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::{Error, ResultExt};

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").wrap_err_as_user(
        "We could not read the contents of the example.txt file.",
        &["Check that the file exists and that you have permission to access it."]
    ))?
}

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.

Getting Started

The easiest way to construct a human-errors Error is to use the user and system helper functions. These allow you to quickly create errors of either kind with a message and advice for how to resolve the issue.

use human_errors;

human_errors::user(
    "We could not find the configuration file.",
    &["Make sure that you've specified a valid config file with the --config option."]
);

human_errors::system(
    "A low-level IO error occurred.",
    &["Please try again later or contact support if the issue persists."]
);

These methods can also be used to wrap existing errors, adding advice on how to best deal with them.

use std::fs;

fn read_config() -> Result<String, human_errors::Error> {
    fs::read_to_string("config.toml").map_err(|err| {
        human_errors::user(
            err,
            &["Make sure that you've specified a valid config file with the --config option."]
        )
    })
}

If you find yourself wanting to add a better error message, you can use the wrap_user and wrap_system methods to add additional context to an existing error.

use std::fs;
use human_errors;

fn read_config() -> Result<String, human_errors::Error> {
    fs::read_to_string("config.toml").map_err(|err| {
        human_errors::wrap_user(
            err,
            "We could not read the 'config.toml' configuration file.",
            &[
                "Make sure that the 'config.toml' configuration file exists.",
                "Ensure that you have permission to read the 'config.toml' file.",
            ]
        )
    })
}

Working with Results

To make working with Result types easier, we provide the ResultExt trait which adds several helper methods to the standard Result type. These include wrap_err_as_user and wrap_err_as_system which allow you to easily convert any error in a Result into a human-errors Error of the desired kind.

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

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

Pretty Printing

Errors produced by this library implement the Display trait to provide a human-friendly rendering of the error message and its advice. However, if you want to customize the rendering further, you can use the pretty feature which enables you to use the pretty function to format errors in a nice, human-readable, way.

use human_errors;

let err = human_errors::user(
    "We could not connect to the database.",
    &["Check that the database server is running.", "Verify your network connection."]
);

eprintln!("{}", human_errors::pretty(err));