App throws TypeLoadException when published trimmed but works fine when published native AOT (no trim warnings)

[DamianEdwards]

Description

Repo: https://github.com/DamianEdwards/RazorSlices/tree/aot/samples/RazorSlices.Samples.WebApp

I'm updating my Razor Slices library to support native AOT and am running into a scenario where the sample app produces no warnings when published as trimmed or as native AOT, and runs successfully when published native AOT, but throws a TypeLoadException when running after publishing trimmed.

The issue appears to be an interface implementation being trimmed from a type that's generated by a source generator. The method in question is a static abstract interface member. Notably, this method is not called via the interface in a generic fashion anywhere, which differs from other generated types in this app using the same pattern. I'm assuming this is the cause of the issue.

 System.TypeLoadException: Type 'RazorSlices.Samples.WebApp.Slices._Layout' from assembly 'RazorSlices.Samples.WebApp, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null' tried to override method 'Create' but does not implement or inherit that method.
         at AspNetCoreGeneratedDocument.Slices_Todos.GetLayout()
         at RazorSlices.RazorSlice.RenderToBufferWriterAsync(IBufferWriter`1 bufferWriter, Func`2 flushAsync, HtmlEncoder htmlEncoder, CancellationToken cancellationToken) in D:\src\GitHub\DamianEdwards\RazorSlices\src\RazorSlices\RazorSlice.cs:line 118
         at RazorSlices.RazorSlice.RenderAsync(IBufferWriter`1 bufferWriter, Func`2 flushAsync, HtmlEncoder htmlEncoder, CancellationToken cancellationToken) in D:\src\GitHub\DamianEdwards\RazorSlices\src\RazorSlices\RazorSlice.cs:line 87
         at RazorSlices.RazorSlicePipeWriterExtensions.RenderToPipeWriterAsync(RazorSlice, PipeWriter, HtmlEncoder , CancellationToken ) in D:\src\GitHub\DamianEdwards\RazorSlices\src\RazorSlices\RazorSlice.PipeWriterExtensions.cs:line 21
         at RazorSliceHttpResultHelpers.ExecuteAsync(RazorSlice, HttpContext, HtmlEncoder , Int32, String) in D:\src\GitHub\DamianEdwards\RazorSlices\src\RazorSlices\RazorSliceHttpResultHelpers.cs:line 22
         at Microsoft.AspNetCore.Http.HttpResults.RazorSliceHttpResult`1.Microsoft.AspNetCore.Http.IResult.ExecuteAsync(HttpContext httpContext) in D:\src\GitHub\DamianEdwards\RazorSlices\src\RazorSlices\RazorSliceHttpResultOfTModel.cs:line 34
         at Microsoft.AspNetCore.Http.Generated.<GeneratedRouteBuilderExtensions_g>F69328E0708B4B584C5AACA22FE2C51A1CF192D6622828F613FC57C583CA77B63__GeneratedRouteBuilderExtensionsCore.ExecuteAsyncExplicit(IResult, HttpContext) in D:\src\GitHub\DamianEdwards\RazorSlices\samples\RazorSlices.Samples.WebApp\Microsoft.AspNetCore.Http.RequestDelegateGenerator\Microsoft.AspNetCore.Http.RequestDelegateGenerator.RequestDelegateGenerator\GeneratedRouteBuilderExtensions.g.cs:line 1075
         at Microsoft.AspNetCore.Http.Generated.<GeneratedRouteBuilderExtensions_g>F69328E0708B4B584C5AACA22FE2C51A1CF192D6622828F613FC57C583CA77B63__GeneratedRouteBuilderExtensionsCore.<>c__DisplayClass3_0.<MapGet1>g__RequestHandler|4(HttpContext httpContext) in D:\src\GitHub\DamianEdwards\RazorSlices\samples\RazorSlices.Samples.WebApp\Microsoft.AspNetCore.Http.RequestDelegateGenerator\Microsoft.AspNetCore.Http.RequestDelegateGenerator.RequestDelegateGenerator\GeneratedRouteBuilderExtensions.g.cs:line 203
         at Microsoft.AspNetCore.Routing.EndpointMiddleware.Invoke(HttpContext httpContext)
         at Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware.Invoke(HttpContext context)
         at Microsoft.AspNetCore.Diagnostics.StatusCodePagesMiddleware.Invoke(HttpContext context)
         at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication`1)

Note that if the app is also configured to publish self-contained, the error message does not include a description which makes it much harder to diagnose the root cause:

