Macro defer_message 

macro_rules! defer_message {
    ($($t:tt)*) => { ... };
}

Queue an R message (rust_message layering, muffled by suppressMessages()) and return normally; emitted when the surrounding guarded call or callback returns.

Same grammar as crate::defer_warning!. Unlike crate::message! a class = … part is accepted and layered in front of rust_message. call = none is accepted for the shared grammar and changes nothing: an R message carries no call, so conditionCall(m) is NULL either way.