Simple Error wrapper to ensure Clone, Debug, and PartialEq.

In general it is recommended that error types implement not just [Error] and it's required [Display], but also [Clone], [Debug], and [PartialEq] although [Eq] is optional. Beyond these additional traits are added as normal such as Copy, PartialOrd, Ord, Hash, etc.

However, there are a number of error types in the standard library, and many more in commonly used traits that do not meet this requirement. This simple crate introduces a new trait, [ExtendedError], which provides these additional requirements and a new concrete type, [FlatError] which provides a way to capture existing errors such that they meet these requirements.

The following demonstrates a new type that meets the requirements of ExtendedError.

use std::{
    error::Error,
    fmt::{Display, Formatter, Result as FmtResult},
};

#[derive(Clone, Debug, PartialEq)]
pub struct MyError;

impl Display for MyError {
    fn fmt(&self, f: &mut Formatter<'_>) -> FmtResult {
        write!(f, "MyError")
    }
}

impl Error for MyError {}

However, the following fails because the error in std::io does not implement either Clone or PartialEq.

use std::{
    error::Error,
    fmt::{Display, Formatter, Result as FmtResult},
    io::Error as IoError,
};

#[derive(Clone, Debug, PartialEq)]
pub enum MyError {
    Io(IoError), // <= this doesn't work.
}

FlatError allows the capture and flattening of these errors into MyError, as shown below. This does however lose the ability to access any specific methods on the flattened error such as last_os_error on std::io::Error.

use flat_error::FlatError;
use std::{
    error::Error,
    fmt::{Display, Formatter, Result as FmtResult},
    io::Error as IoError,
};

#[derive(Clone, Debug, PartialEq)]
pub enum MyError {
    Io(FlatError),
}

The contents of this repository are made available under the following licenses:

Copyright 2025 Simon Johnston <[email protected]>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

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See the enclosed file LICENSE-Apache.

Copyright 2025 Simon Johnston <[email protected]>

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