Dart FFI lookup/asFunction does not accept generic type that extends NativeType

Question

This code snippet defines a generic function that has a type parameter T extends NativeType. Then T is used to define a C function signature to look up symbols from a dynamic library.

import 'dart:ffi';

lookupGeneric<T extends NativeType>() {
  final dylib = DynamicLibrary.open("path");
  final address = dylib.lookup<NativeFunction<Void Function(Pointer<T>)>>("Name");
  final function = address.asFunction<void Function(Pointer<T>)>(isLeaf: false);
  return (address, function);
}

void main() {
  final func = lookupGeneric<Int8>();
}

My issue is that this code fails to compile with the following message:

Can't invoke 'asFunction' because the function signature 'NativeFunction<Void Function(Pointer<T>)>' for the pointer isn't a valid C function signature.

When I replace T for plain NativeType, it compiles without errors:

import 'dart:ffi';

lookupGeneric<T extends NativeType>() {
  final dylib = DynamicLibrary.open("path");
  //                                                 -> CHANGE HERE ˇˇˇˇˇˇˇˇˇˇ
  final address = dylib.lookup<NativeFunction<Void Function(Pointer<NativeType>)>>("Name");
  final function = address.asFunction<void Function(Pointer<T>)>(isLeaf: false);
  return (address, function);
}

void main() {
  final func = lookupGeneric<Int8>();
}

I don't, however, find this a satisfactory solution, and it also doesn't work when T is not used as a pointer.

Can someone explain why NativeType works but T extends NativeType doesn't? What would be the solution to use generic types in dart:ffi?