Human Errors

Errors which make your users' lives easier

This crate provides an Error type which has been designed to make errors something which help guide your users through your application rather than blocking their progress. It has fundamentally been designed with the expectation that any failure can be mitigated (even if that means cutting a GitHub issue) and that explaining to your user how to do so is the fastest way to get them moving again.

Features

• Advice on how to resolve a problem is a fundamental requirement for the creation of an error, making your developers think about the user experience at the point they write the code.
• Wrapping allows you to expose a causal chain which may incorporate advice from multiple layers in the stack - giving users a better sense of what failed and how to fix it.
• Integration with the std::error::Error type allows you to wrap any Box-able error in the causal chain and provide additional context.

Example

use std::fs;
use human_errors::{user_with_internal, Error};

fn main() {
    match read_file() {
        Ok(content) => println!("{}", content),
        Err(err) => eprintln!("{}", err),
    }
}

fn read_file() -> Result<String, Error> {
    fs::read_to_string("example.txt").map_err(|err| user_with_internal(
        "We could not read the contents of the example.txt file.",
        "Check that the file exists and that you have permission to access it.",
        err
    ))?
}

The above code might result in an error which, when printed, shows the following:

Oh no! We could not read the contents of the example.txt file.

This was caused by:
File Not Found

To try and fix this, you can:
 - Check that the file exists and that you have permission to access it.

Conversion

When working with errors from other crates and the standard library, you may find it valuable to implement From<OtherError> conversions into human_errors error types.

To make this as easy as possible, we expose a helper macro which will construct a human errors wrapper in your module which can then be easily extended. This macro will publish all of the familiar helper functions you are used to, including:

• user
• user_with_cause
• user_with_internal
• system
• system_with_cause
• system_with_internal

The errors generated by these helper methods will be of the type you provide (MyError in the example below).

error_shim!(MyError);

impl From<std::num::ParseIntError> for MyError {
    fn from(err: std::num::ParseIntError) -> Self {
        user_with_internal(
            "We could not parse the number you provided.",
            "Make sure that you're providing a number in the form 12345 or -12345.",
            err,
        )
    }
}