Designing a Custom Error Hierarchy with Source Chaining

use std::error::Error;
use std::fmt;
 
#[derive(Debug)]
pub enum DatabaseError {
    QueryFailed(String),
    ConnectionLost,
}
 
impl fmt::Display for DatabaseError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            Self::QueryFailed(q) => write!(f, "Database query failed: {}", q),
            Self::ConnectionLost => write!(f, "Database connection lost"),
        }
    }
}
 
impl Error for DatabaseError {}
 
#[derive(Debug)]
pub struct ApplicationError {
    context: String,
    source: DatabaseError,
}
 
impl fmt::Display for ApplicationError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "Application error occurred: {}", self.context)
    }
}
 
impl Error for ApplicationError {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        Some(&self.source)
    }
}