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Merged
merged 4 commits into from
Oct 27, 2025
Merged

Fix GetSystemTimeZone to return filtered list #121095

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414bb73
Fix GetSystemTimeZone to return filtered list
tarekgh Oct 25, 2025
e6e40b1
Keep ConditionalFact
tarekgh Oct 25, 2025
3d6ae9d
Feedback
tarekgh Oct 26, 2025
dec7c14
Pick the test change from #121033
tarekgh Oct 27, 2025
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18 changes: 15 additions & 3 deletions src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Unix.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -284,7 +284,7 @@ public AdjustmentRule[] GetAdjustmentRules()
return daylightDisplayName;
}

private static void PopulateAllSystemTimeZones(CachedData cachedData)
private static Dictionary<string, TimeZoneInfo> PopulateAllSystemTimeZones(CachedData cachedData)
{
Debug.Assert(Monitor.IsEntered(cachedData));

Expand All @@ -295,13 +295,25 @@ private static void PopulateAllSystemTimeZones(CachedData cachedData)

if (Invariant)
{
return;
return cachedData._systemTimeZones;
}

// The filtered list that shouldn't have any duplicates.
Dictionary<string, TimeZoneInfo> filteredTimeZones = new Dictionary<string, TimeZoneInfo>(StringComparer.OrdinalIgnoreCase)
{
{ UtcId, s_utcTimeZone }
};

foreach (string timeZoneId in GetTimeZoneIds())
{
TryGetTimeZone(timeZoneId, false, out _, out _, cachedData, alwaysFallbackToLocalMachine: true); // populate the cache
if (TryGetTimeZone(timeZoneId, false, out TimeZoneInfo? timeZone, out _, cachedData, alwaysFallbackToLocalMachine: true) == TimeZoneInfoResult.Success &&
timeZone is not null)
{
filteredTimeZones[timeZoneId] = timeZone;
}
}

return filteredTimeZones;
}

/// <summary>
Expand Down
10 changes: 7 additions & 3 deletions src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Win32.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -69,18 +69,19 @@ public AdjustmentRule[] GetAdjustmentRules()
return null;
}

private static void PopulateAllSystemTimeZones(CachedData cachedData)
private static Dictionary<string, TimeZoneInfo> PopulateAllSystemTimeZones(CachedData cachedData)
{
Debug.Assert(Monitor.IsEntered(cachedData));

// Ensure _systemTimeZones is initialized. TryGetTimeZone with Invariant mode depend on that.
cachedData._systemTimeZones ??= new Dictionary<string, TimeZoneInfo>(StringComparer.OrdinalIgnoreCase)
{
{ UtcId, s_utcTimeZone }
};

if (Invariant)
{
return;
return cachedData._systemTimeZones;
}

using (RegistryKey? reg = Registry.LocalMachine.OpenSubKey(TimeZonesRegistryHive, writable: false))
Expand All @@ -89,10 +90,13 @@ private static void PopulateAllSystemTimeZones(CachedData cachedData)
{
foreach (string keyName in reg.GetSubKeyNames())
{
TryGetTimeZone(keyName, false, out _, out _, cachedData); // populate the cache
TryGetTimeZone(keyName, false, out _, out _, cachedData); // should update cache._systemTimeZones
}
}
}

// On Windows, there is no filtered list as _systemTimeZones always not having any duplicates.
return cachedData._systemTimeZones;
}

private static string? GetAlternativeId(string id, out bool idIsIana)
Expand Down
41 changes: 23 additions & 18 deletions src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -149,9 +149,20 @@ internal long GetLocalDateTimeNowTicks(DateTime utcNow, out bool isAmbiguous)
return localTicks;
}


// System time zones list. This could be a superset of the list we return from TimeZoneInfo.GetSystemTimeZones on Linux and macOS.
// This list can contain duplicate time zones with different legacy IDs.
public Dictionary<string, TimeZoneInfo>? _systemTimeZones;

// The sorted readonly collection created after populating _systemTimeZones.
// This collection returned to the callers of TimeZoneInfo.GetSystemTimeZones(skipSorting: false).
public ReadOnlyCollection<TimeZoneInfo>? _readOnlySystemTimeZones;

// The unsorted readonly collection created after populating _systemTimeZones.
// This collection returned to the callers of TimeZoneInfo.GetSystemTimeZones(skipSorting: true).
public ReadOnlyCollection<TimeZoneInfo>? _readOnlyUnsortedSystemTimeZones;

// Alternative IDs usually be IANA names when running on Windows and will be Windows TZ IDs on Linux/macOS.
public Dictionary<string, TimeZoneInfo>? _timeZonesUsingAlternativeIds;
public bool _allSystemTimeZonesRead;
public volatile DateTimeNowCache? _dateTimeNowCache;
Expand Down Expand Up @@ -757,17 +768,14 @@ public static ReadOnlyCollection<TimeZoneInfo> GetSystemTimeZones(bool skipSorti
{
if ((skipSorting ? cachedData._readOnlyUnsortedSystemTimeZones : cachedData._readOnlySystemTimeZones) is null)
{
if (!cachedData._allSystemTimeZonesRead)
{
PopulateAllSystemTimeZones(cachedData);
cachedData._allSystemTimeZonesRead = true;
}
Dictionary<string, TimeZoneInfo>? filteredTimeZones = PopulateAllSystemTimeZones(cachedData);
cachedData._allSystemTimeZonesRead = true;

