Support for AsParameters /2 (#29585)

* generics in What's new /2

* generics in What's new /2

aspnetcore/release-notes/aspnetcore-8.0.md

@@ -160,6 +160,19 @@ The main entry points to subsystems that don't work reliably with native AOT are
 
 :::image type="content" source="../fundamentals/aot/_static/top-level-annnotations.png" alt-text="Visual Studio window showing IL2026 warning message on the AddControllers method that says MVC doesn't currently support native AOT.":::
 
+### Support for AsParameters and automatic metadata generation
+
+In this preview, minimal APIs generated at compile-time include support for parameters decorated with the [`[AsParameters]`](xref:Microsoft.AspNetCore.Http.AsParametersAttribute) attribute and support automatic metadata inference for request and response types. Consider the following code:
+
+:::code language="csharp" source="~/release-notes/sample/ProgramAsParameters.cs" highlight="22":::
+
+The preceding generated code:
+
+* Binds a `projectId` parameter from the query.
+* Binds a `Todo` parameter from the JSON body.
+* Annotates the endpoint metadata to indicate that it accepts a JSON payload.
+* Annotate the endpoint metadata to indicate that it returns a Todo as a JSON payload.
+
 ## Miscellaneous
 
 ### HTTP/3 enabled by default

aspnetcore/release-notes/sample/ProgramAsParameters.cs

@@ -0,0 +1,40 @@
+using System.Text.Json.Serialization;
+using MyFirstAotWebApi;
+
+var builder = WebApplication.CreateSlimBuilder(args);
+
+builder.Services.ConfigureHttpJsonOptions(options =>
+{
+    options.SerializerOptions.TypeInfoResolverChain.Insert(0, AppJsonSerializerContext.Default);
+});
+
+var app = builder.Build();
+
+var sampleTodos = TodoGenerator.GenerateTodos().ToArray();
+
+var todosApi = app.MapGroup("/todos");
+todosApi.MapGet("/", () => sampleTodos);
+todosApi.MapGet("/{id}", (int id) =>
+    sampleTodos.FirstOrDefault(a => a.Id == id) is { } todo
+        ? Results.Ok(todo)
+        : Results.NotFound());
+
+app.MapPost("/todos", ([AsParameters] CreateTodoArgs payload) =>
+{
+    if (payload.TodoToCreate is not null)
+    {
+        return payload.TodoToCreate;
+    }
+    return new Todo(0, "New todo", DateTime.Now, false);
+});
+
+app.Run();
+
+[JsonSerializable(typeof(Todo[]))]
+internal partial class AppJsonSerializerContext : JsonSerializerContext
+{
+
+}
+
+record CreateTodoArgs(int ProjectId, Todo? TodoToCreate);
+record Todo(int Id, string Name, DateTime CreatedAt, bool IsCompleted);