Fix IANA time zone names for Windows system time zones (#15914)

Author: HertzDevil

scripts/generate_windows_zone_names.cr

@@ -25,11 +25,28 @@ entries = nodes.flat_map do |node|
   end
 end.sort!
 
-iana_to_windows_items = entries.map do |tzdata_name, territory, windows_name|
-  {tzdata_name, windows_name}
+ENV["ZONEINFO"] = ZONEINFO_ZIP
+iana_to_windows_items = entries.compact_map do |tzdata_name, territory, windows_name|
+  location = Time::Location.load(tzdata_name)
+  next unless location
+
+  time = Time.local(location).at_beginning_of_year
+  zone1 = time.zone
+  zone2 = (time + 6.months).zone
+
+  # southern hemisphere
+  if zone1.offset > zone2.offset
+    zone1, zone2 = zone2, zone1
+  end
+
+  {tzdata_name, windows_name, zone1.name, zone2.name}
 end.uniq!
 
-ENV["ZONEINFO"] = ZONEINFO_ZIP
+windows_to_iana_items = entries.compact_map do |tzdata_name, territory, windows_name|
+  {windows_name, tzdata_name} if territory == "001"
+end.uniq!
+
+# TODO: remove in 1.17
 windows_zone_names_items = entries.compact_map do |tzdata_name, territory, windows_name|
   next unless territory == "001"
   location = Time::Location.load(tzdata_name)

scripts/windows_zone_names.ecr

@@ -5,18 +5,31 @@
 # DO NOT EDIT
 
 module Crystal::System::Time
-  # These mappings from IANA to Windows time zone names are based on
+  # These mappings from IANA to Windows time zone names and tzdata abbreviations
+  # are based on
   # <%= WINDOWS_ZONE_NAMES_SOURCE %>
-  private class_getter iana_to_windows : Hash(String, String) do
-    data = Hash(String, String).new(initial_capacity: <%= iana_to_windows_items.size %>)
-    <%- iana_to_windows_items.each do |tzdata_name, windows_name| -%>
-      put(data, <%= tzdata_name.inspect %>, <%= windows_name.inspect %>)
+  private class_getter iana_to_windows : Hash(String, {String, String, String}) do
+    data = Hash(String, {String, String, String}).new(initial_capacity: <%= iana_to_windows_items.size %>)
+    <%- iana_to_windows_items.each do |tzdata_name, windows_name, zone1, zone2| -%>
+      put(data, <%= tzdata_name.inspect %>, <%= windows_name.inspect %>, <%= zone1.inspect %>, <%= zone2.inspect %>)
+    <%- end -%>
+    data
+  end
+
+  # These canonical mappings from Windows to IANA time zone names, used for the
+  # local time zone, are based on
+  # <%= WINDOWS_ZONE_NAMES_SOURCE %>
+  private class_getter windows_to_iana : Hash(String, String) do
+    data = Hash(String, String).new(initial_capacity: <%= windows_to_iana_items.size %>)
+    <%- windows_to_iana_items.each do |windows_name, tzdata_name| -%>
+      put(data, <%= windows_name.inspect %>, <%= tzdata_name.inspect %>)
     <%- end -%>
     data
   end
 
   # These mappings from Windows time zone names to tzdata abbreviations are based on
   # <%= WINDOWS_ZONE_NAMES_SOURCE %>
+  # TODO: remove in 1.17
   private class_getter windows_zone_names : Hash(String, {String, String}) do
     data = Hash(String, {String, String}).new(initial_capacity: <%= windows_zone_names_items.size %>)
     <%- windows_zone_names_items.each do |windows_name, zone1, zone2, tzdata_name| -%>

spec/std/time/location_spec.cr

@@ -67,6 +67,14 @@ class Time::Location
           location.utc?.should be_false
           location.fixed?.should be_false
         end
+
+        it "uses IANA zone names for Windows system time zones (#15911)" do
+          location = Location.load("Europe/Lisbon")
+          std_zone = location.zones.find(&.dst?.!).should_not be_nil
+          dst_zone = location.zones.find(&.dst?).should_not be_nil
+          std_zone.name.should eq("WET")
+          dst_zone.name.should eq("WEST")
+        end
       {% end %}
 
