# `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 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!):
<img src="https://raw.githubusercontent.com/zkat/miette/main/images/serde_json.png" alt="Hi! miette also includes a screen-reader-oriented diagnostic printer that's enabled in various situations, such as when you use NO_COLOR or CLICOLOR settings, or on CI. This behavior is also fully configurable and customizable. For example, this is what this particular diagnostic will look like when the narrated printer is enabled:
\
Error: Received some bad JSON from the source. Unable to parse.
Caused by: missing field `foo` at line 1 column 1700
\
Begin snippet for https://api.nuget.org/v3/registration5-gz-semver2/json.net/index.json starting
at line 1, column 1659
\
snippet line 1: gs":["json"],"title":"","version":"1.0.0"},"packageContent":"https://api.nuget.o
highlight starting at line 1, column 1699: last parsing location
\
diagnostic help: This is a bug. It might be in ruget, or it might be in the
source you're using, but it's definitely a bug and should be reported.
diagnostic error code: ruget::api::bad_json
" />
> **NOTE: You must enable the `"fancy"` crate feature to get fancy report
output like in the screenshots above.** You should only do this in your
toplevel crate, as the fancy feature pulls in a number of dependencies that
libraries and such might not want.
### Table of Contents <!-- omit in toc -->
- [About](#about)
- [Features](#features)
- [Installing](#installing)
- [Example](#example)
- [Using](#using)
- [... in libraries](#-in-libraries)
- [... in application code](#-in-application-code)
- [... in `main()`](#-in-main)
- [... diagnostic code URLs](#-diagnostic-code-urls)
- [... snippets](#-snippets)
- [... multiple related errors](#-multiple-related-errors)
- [... delayed source code](#-delayed-source-code)
- [... handler options](#-handler-options)
- [Acknowledgements](#acknowledgements)
- [License](#license)
### 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.
- Replacements for [`anyhow`](https://docs.rs/anyhow)/[`eyre`](https://docs.rs/eyre)
types [`Result`], [`Report`] and the [`miette!`] macro for the
`anyhow!`/`eyre!` macros.
- Generic support for arbitrary [`SourceCode`]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](#about), using ANSI/Unicode text
- single- and multi-line highlighting support
- Screen reader/braille support, gated on [`NO_COLOR`](http://no-color.org/),
and other heuristics.
- Fully customizable graphical theming (or overriding the printers
entirely).
- Cause chain printing
- Turns diagnostic codes into links in [supported terminals](https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda).
### Installing
```sh
$ cargo add miette
```
If you want to use the fancy printer in all these screenshots:
```sh
$ cargo add miette --features fancy
```
### Example
```rust
/*
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 miette::{Diagnostic, SourceSpan};
use thiserror::Error;
#[derive(Error, Debug, Diagnostic)]
#[error("oops!")]
#[diagnostic(
code(oops::my::bad),
url(docsrs),
help("try doing it better next time?")
)]
struct MyBad {
// The Source that we're gonna be printing snippets out of.
// This can be a String if you don't have or care about file names.
#[source_code]
src: NamedSource,
// Snippets and highlights can be included in the diagnostic!
#[label("This bit here")]
bad_bit: SourceSpan,
}
/*
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 miette::{NamedSource, Result};
fn this_fails() -> Result<()> {
// You can use plain strings as a `Source`, or anything that implements
// the one-method `Source` trait.
let src = "source\n text\n here".to_string();
let len = src.len();
Err(MyBad {
src: NamedSource::new("bad_file.rs", src),
bad_bit: (9, 4).into(),
})?;
Ok(())
}
/*
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_hook()`
*/
fn pretend_this_is_main() -> Result<()> {
// kaboom~
this_fails()?;
Ok(())
}
```
And this is the output you'll get if you run this program:
<img src="https://raw.githubusercontent.com/zkat/miette/main/images/single-line-example.png" alt="
Narratable printout:
\
Error: Types mismatched for operation.
Diagnostic severity: error
Begin snippet starting at line 1, column 1
\
snippet line 1: 3 + "5"
label starting at line 1, column 1: int
label starting at line 1, column 1: doesn't support these values.
label starting at line 1, column 1: string
diagnostic help: Change int or string to be the right types and try again.
diagnostic code: nu::parser::unsupported_operation
For more details, see https://docs.rs/nu-parser/0.1.0/nu-parser/enum.ParseError.html#variant.UnsupportedOperation">
### 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`](https://docs.rs/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`.
```rust
// lib/error.rs
use miette::Diagnostic;
use thiserror::Error;
#[derive(Error, Diagnostic, Debug)]
pub enum MyLibError {
#[error(transparent)]
#[diagnostic(code(my_lib::io_error))]
IoError(#[from] std::io::Error),
#[error("Oops it blew up")]
#[diagnostic(code(my_lib::bad_code))]
BadThingHappened,
}
```
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:
```rust
// my_app/lib/my_internal_file.rs
use miette::{IntoDiagnostic, Result};
use semver::Version;
pub fn some_tool() -> Result<Version> {
Ok("1.2.x".parse().into_diagnostic()?)
