Make Source Generator for UseMiddleware

[eerhardt]

When I dotnet publish -c Release -p:PublishAot=true the following app:

var app = new ApplicationBuilder(serviceProvider: null);

UseMiddlewareExtensions.UseMiddleware<HiMiddleware>(app);

public class HiMiddleware
{
    public Task Invoke(HttpContext context)
    {
        Console.WriteLine("hi");
        return Task.CompletedTask;
    }
}

We should create a Source Generator for UseMiddleware so we don't need to use Reflection on NativeAOT. See #45890

Original issue (outdated)

I get the following AOT warnings stemming from the UseMiddleware method:

/_/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/Interpreter/ArrayOperations.cs(23): AOT analysis warning IL3050: System.Linq.Expressions.Interpreter.NewArrayInitInstruction.Run(InterpretedFrame): Using member 'System.Array.CreateInstance(Type,Int32)' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. The code for an array of the specified type might not be available. [C:\DotNetTest\AspNetTest\AspNetTest.csproj]
/_/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/Interpreter/ArrayOperations.cs(52): AOT analysis warning IL3050: System.Linq.Expressions.Interpreter.NewArrayInstruction.Run(InterpretedFrame): Using member 'System.Array.CreateInstance(Type,Int32)' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. The code for an array of the specified type might not be available. [C:\DotNetTest\AspNetTest\AspNetTest.csproj]
/_/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/Interpreter/ArrayOperations.cs(87): AOT analysis warning IL3050: System.Linq.Expressions.Interpreter.NewArrayBoundsInstruction.Run(InterpretedFrame): Using member 'System.Array.CreateInstance(Type,Int32[])' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. The code for an array of the specified type might not be available. [C:\DotNetTest\AspNetTest\AspNetTest.csproj]
/_/src/libraries/System.Linq.Expressions/src/System/Dynamic/Utils/TypeUtils.cs(28): AOT analysis warning IL3050: System.Dynamic.Utils.TypeUtils.GetNullableType(Type): Using member 'System.Type.MakeGenericType(Type[])' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. The native code for this instantiation might not be available at runtime. [C:\DotNetTest\AspNetTest\AspNetTest.csproj]
/_/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/MethodCallExpression.cs(1379): AOT analysis warning IL3050: System.Linq.Expressions.Expression.ApplyTypeArgs(MethodInfo,Type[]): Using member 'System.Reflection.MethodInfo.MakeGenericMethod(Type[])' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. The native code for this instantiation might not be available at runtime. [C:\DotNetTest\AspNetTest\AspNetTest.csproj]
/_/src/libraries/System.Linq.Expressions/src/System/Linq/Expressions/BinaryExpression.cs(2239): AOT analysis warning IL3050: System.Linq.Expressions.Expression.GetResultTypeOfShift(Type,Type): Using member 'System.Type.MakeGenericType(Type[])' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. The native code for this instantiation might not be available at runtime. [C:\DotNetTest\AspNetTest\AspNetTest.csproj]

This causes AOT warnings for ASP.NET apps that want to use EndPoints and Routing because we call UseMiddleware to enable these features:

aspnetcore/src/Http/Routing/src/Builder/EndpointRoutingApplicationBuilderExtensions.cs

Line 62 in f543e35

return builder.UseMiddleware<EndpointRoutingMiddleware>(endpointRouteBuilder);

aspnetcore/src/Http/Routing/src/Builder/EndpointRoutingApplicationBuilderExtensions.cs

Line 113 in f543e35

return builder.UseMiddleware<EndpointMiddleware>();

At a minimum, we should remove the AOT warnings from the above 2 callsites, so we can publish an ASP.NET Web API application for NativeAOT with no warnings.

As a follow up after that, we should consider a mechanism for solving this warning generally, for example with a source generator that generates the necessary code at compile-time.

Thanks for contacting us.

We're moving this issue to the .NET 8 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[JamesNK]

@eerhardt How come these warnings are coming from System.Linq.Expressions files? Has that project not been annotated for AOT yet?

[eerhardt]

Has that project not been annotated for AOT yet?

No, it hasn't. There are a lot of libraries in dotnet/runtime that haven't been annotated for AOT. See dotnet/runtime#75480.

Thanks for contacting us.

We're moving this issue to the .NET 8 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[captainsafia]

Triage: Parking this back in .NET 8 Planning to avoid it surfacing in the triage query.