Rust error handling with thiserror and anyhow

Rust error handling requires defining error types and implementing std::error::Error, which is boilerplate-heavy.

Use thiserror for library errors, anyhow for application errors:

// Library code: use thiserror (typed errors)
use thiserror::Error;

#[derive(Error, Debug)]
enum AppError {
#[error("Database error: {0}")]
Database(#[from] sqlx::Error),

#[error("Not found: {entity} with id {id}")]
NotFound { entity: String, id: i64 },

#[error("Validation failed: {0}")]
Validation(String),

#[error("IO error")]
Io(#[from] std::io::Error),
}

// Automatic From implementations via #[from]
fn get_user(id: i64) -> Result<User, AppError> {
let user = db.query("...").await?; // sqlx::Error -> AppError::Database
Ok(user)
}

// Application code: use anyhow (any error)
use anyhow::{Context, Result};

fn main() -> Result<()> {
let config = read_config()
.context("Failed to read configuration")?;

let db = connect_db(&config.db_url)
.context("Failed to connect to database")?;

start_server(db).context("Server crashed")?;
Ok(())
}
// anyhow wraps any error and adds context chain

thiserror generates Error trait implementations. anyhow erases error types for application code where you just want to propagate and add context.