lib: support setting process.env.TZ on windows

Fixes: #4230
Signed-off-by: James M Snell <[email protected]>

Author: jasnell

src/node_env_var.cc

@@ -4,6 +4,8 @@
 #include "node_external_reference.h"
 #include "node_process.h"
 
+#include "unicode/timezone.h"
+
 #include <time.h>  // tzset(), _tzset()
 
 namespace node {
@@ -69,16 +71,30 @@ std::shared_ptr<KVStore> system_environment = std::make_shared<RealEnvStore>();
 }  // namespace per_process
 
 template <typename T>
-void DateTimeConfigurationChangeNotification(Isolate* isolate, const T& key) {
+void DateTimeConfigurationChangeNotification(Isolate* isolate, const T& key, const char* val = nullptr) {
   if (key.length() == 2 && key[0] == 'T' && key[1] == 'Z') {
+  auto constexpr time_zone_detection = Isolate::TimeZoneDetection::kRedetect;
 #ifdef __POSIX__
     tzset();
 #else
     _tzset();
 #endif
-    auto constexpr time_zone_detection = Isolate::TimeZoneDetection::kRedetect;
     isolate->DateTimeConfigurationChangeNotification(time_zone_detection);
+
+// On windows, the TZ environment is not supported out of the box.
+// By default, v8 will only be able to detect the system configured
+// timezone. This supports using the TZ environment variable to set
+// the default timezone instead.
+#ifndef __POSIX__
+    if (val != nullptr) {
+      icu::UnicodeString id =
+          icu::UnicodeString::fromUTF8(icu::StringPiece(val));
+      icu::TimeZone* tz = icu::TimeZone::createTimeZone(id);
+      if (*tz != icu::TimeZone::getUnknown())
+        icu::TimeZone::adoptDefault(tz);
+    }
   }
+#endif
 }
 
 Maybe<std::string> RealEnvStore::Get(const char* key) const {
@@ -128,7 +144,7 @@ void RealEnvStore::Set(Isolate* isolate,
   if (key.length() > 0 && key[0] == '=') return;
 #endif
   uv_os_setenv(*key, *val);
-  DateTimeConfigurationChangeNotification(isolate, key);
+  DateTimeConfigurationChangeNotification(isolate, key, *val);
 }
 
 int32_t RealEnvStore::Query(const char* key) const {

test/parallel/test-datetime-change-notify.js

@@ -0,0 +1,10 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+
+process.env.TZ = 'UTC';
+assert.match(new Date().toString(), /GMT\+0000/);
+
+process.env.TZ = 'EST';
+assert.match(new Date().toString(), /GMT-05:00/);