err-derive

A failure-like derive macro for the std Error. The source code is mostly copied from failure-derive.

Minimum Rust version: 1.34.0

Motivation

Why yet another error handling library? There already are dozen others, the most popular being:

• failure
• error-chain

The former provides a nice #[derive(Fail)] macro, but it uses its own error type (Fail) and its usage is rather discouraged since std::error::Error is getting fixed to provide the same benefits as Fail.

error-chain does support std::error::Error, but it uses a declarative for generating the error implementation which makes the syntax too obscure in my opinion.

This crate tries to combine both advantages:

• work with std::error::Error
• provide a custom #[derive(Error)] that works just like failure-derive

err-derive is compatible with std, including the recent change to deprecate Error::cause in favour of Error::source, and provides an easy syntax for generating the Display and Error boilerplate (the latter being 99% copied from failure-derive).

Features

err-derive can be applied to your error struct / enum and does the following for you:

• Derive Display implementation
• Derive Error implementation (implementing source to return the cause of the error)
• Derive From<OtherError> implementations

Usage

Cargo.toml:

toml [dependencies] err-derive = "0.1"

Rust code:

```rust,no_run

[cfg(feature = "std")]

use std::error::Error;

[cfg(not(feature = "std"))]

use std::fmt::Display; use std::path::PathBuf;

use err_derive::Error;

[derive(Debug, Error)]

pub enum FormatError { #[error(display = "invalid header (expected: {:?}, got: {:?})", expected, found)] InvalidHeader { expected: String, found: String, }, #[error(display = "missing attribute: {:?}", _0)] MissingAttribute(String), }

[derive(Debug, Error)]

pub enum LoadingError { #[error(display = "could not decode file")] FormatError(#[error(source)] FormatError), #[error(display = "could not find file: {:?}", path)] NotFound { path: PathBuf }, }

fn main() { let myerror: LoadingError = FormatError::MissingAttribute("someattr".to_owned()).into();

print_error(&my_error);

}

[cfg(feature = "std")]

fn print_error(e: &dyn Error) { eprintln!("error: {}", e); let mut cause = e.source(); while let Some(e) = cause { eprintln!("caused by: {}", e); cause = e.source(); } }

[cfg(not(feature = "std"))]

fn print_error(e: &dyn Display) { eprintln!("error: {}", e); } ```

no_std

You can use this library in your #![no_std] projects by disabling the default std feature.

toml [dependencies] err-derive = { version = "...", default-features = false }

Without the default std feature, only the From and Display implementations are derived, as Error requires std.

Credit

Credit goes to @withoutboats and other contributors of failure.

License

This project is dual-licensed under Apache-2.0 / MIT. You're free to choose one of both licenses. Every contribution made to this project is assumed to be licensed according to these terms.

See LICENSE, LICENSE-MIT and LICENSE-APACHE for more information.