TryFindSystemTimeZoneById

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Unix.cs

@@ -271,59 +271,13 @@ private static TimeZoneInfoResult TryGetTimeZoneFromLocalMachine(string id, out
 
         /// <summary>
         /// Helper function for retrieving a TimeZoneInfo object by time_zone_name.
-        /// This function wraps the logic necessary to keep the private
-        /// SystemTimeZones cache in working order
         ///
-        /// This function will either return a valid TimeZoneInfo instance or
-        /// it will throw 'InvalidTimeZoneException' / 'TimeZoneNotFoundException'.
+        /// This function may return null.
+        ///
+        /// assumes cachedData lock is taken
         /// </summary>
-        public static TimeZoneInfo FindSystemTimeZoneById(string id)
-        {
-            // Special case for Utc as it will not exist in the dictionary with the rest
-            // of the system time zones.  There is no need to do this check for Local.Id
-            // since Local is a real time zone that exists in the dictionary cache
-            if (string.Equals(id, UtcId, StringComparison.OrdinalIgnoreCase))
-            {
-                return Utc;
-            }
-
-            ArgumentNullException.ThrowIfNull(id);
-            if (id.Length == 0 || id.Contains('\0'))
-            {
-                throw new TimeZoneNotFoundException(SR.Format(SR.TimeZoneNotFound_MissingData, id));
-            }
-
-            TimeZoneInfo? value;
-            Exception? e;
-
-            TimeZoneInfoResult result;
-
-            CachedData cachedData = s_cachedData;
-
-            lock (cachedData)
-            {
-                result = TryGetTimeZone(id, false, out value, out e, cachedData, alwaysFallbackToLocalMachine: true);
-            }
-
-            if (result == TimeZoneInfoResult.Success)
-            {
-                return value!;
-            }
-            else if (result == TimeZoneInfoResult.InvalidTimeZoneException)
-            {
-                Debug.Assert(e is InvalidTimeZoneException,
-                    "TryGetTimeZone must create an InvalidTimeZoneException when it returns TimeZoneInfoResult.InvalidTimeZoneException");
-                throw e;
-            }
-            else if (result == TimeZoneInfoResult.SecurityException)
-            {
-                throw new SecurityException(SR.Format(SR.Security_CannotReadFileData, id), e);
-            }
-            else
-            {
-                throw new TimeZoneNotFoundException(SR.Format(SR.TimeZoneNotFound_MissingData, id), e);
-            }
-        }
+        private static TimeZoneInfoResult TryGetTimeZone(string id, out TimeZoneInfo? timeZone, out Exception? e, CachedData cachedData)
+            => TryGetTimeZone(id, false, out timeZone, out e, cachedData, alwaysFallbackToLocalMachine: true);
 
         // DateTime.Now fast path that avoids allocating an historically accurate TimeZoneInfo.Local and just creates a 1-year (current year) accurate time zone
         internal static TimeSpan GetDateTimeNowUtcOffsetFromUtc(DateTime time, out bool isAmbiguousLocalDst)

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.Win32.cs

@@ -314,56 +314,13 @@ private static TimeZoneInfo GetLocalTimeZoneFromWin32Data(in TIME_ZONE_INFORMATI
 
         /// <summary>
         /// Helper function for retrieving a TimeZoneInfo object by time_zone_name.
-        /// This function wraps the logic necessary to keep the private
-        /// SystemTimeZones cache in working order
         ///
-        /// This function will either return a valid TimeZoneInfo instance or
-        /// it will throw 'InvalidTimeZoneException' / 'TimeZoneNotFoundException'.
+        /// This function may return null.
+        ///
+        /// assumes cachedData lock is taken
         /// </summary>
-        public static TimeZoneInfo FindSystemTimeZoneById(string id)
-        {
-            ArgumentNullException.ThrowIfNull(id);
-
-            // Special case for Utc to avoid having TryGetTimeZone creating a new Utc object
-            if (string.Equals(id, UtcId, StringComparison.OrdinalIgnoreCase))
-            {
-                return Utc;
-            }
-
-            if (id.Length == 0 || id.Length > MaxKeyLength || id.Contains('\0'))
-            {
-                throw new TimeZoneNotFoundException(SR.Format(SR.TimeZoneNotFound_MissingData, id));
-            }
-
-            TimeZoneInfo? value;
-            Exception? e;
-
-            TimeZoneInfoResult result;
-
-            CachedData cachedData = s_cachedData;
-
-            lock (cachedData)
-            {
-                result = TryGetTimeZone(id, false, out value, out e, cachedData);
-            }
-
-            if (result == TimeZoneInfoResult.Success)
-            {
-                return value!;
-            }
-            else if (result == TimeZoneInfoResult.InvalidTimeZoneException)
-            {
-                throw new InvalidTimeZoneException(SR.Format(SR.InvalidTimeZone_InvalidRegistryData, id), e);
-            }
-            else if (result == TimeZoneInfoResult.SecurityException)
-            {
-                throw new SecurityException(SR.Format(SR.Security_CannotReadRegistryData, id), e);
-            }
-            else
-            {
-                throw new TimeZoneNotFoundException(SR.Format(SR.TimeZoneNotFound_MissingData, id), e);
-            }
-        }
+        private static TimeZoneInfoResult TryGetTimeZone(string id, out TimeZoneInfo? timeZone, out Exception? e, CachedData cachedData)
+            => TryGetTimeZone(id, false, out timeZone, out e, cachedData);
 
