XmlSerializer.Serialize doesn't work when using TrimMode=link

[marek-safar]

Repro: consoleapp-bfe9f43.zip

Run make linked to run with TrimMode=link, and make notlinked to run the same command, except without setting TrimMode.

$ make linked
** Executing linked app
bin/Debug/netcoreapp5.0/osx-x64/publish/myproject
❌ failed: System.InvalidOperationException: There was an error reflecting type 'LinkSdk.Serialization.XmlSerializationTest.Response'.
 ---> System.InvalidOperationException: There was an error reflecting property 'DataUpdates'.
 ---> System.InvalidOperationException: There was an error reflecting type 'LinkSdk.Serialization.XmlSerializationTest.DataUpdates'.
 ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at System.RuntimeType.RuntimeTypeCache.GetDefaultMemberName()
   at System.RuntimeType.GetDefaultMemberName()
   at System.RuntimeType.GetDefaultMembers()
   at System.Xml.Serialization.TypeScope.GetDefaultIndexer(Type type, String memberInfo)
   at System.Xml.Serialization.TypeScope.ImportTypeDesc(Type type, MemberInfo memberInfo, Boolean directReference)
   at System.Xml.Serialization.TypeScope.GetTypeDesc(Type type, MemberInfo source, Boolean directReference, Boolean throwOnError)
   at System.Xml.Serialization.StructModel.GetPropertyModel(PropertyInfo propertyInfo)
   at System.Xml.Serialization.StructModel.GetFieldModel(MemberInfo memberInfo)
   at System.Xml.Serialization.XmlReflectionImporter.InitializeStructMembers(StructMapping mapping, StructModel model, Boolean openModel, String typeName, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportStructLikeMapping(StructModel model, String ns, Boolean openModel, XmlAttributes a, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(TypeModel model, String ns, ImportContext context, String dataType, XmlAttributes a, Boolean repeats, Boolean openModel, RecursionLimiter limiter)
   --- End of inner exception stack trace ---
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(TypeModel model, String ns, ImportContext context, String dataType, XmlAttributes a, Boolean repeats, Boolean openModel, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportAccessorMapping(MemberMapping accessor, FieldModel model, XmlAttributes a, String ns, Type choiceIdentifierType, Boolean rpc, Boolean openModel, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportFieldMapping(StructModel parent, FieldModel model, XmlAttributes a, String ns, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.InitializeStructMembers(StructMapping mapping, StructModel model, Boolean openModel, String typeName, RecursionLimiter limiter)
   --- End of inner exception stack trace ---
   at System.Xml.Serialization.XmlReflectionImporter.InitializeStructMembers(StructMapping mapping, StructModel model, Boolean openModel, String typeName, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportStructLikeMapping(StructModel model, String ns, Boolean openModel, XmlAttributes a, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(TypeModel model, String ns, ImportContext context, String dataType, XmlAttributes a, Boolean repeats, Boolean openModel, RecursionLimiter limiter)
   --- End of inner exception stack trace ---
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(TypeModel model, String ns, ImportContext context, String dataType, XmlAttributes a, Boolean repeats, Boolean openModel, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(TypeModel model, String ns, ImportContext context, String dataType, XmlAttributes a, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportElement(TypeModel model, XmlRootAttribute root, String defaultNamespace, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(Type type, XmlRootAttribute root, String defaultNamespace)
   at System.Xml.Serialization.XmlSerializer..ctor(Type type, String defaultNamespace)
   at System.Xml.Serialization.XmlSerializer..ctor(Type type)
   at LinkSdk.Serialization.XmlSerializationTest.Response.get_Serializer() in /Users/rolf/test/dotnet/consoleapp/Program.cs:line 63
   at LinkSdk.Serialization.XmlSerializationTest.Response.Deserialize(String xml) in /Users/rolf/test/dotnet/consoleapp/Program.cs:line 73
   at LinkSdk.Serialization.XmlSerializationTest.Bug1820_GenericList() in /Users/rolf/test/dotnet/consoleapp/Program.cs:line 188
   at App.Main() in /Users/rolf/test/dotnet/consoleapp/Program.cs:line 27

$ make notlinked
** Executing notlinked app
bin/Debug/netcoreapp5.0/osx-x64/publish/myproject
✅ succeeded: LinkSdk.Serialization.XmlSerializationTest+Response

$ dotnet --version
5.0.100-rc.1.20414.5

*** Moved from dotnet/linker#1454 ***

[marek-safar]

/cc @eerhardt @rolfbjarne

[eerhardt]

In order to make XmlSerializer serialization work with the ILLinker, we will probably need to address dotnet/linker#1087.

