Macro error_rules::ensure

macro_rules! ensure {
    ( $cond:expr, $e:expr ) => { ... };
    ( $cond:expr, $fmt:expr, $($arg:tt),* ) => { ... };
}

Ensure that a boolean expression is true at runtime. If condition is false then invokes bail! macro

/// Usage:

error_rules! {
    self => ("{}", error)
}

fn run() -> Result<()> {
    ensure!(false, "ensure error");
    Ok(())
}

if let Err(e) = run() {
    assert_eq!(e.to_string().as_str(), "ensure error")
} else {
    unreachable!()
}