1, name, utf8_len, NULL, NULL);
+  name[utf8_len] = '\0';
+  return name;
 }
 
 
 int OS::GetTimeZoneOffsetInSeconds(int64_t seconds_since_epoch) {
   tm decomposed;
   // LocalTime will set _timezone.
   bool succeeded = LocalTime(seconds_since_epoch, &decomposed);
   if (succeeded) {
     int inDaylightSavingsTime = decomposed.tm_isdst;
     ASSERT(inDaylightSavingsTime == 0 || inDaylightSavingsTime == 1);
@@ skipping 346 matching lines @@
   // TODO(zra): Remove once VM shuts down cleanly.
   private_flag_windows_run_tls_destructors = false;
   // On Windows we use ExitProcess so that threads can't clobber the exit_code.
   // See: https://code.google.com/p/nativeclient/issues/detail?id=2870
   ::ExitProcess(code);
 }
 
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_WINDOWS)