use chainerror::prelude::v1::*;
use std::error::Error;
use std::io;
use std::result::Result;

fn do_some_io() -> Result<(), Box<dyn Error + Send + Sync>> {
    Err(io::Error::from(io::ErrorKind::NotFound))?;
    Ok(())
}

fn func2() -> Result<(), Box<dyn Error + Send + Sync>> {
    let filename = "foo.txt";
    do_some_io().context(format!("Error reading '{}'", filename))?;
    Ok(())
}

fn func1() -> Result<(), Box<dyn Error + Send + Sync>> {
    if let Err(e) = func2() {
        if let Some(s) = e.source() {
            eprintln!("func2 failed because of '{}'", s);
            Err(e).context("func1 error")?;
        }
    }
    Ok(())
}

fn main() -> Result<(), Box<dyn Error + Send + Sync>> {
    if let Err(e) = func1() {
        eprintln!("{}", e);
        std::process::exit(1);
    }
    Ok(())
}