         // DateTime.Now fast path that avoids allocating an historically accurate TimeZoneInfo.Local and just creates a 1-year (current year) accurate time zone
         internal static TimeSpan GetDateTimeNowUtcOffsetFromUtc(DateTime time, out bool isAmbiguousLocalDst)

src/libraries/System.Private.CoreLib/src/System/TimeZoneInfo.cs

@@ -8,6 +8,7 @@
 using System.Globalization;
 using System.Runtime.CompilerServices;
 using System.Runtime.Serialization;
+using System.Security;
 using System.Threading;
 
 namespace System
@@ -556,6 +557,90 @@ public static DateTimeOffset ConvertTimeBySystemTimeZoneId(DateTimeOffset dateTi
         public static DateTime ConvertTimeBySystemTimeZoneId(DateTime dateTime, string destinationTimeZoneId) =>
             ConvertTime(dateTime, FindSystemTimeZoneById(destinationTimeZoneId));
 
+        /// <summary>
+        /// Helper function for retrieving a <see cref="TimeZoneInfo"/> object by time zone name.
+        /// This function wraps the logic necessary to keep the private
+        /// SystemTimeZones cache in working order.
+        ///
+        /// This function will either return a valid <see cref="TimeZoneInfo"/> instance or
+        /// it will throw <see cref="InvalidTimeZoneException"/> / <see cref="TimeZoneNotFoundException"/> /
+        /// <see cref="SecurityException"/>
+        /// </summary>
+        /// <param name="id">Time zone name.</param>
+        /// <returns>Valid <see cref="TimeZoneInfo"/> instance.</returns>
+        public static TimeZoneInfo FindSystemTimeZoneById(string id)
+        {
+            TimeZoneInfo? value;
+            Exception? e;
+
+            TimeZoneInfoResult result = TryFindSystemTimeZoneById(id, out value, out e);
+            switch (result)
+            {
+                case TimeZoneInfoResult.Success:
+                    return value!;
+                case TimeZoneInfoResult.InvalidTimeZoneException:
+                    Debug.Assert(e is InvalidTimeZoneException,
+                        "TryGetTimeZone must create an InvalidTimeZoneException when it returns TimeZoneInfoResult.InvalidTimeZoneException");
+                    throw e;
+                case TimeZoneInfoResult.SecurityException:
+                    throw new SecurityException(SR.Format(SR.Security_CannotReadFileData, id), e);
+                default:
+                    throw new TimeZoneNotFoundException(SR.Format(SR.TimeZoneNotFound_MissingData, id), e);
+            }
+        }
+
+        /// <summary>
+        /// Helper function for retrieving a <see cref="TimeZoneInfo"/> object by time zone name.
+        /// This function wraps the logic necessary to keep the private
+        /// SystemTimeZones cache in working order.
+        ///
+        /// This function will either return <c>true</c> and a valid <see cref="TimeZoneInfo"/>
+        /// instance or return <c>false</c> and <c>null</c>.
+        /// </summary>
+        /// <param name="id">Time zone name.</param>
+        /// <param name="timeZoneInfo">A valid retrieved <see cref="TimeZoneInfo"/> or <c>null</c>.</param>
+        /// <returns><c>true</c> if the <see cref="TimeZoneInfo"/> object was successfully retrieved, <c>false</c> otherwise.</returns>
+        public static bool TryFindSystemTimeZoneById(string id, [NotNullWhenAttribute(true)] out TimeZoneInfo? timeZoneInfo)
+            => TryFindSystemTimeZoneById(id, out timeZoneInfo, out _) == TimeZoneInfoResult.Success;
+
+        /// <summary>
+        /// Helper function for retrieving a TimeZoneInfo object by time_zone_name.
+        /// This function wraps the logic necessary to keep the private
+        /// SystemTimeZones cache in working order.
+        ///
+        /// This function will either return:
+        /// <c>TimeZoneInfoResult.Success</c> and a valid <see cref="TimeZoneInfo"/>instance and <c>null</c> Exception or
+        /// <c>TimeZoneInfoResult.TimeZoneNotFoundException</c> and <c>null</c> <see cref="TimeZoneInfo"/> and Exception (can be null) or
+        /// other <c>TimeZoneInfoResult</c> and <c>null</c> <see cref="TimeZoneInfo"/> and valid Exception.
+        /// </summary>
+        private static TimeZoneInfoResult TryFindSystemTimeZoneById(string id, out TimeZoneInfo? timeZone, out Exception? e)
+        {
+            // Special case for Utc as it will not exist in the dictionary with the rest
+            // of the system time zones.  There is no need to do this check for Local.Id
+            // since Local is a real time zone that exists in the dictionary cache
+            if (string.Equals(id, UtcId, StringComparison.OrdinalIgnoreCase))
+            {
+                timeZone = Utc;
+                e = default;
+                return TimeZoneInfoResult.Success;
+            }
+
+            ArgumentNullException.ThrowIfNull(id);
+            if (id.Length == 0 || id.Length > MaxKeyLength || id.Contains('\0'))
+            {
+                timeZone = default;
+                e = default;
+                return TimeZoneInfoResult.TimeZoneNotFoundException;
+            }
+
+            CachedData cachedData = s_cachedData;
+
+            lock (cachedData)
+            {
+                return TryGetTimeZone(id, out timeZone, out e, cachedData);
+            }
+        }
+
         /// <summary>
         /// Converts the value of a DateTime object from sourceTimeZone to destinationTimeZone.
         /// </summary>

