Make it possible to resolve the method info from the specific delegate type when using AddRouteHandler

[davidfowl]

For more NativeAOT size savings, we can avoid preserving all type information for methods pointed to by delegates if we enable this. See dotnet/runtime#96166 (comment) for more details.

We essentially need to add another thunk here to allow resolution of MethodInfo from the delegate when using RDG (the request delegate generator).

cc @captainsafia

[captainsafia]

We essentially need to add another thunk here to allow resolution of MethodInfo from the delegate when using RDG (the request delegate generator).

Don't you mean RDF here (compile-time generation)?

I think the proposed API would look like this:

    public RouteHandlerBuilder AddRouteHandler(
        RoutePattern pattern,
        Delegate routeHandler,
        IEnumerable<string>? httpMethods,
        bool isFallback,
        Func<MethodInfo, RequestDelegateFactoryOptions?, RequestDelegateMetadataResult>? inferMetadataFunc,
-        Func<Delegate, RequestDelegateFactoryOptions, RequestDelegateMetadataResult?, RequestDelegateResult> createHandlerRequestDelegateFunc,
+        Func<RequestDelegateFactoryOptions, RequestDelegateMetadataResult?, RequestDelegateResult> createHandlerRequestDelegateFunc,
+        Func<Delegate, MethodInfo> resolveMethodInfo)

[jkotas]

Is the whole purpose of the extra argument to provide routeHandler.Method? Can the extra argument be MethodInfo instead?

[davidfowl]

Actually, you're right, we might just be able to pass it in directly 😄

[captainsafia]

Correct, indeed. Here's the full API proposal.

Proposed API

namespace Microsoft.AspNetCore.Routing;

public static class RouteHandlerServices
{
    public static RouteHandlerBuilder Map(
            IEndpointRouteBuilder endpoints,
            string pattern,
            Delegate handler,
            IEnumerable<string>? httpMethods,
            Func<MethodInfo, RequestDelegateFactoryOptions?, RequestDelegateMetadataResult> populateMetadata,
            Func<Delegate, RequestDelegateFactoryOptions, RequestDelegateMetadataResult?, RequestDelegateResult> createRequestDelegate,
+          MethodInfo? methodInfo)
}

Usage Examples

Example taken from code generated by RDG.

internal static RouteHandlerBuilder MapCore(
            this IEndpointRouteBuilder routes,
            string pattern,
            Delegate handler,
            IEnumerable<string>? httpMethods,
            MetadataPopulator populateMetadata,
            RequestDelegateFactoryFunc createRequestDelegate,
            MethodInfo methodInfo)
        {
            return RouteHandlerServices.Map(routes, pattern, handler, httpMethods, populateMetadata, createRequestDelegate, methodInfo);
        }

Thank you for submitting this for API review. This will be reviewed by @dotnet/aspnet-api-review at the next meeting of the ASP.NET Core API Review group. Please ensure you take a look at the API review process documentation and ensure that:

• The PR contains changes to the reference-assembly that describe the API change. Or, you have included a snippet of reference-assembly-style code that illustrates the API change.
• The PR describes the impact to users, both positive (useful new APIs) and negative (breaking changes).
• Someone is assigned to "champion" this change in the meeting, and they understand the impact and design of the change.

[halter73]

API Review Notes:

• Even though it's pretty much internal, since it's technically public, let's keep the old overload.
• MethodInfo should not be nullable.

API Approved. We have great hopes for how much more we can trim!

namespace Microsoft.AspNetCore.Routing;

public static class RouteHandlerServices
{
    public static RouteHandlerBuilder Map(
            IEndpointRouteBuilder endpoints,
            string pattern,
            Delegate handler,
            IEnumerable<string>? httpMethods,
            Func<MethodInfo, RequestDelegateFactoryOptions?, RequestDelegateMetadataResult> populateMetadata,
            Func<Delegate, RequestDelegateFactoryOptions, RequestDelegateMetadataResult?, RequestDelegateResult> createRequestDelegate);

+    public static RouteHandlerBuilder Map(
+            IEndpointRouteBuilder endpoints,
+            string pattern,
+            Delegate handler,
+            IEnumerable<string>? httpMethods,
+            Func<MethodInfo, RequestDelegateFactoryOptions?, RequestDelegateMetadataResult> populateMetadata,
+            Func<Delegate, RequestDelegateFactoryOptions, RequestDelegateMetadataResult?, RequestDelegateResult> createRequestDelegate,
+            MethodInfo methodInfo);
}

[davidfowl]

Any reason this isn't an optional parameter?