facet-error

facet-error

A thiserror replacement powered by facet reflection. This crate is a plugin for #[derive(Facet)] that generates Display and Error trait implementations from doc comments.

Usage

use facet::Facet;

#[derive(Facet, Debug)]
#[facet(derive(Error))]
#[repr(u8)]
pub enum MyError {
    /// something went wrong
    Unknown,

    /// invalid value: {0}
    InvalidValue(String),

    /// invalid header (expected {expected}, found {found})
    InvalidHeader { expected: String, found: String },
}

This generates:

• impl Display for MyError using doc comments as format strings
• impl Error for MyError with proper source() implementation
• Field interpolation works automatically for struct variants (e.g., {expected}, {found})
• Tuple variants support positional interpolation (e.g., {0})

Features

• Doc-driven Display: Doc comments become your error messages
• Field interpolation: Reference struct fields by name in messages
• Zero boilerplate: No manual Display or Error implementations
• Integration with facet: Works seamlessly with the facet reflection system

Future Work

• #[facet(error::source)] - mark fields as error sources
• #[facet(error::from)] - generate From implementations
• Support for error wrapping and transparent delegation

Sponsors

Thanks to all individual sponsors:

...along with corporate sponsors:

...without whom this work could not exist.

Special thanks

The facet logo was drawn by Misiasart.

License

Licensed under either of:

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.