Code shared from the Rust Playground

playground.rs

#![feature(try_trait)]
enum InnerError {
    NoneError,
}

trait CustomError: std::error::Error {
    fn description(&self) -> &str;
    fn cause(&self) -> Option<&std::error::Error> {
        None
    }
}

impl std::fmt::Display for InnerError {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        let msg = match &self {
            InnerError::NoneError => "NoneError",
        };
        write!(f, "{}", msg)
    }
}

impl std::fmt::Debug for InnerError {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "{}", format!("{}", self))
    }
}

impl std::error::Error for InnerError {
    fn description(&self) -> &str {
        match &self {
            InnerError::NoneError => "std::error::Error NoneError",
        }
    }
}

impl CustomError for InnerError {
    fn description(&self) -> &str {
        match &self {
            InnerError::NoneError => "CustomError NoneError",
        }
    }
}

fn res() -> Result<i32, Box<dyn CustomError>> {
    let a = None;
    let b = a?;
    Ok(b)
}

impl From<std::option::NoneError> for Box<dyn CustomError> {
    fn from(_: std::option::NoneError) -> Self {
        Box::new(InnerError::NoneError)
    }
}

fn main() {
    match res() {
        Ok(v) => println!("Recieve {}", v),
        Err(e) => eprintln!("Error {:?}", e),
    }
}