Port 13553 "Fix transition offset logic" to master

Author: MaximLipnin

mcs/class/corlib/System/TimeZoneInfo.cs

@@ -805,7 +805,7 @@ public TimeSpan GetUtcOffset (DateTimeOffset dateTimeOffset)
 			return GetUtcOffset (dateTimeOffset.UtcDateTime, out isDST);
 		}
 
-		private TimeSpan GetUtcOffset (DateTime dateTime, out bool isDST)
+		private TimeSpan GetUtcOffset (DateTime dateTime, out bool isDST, bool forOffset = false)
 		{
 			isDST = false;
 
@@ -817,7 +817,7 @@ private TimeSpan GetUtcOffset (DateTime dateTime, out bool isDST)
 				tz = TimeZoneInfo.Local;
 
 			bool isTzDst;
-			var tzOffset = GetUtcOffsetHelper (dateTime, tz, out isTzDst);
+			var tzOffset = GetUtcOffsetHelper (dateTime, tz, out isTzDst, forOffset);
 
 			if (tz == this) {
 				isDST = isTzDst;
@@ -828,11 +828,11 @@ private TimeSpan GetUtcOffset (DateTime dateTime, out bool isDST)
 			if (!TryAddTicks (dateTime, -tzOffset.Ticks, out utcDateTime, DateTimeKind.Utc))
 				return BaseUtcOffset;
 
-			return GetUtcOffsetHelper (utcDateTime, this, out isDST);
+			return GetUtcOffsetHelper (utcDateTime, this, out isDST, forOffset);
 		}
 
 		// This is an helper method used by the method above, do not use this on its own.
-		private static TimeSpan GetUtcOffsetHelper (DateTime dateTime, TimeZoneInfo tz, out bool isDST)
+		private static TimeSpan GetUtcOffsetHelper (DateTime dateTime, TimeZoneInfo tz, out bool isDST, bool forOffset = false)
 		{
 			if (dateTime.Kind == DateTimeKind.Local && tz != TimeZoneInfo.Local)
 				throw new Exception ();
@@ -843,7 +843,7 @@ private static TimeSpan GetUtcOffsetHelper (DateTime dateTime, TimeZoneInfo tz,
 				return TimeSpan.Zero;
 
 			TimeSpan offset;
-			if (tz.TryGetTransitionOffset(dateTime, out offset, out isDST))
+			if (tz.TryGetTransitionOffset(dateTime, out offset, out isDST, forOffset))
 				return offset;
 
 			if (dateTime.Kind == DateTimeKind.Utc) {
@@ -870,10 +870,12 @@ private static TimeSpan GetUtcOffsetHelper (DateTime dateTime, TimeZoneInfo tz,
 
 			if (tzRule != null && tz.IsInDST (tzRule, dateTime)) {
 				// Replicate what .NET does when given a time which falls into the hour which is lost when
-				// DST starts. isDST should always be true but the offset should be BaseUtcOffset without the
+				// DST starts. isDST should be false and the offset should be BaseUtcOffset without the
 				// DST delta while in that hour.
-				isDST = true;
+				if (forOffset)
+					isDST = true;
 				if (tz.IsInDST (tzRule, dstUtcDateTime)) {
+					isDST = true;
 					return tz.BaseUtcOffset + tzRule.DaylightDelta;
 				} else {
 					return tz.BaseUtcOffset;
@@ -982,7 +984,21 @@ internal bool IsDaylightSavingTime (DateTime dateTime, TimeZoneInfoOptions flags
 
 		public bool IsDaylightSavingTime (DateTimeOffset dateTimeOffset)
 		{
-			return IsDaylightSavingTime (dateTimeOffset.DateTime);
+			var dateTime = dateTimeOffset.DateTime;
+			
+			if (dateTime.Kind == DateTimeKind.Local && IsInvalidTime (dateTime))
+				throw new ArgumentException ("dateTime is invalid and Kind is Local");
+
+			if (this == TimeZoneInfo.Utc)
+				return false;
+			
+			if (!SupportsDaylightSavingTime)
+				return false;
+
+			bool isDst;
+			GetUtcOffset (dateTime, out isDst, true);
+
+			return isDst;
 		}
 
 		internal DaylightTime GetDaylightChanges (int year)
@@ -1219,7 +1235,7 @@ private AdjustmentRule GetApplicableRule (DateTime dateTime)
 			return null;
 		}
 
-		private bool TryGetTransitionOffset (DateTime dateTime, out TimeSpan offset,out bool isDst)
+		private bool TryGetTransitionOffset (DateTime dateTime, out TimeSpan offset, out bool isDst, bool forOffset = false)
 		{
 			offset = BaseUtcOffset;
 			isDst = false;
@@ -1240,13 +1256,22 @@ private bool TryGetTransitionOffset (DateTime dateTime, out TimeSpan offset,out
 					return false;
 			}
 
