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error-stack

error-stack is a context-aware error-handling library that supports arbitrary attached user data.

Read our announcement post for the story behind its origins.

The library enables building a Report around an error as it propagates:

use std::fmt;

use error_stack::{Context, IntoReport, Report, Result, ResultExt};

#[derive(Debug)]
struct ParseExperimentError;

impl fmt::Display for ParseExperimentError {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt.write_str("invalid experiment description")
    }
}

impl Context for ParseExperimentError {}

fn parse_experiment(description: &str) -> Result<(u64, u64), ParseExperimentError> {
    let value = description
        .parse()
        .into_report()
        .attach_printable_lazy(|| format!("{description:?} could not be parsed as experiment"))
        .change_context(ParseExperimentError)?;

    Ok((value, 2 * value))
}

#[derive(Debug)]
struct ExperimentError;

impl fmt::Display for ExperimentError {
    fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
        fmt.write_str("experiment error: could not run experiment")
    }
}

impl Context for ExperimentError {}

fn start_experiments(
    experiment_ids: &[usize],
    experiment_descriptions: &[&str],
) -> Result<Vec<u64>, ExperimentError> {
    let experiments = experiment_ids
        .iter()
        .map(|exp_id| {
            let description = experiment_descriptions.get(*exp_id).ok_or_else(|| {
                Report::new(ExperimentError)
                    .attach_printable(format!("experiment {exp_id} has no valid description"))
            })?;

            let experiment = parse_experiment(description)
                .attach_printable(format!("experiment {exp_id} could not be parsed"))
                .change_context(ExperimentError)?;

            Ok(move || experiment.0 * experiment.1)
        })
        .collect::<Result<Vec<_>, ExperimentError>>()
        .attach_printable("unable to set up experiments")?;

    Ok(experiments.iter().map(|experiment| experiment()).collect())
}

fn main() -> Result<(), ExperimentError> {
    let experiment_ids = &[0, 2];
    let experiment_descriptions = &["10", "20", "3o"];
    start_experiments(experiment_ids, experiment_descriptions)?;

    Ok(())
}

This will most likely result in an error and print

Error: experiment error: could not run experiment
├╴at examples/demo.rs:51:18
├╴unable to set up experiments
│
├─▶ invalid experiment description
│   ├╴at examples/demo.rs:21:10
│   ╰╴experiment 2 could not be parsed
│
╰─▶ invalid digit found in string
    ├╴at examples/demo.rs:19:10
    ├╴backtrace with 31 frames (1)
    ╰╴"3o" could not be parsed as experiment

━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

backtrace no. 1
   0: std::backtrace_rs::backtrace::libunwind::trace
             at /rustc/e972bc8083d5228536dfd42913c8778b6bb04c8e/library/std/src/../../backtrace/src/backtrace/libunwind.rs:93:5
   1: std::backtrace_rs::backtrace::trace_unsynchronized
             at /rustc/e972bc8083d5228536dfd42913c8778b6bb04c8e/library/std/src/../../backtrace/src/backtrace/mod.rs:66:5
   2: std::backtrace::Backtrace::create
             at /rustc/e972bc8083d5228536dfd42913c8778b6bb04c8e/library/std/src/backtrace.rs:332:13
   3: core::ops::function::FnOnce::call_once
             at /rustc/e972bc8083d5228536dfd42913c8778b6bb04c8e/library/core/src/ops/function.rs:250:5
   4: core::bool::<impl bool>::then
             at /rustc/e972bc8083d5228536dfd42913c8778b6bb04c8e/library/core/src/bool.rs:71:24
   5: error_stack::report::Report<C>::from_frame
             at ./src/report.rs:288:25
   6: error_stack::report::Report<C>::new
             at ./src/report.rs:274:9
   7: error_stack::context::<impl core::convert::From<C> for error_stack::report::Report<C>>::from
             at ./src/context.rs:83:9
   8: <core::result::Result<T,E> as error_stack::result::IntoReport>::into_report
             at ./src/result.rs:203:31
   (For this example: additional frames have been removed)

Usage

Please see the documentation.

For more examples of error-stack in use, please check out the examples folder.

Contributors

error-stack was created and is maintained by HASH. As an open-source project, we gratefully accept external contributions and have published a contributing guide that outlines the process. If you have questions, please reach out to us on our Discord server.

License

error-stack is available under a number of different open-source licenses. Please see the LICENSE file to review your options.