src/libraries/System.Runtime/ref/System.Runtime.cs

@@ -5610,6 +5610,7 @@ public static void ClearCachedData() { }
         public override bool Equals([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] object? obj) { throw null; }
         public bool Equals([System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] System.TimeZoneInfo? other) { throw null; }
         public static System.TimeZoneInfo FindSystemTimeZoneById(string id) { throw null; }
+        public static bool TryFindSystemTimeZoneById(string id, [System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out System.TimeZoneInfo? timeZoneInfo) { throw null; }
         public static System.TimeZoneInfo FromSerializedString(string source) { throw null; }
         public System.TimeZoneInfo.AdjustmentRule[] GetAdjustmentRules() { throw null; }
         public System.TimeSpan[] GetAmbiguousTimeOffsets(System.DateTime dateTime) { throw null; }

src/libraries/System.Runtime/tests/System/TimeZoneInfoTests.cs

@@ -166,11 +166,13 @@ public static void LibyaTimeZone()
             try
             {
                 tripoli = TimeZoneInfo.FindSystemTimeZoneById(s_strLibya);
+                Assert.True(TimeZoneInfo.TryFindSystemTimeZoneById(s_strLibya, out _));
             }
             catch (Exception /* TimeZoneNotFoundException in netstandard1.7 test*/ )
             {
                 // Libya time zone not found
                 Console.WriteLine("Warning: Libya time zone is not exist in this machine");
+                Assert.False(TimeZoneInfo.TryFindSystemTimeZoneById(s_strLibya, out _));
                 return;
             }
 
@@ -189,6 +191,7 @@ public static void TestYukonTZ()
             try
             {
                 TimeZoneInfo yukon = TimeZoneInfo.FindSystemTimeZoneById("Yukon Standard Time");
+                Assert.True(TimeZoneInfo.TryFindSystemTimeZoneById("Yukon Standard Time", out _));
 
                 // First, ensure we have the updated data
                 TimeZoneInfo.AdjustmentRule[] rules = yukon.GetAdjustmentRules();
@@ -214,13 +217,16 @@ public static void TestYukonTZ()
             catch (TimeZoneNotFoundException)
             {
                 // Some Windows versions don't carry the complete TZ data. Ignore the tests on such versions.
+                Assert.False(TimeZoneInfo.TryFindSystemTimeZoneById("Yukon Standard Time", out _));
+                return;
             }
         }
 
         [Fact]
         public static void RussianTimeZone()
         {
             TimeZoneInfo tz = TimeZoneInfo.FindSystemTimeZoneById(s_strRussian);
+            Assert.True(TimeZoneInfo.TryFindSystemTimeZoneById(s_strRussian, out _));
             var inputUtcDate = new DateTime(2013, 6, 1, 0, 0, 0, DateTimeKind.Utc);
 
