rust-error-handling

# Rust Error Handling Rust-specific error handling patterns that extend the base error handling skill. ## Rules - Use `thiserror` for defining library error types - Use `anyhow` for application-level error handling - Implement `std::error::Error` trait for custom error types - Use the `?` operator for ergonomic error propagation - Prefer `Result<T, E>` over panicking for recoverable errors - Use `unwrap()` only in tests or when failure is impossible ## Examples ```rust // Define library errors with thiserror use thiserror::Error; #[derive(Error, Debug)] pub enum ConfigError { #[error("failed to read config file: {0}")] Io(#[from] std::io::Error), #[error("invalid config format: {0}")] Parse(#[from] toml::de::Error), #[error("missing required field: {field}")] MissingField { field: String }, } ``` ```rust // Application-level error handling with anyhow use anyhow::{Context, Result}; fn load_config(path: &str) -> Result<Config> { let content = std::fs::read_to_string(path) .with_context(|| format!("failed to read config from {}", path))?; let config: Config = toml::from_str(&content) .context("failed to parse config TOML")?; Ok(config) } ``` ## Checklist - [ ] Custom error types use `thiserror` derive - [ ] Error context is added with `anyhow::Context` - [ ] No `unwrap()` calls in production code paths - [ ] `Result` is used instead of `panic!` for recoverable errors