backtrace in Error

gistfile1.rs

#![feature(std_misc)]
#![feature(unmarked_api)]
use std::rt::backtrace;

use std::path::PathBuf;
use std::result::Result;
use std::error::Error;

pub type MResult<T> = std::result::Result<T, MyError>;

#[derive(Debug,Clone)]
pub struct MyError {
    desc: String,
    backtrace: String
}

fn get_backtrace() -> String {
        let mut m = Vec::new();
        backtrace::write(&mut m).ok().
            map_or("No backtrace".to_string(), 
                   |_| String::from_utf8_lossy(&m).to_string())
}

impl<T:std::error::Error> From<T> for MyError {
    fn from(e: T) -> MyError {
        MyError { desc: e.description().to_string(),
                  backtrace: get_backtrace()
        }
    }
}

fn doit() -> MResult<String> {
    let f = [-1;15];
    let s = try!(std::str::from_utf8(&f));
    Ok(s.to_string())
}


fn main() {
    let res = doit();  // should error
    let s = match res {
        Ok(s) => s,
        Err(e) => {
            println!("Got an error: {}",e.desc);
            println!("{}", e.backtrace);
            return;
        }
    };
    println!("Didn't error! result was {}", s);
}