Imported Upstream version 4.8.0.309

Former-commit-id: 5f9c6ae75f295e057a7d2971f3a6df4656fa8850

mcs/class/referencesource/System.Xml/InternalApis/Clr/inc/AppContextDefaultValues.cs

@@ -3,6 +3,15 @@
 //   Copyright (c) Microsoft Corporation.  All rights reserved.
 // 
 // ==--==
+
+// There are cases where we have multiple assemblies that are going to import this file and 
+// if they are going to also have InternalsVisibleTo between them, there will be a compiler warning
+// that the type is found both in the source and in a referenced assembly. The compiler will prefer 
+// the version of the type defined in the source
+//
+// In order to disable the warning for this type we are disabling this warning for this entire file.
+#pragma warning disable 436
+
 using System;
 using System.Collections.Generic;
 
@@ -167,3 +176,5 @@ namespace System
         static partial void PopulateDefaultValuesPartial(string platformIdentifier, string profile, int version);
     }
 }
+
+#pragma warning restore 436

mcs/class/referencesource/System.Xml/InternalApis/Clr/inc/LocalAppContext.cs

@@ -4,6 +4,14 @@
 // 
 // ==--==
 
+// There are cases where we have multiple assemblies that are going to import this file and 
+// if they are going to also have InternalsVisibleTo between them, there will be a compiler warning
+// that the type is found both in the source and in a referenced assembly. The compiler will prefer 
+// the version of the type defined in the source
+//
+// In order to disable the warning for this type we are disabling this warning for this entire file.
+#pragma warning disable 436
+
 // NOTE: This file should not be included in mscorlib. This should only be included in FX libraries that need to provide switches
 using System;
 using System.Collections.Generic;
@@ -126,3 +134,5 @@ namespace System
         }
     }
 }
+
+#pragma warning restore 436

mcs/class/referencesource/System.Xml/System/Xml/Core/AppContextDefaultValues.Defaults.cs

@@ -28,6 +28,10 @@ namespace System
                             LocalAppContext.DefineSwitchDefault("Switch.System.Xml.DontThrowOnInvalidSurrogatePairs", true);
                             LocalAppContext.DefineSwitchDefault("Switch.System.Xml.IgnoreEmptyKeySequences", true);
                         }
+                        if (version <= 40601)
+                        {
+                            LocalAppContext.DefineSwitchDefault("Switch.System.Xml.IgnoreKindInUtcTimeSerialization", true);
+                        }
                         break;
                     }
                 case "WindowsPhone":
@@ -37,6 +41,7 @@ namespace System
                         {
                             LocalAppContext.DefineSwitchDefault("Switch.System.Xml.DontThrowOnInvalidSurrogatePairs", true);
                             LocalAppContext.DefineSwitchDefault("Switch.System.Xml.IgnoreEmptyKeySequences", true);
+                            LocalAppContext.DefineSwitchDefault("Switch.System.Xml.IgnoreKindInUtcTimeSerialization", true);
                         }
                         break;
                     }

mcs/class/referencesource/System.Xml/System/Xml/Core/LocalAppContextSwitches.cs

@@ -29,5 +29,15 @@ namespace System
                 return LocalAppContext.GetCachedSwitchValue(@"Switch.System.Xml.IgnoreEmptyKeySequences", ref _ignoreEmptyKeySequences);
             }
         }
+
+        private static int _ignoreKindInUtcTimeSerialization;
+        public static bool IgnoreKindInUtcTimeSerialization
+        {
+            [MethodImpl(MethodImplOptions.AggressiveInlining)]
+            get
+            {
+                return LocalAppContext.GetCachedSwitchValue(@"Switch.System.Xml.IgnoreKindInUtcTimeSerialization", ref _ignoreKindInUtcTimeSerialization);
+            }
+        }
     }
 }

mcs/class/referencesource/System.Xml/System/Xml/Serialization/Xmlcustomformatter.cs

@@ -77,7 +77,14 @@ namespace System.Xml.Serialization {
         }
 
         internal static string FromTime(DateTime value) {
-            return XmlConvert.ToString(DateTime.MinValue + value.TimeOfDay, "HH:mm:ss.fffffffzzzzzz");
+            if (!LocalAppContextSwitches.IgnoreKindInUtcTimeSerialization && value.Kind == DateTimeKind.Utc)
+            {
+                return XmlConvert.ToString(DateTime.MinValue + value.TimeOfDay, "HH:mm:ss.fffffffZ");
+            }
+            else
+            {
+                return XmlConvert.ToString(DateTime.MinValue + value.TimeOfDay, "HH:mm:ss.fffffffzzzzzz");
+            }
         }
 
         internal static string FromDateTime(DateTime value) {
@@ -337,7 +344,14 @@ namespace System.Xml.Serialization {
         }
 
         internal static DateTime ToTime(string value) {
-            return DateTime.ParseExact(value, allTimeFormats, DateTimeFormatInfo.InvariantInfo, DateTimeStyles.AllowLeadingWhite|DateTimeStyles.AllowTrailingWhite|DateTimeStyles.NoCurrentDateDefault);
+            if (!LocalAppContextSwitches.IgnoreKindInUtcTimeSerialization)
+            {
+                return DateTime.ParseExact(value, allTimeFormats, DateTimeFormatInfo.InvariantInfo, DateTimeStyles.AllowLeadingWhite | DateTimeStyles.AllowTrailingWhite | DateTimeStyles.NoCurrentDateDefault | DateTimeStyles.RoundtripKind);
+            }
+            else
+            {
+                return DateTime.ParseExact(value, allTimeFormats, DateTimeFormatInfo.InvariantInfo, DateTimeStyles.AllowLeadingWhite | DateTimeStyles.AllowTrailingWhite | DateTimeStyles.NoCurrentDateDefault);
+            }
         }
 
         internal static char ToChar(string value) {