![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 <code>foo</code> 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](https://raw.githubusercontent.com/zkat/miette/main/images/serde_json.png)
mietteYou run miette? You run her code like the software? Oh. Oh! Error code for coder! Error code for One Thousand Lines!
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.
Diagnostic] protocol, compatible (and dependent on)
[std::error::Error].Diagnostic].anyhow/eyre
types [Result], [Report] and the [miette!] macro for the
anyhow!/eyre! macros.SourceCode]s for snippet data, with
default support for Strings included.The miette crate also comes bundled with a default [ReportHandler] with
the following features:
NO_COLOR,
and other heuristics.sh
$ cargo add miette
If you want to use the fancy printer in all these screenshots:
sh
$ cargo add miette --features fancy
``rust
/*
You can derive aDiagnosticfrom anystd::error::Error` type.
thiserror is a great way to define them, and plays nicely with miette!
*/
use miette::{Diagnostic, SourceSpan};
use thiserror::Error;
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. #[sourcecode] src: NamedSource, // Snippets and highlights can be included in the diagnostic! #[label("This bit here")] badbit: 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 thisfails() -> 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".tostring();
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 pretendthisismain() -> Result<()> {
// kaboom~
thisfails()?;
Ok(())
} ```
And this is the output you'll get if you run this program:
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.
```rust // lib/error.rs use miette::{Diagnostic, SourceSpan}; use thiserror::Error;
pub enum MyLibError { #[error(transparent)] #[diagnostic(code(mylib::ioerror))] 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),
}
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.
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::Errors 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 // myapp/lib/myinternal_file.rs use miette::{IntoDiagnostic, Result}; use semver::Version;
pub fn sometool() -> Result
miette also includes an anyhow/eyre-style Context/WrapErr traits
that you can import to add ad-hoc context messages to your Diagnostics, as
well, though you'll still need to use .into_diagnostic() to make use of
it:
```rust // myapp/lib/myinternal_file.rs use miette::{IntoDiagnostic, Result, WrapErr}; use semver::Version;
pub fn sometool() -> Result
To construct your own simple adhoc error use the [miette!] macro: ```rust // myapp/lib/myinternal_file.rs use miette::{miette, IntoDiagnostic, Result, WrapErr}; use semver::Version;
pub fn sometool() -> Result
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 pretendthisismain() -> Result<()> { let version: Version = "1.2.x".parse().intodiagnostic()?; 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"] }
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;
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;
code(my_app::my_error),
// Will link users to https://docs.rs/my_crate/0.0.0/my_crate/struct.MyErr.html
url(docsrs)
)]
struct MyErr; ```
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;
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>,
} ```
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;
struct Foo; ```
The other is by programmatically supplying the help text as a field to your diagnostic:
```rust use miette::Diagnostic; use thiserror::Error;
struct Foo {
#[help]
advice: OptionString
}
let err = Foo { advice: Some("try doing this instead".to_string()), }; ```
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;
struct MyError {
#[related]
others: Vec
Sometimes it makes sense to add source code to the error message later.
One option is to use with_source_code()
method for that:
```rust use miette::{Diagnostic, SourceSpan}; use thiserror::Error;
pub struct MyErrorType { // Note: label but no source code #[label] err_span: SourceSpan, }
fn dosomething() -> miette::Result<()> { // This function emits actual error with label return Err(MyErrorType { errspan: (7..11).into(), })?; }
fn main() -> miette::Result<()> { dosomething().maperr(|error| { // And this code provides the source code for inner error error.withsourcecode(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;
pub struct InnerError { // Note: label but no source code #[label] err_span: SourceSpan, }
pub struct MultiError {
// Note source code by no labels
#[sourcecode]
sourcecode: String,
// The source code above is used for these errors
#[related]
related: Vec
fn dosomething() -> Result<(), Vec
fn main() -> miette::Result<()> { dosomething().maperr(|errlist| MultiError { sourcecode: "source code".into(), related: err_list, })?; Ok(()) } ```
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;
struct MyError { #[source] #[diagnosticsource] thecause: OtherError, }
struct OtherError; ```
[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::sethook(Box::new(|| { Box::new( miette::MietteHandlerOpts::new() .terminallinks(true) .unicode(false) .contextlines(3) .tab_width(4) .build(), ) }))
```
See the docs for [MietteHandlerOpts] for more details on what you can
customize!
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".tostring(); let report = miette!( labels = vec[ LabeledSpan::at(12..13, "this should be 6"), ], help = "'*' has greater precedence than '+'", "Wrong answer" ).withsource_code(source); println!("{:?}", report) ```
miette was not developed in a void. It owes enormous credit to various
other projects and their authors:
anyhow and 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 for setting the standard
for library-level error definitions, and for being the inspiration behind
miette'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!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.