Fix time zone issue when jumping into DST (#16430)

Addresses an issue with jumping into DST for some time zones when the incorrect date-time offset is returned for date-time in UTC (which comes from DateTime.Now). The fix is to just check if the incoming date-time is in UTC.

Also added a set of tests for some time zones to verify jumping into DST in general.

Fixes https://github.com/mono/mono/issues/16395

mcs/class/corlib/System/TimeZoneInfo.cs

@@ -1252,10 +1252,13 @@ namespace System
 					return false;
 			}
 
+			var isUtc = false;
 			if (dateTime.Kind != DateTimeKind.Utc) {
 				if (!TryAddTicks (date, -BaseUtcOffset.Ticks, out date, DateTimeKind.Utc))
 					return false;
-			}
+			} else
+				isUtc = true;
+
 
 			AdjustmentRule current = GetApplicableRule (date);
 			if (current != null) {
@@ -1267,7 +1270,7 @@ namespace System
 					if (forOffset)
 						isDst = true;
 					offset = baseUtcOffset; 
-					if (date >= new DateTime (tStart.Ticks + current.DaylightDelta.Ticks, DateTimeKind.Utc))
+					if (isUtc || (date >= new DateTime (tStart.Ticks + current.DaylightDelta.Ticks, DateTimeKind.Utc)))
 					{
 						offset += current.DaylightDelta;
 						isDst = true;