       it "invalid timezone identifier" do

src/crystal/system/win32/time.cr

@@ -72,7 +72,12 @@ module Crystal::System::Time
   def self.load_localtime : ::Time::Location?
     if LibC.GetDynamicTimeZoneInformation(out info) != LibC::TIME_ZONE_ID_INVALID
       windows_name = String.from_utf16(info.timeZoneKeyName.to_slice, truncate_at_null: true)
-      initialize_location_from_TZI(pointerof(info).as(LibC::TIME_ZONE_INFORMATION*).value, "Local", windows_name)
+
+      return unless canonical_iana_name = windows_to_iana[windows_name]?
+      return unless windows_info = iana_to_windows[canonical_iana_name]?
+      _, stdname, dstname = windows_info
+
+      initialize_location_from_TZI(pointerof(info).as(LibC::TIME_ZONE_INFORMATION*).value, "Local", windows_name, stdname, dstname)
     end
   end
 
@@ -90,7 +95,8 @@ module Crystal::System::Time
     daylightDate : LibC::SYSTEMTIME
 
   def self.load_iana_zone(iana_name : String) : ::Time::Location?
-    return unless windows_name = iana_to_windows[iana_name]?
+    return unless windows_info = iana_to_windows[iana_name]?
+    windows_name, stdname, dstname = windows_info
 
     WindowsRegistry.open?(LibC::HKEY_LOCAL_MACHINE, REGISTRY_TIME_ZONES) do |key_handle|
       WindowsRegistry.open?(key_handle, windows_name.to_utf16) do |sub_handle|
@@ -106,14 +112,12 @@ module Crystal::System::Time
         )
         WindowsRegistry.get_raw(sub_handle, Std, tzi.standardName.to_slice.to_unsafe_bytes)
         WindowsRegistry.get_raw(sub_handle, Dlt, tzi.daylightName.to_slice.to_unsafe_bytes)
-        initialize_location_from_TZI(tzi, iana_name, windows_name)
+        initialize_location_from_TZI(tzi, iana_name, windows_name, stdname, dstname)
       end
     end
   end
 
-  private def self.initialize_location_from_TZI(info, name, windows_name)
-    stdname, dstname = normalize_zone_names(info)
-
+  private def self.initialize_location_from_TZI(info, name, windows_name, stdname, dstname)
     if info.standardDate.wMonth == 0_u16 || info.daylightDate.wMonth == 0_u16
       # No DST
       zone = ::Time::Location::Zone.new(stdname, info.bias * BIAS_TO_OFFSET_FACTOR, false)
@@ -140,27 +144,6 @@ module Crystal::System::Time
     ::Time::TZ::MonthWeekDay.new(time.wMonth.to_i8, time.wDay.to_i8, time.wDayOfWeek.to_i8, seconds)
   end
 
-  # Normalizes the names of the standard and dst zones.
-  private def self.normalize_zone_names(info : LibC::TIME_ZONE_INFORMATION) : Tuple(String, String)
-    stdname, _ = String.from_utf16(info.standardName.to_slice.to_unsafe)
-
-    if normalized_names = windows_zone_names[stdname]?
-      return normalized_names
-    end
-
-    dstname, _ = String.from_utf16(info.daylightName.to_slice.to_unsafe)
-
-    if english_name = translate_zone_name(stdname, dstname)
-      if normalized_names = windows_zone_names[english_name]?
-        return normalized_names
-      end
-    end
-
-    # As a last resort, return the raw names as provided by TIME_ZONE_INFORMATION.
-    # They are most probably localized and we couldn't find a translation.
-    return stdname, dstname
-  end
-
   REGISTRY_TIME_ZONES = System.wstr_literal %q(SOFTWARE\Microsoft\Windows NT\CurrentVersion\Time Zones)
   Std                 = System.wstr_literal "Std"
   Dlt                 = System.wstr_literal "Dlt"