Macro precondition 

macro_rules! precondition {
    ($condition:expr) => { ... };
    ($condition:expr, $message:literal) => { ... };
    ($condition:expr, $($arg:tt)*) => { ... };
}

Equivalent to a no op when used with an unmodified Rust compiler. When compiled with MIRAI, this causes MIRAI to assume the condition at the point where it appears in a function, but to also add it a precondition that must be verified by the caller of the function.