}
```
`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:
```rust
// my_app/lib/my_internal_file.rs
use miette::{IntoDiagnostic, Result, WrapErr};
use semver::Version;
pub fn some_tool() -> Result<Version> {
Ok("1.2.x"
.parse()
.into_diagnostic()
.wrap_err("Parsing this tool's semver version failed.")?)
}
```
#### ... 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.
> **NOTE:** You must enable the `"fancy"` crate feature to get fancy report
output like in the screenshots here.** You should only do this in your
toplevel crate, as the fancy feature pulls in a number of dependencies that
libraries and such might not want.
```rust
use miette::{IntoDiagnostic, Result};
use semver::Version;
fn pretend_this_is_main() -> Result<()> {
let version: Version = "1.2.x".parse().into_diagnostic()?;
println!("{}", version);
Ok(())
}
```
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:
```toml
miette = { version = "X.Y.Z", features = ["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:
<img
src="https://raw.githubusercontent.com/zkat/miette/main/images/code_linking.png"
alt=" Example showing the graphical report printer for miette
pretty-printing an error code. The code is underlined and followed by text
saying to 'click here'. A hover tooltip shows a full-fledged URL that can be
Ctrl+Clicked to open in a browser.
\
This feature is also available in the narratable printer. It will add a line
after printing the error code showing a plain URL that you can visit.
">
To use this, you can add a `url()` sub-param to your `#[diagnostic]`
attribute:
```rust
use miette::Diagnostic;
use thiserror::Error;
#[derive(Error, Diagnostic, Debug)]
#[error("kaboom")]
#[diagnostic(
code(my_app::my_error),
// You can do formatting!
url("https://my_website.com/error_codes#{}", self.code().unwrap())
)]
struct MyErr;
```
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:
```rust
use miette::Diagnostic;
use thiserror::Error;
#[derive(Error, Diagnostic, Debug)]
#[diagnostic(
code(my_app::my_error),
// Will link users to https://docs.rs/my_crate/0.0.0/my_crate/struct.MyErr.html
url(docsrs)
)]
#[error("kaboom")]
struct MyErr;
```
#### ... snippets
Along with its general error handling and reporting features, `miette` also
includes facilities for adding error spans/annotations/labels 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 [`SourceCode`]
and, along with the latter, gives `miette` all the information it needs to
pretty-print some snippets! You can also use your own `Into<SourceSpan>`
types as label spans.
The easiest way to define errors like this is to use the
`derive(Diagnostic)` macro:
```rust
use miette::{Diagnostic, SourceSpan};
use thiserror::Error;
#[derive(Diagnostic, Debug, Error)]
#[error("oops")]
#[diagnostic(code(my_lib::random_error))]
pub struct MyErrorType {
// The `Source` that miette will use.
#[source_code]
src: String,
// This will underline/mark the specific code inside the larger
// snippet context.
#[label = "This is the highlight"]
err_span: SourceSpan,
// You can add as many labels as you want.
// They'll be rendered sequentially.
#[label("This is bad")]
snip2: (usize, usize), // `(usize, usize)` is `Into<SourceSpan>`!
// Snippets can be optional, by using Option:
#[label("some text")]
snip3: Option<SourceSpan>,
// with or without label text
#[label]
snip4: Option<SourceSpan>,
}
```
##### ... help text
`miette` provides two facilities for supplying help text for your errors:
The first is the `#[help()]` format attribute that applies to structs or
enum variants:
```rust
use miette::Diagnostic;
use thiserror::Error;
#[derive(Debug, Diagnostic, Error)]
#[error("welp")]
#[diagnostic(help("try doing this instead"))]
struct Foo;
```
The other is by programmatically supplying the help text as a field to
your diagnostic:
```rust
use miette::Diagnostic;
use thiserror::Error;
#[derive(Debug, Diagnostic, Error)]
#[error("welp")]
#[diagnostic()]
struct Foo {
#[help]
advice: Option<String>, // Can also just be `String`
}
let err = Foo {
advice: Some("try doing this instead".to_string()),
};
```
#### ... multiple related errors
`miette` supports collecting multiple errors into a single diagnostic, and
printing them all together nicely.
To do so, use the `#[related]` tag on any `IntoIter` field in your
`Diagnostic` type:
```rust
use miette::Diagnostic;
use thiserror::Error;
#[derive(Debug, Error, Diagnostic)]
#[error("oops")]
struct MyError {
#[related]
others: Vec<MyError>,
}
```
#### ... delayed source code
Sometimes it makes sense to add source code to the error message later.
