Simplify invalid message evidence verification

[fjarri]

Every protocol defines several verify_*_is_invalid to check invalid message evidence. An example implementation looks like this:

fn verify_echo_broadcast_is_invalid(
    deserializer: &Deserializer,
    round_id: &RoundId,
    message: &EchoBroadcast,
) -> Result<(), MessageValidationError> {
    match round_id {
        r if r == &RoundId::new(1) => message.verify_is_not::<Round1EchoBroadcast>(deserializer),
        r if r == &RoundId::new(2) => message.verify_is_not::<Round2EchoBroadcast<P>>(deserializer),
        r if r == &RoundId::new(3) => message.verify_is_some(),
        _ => Err(MessageValidationError::InvalidEvidence("Invalid round number".into())),
    }
}

How can this be simplified? Seems like it'll have to be a macro. Something that seems possible is a macro for every method, something like

echo_broadcast_types! {
    1 => Round1EchoBroadcast,
    2 => Round2EchoBroadcast<P>,
    3 => _,
}

direct_message_types! {
...
}

// etc

Even better, if we could merge all message parts into one macro, something like

message_types! {
    1 => (Round1EchoBroadcast, _, _),
    2 => (Round2EchoBroadcast<P>, _, _),
    3 => (_, _, Round3Broadcast),
}

but I am not sure if it is possible in Rust, because it will require transposing the variable length token sequence.