Evaluation order

Consider this log invocation:

#![allow(unused)]
fn main() {
extern crate defmt;
defmt::info!("x={=?}", foo());

fn foo() -> u8 {
    defmt::info!("Hello");
    42
}
}

Depending on when foo is invoked this can result in potential re-entrancy / nesting and cause info!("Hello") to be lost. So we'll make the macro evaluate format arguments before the acquire operation. Something like this: (core::fmt does a similar match operation)

#![allow(unused)]
fn main() {
struct Logger;
impl Logger {
    fn acquire() -> Option<Self> { None }
}
fn foo() -> u8 { 0 }
match (foo()) { // evaluate formatting arguments
    (_0) => {
        if let Some(logger) = Logger::acquire() {
            // serialize `_0`, etc.
        }
    }
}
}