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//! Zero-fuss debug tracing macro.
//!
//! Cargo.toml:
//! ```text
//! [dependencies]
//! eztrace = "*"
//! ```
//!
//! Usage:
//! ```
//! #[macro_use]
//! extern crate eztrace;
//! # fn main() {
//! # let (my_variable, other_variable) = (42, 237);
//! trace!(my_variable, other_variable);
//! # }
//! ```
//!
//! Prints this:
//! ```text
//! my_variable, other_variable: 42 237
//! ```

/// Prints out variables and their debug representation.
///
/// Non-`Copy` types do what you would hope.
///
/// # Examples
///
/// Basic usage:
///
/// ```
/// # #[macro_use] extern crate eztrace;
/// let a = 3;
/// let b = 4;
/// let c = 5;
/// trace!(a, b, c);
/// // a, b, c: 3 4 5
/// trace!(a * a + b * b, c * c);
/// // a * a + b * b, c * c: 25 25
/// ```
///
/// To print just the file & line:
///
/// ```
/// # #[macro_use] extern crate eztrace;
/// trace!();
/// // eztrace.rs:1
/// ```
#[macro_export]
macro_rules! trace {
    () => {
        println!(trace!(@line));
    };
    ($($IT:expr),* $(,)*) => {
        println!(
            trace!(@fmt $($IT),*),
            $(&$IT),*
        );
    };
    (@line) => {
        concat!(
            file!(), ":", line!(),
        )
    };
    (@fmt $($IT:expr),*) => {
        concat!(
            trace!(@stringify $($IT,)*),
            ":",
            $(trace!(@fmtcode $IT)),*
        )
    };
    (@fmtcode $_:expr) => {
        " {:?}"
    };
    (@stringify $HEAD:expr, $($IT:expr,)*) => {
        concat!(
            stringify!($HEAD),
            $(
                ", ",
                stringify!($IT),
            )*
        )
    };
}


#[cfg(test)]
mod tests {
    #[test]
    fn no_move() {
        let string = format!("hey");
        trace!(string, 9);
        trace!(string, string);
        trace!(
            string,
            string,
            string,
        );
    }

    #[test]
    fn single_eval_per_arg() {
        let mut n = 0;
        fn incr(i: &mut usize) { *i += 1; }
        trace!(
            "check that each argument",
            "is only evaluated",
            "once",
            incr(&mut n),
        );
        trace!(n);
        assert_eq!(n, 1);
    }

    #[test]
    fn empty() {
        trace!();
    }

    #[test]
    fn single() {
        trace!("hello");
    }

    #[test]
    fn multi() {
        trace!("hello", "world!");
    }

    #[test]
    fn the_docs() {
        let a = 3;
        let b = 4;
        let c = 5;
        trace!(a, b, c);
        // a, b, c: 3 4 5
        trace!(a * a + b * b, c * c);
        // a * a + b * b, c * c: 25 25
        trace!();
    }
}