Macro bail

macro_rules! bail {
    ($($key:ident = $value:expr,)* $fmt:literal $($arg:tt)*) => { ... };
    ($err:expr $(,)?) => { ... };
}

Return early with an error.

This macro is equivalent to return Err(From::from($err)).

Example

if !has_permission(user, resource) {
     bail!("permission denied for accessing {resource}");
}

#[derive(Error, Debug)]
enum ScienceError {
    #[error("recursion limit exceeded")]
    RecursionLimitExceeded,
    ...
}

if depth > MAX_DEPTH {
    bail!(ScienceError::RecursionLimitExceeded);
}

use miette::{bail, Result, Severity};

fn divide(x: f64, y: f64) -> Result<f64> {
    if y.abs() < 1e-3 {
        bail!(
            severity = Severity::Warning,
             "dividing by value ({y}) close to 0"
        );
    }
    Ok(x / y)
}