/// Return early with an error if a condition is not satisfied.
///
/// This macro is equivalent to `if !condition { return Err(From::from($err)) }`.
///
/// Similar to `assert!`, `ensure!` takes a condition and exits the function
/// if the condition fails. Unlike `assert!`, `ensure!` returns an `Error`,
/// it does not panic.
///
/// # Example
///
/// ```
/// # use anyhow::{ensure, Result};
/// #
/// #
/// # fn main() -> Result<()> {
/// #     let user = 0;
/// #     let resource = 0;
/// #
/// ensure!(user == 0, "only user 0 is allowed");
/// #     Ok(())
/// # }
/// ```
///
/// ```
/// # use anyhow::{ensure, Result};
/// # use std::fmt::{self, Display};
/// #
/// # #[derive(Debug)]
/// # enum ScienceError {
/// #     RecursionLimitExceeded,
/// # }
/// #
/// # impl std::error::Error for ScienceError {}
/// #
/// # impl Display for ScienceError {
/// #     fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
/// #         unimplemented!()
/// #     }
/// # }
/// #
/// # const MAX_DEPTH: usize = 1;
/// #
/// # const IGNORE: &str = stringify! {
/// #[derive(Error, Debug)]
/// enum ScienceError {
///     #[error(display = "recursion limit exceeded")]
///     RecursionLimitExceeded,
///     ...
/// }
/// # };
///
/// # fn main() -> Result<()> {
/// #     let depth = 0;
/// #
/// ensure!(depth <= MAX_DEPTH, ScienceError::RecursionLimitExceeded);
/// #     Ok(())
/// # }
/// ```
#[macro_export]
macro_rules! ensure {
    ($cond:expr, $err:expr $(,)?) => {
        if !($cond) {
            return std::result::Result::Err($crate::anyhow!($err));
        }
    };
    ($cond:expr, $fmt:expr, $($arg:tt)*) => {
        if !($cond) {
            return std::result::Result::Err($crate::anyhow!($fmt, $($arg)*));
        }
    };
}

    }
}
#[cfg(test)]
mod test {
    #[test]
    fn ensure() {
        let f = || {
            ensure!(1 + 1 == 2, "This is correct");
            Ok(())
        };
        assert!(f().is_ok());
        let v = 1;
        let f = || {
            ensure!(v + v == 2, "This is correct, v: {}", v);
            Ok(())
        };
        assert!(f().is_ok());
        let f = || {
            ensure!(v + v == 1, "This is not correct, v: {}", v);
            Ok(())
        };
        assert!(f().is_err());