error: `params = "named"` can only be used to generate a client (on a trait annotated with #[rpc(client)]). At this time the server does not support named parameters.
 --> $DIR/attr-named-params-on-server.rs:4:1
  |
4 | / pub trait Rpc {
5 | |     /// Returns a protocol version
6 | |     #[rpc(name = "add", params = "named")]
7 | |     fn add(&self, a: u32, b: u32) -> Result<String>;
8 | | }
  | |_^