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 library for Rust. It includes a series of
traits/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!):
Table of Contents
Features
- Generic [Diagnostic] protocol, compatible (and dependent on)
std::error::Error
. - Unique error codes on every [Diagnostic].
- Custom links to get more details on error codes.
- Super handy derive macro for defining diagnostic metadata.
anyhow
/eyre
-compatible error wrapper type, [Report], which can be returned frommain
.- Generic support for arbitrary [Source]s for snippet data, with default support for
String
s included.
The miette
crate also comes bundled with a default [ReportHandler] with the following features:
- Fancy graphical diagnostic output, using ANSI/Unicode text
- single- and multi-line highlighting support
- Screen reader/braille support, gated on
NO_COLOR
, and other heuristics. - Fully customizable graphical theming (or overriding the printers entirely).
- Cause chain printing
- Turns diagnostic codes into links in supported terminals.
Installing
Using cargo-edit
:
If you want to use the fancy printer in all these screenshots:
Example
/*
You can derive a Diagnostic from any `std::error::Error` type.
`thiserror` is a great way to define them, and plays nicely with `miette`!
*/
use ;
use Error;
/*
Now let's define a function!
Use this Result type (or its expanded version) as the return type
throughout your app (but NOT your libraries! Those should always return concrete
types!).
*/
use ;
/*
Now to get everything printed nicely, just return a Result<()>
and you're all set!
Note: You can swap out the default reporter for a custom one using `miette::set_reporter()`
*/
And this is the output you'll get if you run this program:
Using
... in libraries
miette
is fully compatible with library usage. Consumers who don't know
about, or don't want, miette
features can safely use its error types as
regular [std::error::Error].
We highly recommend using something like thiserror
to define unique error types and error wrappers for your library.
While miette
integrates smoothly with thiserror
, it is not required. If
you don't want to use the [Diagnostic] derive macro, you can implement the
trait directly, just like with std::error::Error
.
// lib/error.rs
use Error;
use Diagnostic;
Then, return this error type from all your fallible public APIs. It's a best
practice to wrap any "external" error types in your error enum
instead of
using something like [Report] in a library.
... in application code
Application code tends to work a little differently than libraries. You don't always need or care to define dedicated error wrappers for errors coming from external libraries and tools.
For this situation, miette
includes two tools: [Report] and
[IntoDiagnostic]. They work in tandem to make it easy to convert regular
std::error::Error
s into [Diagnostic]s. Additionally, there's a
[Result] type alias that you can use to be more terse.
When dealing with non-Diagnostic
types, you'll want to .into_diagnostic()
them:
// my_app/lib/my_internal_file.rs
use ;
use Version;
miette
also includes an anyhow
/eyre
-style Context
/WrapErr
traits that
you can import to add ad-hoc context messages to your Diagnostic
s, as well,
though you'll still need to use .into_diagnostic()
to make use of it:
// my_app/lib/my_internal_file.rs
use ;
use Version;
... in main()
main()
is just like any other part of your application-internal code. Use
Result
as your return value, and it will pretty-print your
diagnostics automatically.
use ;
use Version;
Please note: in order to get fancy diagnostic rendering with all the pretty
colors and arrows, you should install miette
with the fancy
feature
enabled:
= { = "X.Y.Z", = ["fancy"] }
... diagnostic code URLs
miette
supports providing a URL for individual diagnostics. This URL will be
displayed as an actual link in supported terminals, like so:
To use this, you can add a url()
sub-param to your #[diagnostic]
attribute:
use Diagnostic;
use Error;
;
Additionally, if you're developing a library and your error type is exported
from your crate's top level, you can use a special url(docsrs)
option
instead of manually constructing the URL. This will automatically create a
link to this diagnostic on docs.rs
, so folks can just go straight to
your (very high quality and detailed!) documentation on this diagnostic:
use Diagnostic;
use Error;
;
... snippets
Along with its general error handling and reporting features, miette
also
includes facilities for adding error spans and annotations/highlights to your
output. This can be very useful when an error is syntax-related, but you can
even use it to print out sections of your own source code!
To achieve this, miette
defines its own lightweight [SourceSpan] type. This
is a basic byte-offset and length into an associated [Source] and, along with
the latter, gives miette
all the information it needs to pretty-print some
snippets!
The easiest way to define errors like this is to use the derive(Diagnostic)
macro:
use ;
use Error;
Acknowledgements
miette
was not developed in a void. It owes enormous credit to various other projects and their authors:
anyhow
andcolor-eyre
: these two enormously influential error handling libraries have pushed forward the experience of application-level error handling and error reporting.miette
'sReport
type is an attempt at a very very rough version of theirReport
types.thiserror
for setting the standard for library-level error definitions, and for being the inspiration behindmiette
's derive macro.rustc
and @estebank for their state-of-the-art work in compiler diagnostics.ariadne
for pushing forward how pretty these diagnostics can really look!
License
miette
is released to the Rust community under the Apache license 2.0.
It also includes code taken from eyre
,
and some from thiserror
, also under
the Apache License. Some code is taken from
ariadne
, which is MIT licensed.