Connection id "0HN3VJ6M4UE06", Request id "0HN3VJ6M4UE06:00000001": An unhandled exception was thrown by the application.
      System.TypeLoadException
         at AspNetCoreGeneratedDocument.Slices_Todos.GetLayout()
         at RazorSlices.RazorSlice.RenderToBufferWriterAsync(IBufferWriter`1 bufferWriter, Func`2 flushAsync, HtmlEncoder htmlEncoder, CancellationToken cancellationToken) in D:\src\GitHub\DamianEdwards\RazorSlices\src\RazorSlices\RazorSlice.cs:line 118
         at RazorSlices.RazorSlice.RenderAsync(IBufferWriter`1 bufferWriter, Func`2 flushAsync, HtmlEncoder htmlEncoder, CancellationToken cancellationToken) in D:\src\GitHub\DamianEdwards\RazorSlices\src\RazorSlices\RazorSlice.cs:line 87
         at RazorSlices.RazorSlicePipeWriterExtensions.RenderToPipeWriterAsync(RazorSlice, PipeWriter, HtmlEncoder , CancellationToken ) in D:\src\GitHub\DamianEdwards\RazorSlices\src\RazorSlices\RazorSlice.PipeWriterExtensions.cs:line 21
         at RazorSliceHttpResultHelpers.ExecuteAsync(RazorSlice, HttpContext, HtmlEncoder , Int32, String) in D:\src\GitHub\DamianEdwards\RazorSlices\src\RazorSlices\RazorSliceHttpResultHelpers.cs:line 22
         at Microsoft.AspNetCore.Http.HttpResults.RazorSliceHttpResult`1.Microsoft.AspNetCore.Http.IResult.ExecuteAsync(HttpContext httpContext) in D:\src\GitHub\DamianEdwards\RazorSlices\src\RazorSlices\RazorSliceHttpResultOfTModel.cs:line 34
         at Microsoft.AspNetCore.Http.Generated.<GeneratedRouteBuilderExtensions_g>FCB64269D8A4C26C2E072E32ACF06A96ADD7E2DEE99BD0C9B78931C09283D15A4__GeneratedRouteBuilderExtensionsCore.ExecuteAsyncExplicit(IResult, HttpContext) in D:\src\GitHub\DamianEdwards\RazorSlices\samples\RazorSlices.Samples.WebApp\obj\Release\net8.0\win-x64\generated\Microsoft.AspNetCore.Http.RequestDelegateGenerator\Microsoft.AspNetCore.Http.RequestDelegateGenerator.RequestDelegateGenerator\GeneratedRouteBuilderExtensions.g.cs:line 1075
         at Microsoft.AspNetCore.Http.Generated.<GeneratedRouteBuilderExtensions_g>FCB64269D8A4C26C2E072E32ACF06A96ADD7E2DEE99BD0C9B78931C09283D15A4__GeneratedRouteBuilderExtensionsCore.<>c__DisplayClass3_0.<MapGet1>g__RequestHandler|4(HttpContext httpContext) in D:\src\GitHub\DamianEdwards\RazorSlices\samples\RazorSlices.Samples.WebApp\obj\Release\net8.0\win-x64\generated\Microsoft.AspNetCore.Http.RequestDelegateGenerator\Microsoft.AspNetCore.Http.RequestDelegateGenerator.RequestDelegateGenerator\GeneratedRouteBuilderExtensions.g.cs:line 203
         at Microsoft.AspNetCore.Routing.EndpointMiddleware.Invoke(HttpContext httpContext)
         at Microsoft.AspNetCore.StaticFiles.StaticFileMiddleware.Invoke(HttpContext context)
         at Microsoft.AspNetCore.Diagnostics.StatusCodePagesMiddleware.Invoke(HttpContext context)
         at Microsoft.AspNetCore.Server.Kestrel.Core.Internal.Http.HttpProtocol.ProcessRequests[TContext](IHttpApplication`1)

Reproduction Steps

1. Clone https://github.com/DamianEdwards/RazorSlices and checkout the aot branch
2. Navigate to .\samples\RazorSlices.Samples.WebApp\
3. Run dotnet publish to publish the app as native AOT
4. Run .\bin\Release\net8.0\win-x64\publish\RazorSlices.Samples.WebApp.exe to run the published app
5. Open a browser and navigate to http://localhost:5000/ and click around the pages of the site, seeing it works
6. Stop the app
7. Edit the RazorSlices.Samples.WebApp.csproj file so that <PublishAot>true</PublishAot> is commented out and <PublishTrimmed>true</PublishTrimmed>, e.g.:

   <!--<PublishAot>true</PublishAot>-->
   <PublishTrimmed>true</PublishTrimmed>
   <!--<PublishSingleFile>true</PublishSingleFile>-->

8.Run dotnet publish to publish the app trimmed
9. Run .\bin\Release\net8.0\win-x64\publish\RazorSlices.Samples.WebApp.exe to run the published app
10. Open a browser and navigate to http://localhost:5000/
11. Note the exception message in the terminal the app was run from

Expected behavior

As not trim warnings are produced on publish, and the app works as expected when published native AOT, I expect it to work when published trimmed.

