error-chain.rs

// `error_chain!` can recurse deeply
#![recursion_limit = "1024"]

#[macro_use]
extern crate error_chain;

// We'll put our errors in an `errors` module, and other modules in
// this crate will `use errors::*;` to get access to everything
// `error_chain!` creates.
mod errors {
    // Create the Error, ErrorKind, ResultExt, and Result types
    error_chain! { }
}

use errors::*;

fn main() {
    if let Err(ref e) = run() {
        use ::std::io::Write;
        let stderr = &mut ::std::io::stderr();
        let errmsg = "Error writing to stderr";

        writeln!(stderr, "error: {}", e).expect(errmsg);

        for e in e.iter().skip(1) {
            writeln!(stderr, "caused by: {}", e).expect(errmsg);
        }

        // The backtrace is not always generated. Try to run this example
        // with `RUST_BACKTRACE=1`.
        if let Some(backtrace) = e.backtrace() {
            writeln!(stderr, "backtrace: {:?}", backtrace).expect(errmsg);
        }

        ::std::process::exit(1);
    }
}

// Most functions will return the `Result` type, imported from the
// `errors` module. It is a typedef of the standard `Result` type
// for which the error type is always our own `Error`.
fn run() -> Result<()> {
    use std::fs::File;

    // Use chain_err to attach your own context to errors
    File::open("my secret file")
        .chain_err(|| "unable to open my secret file")?;

    // Use the `bail!` macro to return an error Result, ala `println!`
    bail!("giving up");
}