One option is to use [`with_source_code()`](Report::with_source_code)
method for that:
```rust
use miette::{Diagnostic, SourceSpan};
use thiserror::Error;
#[derive(Diagnostic, Debug, Error)]
#[error("oops")]
#[diagnostic()]
pub struct MyErrorType {
// Note: label but no source code
#[label]
err_span: SourceSpan,
}
fn do_something() -> miette::Result<()> {
// This function emits actual error with label
return Err(MyErrorType {
err_span: (7..11).into(),
})?;
}
fn main() -> miette::Result<()> {
do_something().map_err(|error| {
// And this code provides the source code for inner error
error.with_source_code(String::from("source code"))
})
}
```
Also source code can be provided by a wrapper type. This is especially
useful in combination with `related`, when multiple errors should be
emitted at the same time:
```rust
use miette::{Diagnostic, Report, SourceSpan};
use thiserror::Error;
#[derive(Diagnostic, Debug, Error)]
#[error("oops")]
#[diagnostic()]
pub struct InnerError {
// Note: label but no source code
#[label]
err_span: SourceSpan,
}
#[derive(Diagnostic, Debug, Error)]
#[error("oops: multiple errors")]
#[diagnostic()]
pub struct MultiError {
// Note source code by no labels
#[source_code]
source_code: String,
// The source code above is used for these errors
#[related]
related: Vec<InnerError>,
}
fn do_something() -> Result<(), Vec<InnerError>> {
Err(vec![
InnerError {
err_span: (0..6).into(),
},
InnerError {
err_span: (7..11).into(),
},
])
}
fn main() -> miette::Result<()> {
do_something().map_err(|err_list| MultiError {
source_code: "source code".into(),
related: err_list,
})?;
Ok(())
}
```
#### ... Diagnostic-based error sources.
When one uses the `#[source]` attribute on a field, that usually comes
from `thiserror`, and implements a method for
[`std::error::Error::source`]. This works in many cases, but it's lossy:
if the source of the diagnostic is a diagnostic itself, the source will
simply be treated as an `std::error::Error`.
While this has no effect on the existing _reporters_, since they don't use
that information right now, APIs who might want this information will have
no access to it.
If it's important for you for this information to be available to users,
you can use `#[diagnostic_source]` alongside `#[source]`. Not that you
will likely want to use _both_:
```rust
use miette::Diagnostic;
use thiserror::Error;
#[derive(Debug, Diagnostic, Error)]
#[error("MyError")]
struct MyError {
#[source]
#[diagnostic_source]
the_cause: OtherError,
}
#[derive(Debug, Diagnostic, Error)]
#[error("OtherError")]
struct OtherError;
```
#### ... handler options
[`MietteHandler`] is the default handler, and is very customizable. In
most cases, you can simply use [`MietteHandlerOpts`] to tweak its behavior
instead of falling back to your own custom handler.
Usage is like so:
```rust
See the docs for [`MietteHandlerOpts`] for more details on what you can
customize!
### Acknowledgements
`miette` was not developed in a void. It owes enormous credit to various
other projects and their authors:
- [`anyhow`](http://crates.io/crates/anyhow) and
[`color-eyre`](https://crates.io/crates/color-eyre): these two
enormously influential error handling libraries have pushed forward the
experience of application-level error handling and error reporting.
`miette`'s `Report` type is an attempt at a very very rough version of
their `Report` types.
- [`thiserror`](https://crates.io/crates/thiserror) for setting the
standard for library-level error definitions, and for being the
inspiration behind `miette`'s derive macro.
- `rustc` and [@estebank](https://github.com/estebank) for their
state-of-the-art work in compiler diagnostics.
- [`ariadne`](https://crates.io/crates/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](./LICENSE).
It also includes code taken from [`eyre`](https://github.com/yaahc/eyre),
and some from [`thiserror`](https://github.com/dtolnay/thiserror), also
under the Apache License. Some code is taken from
[`ariadne`](https://github.com/zesterer/ariadne), which is MIT licensed.
[`miette!`]: https://docs.rs/miette/latest/miette/macro.miette.html
[`std::error::Error`]: https://doc.rust-lang.org/nightly/std/error/trait.Error.html
[`Diagnostic`]: https://docs.rs/miette/latest/miette/trait.Diagnostic.html
[`IntoDiagnostic`]: https://docs.rs/miette/latest/miette/trait.IntoDiagnostic.html
[`MietteHandlerOpts`]: https://docs.rs/miette/latest/miette/struct.MietteHandlerOpts.html
[`MietteHandler`]: https://docs.rs/miette/latest/miette/struct.MietteHandler.html
[`Report`]: https://docs.rs/miette/latest/miette/struct.Report.html
[`ReportHandler`]: https://docs.rs/miette/latest/miette/struct.ReportHandler.html
[`Result`]: https://docs.rs/miette/latest/miette/type.Result.html
[`SourceCode`]: https://docs.rs/miette/latest/miette/struct.SourceCode.html
[`SourceSpan`]: https://docs.rs/miette/latest/miette/struct.SourceSpan.html