[rolfbjarne]

Here is another test case: linkertestcase-d179b60.zip

$ ./test.sh 
+ dotnet --version
5.0.100-rc.1.20426.3
+ dotnet publish -r osx-x64 --self-contained true -p:MonoAOT=true -p:VM=mono -p:PublishTrimmed=true Executable/Executable.csproj /bl:x.binlog
Microsoft (R) Build Engine version 16.8.0-preview-20425-03+384d02a5f for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

/usr/local/share/dotnet/sdk/5.0.100-rc.1.20426.3/MSBuild.dll -distributedlogger:Microsoft.DotNet.Tools.MSBuild.MSBuildLogger,/usr/local/share/dotnet/sdk/5.0.100-rc.1.20426.3/dotnet.dll*Microsoft.DotNet.Tools.MSBuild.MSBuildForwardingLogger,/usr/local/share/dotnet/sdk/5.0.100-rc.1.20426.3/dotnet.dll -maxcpucount -property:RuntimeIdentifier=osx-x64 -property:SelfContained=true -p:MonoAOT=true -p:VM=mono -p:PublishTrimmed=true -restore -target:Publish -verbosity:m /bl:x.binlog Executable/Executable.csproj
  Determining projects to restore...
  Restored /Users/rolf/test/linkertestcase/Executable/Executable.csproj (in 159 ms).
  You are using a preview version of .NET. See: https://aka.ms/dotnet-core-preview
  Executable -> /Users/rolf/test/linkertestcase/Executable/bin/Debug/net5.0/osx-x64/Executable.dll
  Optimizing assemblies for size, which may change the behavior of the app. Be sure to test after publishing. See: https://aka.ms/dotnet-illink
  Executable -> /Users/rolf/test/linkertestcase/Executable/bin/Debug/net5.0/osx-x64/publish/
+ ./Executable/bin/Debug/net5.0/osx-x64/publish/Executable
Unhandled exception. System.InvalidOperationException: There was an error reflecting type 'XmlResult`1[System.String]'.
 ---> System.InvalidOperationException: There was an error reflecting property 'Result'.
 ---> System.InvalidOperationException: You need to add XmlChoiceIdentifierAttribute to the 'Result' member.
   at System.Xml.Serialization.XmlReflectionImporter.CheckAmbiguousChoice(XmlAttributes a, Type accessorType, String accessorName)
   at System.Xml.Serialization.XmlReflectionImporter.ImportAccessorMapping(MemberMapping accessor, FieldModel model, XmlAttributes a, String ns, Type choiceIdentifierType, Boolean rpc, Boolean openModel, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportFieldMapping(StructModel parent, FieldModel model, XmlAttributes a, String ns, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.InitializeStructMembers(StructMapping mapping, StructModel model, Boolean openModel, String typeName, RecursionLimiter limiter)
   --- End of inner exception stack trace ---
   at System.Xml.Serialization.XmlReflectionImporter.InitializeStructMembers(StructMapping mapping, StructModel model, Boolean openModel, String typeName, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportStructLikeMapping(StructModel model, String ns, Boolean openModel, XmlAttributes a, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(TypeModel model, String ns, ImportContext context, String dataType, XmlAttributes a, Boolean repeats, Boolean openModel, RecursionLimiter limiter)
   --- End of inner exception stack trace ---
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(TypeModel model, String ns, ImportContext context, String dataType, XmlAttributes a, Boolean repeats, Boolean openModel, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(TypeModel model, String ns, ImportContext context, String dataType, XmlAttributes a, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportElement(TypeModel model, XmlRootAttribute root, String defaultNamespace, RecursionLimiter limiter)
   at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping(Type type, XmlRootAttribute root, String defaultNamespace)
   at System.Xml.Serialization.XmlSerializer..ctor(Type type, String defaultNamespace)
   at System.Xml.Serialization.XmlSerializer..ctor(Type type)
   at XmlSerializationTest.GenericProperty_Bug5543() in /Users/rolf/test/linkertestcase/Executable/Program.cs:line 41
   at C.Main() in /Users/rolf/test/linkertestcase/Executable/Program.cs:line 59
./test.sh: line 6: 97907 Abort trap: 6           ./Executable/bin/Debug/net5.0/osx-x64/publish/Executable