From b429e70c935a6cc919e3bdcaa3375d8ace514ea1 Mon Sep 17 00:00:00 2001
From: Sergio Pedri <sergio0694@live.com>
Date: Tue, 7 May 2024 11:13:37 -0700
Subject: [PATCH] Add 'CsWinRTUseUtcDateTimeOffsetMarshalling' switch

---
 nuget/Microsoft.Windows.CsWinRT.targets       |  6 +++++
 .../Configuration/FeatureSwitches.cs          | 25 ++++++++++++++++---
 .../Configuration/ILLink.Substitutions.xml    |  4 +++
 src/WinRT.Runtime/Projections/SystemTypes.cs  | 10 ++++++++
 4 files changed, 42 insertions(+), 3 deletions(-)

diff --git a/nuget/Microsoft.Windows.CsWinRT.targets b/nuget/Microsoft.Windows.CsWinRT.targets
index 4d60abd31..555dc0d00 100644
--- a/nuget/Microsoft.Windows.CsWinRT.targets
+++ b/nuget/Microsoft.Windows.CsWinRT.targets
@@ -251,6 +251,7 @@ $(CsWinRTInternalProjection)
   <PropertyGroup>
     <CsWinRTEnableDynamicObjectsSupport Condition="'$(CsWinRTEnableDynamicObjectsSupport)' == ''">true</CsWinRTEnableDynamicObjectsSupport>
     <CsWinRTUseExceptionResourceKeys Condition="'$(CsWinRTUseExceptionResourceKeys)' == ''">false</CsWinRTUseExceptionResourceKeys>
+    <CsWinRTUseUtcDateTimeOffsetMarshalling Condition="'$(CsWinRTUseUtcDateTimeOffsetMarshalling)' == ''">false</CsWinRTUseUtcDateTimeOffsetMarshalling>
     <CsWinRTEnableDefaultCustomTypeMappings Condition="'$(CsWinRTEnableDefaultCustomTypeMappings)' == ''">true</CsWinRTEnableDefaultCustomTypeMappings>
     <CsWinRTEnableICustomPropertyProviderSupport Condition="'$(CsWinRTEnableICustomPropertyProviderSupport)' == ''">true</CsWinRTEnableICustomPropertyProviderSupport>
     <CsWinRTEnableIReferenceSupport Condition="'$(CsWinRTEnableIReferenceSupport)' == ''">true</CsWinRTEnableIReferenceSupport>
@@ -272,6 +273,11 @@ $(CsWinRTInternalProjection)
     <RuntimeHostConfigurationOption Include="CSWINRT_USE_EXCEPTION_RESOURCE_KEYS"
                                     Value="$(CsWinRTUseExceptionResourceKeys)"
                                     Trim="true" />
+
+    <!-- CSWINRT_USE_UTC_DATETIMEOFFSET_MARSHALLING switch -->
+    <RuntimeHostConfigurationOption Include="CSWINRT_USE_UTC_DATETIMEOFFSET_MARSHALLING"
+                                    Value="$(CsWinRTUseUtcDateTimeOffsetMarshalling)"
+                                    Trim="true" />
                                   
     <!-- CSWINRT_ENABLE_DEFAULT_CUSTOM_TYPE_MAPPINGS switch -->
     <RuntimeHostConfigurationOption Include="CSWINRT_ENABLE_DEFAULT_CUSTOM_TYPE_MAPPINGS"
diff --git a/src/WinRT.Runtime/Configuration/FeatureSwitches.cs b/src/WinRT.Runtime/Configuration/FeatureSwitches.cs
index be6850505..a17eb0953 100644
--- a/src/WinRT.Runtime/Configuration/FeatureSwitches.cs
+++ b/src/WinRT.Runtime/Configuration/FeatureSwitches.cs
@@ -24,13 +24,18 @@ internal static class FeatureSwitches
     /// <summary>
     /// The configuration property name for <see cref="EnableDynamicObjectsSupport"/>.
     /// </summary>
-    private const string EnablesDynamicObjectsSupportPropertyName = "CSWINRT_ENABLE_DYNAMIC_OBJECTS_SUPPORT";
+    private const string EnableDynamicObjectsSupportPropertyName = "CSWINRT_ENABLE_DYNAMIC_OBJECTS_SUPPORT";
 
     /// <summary>
-    /// The configuration property name for <see cref="UseExceptionResourceKeys"/>.
+    /// The configuration property name for <see cref="UseUtcDateTimeOffsetMarshalling"/>.
     /// </summary>
     private const string UseExceptionResourceKeysPropertyName = "CSWINRT_USE_EXCEPTION_RESOURCE_KEYS";
 
+    /// <summary>
+    /// The configuration property name for <see cref="UseExceptionResourceKeys"/>.
+    /// </summary>
+    private const string UseUtcDateTimeOffsetMarshallingPropertyName = "CSWINRT_USE_UTC_DATETIMEOFFSET_MARSHALLING";
+
     /// <summary>
     /// The configuration property name for <see cref="EnableDefaultCustomTypeMappings"/>.
     /// </summary>
@@ -61,6 +66,11 @@ internal static class FeatureSwitches
     /// </summary>
     private static int _useExceptionResourceKeys;
 