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

@@ -53,6 +53,11 @@ namespace MonoTests.System
 					return "New Zealand Standard Time";
 				case "Europe/Athens":
 					return "GTB Standard Time";
+				case "Europe/Chisinau":
+					return "E. Europe Standard Time";
+				case "America/New_York":
+					return "Eastern Standard Time";
+				case "America/Chicago":
 				case "US/Eastern":
 					return "Eastern Standard Time";
 				case "US/Central":
@@ -63,18 +68,57 @@ namespace MonoTests.System
 				case "Australia/Melbourne":
 					return "AUS Eastern Standard Time";
 				case "Europe/Brussels":
+				case "Europe/Copenhagen":
+				case "Europe/Paris":
+				case "Europe/Madrid":
 					return "Romance Standard Time";
 				case "Africa/Kinshasa":
 					return "W. Central Africa Standard Time";
 				case "Europe/Rome":
 				case "Europe/Vatican":
+				case "Europe/Vienna":
+				case "Europe/Berlin":
+				case "Europe/Luxembourg":
+				case "Europe/Malta":
+				case "Europe/Monaco":
+				case "Europe/Amsterdam":
+				case "Europe/Oslo":
+				case "Europe/San_Marino":
 					return "W. Europe Standard Time";
 				case "Canada/Eastern":
 					return "Eastern Standard Time";
 				case "Asia/Tehran":
 					return "Iran Standard Time";
 				case "Europe/Guernsey":
+				case "Europe/Dublin":
+				case "Europe/Isle_of_Man":
+				case "Europe/Jersey":
+				case "Europe/Lisbon":
+				case "Europe/London":
 					return "GMT Standard Time";
+				case "America/Havana":
+					return "Cuba Standard Time";
+				case "America/Anchorage":
+					return "Alaskan Standard Time";
+				case "Atlantic/Azores":
+					return "Azores Standard Time";
+				case "Asia/Jerusalem":
+					return "Israel Standard Time";
+				case "Asia/Amman":
+					return "Jordan Standard Time";
+				case "Europe/Tirane":
+				case "Europe/Warsaw":
+					return "Central European Standard Time";
+				case "Europe/Sofia":
+				case "Europe/Tallinn":
+				case "Europe/Riga":
+				case "Europe/Vilnius":
+				case "Europe/Kiev":
+					return "FLE Standard Time";
+				case "Europe/Prague":
+				case "Europe/Budapest":
+				case "Europe/Bratislava":
+					return "Central Europe Standard Time";
 				default:
 					Assert.Fail ($"No mapping defined for zone id '{id}'");
 					return null;
@@ -905,6 +949,218 @@ namespace MonoTests.System
 				Assert.AreEqual (new TimeSpan (0, 0, 0), tzi.GetUtcOffset (date));
 #endif
 			}
+
+			[Test]
+			public void Bug_16395 ()
+			{
+				// Cuba, Havana (Cuba Standard Time):    Jumps ahead at 12:00 AM on 3/8/2020 to 1:00 AM
+				CheckJumpingIntoDST ("America/Havana",
+									new DateTime (2020, 3, 8, 0, 0, 0), new DateTime (2020, 3, 8, 0, 30, 0), new DateTime (2020, 3, 8, 1, 0, 0), 
+									new TimeSpan (-5, 0, 0), new TimeSpan (-4, 0, 0));
+
+				// US, Kansas City, MO (US Central Time):    Jumps ahead at 2:00 AM on 3/8/2020 to 3:00 AM
+				CheckJumpingIntoDST ("America/Chicago",
+									new DateTime (2020, 3, 8, 2, 0, 0), new DateTime (2020, 3, 8, 2, 30, 0), new DateTime (2020, 3, 8, 3, 0, 0),
+									new TimeSpan (-6, 0, 0), new TimeSpan (-5, 0, 0));
+
+				// Anchorage, AK (Alaska Time):    Jumps ahead at 2:00 AM on 3/8/2020 to 3:00 AM
+				CheckJumpingIntoDST ("America/Anchorage",
+									new DateTime (2020, 3, 8, 2, 0, 0), new DateTime (2020, 3, 8, 2, 30, 0), new DateTime (2020, 3, 8, 3, 0, 0),
+									new TimeSpan (-9, 0, 0), new TimeSpan (-8, 0, 0));
+
+				// Azores ST (Ponta Delgada, Portugal):    Jumps ahead at 12:00 AM on 3/29/2020 to 1:00 AM
+				CheckJumpingIntoDST ("Atlantic/Azores",
+									new DateTime (2020, 3, 29, 0, 0, 0), new DateTime (2020, 3, 29, 0, 30, 0), new DateTime (2020, 3, 29, 1, 0, 0),
+									new TimeSpan (-1, 0, 0), new TimeSpan (0, 0, 0));
+									
+				// Iran, Tehran (Iran ST):    Jumps ahead at 12:00 AM on 3/21/2020 to 1:00 AM
+				CheckJumpingIntoDST ("Asia/Tehran",
+									new DateTime (2020, 3, 21, 0, 0, 0), new DateTime (2020, 3, 21, 0, 30, 0), new DateTime (2020, 3, 21, 1, 0, 0),
+									new TimeSpan (3, 30, 0), new TimeSpan (4, 30, 0));
+									
