Macro fail::fail_point

macro_rules! fail_point {
    ($name:expr) => { ... };
    ($name:expr, $e:expr) => { ... };
    ($name:expr, $cond:expr, $e:expr) => { ... };
}

The only entry to define a fail point.

When a fail point is defined, it's referenced via the name. For example, library A defines a fail point in lib.rs as follows:

pub fn f() {
    fail_point!("p1");
}

mod my {
    pub fn f() {
        fail_point!("p2");
    }
}

$e is used to transform a string to the return type of outer function or closure. If you don't need to return early or a specified value, then you can use the fail_point!($name).

If you provide an additional condition $cond, then the condition will be evaluated before the fail point is actually checked.