-			AdjustmentRule current = GetApplicableRule(date);
+			AdjustmentRule current = GetApplicableRule (date);
 			if (current != null) {
-				DateTime tStart = TransitionPoint(current.DaylightTransitionStart, date.Year);
-				DateTime tEnd = TransitionPoint(current.DaylightTransitionEnd, date.Year);
+				DateTime tStart = TransitionPoint (current.DaylightTransitionStart, date.Year);
+				DateTime tEnd = TransitionPoint (current.DaylightTransitionEnd, date.Year);
+				TryAddTicks (tStart, -BaseUtcOffset.Ticks, out tStart, DateTimeKind.Utc);
+				TryAddTicks (tEnd, -BaseUtcOffset.Ticks, out tEnd, DateTimeKind.Utc);
 				if ((date >= tStart) && (date <= tEnd)) {
-					offset = baseUtcOffset + current.DaylightDelta; 
-					isDst = true;
+					if (forOffset)
+						isDst = true;
+					offset = baseUtcOffset; 
+					if (date >= new DateTime (tStart.Ticks + current.DaylightDelta.Ticks, DateTimeKind.Utc))
+					{
+						offset += current.DaylightDelta;
+						isDst = true;
+					}
+
 					return true;
 				}
 			}

mcs/class/corlib/Test/System/TimeZoneInfoTest.cs

@@ -55,6 +55,8 @@ public static string MapTimeZoneId (string id)
 					return "GTB Standard Time";
 				case "US/Eastern":
 					return "Eastern Standard Time";
+				case "US/Central":
+					return "Central Standard Time";
 				case "US/Pacific":
 					return "Pacific Standard Time";
 				case "Australia/Sydney":
@@ -760,13 +762,18 @@ public void TestAthensDST ()
 			[Test]
 			public void TestAthensDST_InDSTDelta ()
 			{
-				// In .NET GetUtcOffset() returns the BaseUtcOffset for times within the hour
-				// lost when DST starts but IsDaylightSavingTime() returns true.
+				// In .NET/.Net Core GetUtcOffset() returns the BaseUtcOffset for times within the hour
+				// lost when DST starts and IsDaylightSavingTime() returns false for datetime and true for datetimeoffset
 
 				TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById (MapTimeZoneId ("Europe/Athens"));
 
-				var date = new DateTime (2014, 3, 30 , 3, 0, 0);
-				Assert.IsTrue (tzi.IsDaylightSavingTime (date));
+				var date = new DateTime (2014, 3, 30 , 2, 0, 0);
+				Assert.IsFalse (tzi.IsDaylightSavingTime (date));
+				Assert.AreEqual (new TimeSpan (2, 0, 0), tzi.GetUtcOffset (date));
+				Assert.IsFalse (tzi.IsDaylightSavingTime (new DateTimeOffset (date, tzi.GetUtcOffset (date))));
+
+				date = new DateTime (2014, 3, 30 , 3, 0, 0);
+				Assert.IsFalse (tzi.IsDaylightSavingTime (date));
 				Assert.AreEqual (new TimeSpan (2, 0, 0), tzi.GetUtcOffset (date));
 				Assert.IsTrue (tzi.IsDaylightSavingTime (new DateTimeOffset (date, tzi.GetUtcOffset (date))));
 
@@ -842,6 +849,31 @@ public void TestIsDST_DateTimeOffset ()
 				dateOffset = new DateTimeOffset (date, offset);
 				Assert.IsTrue (tzi.IsDaylightSavingTime (dateOffset));
 			}
+
+			// https://github.com/mono/mono/issues/9664
+			[Test]
+			public void Bug_9664 ()
+			{
+				TimeZoneInfo tzi = TimeZoneInfo.FindSystemTimeZoneById (MapTimeZoneId ("US/Central"));
+				var date = new DateTime (2019, 3, 9, 21, 0, 0);
+				Assert.IsFalse (tzi.IsDaylightSavingTime (date));
+				Assert.AreEqual (new TimeSpan (-6, 0, 0), tzi.GetUtcOffset (date));
+
+				tzi = TimeZoneInfo.FindSystemTimeZoneById (MapTimeZoneId ("US/Central"));
+				date = new DateTime (2019, 3, 10, 2, 0, 0);
+				Assert.IsFalse (tzi.IsDaylightSavingTime (date));
+				Assert.AreEqual (new TimeSpan (-6, 0, 0), tzi.GetUtcOffset (date));
+
+				tzi = TimeZoneInfo.FindSystemTimeZoneById (MapTimeZoneId ("US/Central"));
+				date = new DateTime (2019, 3, 10, 2, 30, 0);
+				Assert.IsFalse (tzi.IsDaylightSavingTime (date));
+				Assert.AreEqual (new TimeSpan (-6, 0, 0), tzi.GetUtcOffset (date));
+
+				tzi = TimeZoneInfo.FindSystemTimeZoneById (MapTimeZoneId ("US/Central"));
+				date = new DateTime (2019, 3, 10, 3, 0, 0);
+				Assert.IsTrue (tzi.IsDaylightSavingTime (date));
+				Assert.AreEqual (new TimeSpan (-5, 0, 0), tzi.GetUtcOffset (date));
+			}
 		}
 
 		[TestFixture]