vincent119/rust-error-handling

Rust 錯誤處理

Library 錯誤設計（M-ERRORS-CANONICAL-STRUCTS）

使用 canonical error struct，不用 enum：

use std::fmt;

#[derive(Debug)]
pub struct ParseConfigError {
    kind: ParseConfigErrorKind,
    source: Option<Box<dyn std::error::Error + Send + Sync>>,
}

#[derive(Debug)]
enum ParseConfigErrorKind {
    InvalidFormat,
    MissingField(&'static str),
    IoError,
}

impl fmt::Display for ParseConfigError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match &self.kind {
            ParseConfigErrorKind::InvalidFormat => write!(f, "invalid config format"),
            ParseConfigErrorKind::MissingField(field) => write!(f, "missing field: {field}"),
            ParseConfigErrorKind::IoError => write!(f, "io error reading config"),
        }
    }
}

impl std::error::Error for ParseConfigError {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        self.source.as_deref()
    }
}

Application 錯誤（M-APP-ERROR）

Application 層可用 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")?;
    Ok(config)
}

thiserror（Library 快速定義）

use thiserror::Error;

#[derive(Debug, Error)]
pub enum ServiceError {
    #[error("not found: {0}")]
    NotFound(String),
    #[error("unauthorized")]
    Unauthorized,
    #[error(transparent)]
    Internal(#[from] anyhow::Error),
}

規則

• Library crate：自訂 error struct/enum + std::error::Error
• Application crate：anyhow::Result 或 eyre::Result
• 禁止 unwrap()/expect() 在 production path
• 用 ? 傳播；用 .context() 加上下文
• Panic 僅用於不可恢復的程式 bug