             DateTime russiaTime = TimeZoneInfo.ConvertTime(inputUtcDate, tz);
@@ -2060,6 +2066,15 @@ public static void ClearCachedData()
             {
                 TimeZoneInfo.ConvertTime(DateTime.Now, local, cst);
             });
+
+            Assert.True(TimeZoneInfo.TryFindSystemTimeZoneById(s_strSydney, out cst));
+            local = TimeZoneInfo.Local;
+
+            TimeZoneInfo.ClearCachedData();
+            Assert.ThrowsAny<ArgumentException>(() =>
+            {
+                TimeZoneInfo.ConvertTime(DateTime.Now, local, cst);
+            });
         }
 
         [Fact]
@@ -2721,6 +2736,9 @@ public static void EnsureUtcObjectSingleton()
             TimeZoneInfo utcObject = TimeZoneInfo.GetSystemTimeZones().Single(x => x.Id.Equals("UTC", StringComparison.OrdinalIgnoreCase));
             Assert.True(ReferenceEquals(utcObject, TimeZoneInfo.Utc));
             Assert.True(ReferenceEquals(TimeZoneInfo.FindSystemTimeZoneById("UTC"), TimeZoneInfo.Utc));
+
+            Assert.True(TimeZoneInfo.TryFindSystemTimeZoneById("UTC", out TimeZoneInfo tz));
+            Assert.True(ReferenceEquals(tz, TimeZoneInfo.Utc));
         }
 
         [ConditionalTheory(typeof(PlatformDetection), nameof(PlatformDetection.IsNotBrowser))]
@@ -2748,11 +2766,20 @@ public static void UsingAlternativeTimeZoneIdsTest(string windowsId, string iana
 
                 Assert.Equal(tzi1.BaseUtcOffset, tzi2.BaseUtcOffset);
                 Assert.NotEqual(tzi1.Id, tzi2.Id);
+
+                Assert.True(TimeZoneInfo.TryFindSystemTimeZoneById(ianaId, out tzi1));
+                Assert.True(TimeZoneInfo.TryFindSystemTimeZoneById(windowsId, out tzi2));
+
+                Assert.Equal(tzi1.BaseUtcOffset, tzi2.BaseUtcOffset);
+                Assert.NotEqual(tzi1.Id, tzi2.Id);
             }
             else
             {
                 Assert.Throws<TimeZoneNotFoundException>(() => TimeZoneInfo.FindSystemTimeZoneById(s_isWindows ? ianaId : windowsId));
                 TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById(s_isWindows ? windowsId : ianaId);
+
+                Assert.False(TimeZoneInfo.TryFindSystemTimeZoneById(s_isWindows ? ianaId : windowsId, out _));
+                Assert.True(TimeZoneInfo.TryFindSystemTimeZoneById(s_isWindows ? windowsId : ianaId, out _));
             }
         }
 
@@ -2800,6 +2827,8 @@ public static void UnsupportedImplicitConversionTest()
             string nonNativeTzName = s_isWindows ? "America/Los_Angeles" : "Pacific Standard Time";
 
             Assert.Throws<TimeZoneNotFoundException>(() => TimeZoneInfo.FindSystemTimeZoneById(nonNativeTzName));
+
+            Assert.False(TimeZoneInfo.TryFindSystemTimeZoneById(nonNativeTzName, out _));
         }
 
         [ConditionalTheory(nameof(SupportIanaNamesConversion))]
@@ -2948,6 +2977,23 @@ public static void ChangeLocalTimeZone(string id)
                 TimeZoneInfo.ClearCachedData();
                 Environment.SetEnvironmentVariable("TZ", originalTZ);
             }
+
+            try
+            {
+                TimeZoneInfo.ClearCachedData();
+                Environment.SetEnvironmentVariable("TZ", id);
+
+                TimeZoneInfo localtz = TimeZoneInfo.Local;
+                Assert.True(TimeZoneInfo.TryFindSystemTimeZoneById(id, out TimeZoneInfo tz));
+
+                Assert.Equal(tz.StandardName, localtz.StandardName);
+                Assert.Equal(tz.DisplayName, localtz.DisplayName);
+            }
+            finally
+            {
+                TimeZoneInfo.ClearCachedData();
+                Environment.SetEnvironmentVariable("TZ", originalTZ);
+            }
         }
 
         [Fact]