+				// Israel, Jerusalem (Israel ST):    Jumps ahead at 2:00 AM on 3/27/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Asia/Jerusalem",
+									new DateTime (2020, 3, 27, 2, 0, 0), new DateTime (2020, 3, 27, 2, 30, 0), new DateTime (2020, 3, 27, 3, 0, 0),
+									new TimeSpan (2, 0, 0), new TimeSpan (3, 0, 0));
+
+				// Jordan, Amman (Eastern European ST):    Jumps ahead at 12:00 AM on 3/27/2020 to 1:00 AM
+				CheckJumpingIntoDST ("Asia/Amman",
+									new DateTime (2020, 3, 27, 0, 0, 0), new DateTime (2020, 3, 27, 0, 30, 0), new DateTime (2020, 3, 27, 1, 0, 0),
+									new TimeSpan (2, 0, 0), new TimeSpan (3, 0, 0));
+
+				// Albania, Tirana (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Tirane",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Austria, Vienna (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Vienna",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Belgium, Brussels (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Brussels",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Bulgaria, Sofia (Eastern European ST):    Jumps ahead at 3:00 AM on 3/29/2020 to 4:00 AM
+				CheckJumpingIntoDST ("Europe/Sofia",
+									new DateTime (2020, 3, 29, 3, 0, 0), new DateTime (2020, 3, 29, 3, 30, 0), new DateTime (2020, 3, 29, 4, 0, 0),
+									new TimeSpan (2, 0, 0), new TimeSpan (3, 0, 0));
+
+				// Czechia, Prague (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Prague",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Denmark, Copenhagen (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Copenhagen",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Estonia, Tallinn (Eastern European ST):    Jumps ahead at 3:00 AM on 3/29/2020 to 4:00 AM
+				CheckJumpingIntoDST ("Europe/Tallinn",
+									new DateTime (2020, 3, 29, 3, 0, 0), new DateTime (2020, 3, 29, 3, 30, 0), new DateTime (2020, 3, 29, 4, 0, 0),
+									new TimeSpan (2, 0, 0), new TimeSpan (3, 0, 0));
+
+				// France, Paris (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Paris",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Germany, Berlin (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Berlin",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Greece, Athens (Eastern European ST):    Jumps ahead at 3:00 AM on 3/29/2020 to 4:00 AM
+				CheckJumpingIntoDST ("Europe/Athens",
+									new DateTime (2020, 3, 29, 3, 0, 0), new DateTime (2020, 3, 29, 3, 30, 0), new DateTime (2020, 3, 29, 4, 0, 0),
+									new TimeSpan (2, 0, 0), new TimeSpan (3, 0, 0));
+
+				// Guernsey (UK)    Jumps ahead at 1:00 AM on 3/29/2020 to 2:00 AM
+				CheckJumpingIntoDST ("Europe/Guernsey",
+									new DateTime (2020, 3, 29, 1, 0, 0), new DateTime (2020, 3, 29, 1, 30, 0), new DateTime (2020, 3, 29, 2, 0, 0),
+									new TimeSpan (0, 0, 0), new TimeSpan (1, 0, 0));
+
+				// Holy See, Vatican City (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Vatican",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Hungary, Budapest (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Budapest",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// // Ireland, Dublin (Greenwich Mean Time -> Irish Standard Time):    Jumps ahead at 1:00 AM on 3/29/2020 to 2:00 AM
+				// CheckJumpingIntoDST ("Europe/Dublin",
+				// 					new DateTime (2020, 3, 29, 1, 0, 0), new DateTime (2020, 3, 29, 1, 30, 0), new DateTime (2020, 3, 29, 2, 0, 0),
+				// 					new TimeSpan (0, 0, 0), new TimeSpan (1, 0, 0));
+
+				// UK, Douglas, Isle of Man (GMT+1:00):    Jumps ahead at 1:00 AM on 3/29/2020 to 2:00 AM
+				CheckJumpingIntoDST ("Europe/Isle_of_Man",
+									new DateTime (2020, 3, 29, 1, 0, 0), new DateTime (2020, 3, 29, 1, 30, 0), new DateTime (2020, 3, 29, 2, 0, 0),
+									new TimeSpan (0, 0, 0), new TimeSpan (1, 0, 0));
+
+				// Italy, Rome (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Rome",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Jersey (UK):   Jumps ahead at 1:00 AM on 3/29/2020 to 2:00 AM
+				CheckJumpingIntoDST ("Europe/Jersey",
