unsafeaccessorattribute support for generic params

docs/core/whats-new/dotnet-9/runtime.md

@@ -54,6 +54,12 @@ Two new attributes make it possible to define [feature switches](https://github.
 
   When built with `<PublishAot>true</PublishAot>`, the call to `Feature.Implementation()` doesn't produce analyzer warning [IL3050](../../deploying/native-aot/warnings/il3050.md), and `Feature.Implementation` code is removed when publishing.
 
+## UnsafeAccessorAttribute supports generic parameters
+
+The <xref:System.Runtime.CompilerServices.UnsafeAccessorAttribute> feature allows unsafe access to type members that are unaccessible to the caller. This feature was designed in .NET 8 but implemented without support for generic parameters. .NET 9 adds support for generic parameters for CoreCLR and native AOT scenarios. The following code shows example usage.
+
+:::code language="csharp" source="../snippets/dotnet-9/csharp/UnsafeAccessor.cs":::
+
 ## Performance improvements
 
 The following performance improvements have been made for .NET 9:

docs/core/whats-new/snippets/dotnet-9/csharp/UnsafeAccessor.cs

@@ -0,0 +1,26 @@
+using System.Runtime.CompilerServices;
+
+public class Class<T>
+{
+    private T? _field;
+    private void M<U>(T t, U u) { }
+}
+
+class Accessors<V>
+{
+    [UnsafeAccessor(UnsafeAccessorKind.Field, Name = "_field")]
+    public extern static ref V GetSetPrivateField(Class<V> c);
+
+    [UnsafeAccessor(UnsafeAccessorKind.Method, Name = "M")]
+    public extern static void CallM<W>(Class<V> c, V v, W w);
+}
+
+internal class UnsafeAccessorExample
+{
+    public void AccessGenericType(Class<int> c)
+    {
+        ref int f = ref Accessors<int>.GetSetPrivateField(c);
+
+        Accessors<int>.CallM<string>(c, 1, string.Empty);
+    }
+}