Macro declare_server_traits

macro_rules! declare_server_traits {
    ($($name:ident {
        $(fn $method:ident($($arg:ident: $arg_ty:ty),* $(,)?) $(-> $ret_ty:ty)?;)*
    }),* $(,)?) => { ... };
}

🔬This is a nightly-only experimental API. (proc_macro_internals #27812)