https://github.com/zkat/miette

Fancy extension for std::error::Error with pretty, detailed diagnostic printing.
https://github.com/zkat/miette

error-handling error-reporting hacktoberfest hacktoberfest2021 rust

Last synced: 15 days ago
JSON representation

Fancy extension for std::error::Error with pretty, detailed diagnostic printing.

• Host: GitHub
• URL: https://github.com/zkat/miette
• Owner: zkat
• License: apache-2.0
• Created: 2021-08-03T02:30:49.000Z (over 3 years ago)
• Default Branch: main
• Last Pushed: 2024-09-26T16:32:58.000Z (about 2 months ago)
• Last Synced: 2024-10-27T10:06:40.572Z (17 days ago)
• Topics: error-handling, error-reporting, hacktoberfest, hacktoberfest2021, rust
• Language: Rust
• Homepage: https://docs.rs/miette
• Size: 1.86 MB
• Stars: 2,001
• Watchers: 15
• Forks: 114
• Open Issues: 79
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGELOG.md
  • Contributing: CONTRIBUTING.md
  • Funding: .github/FUNDING.yml
  • License: LICENSE
  • Code of conduct: CODE_OF_CONDUCT.md

Awesome Lists containing this project

README

        

# `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!):



> **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 

- [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)

  - [... help text](#-help-text)

  - [... severity level](#-severity-level)

  - [... multiple related errors](#-multiple-related-errors)

  - [... delayed source code](#-delayed-source-code)

  - [... handler options](#-handler-options)

  - [... dynamic diagnostics](#-dynamic-diagnostics)

  - [... syntax highlighting](#-syntax-highlighting)

  - [... collection of labels](#-collection-of-labels)

- [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();

    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:



### 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, SourceSpan};

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,

    #[error(transparent)]

    // Use `#[diagnostic(transparent)]` to wrap another [`Diagnostic`]. You won't see labels otherwise

    #[diagnostic(transparent)]

    AnotherError(#[from] AnotherError),

}

#[derive(Error, Diagnostic, Debug)]

#[error("another error")]

pub struct AnotherError {

   #[label("here")]

   pub at: SourceSpan

}

```

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 {

    "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 {

    "1.2.x"

        .parse()

        .into_diagnostic()

        .wrap_err("Parsing this tool's semver version failed.")

}

```

To construct your own simple adhoc error use the [miette!] macro:

```rust

// my_app/lib/my_internal_file.rs

use miette::{miette, Result};

use semver::Version;

pub fn some_tool() -> Result {

    let version = "1.2.x";

    version

        .parse()

        .map_err(|_| miette!("Invalid version {}", version))

}

```

There are also similar [bail!] and [ensure!] macros.

#### ... 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"] }

```

Another way to display a diagnostic is by printing them using the debug formatter.

This is, in fact, what returning diagnostics from main ends up doing.

To do it yourself, you can write the following:

```rust

use miette::{IntoDiagnostic, Result};

use semver::Version;

fn just_a_random_function() {

    let version_result: Result = "1.2.x".parse().into_diagnostic();

    match version_result {

        Err(e) => println!("{:?}", e),

        Ok(version) => println!("{}", version),

    }

}

```

#### ... 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:

```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`

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`!

    // Snippets can be optional, by using Option:

    #[label("some text")]

    snip3: Option,

    // with or without label text

    #[label]

    snip4: Option,

}

```

#### ... 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, // Can also just be `String`

}

let err = Foo {

    advice: Some("try doing this instead".to_string()),

};

```

#### ... severity level

`miette` provides a way to set the severity level of a diagnostic.

```rust

use miette::Diagnostic;

use thiserror::Error;

#[derive(Debug, Diagnostic, Error)]

#[error("welp")]

#[diagnostic(severity(Warning))]

struct Foo;

```

#### ... 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,

}

```

#### ... 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,

}

fn do_something() -> Result<(), Vec> {

    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

miette::set_hook(Box::new(|_| {

    Box::new(

        miette::MietteHandlerOpts::new()

            .terminal_links(true)

            .unicode(false)

            .context_lines(3)

            .tab_width(4)

            .break_words(true)

            .build(),

    )

}))

```

See the docs for [`MietteHandlerOpts`] for more details on what you can

customize!