Actual behavior

The app throws an exception at runtime after being published trimmed.

Regression?

Not sure but it repros with both SDK versions 8.0.106 and 8.0.300 on Windows x64

Known Workarounds

None

Configuration

Windows 11 x64
.NET SDK 8.0.106 and 8.0.300

Other information

No response

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @sbomer, @vitek-karas
See info in area-owners.md if you want to be subscribed.

[DamianEdwards]

Here's a minimal repro console app. Publish this native AOT it works, publish it trimmed it throws TypeLoadException. Repros on .NET 7 too:

// Get message via generic method
var message = MessageFactory.GetMessage<TypeWithStaticMessage>();
Console.WriteLine(message);

// Get message directly from type
var message2 = TypeWithStaticMessage2.GetMessage();
Console.WriteLine(message2);

public static class MessageFactory
{
    public static string GetMessage<T>() where T : ITypeWithStaticMessage
    {
        return T.GetMessage();
    }
}

public class TypeWithStaticMessage : ITypeWithStaticMessage
{
    // Force the string to have dynamic element so that it doesn't get compiled in as a literal
    public static string GetMessage() => $"Hello from {nameof(TypeWithStaticMessage)}, the time is {TimeOnly.FromDateTime(DateTime.Now)}";
}

public class TypeWithStaticMessage2 : ITypeWithStaticMessage
{
    // Force the string to have dynamic element so that it doesn't get compiled in as a literal
    public static string GetMessage() => $"Hello from {nameof(TypeWithStaticMessage2)}, the time is {TimeOnly.FromDateTime(DateTime.Now)}";
}

public interface ITypeWithStaticMessage
{
    abstract static string GetMessage();
}

[DamianEdwards]

Figured out a workaround by changing the method name and then make the generated types explicitly implement the interface methods and forcing the non-interface methods to call through a generated factory method that then invokes the explicitly implemented methods via the interface. Fair amount of indirection but doing it this way results in the interface implementation on the types themselves not being stripped.

[DamianEdwards]

Is this a change we'd backport to 8.x?

[jtschuster]

I think it might be worth it to backport since it's an LTS. It's not a particularly convoluted corner case, the workaround isn't great, and the fix wasn't too big. @sbomer @agocke thoughts?

[agocke]

Seems reasonable , if we believe risk is low

[jtschuster]

Figured out a workaround by changing the method name and then make the generated types explicitly implement the interface methods and forcing the non-interface methods to call through a generated factory method that then invokes the explicitly implemented methods via the interface.

@DamianEdwards Does the app work if you just added an explicit implementation that forwards to the public static method? I don't think the call through a factory method should be necessary. I haven't looked into all the usage patterns that would affect trimmed output, but the minimal repro works with this.

// Get message via generic method
var message = MessageFactory.GetMessage<TypeWithStaticMessage>();
Console.WriteLine(message);

// Get message directly from type
var message2 = TypeWithStaticMessage2.GetMessage();
Console.WriteLine(message2);

public static class MessageFactory
{
    public static string GetMessage<T>() where T : ITypeWithStaticMessage
    {
        return T.GetMessage();
    }
}

public class TypeWithStaticMessage : ITypeWithStaticMessage
{
+   static string ITypeWithStaticMessage.GetMessage() => GetMessage();
    // Force the string to have dynamic element so that it doesn't get compiled in as a literal
    public static string GetMessage() => $"Hello from {nameof(TypeWithStaticMessage)}, the time is {TimeOnly.FromDateTime(DateTime.Now)}";
}

public class TypeWithStaticMessage2 : ITypeWithStaticMessage
{
+   static string ITypeWithStaticMessage.GetMessage() => GetMessage();
    // Force the string to have dynamic element so that it doesn't get compiled in as a literal
    public static string GetMessage() => $"Hello from {nameof(TypeWithStaticMessage2)}, the time is {TimeOnly.FromDateTime(DateTime.Now)}";
}

public interface ITypeWithStaticMessage
{
    abstract static string GetMessage();
}

[DamianEdwards]

Ah interesting. Let me update my generator to just do that and I'll let you know.

[DamianEdwards]

Yep that worked, thanks!

FYI DamianEdwards/RazorSlices#52