The failure from Unwrapping an "Err" does not tell you what error it was

[wackywendell]

Right now, if you call result.unwrap() for a variable result that is an Err, the program fails but does not tell you what was in the Err. For example:

fn main() {
    let test_err : Result<(), ~str> = Err(~"no reason whatsoever.");
    let _ = test_err.unwrap();
}

Output:
task '<main>' failed at 'called Result::unwrap()on anErr value', /build/rust-git/src/rust/src/libstd/result.rs:187

It would be convenient if failing on a Result<T, E : Show> also displayed the error it was failing on, so, for example, you could call let value = result.unwrap() in the main function of a program and know that it would tell you not only if an error occurred but also what that error was.