miette

you run miette? You run her code like the software? Oh. Oh! Error code for coder! Error code for One Thousand Lines!

About

miette is a diagnostic definition library for Rust. It includes a series of protocols that allow you to hook into its error reporting facilities, and even write your own error reports! It lets you define error types that can print out like this (or in any format you like!):

Error: Error[oops::my::bad]: oops it broke!

[bad_file.rs] This is the part that broke:

    1  | source
    2  |   text
    ⫶  |   ^^^^ this bit here
    3  |     here

﹦try doing it better next time?

The [Diagnostic] trait in miette is an extension of std::error::Error that adds various facilities like [Severity], error codes that could be looked up by users, and snippet display with support for multiline reports, arbitrary [Source]s, and pretty printing.

While the miette crate bundles some baseline implementations for [Source] and [DiagnosticReporter], it's intended to define a protocol that other crates can build on top of to provide rich error reporting, and encourage an ecosystem that leans on this extra metadata to provide it for others in a way that's compatible with [std::error::Error]

Installing

Using cargo-edit:

$ cargo add miette

Example and Guide

/*
You can derive a Diagnostic from any `std::error::Error` type.

`thiserror` is a great way to define them so, and plays extremely nicely with `miette`!
*/
use miette::Diagnostic;
use thiserror::Error;

#[derive(Error, Diagnostic)]
#[error("oops it broke!")]
#[diagnostic(
    code(oops::my::bad),
    severity(Warning),
    help("try doing it better next time?"),
)]
struct MyBad {
    src: String,
    // Snippets and highlights can be included in the diagnostic!
    #[snippet(src, "This is the part that broke")]
    snip: SourceSpan,
    #[highlight(snip)]
    bad_bit: SourceSpan,
}

/*
Then, we implement `std::fmt::Debug` using the included `MietteReporter`,
which is able to pretty print diagnostics reasonably well.

You can use any reporter you want here, or no reporter at all,
but `Debug` is required by `std::error::Error`, so you need to at
least derive it.

Make sure you pull in the `miette::DiagnosticReporter` trait!.
*/
use std::fmt;

use miette::{DiagnosticReporter, MietteReporter};

impl fmt::Debug for MyBad {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        MietteReporter.debug(self, f)
    }
}

/*
Now we can use `miette`~
*/
use miette::{MietteError, SourceSpan};

fn pretend_this_is_main() -> Result<(), MyBad> {
    // You can use plain strings as a `Source`, bu the protocol is fully extensible!
    let src = "source\n  text\n    here".to_string();
    let len = src.len();

    Err(MyBad {
        src,
        snip: ("bad_file.rs", 0, len).into(),
        bad_bit: ("this bit here", 9, 3).into(),
    })
}

And this is the output you'll get if you run this program:

Error: Error[oops::my::bad]: oops it broke!

[bad_file.rs] This is the part that broke:

    1  | source
    2  |   text
    ⫶  |   ^^^^ this bit here
    3  |     here

﹦try doing it better next time?

License

miette is released to the Rust community under the MIT license.

It also includes some code taken from eyre, also under the MIT license.