Add support for RouteHandlerInvocationContext<> overloads

[captainsafia]

Closes #40514.

• Add T4 generator for RouteHandlerInvocationContext<> overloads of various arity (supports up to 10 arguments)
• Update code generation to use new generic overloads when the number of handler arguments is < 10
• Add GetParameter<T>(int index) API to RouteHandlerInvocationContext
• Make HttpContext and Parameters properties on RouteHandlerInvocationContext virtual

API Changes

- public sealed class RouteHandlerInvocationContext
+ public class RouteHandlerInvocationContext
{
-  public HttpContext HttpContext { get; }
+ public virtual HttpContext HttpContext { get; }

- public List<object?> Parameters { get; }
+ public virtual List<object?> Parameters { get; }

+ public virtual T GetParameter<T>(int index) { }
}

Perf Impact

app.MapGet("/print/{name}/{age}", (string name, int age) => $"Hello, {name}! You're {age} years old.")
    .AddFilter(async (context, next) =>
    {
        var name = context.Parameters[0];
        var age = context.Parameters[1];
        return await next(context);
    });

> 1..1000 | % { curl http://localhost:5000/print/foo/27 }

Before:

Type	Allocations
- Microsoft.AspNetCore.Routing.Matching.CandidateState[1]	1,000
- Microsoft.AspNetCore.Routing.RouteValueDictionary	1,000
- Microsoft.AspNetCore.Http.RouteHandlerInvocationContext	1,000

Allocations for System.Object[] in non-generic RHIC

Type	Allocations
+ System.Object[]	1,692

Function Name	Allocations	Bytes	Module Name
+ dynamicClass.lambda_method2(00007FF9875983D8, object, 00007FF986FB5068)	1,000	40,000	anonymously hosted dynamicmethods assembly

After:

Type	Allocations
- Program.<>c.<<<Main>$>b__0_1>d	1,000
- Microsoft.AspNetCore.Http.RouteHandlerInvocationContext<System.String, System.Int32>	1,000
- Microsoft.AspNetCore.Routing.Matching.CandidateState[1]	1,000
- Microsoft.AspNetCore.Routing.RouteValueDictionary	1,000

Type	Allocations
+ System.Object[]	690

[davidfowl]

Where are the object[] allocations coming from?

[captainsafia]

Where are the object[] allocations coming from?

The ~1000 allocations before the change are from the object's array initialized in the invocation pipeline when we do the boxing. The rest are more dispersed.

Function Name	Allocations	Bytes	Module Name
- dynamicClass.lambda_method2(00007FF9875983D8, object, 00007FF986FB5068)	1,000	40,000	anonymously hosted dynamicmethods assembly
- Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(Microsoft.Extensions.DependencyInjection.ServiceLookup.ConstructorCallSite, Microsoft.Extensions.DependencyInjection.ServiceLookup.RuntimeResolverContext)	4	160	microsoft.extensions.dependencyinjection
- System.Collections.Generic.EnumerableHelpers.ToArray<T>(System.Collections.Generic.IEnumerable<T>)	2	80	system.linq.il
- System.Collections.Generic.List<T>.ToArray()	1	40	System.Private.CoreLib.il
- Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.UseMiddleware.AnonymousMethod__0(Microsoft.AspNetCore.Http.RequestDelegate)	1	40	microsoft.aspnetcore.http.abstractions
- Microsoft.AspNetCore.Certificates.Generation.CertificateManager+CertificateManagerEventSource.ListCertificatesStart(System.Security.Cryptography.X509Certificates.StoreLocation, System.Security.Cryptography.X509Certificates.StoreName)	1	40	microsoft.aspnetcore.server.kestrel.core
- System.ParamsArray.cctor()	1	40	System.Private.CoreLib.il

[halter73]

Given this, I think we should change the type of RouteHandlerInvocationContext.Arguments to IReadOnlyList<object?>.

[captainsafia]

I don't think so.

The type we use for Arguments will be used in both the generic and non-generic overloads. For the non-generic overload, we have to use IList to support in-place modification of items in the list.

One option is that we could change the behavior of the implementation so that if you're using the non-generic variant (more than 10 arguments) you're not able to make modifications to parameters. For scenarios where you're using ten arguments or less, you'll be able to modify in-place using the custom setter in the generic overloads.

[captainsafia]

Actually, nevermind. We cannot do this anyway. The IReadOnlyList implementation does not support a setter on this[index] so we would be able to use it for generic variants anways.

[davidfowl]

I wonder if we can include this in the global directory.props

cc @dougbu

[dougbu]

You mean notice a project contains a .tt file and add the <Service /> element @davidfowl❔ That may work but VS would rewrite it the next time someone opens the project IIRC.

We only have 3 projects containing this <Service /> after this PR. How big an issue is this❔

[davidfowl]

It's not an issue, I would just like to clean it up as we plan to code generate more things.

[dougbu]

It's up to you @davidfowl whether to centralize things in this PR. I recommend testing if the code in our root Directory.Build.props prevents VS rewriting the project to list the <Service/>. If "Save All" is fine after adding a new .tt file, you're good to go. Otherwise, the extra code will become redundant and something we'll end up fighting.

The specific approach would be something like

<ItemGroup>
  <_GeneratorSources Include="$(MSBuildProjectDirectory)\**\*.tt" />
</ItemGroup>
<ItemGroup>
  <Service Condition=" '@(_GeneratorSources->Count()) ' != '0' " Include="{508349b6-6b84-4df5-91f0-309beebad82d}" />
</ItemGroup>

[davidfowl]

cc @mhutch I'm trying to resurrect t4

[captainsafia]

🆙 📅 : Can I get another look at this?

[BrennanConroy]

Was this name discussed/approved?

[davidfowl]

Yes