Code shared from the Rust Playground

kv-log-macro.rs

#[macro_export]
macro_rules! info {
    // info!("...")
    ($e:expr) => {
        $crate::info_impl!(($e));
    };

    // info!("...", args...)
    ($e:expr, $($rest:tt)*) => {
        $crate::info_impl!(($e) $($rest)*);
    };
}

#[macro_export]
#[doc(hidden)]
macro_rules! info_impl {
    // End of macro input
    (($($e:expr),*)) => {
        println!("msg={:?}", format!($($e),*));
    };

    // Trailing k-v pairs containing no trailing comma
    (($($e:expr),*) { $($key:ident : $value:expr),* }) => {
        println!("msg={:?}", format!($($e),*));
        $(
            println!("  {}={:?}", stringify!($key), $value);
        )*
    };

    // Trailing k-v pairs with trailing comma
    (($($e:expr),*) { $($key:ident : $value:expr,)* }) => {
        $crate::info_impl!(($($e),*) { $($key : $value),* });
    };

    // Last expression arg with no trailing comma
    (($($e:expr),*) $arg:expr) => {
        $crate::info_impl!(($($e,)* $arg));
    };

    // Expression arg
    (($($e:expr),*) $arg:expr, $($rest:tt)*) => {
        $crate::info_impl!(($($e,)* $arg) $($rest)*);
    };
}

fn main() {
    info!("hello");
    info!("hello",);
    info!("hello {}", "cats");
    info!("hello {}", "cats",);
    info!("hello {}", "cats", {
        cat_1: "chashu",
        cat_2: "nori",
    });
}