+    /// <summary>
+    /// The backing field for <see cref="UseUtcDateTimeOffsetMarshalling"/>.
+    /// </summary>
+    private static int _useUtcDateTimeOffsetMarshalling;
+
     /// <summary>
     /// The backing field for <see cref="EnableDefaultCustomTypeMappings"/>.
     /// </summary>
@@ -87,7 +97,7 @@ internal static class FeatureSwitches
     public static bool EnableDynamicObjectsSupport
     {
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        get => GetConfigurationValue(EnablesDynamicObjectsSupportPropertyName, ref _enableDynamicObjectsSupportEnabled, true);
+        get => GetConfigurationValue(EnableDynamicObjectsSupportPropertyName, ref _enableDynamicObjectsSupportEnabled, true);
     }
 
     /// <summary>
@@ -99,6 +109,15 @@ public static bool UseExceptionResourceKeys
         get => GetConfigurationValue(UseExceptionResourceKeysPropertyName, ref _useExceptionResourceKeys, false);
     }
 
+    /// <summary>
+    /// Gets a value indicating whether or not <see cref="DateTimeOffset"/> values should be marshalled as UTC (defaults to <see langword="false"/>).
+    /// </summary>
+    public static bool UseUtcDateTimeOffsetMarshalling
+    {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
+        get => GetConfigurationValue(UseUtcDateTimeOffsetMarshallingPropertyName, ref _useUtcDateTimeOffsetMarshalling, false);
+    }
+
     /// <summary>
     /// Gets a value indicating whether or not <see cref="Projections"/> should initialize all default type mappings automatically (defaults to <see langword="true"/>).
     /// </summary>
diff --git a/src/WinRT.Runtime/Configuration/ILLink.Substitutions.xml b/src/WinRT.Runtime/Configuration/ILLink.Substitutions.xml
index 8a04a92b3..cfaaf5110 100644
--- a/src/WinRT.Runtime/Configuration/ILLink.Substitutions.xml
+++ b/src/WinRT.Runtime/Configuration/ILLink.Substitutions.xml
@@ -10,6 +10,10 @@
       <method signature="System.Boolean get_UseExceptionResourceKeys()" body="stub" value="false" feature="CSWINRT_USE_EXCEPTION_RESOURCE_KEYS" featurevalue="false"/>
       <method signature="System.Boolean get_UseExceptionResourceKeys()" body="stub" value="true" feature="CSWINRT_USE_EXCEPTION_RESOURCE_KEYS" featurevalue="true"/>
         
+      <!-- CSWINRT_USE_UTC_DATETIMEOFFSET_MARSHALLING switch -->
+      <method signature="System.Boolean get_UseUtcDateTimeOffsetMarshalling()" body="stub" value="false" feature="CSWINRT_USE_UTC_DATETIMEOFFSET_MARSHALLING" featurevalue="false"/>
+      <method signature="System.Boolean get_UseUtcDateTimeOffsetMarshalling()" body="stub" value="true" feature="CSWINRT_USE_UTC_DATETIMEOFFSET_MARSHALLING" featurevalue="true"/>
+        
       <!-- CSWINRT_ENABLE_DEFAULT_CUSTOM_TYPE_MAPPINGS switch -->
       <method signature="System.Boolean get_EnableDefaultCustomTypeMappings()" body="stub" value="false" feature="CSWINRT_ENABLE_DEFAULT_CUSTOM_TYPE_MAPPINGS" featurevalue="false"/>
       <method signature="System.Boolean get_EnableDefaultCustomTypeMappings()" body="stub" value="true" feature="CSWINRT_ENABLE_DEFAULT_CUSTOM_TYPE_MAPPINGS" featurevalue="true"/>
diff --git a/src/WinRT.Runtime/Projections/SystemTypes.cs b/src/WinRT.Runtime/Projections/SystemTypes.cs
index aebcdf4b8..2b2bc9d64 100644
--- a/src/WinRT.Runtime/Projections/SystemTypes.cs
+++ b/src/WinRT.Runtime/Projections/SystemTypes.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Runtime.InteropServices;
+using WinRT;
 
 namespace ABI.System
 {
@@ -86,6 +87,15 @@ public static Marshaler CreateMarshaler(global::System.DateTimeOffset value)
         public static global::System.DateTimeOffset FromAbi(DateTimeOffset value)
         {
             var utcTime = new global::System.DateTimeOffset(value.UniversalTime + ManagedUtcTicksAtNativeZero, global::System.TimeSpan.Zero);
+
+            if (FeatureSwitches.UseUtcDateTimeOffsetMarshalling)
+            {
+                return utcTime;
+            }
+            
+            // Backwards-compat: validate the local time and return that instead of the UTC one.
+            // We can't make this the default behavior, as people might have taken a dependency
+            // on this, since it's been here for quite a while. So, we have a feature switch instead.
             var offset = TimeZoneInfo.Local.GetUtcOffset(utcTime);
             long localTicks = utcTime.Ticks + offset.Ticks;
             if (localTicks < DateTime.MinValue.Ticks || localTicks > DateTime.MaxValue.Ticks)