+									new DateTime (2020, 3, 29, 1, 0, 0), new DateTime (2020, 3, 29, 1, 30, 0), new DateTime (2020, 3, 29, 2, 0, 0),
+									new TimeSpan (0, 0, 0), new TimeSpan (1, 0, 0));
+
+				// Latvia, Riga (Eastern European ST):    Jumps ahead at 3:00 AM on 3/29/2020 to 4:00 AM
+				CheckJumpingIntoDST ("Europe/Riga",
+									new DateTime (2020, 3, 29, 3, 0, 0), new DateTime (2020, 3, 29, 3, 30, 0), new DateTime (2020, 3, 29, 4, 0, 0),
+									new TimeSpan (2, 0, 0), new TimeSpan (3, 0, 0));
+
+				// Lithuania, Vilnius (Eastern European ST):    Jumps ahead at 3:00 AM on 3/29/2020 to 4:00 AM
+				CheckJumpingIntoDST ("Europe/Vilnius",
+									new DateTime (2020, 3, 29, 3, 0, 0), new DateTime (2020, 3, 29, 3, 30, 0), new DateTime (2020, 3, 29, 4, 0, 0),
+									new TimeSpan (2, 0, 0), new TimeSpan (3, 0, 0));
+
+				// Luxembourg, Luxembourg (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Luxembourg",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Malta, Valletta (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Malta",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Moldova, Chişinău (Eastern European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Chisinau",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (2, 0, 0), new TimeSpan (3, 0, 0));
+
+				// Monaco, Monaco (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Monaco",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Netherlands, Amsterdam (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Amsterdam",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Norway, Oslo (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Oslo",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Poland, Warsaw (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Warsaw",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Portugal, Lisbon (Western European ST):    Jumps ahead at 1:00 AM on 3/29/2020 to 2:00 AM
+				CheckJumpingIntoDST ("Europe/Lisbon",
+									new DateTime (2020, 3, 29, 1, 0, 0), new DateTime (2020, 3, 29, 1, 30, 0), new DateTime (2020, 3, 29, 2, 0, 0),
+									new TimeSpan (0, 0, 0), new TimeSpan (1, 0, 0));
+
+				// San Marino, San Marino (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/San_Marino",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Slovakia, Bratislava (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Bratislava",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Spain, Madrid (Central European ST):    Jumps ahead at 2:00 AM on 3/29/2020 to 3:00 AM
+				CheckJumpingIntoDST ("Europe/Madrid",
+									new DateTime (2020, 3, 29, 2, 0, 0), new DateTime (2020, 3, 29, 2, 30, 0), new DateTime (2020, 3, 29, 3, 0, 0),
+									new TimeSpan (1, 0, 0), new TimeSpan (2, 0, 0));
+
+				// Ukraine, Kiev (Eastern European ST):    Jumps ahead at 3:00 AM on 3/29/2020 to 4:00 AM
+				CheckJumpingIntoDST ("Europe/Kiev",
+									new DateTime (2020, 3, 29, 3, 0, 0), new DateTime (2020, 3, 29, 3, 30, 0), new DateTime (2020, 3, 29, 4, 0, 0),
+									new TimeSpan (2, 0, 0), new TimeSpan (3, 0, 0));
+
+				// United Kingdom, London (British ST):    Jumps ahead at 1:00 AM on 3/29/2020 to 2:00 AM
+				CheckJumpingIntoDST ("Europe/London",
+									new DateTime (2020, 3, 29, 1, 0, 0), new DateTime (2020, 3, 29, 1, 30, 0), new DateTime (2020, 3, 29, 2, 0, 0),
+									new TimeSpan (0, 0, 0), new TimeSpan (1, 0, 0));
+			}
+
+			void CheckJumpingIntoDST (string tzId, DateTime dstDeltaStart, DateTime inDstDelta, DateTime dstDeltaEnd, TimeSpan baseOffset, TimeSpan dstOffset)
+			{
+				var tzi = TimeZoneInfo.FindSystemTimeZoneById (MapTimeZoneId (tzId));
+				Assert.IsFalse (tzi.IsDaylightSavingTime (dstDeltaStart), $"{tzId}: #1");
+				Assert.AreEqual (baseOffset, tzi.GetUtcOffset (dstDeltaStart), $"{tzId}: #2");
+
+				Assert.IsFalse (tzi.IsDaylightSavingTime (inDstDelta), $"{tzId}: #3");
+				Assert.AreEqual (baseOffset, tzi.GetUtcOffset (inDstDelta), $"{tzId}: #4");
+
+				Assert.IsTrue (tzi.IsDaylightSavingTime (dstDeltaEnd), $"{tzId}: #5");
+				Assert.AreEqual (dstOffset, tzi.GetUtcOffset (dstDeltaEnd), $"{tzId}: #6");
+			}
 		}
 		
 		[TestFixture]