Fix Rust print_err! macro

Feedback & Bugs
#1

Hello.
Could you please fix the Rust print_err! macro so that we do not get a warning when using it, please?

The macro:

macro_rules! print_err {
    ($($arg:tt)*) => (
        {
            use std::io::Write;
            writeln!(&mut ::std::io::stderr(), $($arg)*);
        }
    )
}

could be updated to:

macro_rules! print_err {
    ($($arg:tt)*) => (
        {
            use std::io::Write;
            writeln!(&mut ::std::io::stderr(), $($arg)*).ok();
        }
    )
}

(added .ok() at the end of the writeln! line)

Thanks to fix it.

By the way, thanks for adding Rust!

#2

I don’t have any warning when I use this macro but I can add the .ok() after the writeln!.

#3

Oh, the warning is when compiling locally (not on the CodinGame server) so when using cargo build.
It is a bit annoying to get a warning when using this command (that we can use to avoid sending code that does not compile to the server).
So it would be very nice to add it.
Thanks.