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

[vitek-karas]

If this is for Xamarin only, then we should run the test in what will be a Xamarin-like environment. So most notably, Xamarin only trims framework assemblies (just like Blazor) and not the app. I'm guessing, but the types the tests are failing on are probably from "the app".

Otherwise if the goal is to make XmlSerializer work for any trimmed app - or for Xamarin when trimming is enabled on the app itself, then we need either a source generator (or fix sgen and use that instead, which is basically a source generator as well) or new linker functionality.

[eerhardt]

My current work here is to make XmlSerializer work by default when TrimMode=link is used in any app. (This is analogous to the Xamarin-like environment referenced above). It is currently broken whenever System.Private.Xml.dll is being link trimmed.

As for my previous comment and the blocked label - these only apply when the whole app is trimmed (or more correctly - XmlSerialize fails when the Type you are serializing is in an assembly that is being link trimmed). I think we should move that to a separate issue, and leave this issue for the scenarios logged above.

[eerhardt]

@rolfbjarne -

I just tried your repro in #41389 (comment). That test fails even if the app isn't trimmed.

System.InvalidOperationException: You need to add XmlChoiceIdentifierAttribute to the 'Result' member.

This same exception which you mention above occurs for a regular (untrimmed) net5.0 app.

[rolfbjarne]

@rolfbjarne -

I just tried your repro in #41389 (comment). That test fails even if the app isn't trimmed.

System.InvalidOperationException: You need to add XmlChoiceIdentifierAttribute to the 'Result' member.

This same exception which you mention above occurs for a regular (untrimmed) net5.0 app.

Looks like I diagnosed that test case wrong, it seems to be different than the original issue reported here, so I'll have another look at it.