grpc.aio.ServerInterceptor is incompatible with async RPC methods

The grpc.aio.ServerInterceptor is currently annotated using grpc.RpcMethodHandler. However the interface for grpc.RpcMethodHandler is not compatible with async RPC methods. The correct stub for an async version would make use of Awaitable and AsyncIterator:

class RpcMethodHandler(abc.ABC, Generic[_TRequest, _TResponse]):
    request_streaming: bool
    response_streaming: bool

    # XXX: not clear from docs whether this is optional or not
    request_deserializer: _Deserializer[_TRequest] | None

    # XXX: not clear from docs whether this is optional or not
    response_serializer: _Serializer[_TResponse] | None

    unary_unary: Callable[[_TRequest, ServicerContext], Awaitable[_TResponse]] | None

    unary_stream: Callable[[_TRequest, ServicerContext], AsyncIterator[_TResponse]] | None

    stream_unary: Callable[[Iterator[_TRequest], ServicerContext], Awaitable[_TResponse]] | None

    stream_stream: Callable[[Iterator[_TRequest], ServicerContext], AsyncIterator[_TResponse]] | None

stubs/grpcio/grpc/aio/init.pyi の374～383行付近を調べ、interceptor のアノテーションを issue に記載されている async RpcMethodHandler の形状と比較します。オープンな pull request #15497 を確認します。Awaitable と AsyncIterator を使用する async RPC メソッドを、既存の handler インターフェースと競合せずにスタブが受け入れられれば完了です。