if (cachedData._systemTimeZones != null)
if (filteredTimeZones is not null)
{
// return a collection of the cached system time zones
TimeZoneInfo[] array = new TimeZoneInfo[cachedData._systemTimeZones.Count];
cachedData._systemTimeZones.Values.CopyTo(array, 0);
// return a collection of the filtered cached system time zones
TimeZoneInfo[] array = new TimeZoneInfo[filteredTimeZones.Count];
filteredTimeZones.Values.CopyTo(array, 0);

if (!skipSorting)
{
Expand Down Expand Up @@ -1205,18 +1213,15 @@ private static TimeZoneInfoResult TryGetTimeZoneUsingId(string id, bool dstDisab
}

// check the cache
if (cachedData._systemTimeZones != null)
if (cachedData._systemTimeZones?.TryGetValue(id, out value) is true)
{
if (cachedData._systemTimeZones.TryGetValue(id, out value))
if (dstDisabled && value._supportsDaylightSavingTime)
{
if (dstDisabled && value._supportsDaylightSavingTime)
{
// we found a cache hit but we want a time zone without DST and this one has DST data
value = CreateCustomTimeZone(value._id, value._baseUtcOffset, value._displayName, value._standardDisplayName);
}

return result;
// we found a cache hit but we want a time zone without DST and this one has DST data
value = CreateCustomTimeZone(value._id, value._baseUtcOffset, value._displayName, value._standardDisplayName);
}

return result;
}

if (Invariant)
Expand Down
53 changes: 51 additions & 2 deletions src/libraries/System.Runtime/tests/System.Runtime.Tests/System/TimeZoneInfoTests.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -2766,8 +2766,7 @@ public static void FijiTimeZoneTest()
}
}

[ConditionalFact]
[ActiveIssue("https://github.com/dotnet/runtime/issues/64111", TestPlatforms.Linux)]
[Fact]
[ActiveIssue("https://github.com/dotnet/runtime/issues/117731", TestPlatforms.Android)]
public static void NoBackwardTimeZones()
{
Expand All @@ -2776,6 +2775,15 @@ public static void NoBackwardTimeZones()
throw new SkipTestException("This test won't work on API level < 26");
}

// Clear cached data to always ensure predictable results
TimeZoneInfo.ClearCachedData();
if (SupportLegacyTimeZoneNames)
{
// Get legacy time zone "UCT" and ensure is not included in list returned by TimeZoneInfo.GetSystemTimeZones
// to ensure no duplicates display names as we should have "UTC" in the list.
TimeZoneInfo uct = TimeZoneInfo.FindSystemTimeZoneById("UCT");
}

ReadOnlyCollection<TimeZoneInfo> tzCollection = TimeZoneInfo.GetSystemTimeZones();
HashSet<String> tzDisplayNames = new HashSet<String>();

Expand All @@ -2786,6 +2794,47 @@ public static void NoBackwardTimeZones()
Assert.Equal(tzCollection.Count, tzDisplayNames.Count);
}

[Fact]
public static void TestGetSystemTimeZones()
{
TimeZoneInfo.ClearCachedData(); // Start clean
ReadOnlyCollection<TimeZoneInfo> tzCollection1 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
ReadOnlyCollection<TimeZoneInfo> tzCollection2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
Assert.Equal(tzCollection1.Count, tzCollection2.Count);
foreach (TimeZoneInfo timezone in tzCollection1)
{
Assert.Contains(timezone, tzCollection2);
}

TimeZoneInfo.ClearCachedData(); // Start again as clean
tzCollection1 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
tzCollection2 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
Assert.Equal(tzCollection1.Count, tzCollection2.Count);
foreach (TimeZoneInfo timezone in tzCollection1)
{
Assert.Contains(timezone, tzCollection2);
}

TimeZoneInfo.ClearCachedData(); // Start clean
if (SupportLegacyTimeZoneNames)
{
// Get legacy time zone "UCT" and ensure is not included in list returned by TimeZoneInfo.GetSystemTimeZones
// to ensure no duplicates display names as we should have "UTC" in the list.
TimeZoneInfo uct = TimeZoneInfo.FindSystemTimeZoneById("UCT");
}

ReadOnlyCollection<TimeZoneInfo> tzCollection3 = TimeZoneInfo.GetSystemTimeZones(skipSorting: true);
ReadOnlyCollection<TimeZoneInfo> tzCollection4 = TimeZoneInfo.GetSystemTimeZones(skipSorting: false);
Assert.Equal(tzCollection3.Count, tzCollection4.Count);
Assert.Equal(tzCollection1.Count, tzCollection4.Count);
foreach (TimeZoneInfo timezone in tzCollection3)
{
Assert.Contains(timezone, tzCollection4);
}

Assert.DoesNotContain(tzCollection4, t => t.Id == "UCT");
}

[Fact]
[PlatformSpecific(TestPlatforms.Android | TestPlatforms.iOS | TestPlatforms.tvOS)]
[Trait(XunitConstants.Category, "AdditionalTimezoneChecks")]
Expand Down
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