thiserror 1.0.2

on Rust Cargo

Add a #[from] attribute to request an implementation of std::convert::From from your error's source error types, making it easy to build your error via the ? operator.

use thiserror::Error;

#[derive(Error, Debug)]
pub enum Error {
    Io(#[from] io::Error),
    Json(#[from] serde_json::Error),
    Regex(#[from] regex::Error),
    Other(#[from] anyhow::Error),
}

We only permit From to be derived from the error's source field, not any arbitrary other field. Notice that this allows #[from] to imply #[source] so you don't need to also specify #[source] explicitly.

The variant must not contain any other fields beyond the source error and possibly a backtrace. A backtrace is captured from within the From impl if there is a field for it.

#[derive(Error, Debug)]
pub enum MyError {
    Io {
        #[from]
        source: io::Error,
        backtrace: Backtrace,
    },
}

Named fields with the name source are assumed to be the error source and so no longer require an explicit #[source] attribute.

Enum variants now inherit the #[error(...)] attribute from atop the enum if there is one.

use thiserror::Error;

#[derive(Error, Debug)]
#[error("{0}")] // applies to every variant without its own attr
pub enum Error {
    Io(io::Error),
    Json(serde_json::Error),
    Regex(regex::Error),
    #[error("unknown error")]
    Unknown,
}