Derive basic error type infrastruture for enum types.

Supports unnamed and unit enum variants, and uses the type definition to derive std::fmt::Display and std::error:Error for the error type, as well as std::from::From<T> for any unnamed variant with one parameter inferred to be an error type (currently determined by whether it's type name is Error).

Default behaviour can be overridden with the auto_error attribute

• format_str takes a string which becomes the format string for that variant
• make_from forces derivation of std::from::From when set to true
• err forces the std::error::Error implementation to return the inner type during calls to source, or in other words to treat the inner type as an error type.

From derivation and source returning work only for variants with a single field.

Example

#[derive(AutoError)]
use autoerror::AutoError;

enum Error {
    #[auto_error(format_str="Document not found")]
    NotFound,
    IO(std::io::Error),
    #[auto_error(make_from=true)]
    Other(String),
}