Print error and its source

print_low_level_error.rs

use std::error::Error;
use std::fs::File;
use std::io;
use std::io::prelude::*;
use std::io::{stderr, Write};

fn main() {
    let r = read_file("wrong.test"); // read_file(r"/Users/nyinyithan/Downloads/test.json");
    match r {
        Ok(txt) => println!("{}", txt),
        Err(e) => print_error(&e),
    }
}

fn read_file(file_name: &str) -> io::Result<String> {
    let mut f = File::open(file_name)?;
    let mut text = String::new();
    f.read_to_string(&mut text).map(|x| x.to_string())?;
    Ok(text)
}

fn print_error(mut error: &dyn Error) {
    let _ = writeln!(stderr(), "error: {}", error);
    while let Some(e) = error.source() {
        let _ = writeln!(stderr(), "caused by: {}", e);
        error = e;
    }
}