Use ReflectionOnly as data contract serializer option for iOS/tvOS/MacCatalyst

src/libraries/System.Private.DataContractSerialization/src/System/Runtime/Serialization/DataContractSerializer.cs

@@ -34,7 +34,16 @@ public sealed class DataContractSerializer : XmlObjectSerializer
         private ISerializationSurrogateProvider? _serializationSurrogateProvider;
         private bool _serializeReadOnlyTypes;
 
-        private static SerializationOption _option = IsReflectionBackupAllowed() ? SerializationOption.ReflectionAsBackup : SerializationOption.CodeGenOnly;
+        private static SerializationOption _option = GetDefaultSerializationOption();
+        private static SerializationOption GetDefaultSerializationOption()
+        {
+            if (OperatingSystem.IsIOS() || OperatingSystem.IsTvOS() || OperatingSystem.IsMacCatalyst())
+            {
+                return SerializationOption.ReflectionOnly;
+            }
+
+            return IsReflectionBackupAllowed() ? SerializationOption.ReflectionAsBackup : SerializationOption.CodeGenOnly;
+        }
         private static bool _optionAlreadySet;
         internal static SerializationOption Option
         {

src/tests/FunctionalTests/iOS/Simulator/XmlFormatWriterGeneratorAOT/Program.cs

@@ -0,0 +1,30 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System;
+using System.Collections.Generic;
+using System.Runtime.InteropServices;
+using System.Runtime.Serialization;
+using System.Threading;
+using System.Threading.Tasks;
+using System.Xml;
+
+public static class Program
+{
+    [DllImport("__Internal")]
+    public static extern void mono_ios_set_summary (string value);
+
+    public static async Task<int> Main(string[] args)
+    {
+        mono_ios_set_summary($"Starting functional test");
+
+        var ds = new DataContractSerializer (typeof (IEnumerable<int>));
+        using (var xw = XmlWriter.Create (System.IO.Stream.Null))
+	        ds.WriteObject (xw, new int [] { 1, 2, 3 });
+
+        Console.WriteLine("Done!");
+        await Task.Delay(5000);
+
+        return 42;
+    }
+}

src/tests/FunctionalTests/iOS/Simulator/XmlFormatWriterGeneratorAOT/iOS.Simulator.XmlFormatWriterGeneratorAot.Test.csproj

@@ -0,0 +1,19 @@
+<Project Sdk="Microsoft.NET.Sdk" TreatAsLocalProperty="MonoForceInterpreter">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <MonoForceInterpreter>false</MonoForceInterpreter>
+    <RunAOTCompilation>true</RunAOTCompilation>
+    <TestRuntime>true</TestRuntime>
+    <TargetFrameworks>$(NetCoreAppCurrent)</TargetFrameworks>
+    <TargetOS Condition="'$(TargetOS)' == ''">iOSSimulator</TargetOS>
+    <MainLibraryFileName>iOS.Simulator.XmlFormatWriterGeneratorAot.Test.dll</MainLibraryFileName>
+    <IncludesTestRunner>false</IncludesTestRunner>
+    <ExpectedExitCode>42</ExpectedExitCode>
+    <EnableAggressiveTrimming>true</EnableAggressiveTrimming>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <Compile Include="Program.cs" />
+  </ItemGroup>
+</Project>