#### ... dynamic diagnostics

If you...

- ...don't know all the possible errors upfront

- ...need to serialize/deserialize errors

  then you may want to use [`miette!`], [`diagnostic!`] macros or

  [`MietteDiagnostic`] directly to create diagnostic on the fly.

```rust

let source = "2 + 2 * 2 = 8".to_string();

let report = miette!(

  labels = vec![

      LabeledSpan::at(12..13, "this should be 6"),

  ],

  help = "'*' has greater precedence than '+'",

  "Wrong answer"

).with_source_code(source);

println!("{:?}", report)

```

#### ... syntax highlighting

`miette` can be configured to highlight syntax in source code snippets.

To use the built-in highlighting functionality, you must enable the

`syntect-highlighter` crate feature. When this feature is enabled, `miette` will

automatically use the [`syntect`] crate to highlight the `#[source_code]`

field of your [`Diagnostic`].

Syntax detection with [`syntect`] is handled by checking 2 methods on the [`SpanContents`] trait, in order:

* [`language()`](SpanContents::language) - Provides the name of the language

  as a string. For example `"Rust"` will indicate Rust syntax highlighting.

  You can set the language of the [`SpanContents`] produced by a

  [`NamedSource`] via the [`with_language`](NamedSource::with_language)

  method.

* [`name()`](SpanContents::name) - In the absence of an explicitly set

  language, the name is assumed to contain a file name or file path.

  The highlighter will check for a file extension at the end of the name and

  try to guess the syntax from that.

If you want to use a custom highlighter, you can provide a custom

implementation of the [`Highlighter`](highlighters::Highlighter)

trait to [`MietteHandlerOpts`] by calling the

[`with_syntax_highlighting`](MietteHandlerOpts::with_syntax_highlighting)

method. See the [`highlighters`] module docs for more details.

#### ... collection of labels

When the number of labels is unknown, you can use a collection of `SourceSpan`

(or any type convertible into `SourceSpan`). For this, add the `collection`

parameter to `label` and use any type than can be iterated over for the field.

```rust

#[derive(Debug, Diagnostic, Error)]

#[error("oops!")]

struct MyError {

    #[label("main issue")]

    primary_span: SourceSpan,

    #[label(collection, "related to this")]

    other_spans: Vec>,

}

let report: miette::Report = MyError {

    primary_span: (6, 9).into(),

    other_spans: vec![19..26, 30..41],

}.into();

println!("{:?}", report.with_source_code("About something or another or yet another ...".to_string()));

```

A collection can also be of `LabeledSpan` if you want to have different text

for different labels. Labels with no text will use the one from the `label`

attribute

```rust

#[derive(Debug, Diagnostic, Error)]

#[error("oops!")]

struct MyError {

    #[label("main issue")]

    primary_span: SourceSpan,

    #[label(collection, "related to this")]

    other_spans: Vec, // LabeledSpan

}

let report: miette::Report = MyError {

    primary_span: (6, 9).into(),

    other_spans: vec![

        LabeledSpan::new(None, 19, 7), // Use default text `related to this`

        LabeledSpan::new(Some("and also this".to_string()), 30, 11), // Use specific text

    ],

}.into();

println!("{:?}", report.with_source_code("About something or another or yet another ...".to_string()));

```

### MSRV

This crate requires rustc 1.70.0 or later.

### 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

[`diagnostic!`]: https://docs.rs/miette/latest/miette/macro.diagnostic.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

[`MietteDiagnostic`]: https://docs.rs/miette/latest/miette/struct.MietteDiagnostic.html

[`Report`]: https://docs.rs/miette/latest/miette/struct.Report.html

[`ReportHandler`]: https://docs.rs/miette/latest/miette/trait.ReportHandler.html

[`Result`]: https://docs.rs/miette/latest/miette/type.Result.html

[`SourceCode`]: https://docs.rs/miette/latest/miette/trait.SourceCode.html

[`SourceSpan`]: https://docs.rs/miette/latest/miette/struct.SourceSpan.html