eyre ==== [![Build Status][actions-badge]][actions-url] [![Latest Version](https://img.shields.io/crates/v/eyre.svg)](https://crates.io/crates/eyre) [![Rust Documentation](https://img.shields.io/badge/api-rustdoc-blue.svg)](https://docs.rs/eyre) [actions-badge]: https://github.com/yaahc/eyre/workflows/Continuous%20integration/badge.svg [actions-url]: https://github.com/yaahc/eyre/actions?query=workflow%3A%22Continuous+integration%22 This library provides [`eyre::Report`][Report], a trait object based error handling type for easy idiomatic error handling and reporting in Rust applications. This crate is a fork of [`anyhow`] by @dtolnay with a support for customized `Reports`. For more details on customization checkout the docs on [`eyre::EyreHandler`]. ```toml [dependencies] eyre = "0.5" ``` ## Custom Report Handlers The heart of this crate is its ability to swap out the Handler type to change what information is carried alongside errors and how the end report is formatted. This crate is meant to be used alongside companion crates that customize its behavior. Below is a list of known crates that export report handlers for eyre and short summaries of what features they provide. - [`stable-eyre`]: Switches the backtrace type from `std`'s to `backtrace-rs`'s so that it can be captured on stable. The report format is identical to `DefaultHandler`'s report format. - [`color-eyre`]: Captures a `backtrace::Backtrace` and a `tracing_error::SpanTrace`. Provides a `Help` trait for attaching warnings and suggestions to error reports. The end report is then pretty printed with the help of [`color-backtrace`], [`color-spantrace`], and `ansi_term`. Check out the README on [`color-eyre`] for screenshots of the report format. - [`simple-eyre`]: A minimal `EyreHandler` that captures no additional information, for when you do not wish to capture `Backtrace`s with errors. - [`jane-eyre`]: A a report handler crate that exists purely for the pun. Currently just re-exports `color-eyre`. ## Details - Use `Result`, or equivalently `eyre::Result`, as the return type of any fallible function. Within the function, use `?` to easily propagate any error that implements the `std::error::Error` trait. ```rust use eyre::Result; fn get_cluster_info() -> Result { let config = std::fs::read_to_string("cluster.json")?; let map: ClusterMap = serde_json::from_str(&config)?; Ok(map) } ``` - Wrap a lower level error with a new error created from a message to help the person troubleshooting understand what the chain of failures that occured. A low-level error like "No such file or directory" can be annoying to debug without more information about what higher level step the application was in the middle of. ```rust use eyre::{WrapErr, Result}; fn main() -> Result<()> { ... it.detach().wrap_err("Failed to detach the important thing")?; let content = std::fs::read(path) .wrap_err_with(|| format!("Failed to read instrs from {}", path))?; ... } ``` ```console Error: Failed to read instrs from ./path/to/instrs.json Caused by: No such file or directory (os error 2) ``` - Downcasting is supported and can be by value, by shared reference, or by mutable reference as needed. ```rust // If the error was caused by redaction, then return a // tombstone instead of the content. match root_cause.downcast_ref::() { Some(DataStoreError::Censored(_)) => Ok(Poll::Ready(REDACTED_CONTENT)), None => Err(error), } ``` - If using the nightly channel, a backtrace is captured and printed with the error if the underlying error type does not already provide its own. In order to see backtraces, they must be enabled through the environment variables described in [`std::backtrace`]: - If you want panics and errors to both have backtraces, set `RUST_BACKTRACE=1`; - If you want only errors to have backtraces, set `RUST_LIB_BACKTRACE=1`; - If you want only panics to have backtraces, set `RUST_BACKTRACE=1` and `RUST_LIB_BACKTRACE=0`. The tracking issue for this feature is [rust-lang/rust#53487]. [`std::backtrace`]: https://doc.rust-lang.org/std/backtrace/index.html#environment-variables [rust-lang/rust#53487]: https://github.com/rust-lang/rust/issues/53487 - Eyre works with any error type that has an impl of `std::error::Error`, including ones defined in your crate. We do not bundle a `derive(Error)` macro but you can write the impls yourself or use a standalone macro like [thiserror]. ```rust use thiserror::Error; #[derive(Error, Debug)] pub enum FormatError { #[error("Invalid header (expected {expected:?}, got {found:?})")] InvalidHeader { expected: String, found: String, }, #[error("Missing attribute: {0}")] MissingAttribute(String), } ``` - One-off error messages can be constructed using the `eyre!` macro, which supports string interpolation and produces an `eyre::Report`. ```rust return Err(eyre!("Missing attribute: {}", missing)); ``` ## No-std support **NOTE**: tests are currently broken for `no_std` so I cannot guarantee that everything works still. I'm waiting for upstream fixes to be merged rather than fixing them myself, so bear with me. In no_std mode, the same API is almost all available and works the same way. To depend on Eyre in no_std mode, disable our default enabled "std" feature in Cargo.toml. A global allocator is required. ```toml [dependencies] eyre = { version = "0.5", default-features = false } ``` Since the `?`-based error conversions would normally rely on the `std::error::Error` trait which is only available through std, no_std mode will require an explicit `.map_err(Report::msg)` when working with a non-Eyre error type inside a function that returns Eyre's error type. ## Comparison to failure The `eyre::Report` type works something like `failure::Error`, but unlike failure ours is built around the standard library's `std::error::Error` trait rather than a separate trait `failure::Fail`. The standard library has adopted the necessary improvements for this to be possible as part of [RFC 2504]. [RFC 2504]: https://github.com/rust-lang/rfcs/blob/master/text/2504-fix-error.md ## Comparison to thiserror Use Eyre if you don't care what error type your functions return, you just want it to be easy. This is common in application code. Use [thiserror] if you are a library that wants to design your own dedicated error type(s) so that on failures the caller gets exactly the information that you choose. [thiserror]: https://github.com/dtolnay/thiserror ## Compatibility with `anyhow` This crate does its best to be usable as a drop in replacement of `anyhow` and vice-versa by `re-exporting` all of the renamed APIs with the names used in `anyhow`. There are two main incompatibilities that you might encounter when porting a codebase from `anyhow` to `eyre`: - type inference errors when using `eyre!` - `.context` not being implemented for `Option` #### Type Inference Errors The type inference issue is caused by the generic parameter, which isn't present in `anyhow::Error`. Specifically, the following works in anyhow: ```rust use anyhow::anyhow; // Works let val = get_optional_val().ok_or_else(|| anyhow!("failed to get value")).unwrap_err(); ``` Where as with `eyre!` this will fail due to being unable to infer the type for the Handler parameter. The solution to this problem, should you encounter it, is to give the compiler a hint for what type it should be resolving to, either via your return type or a type annotation. ```rust,compile_fail use eyre::eyre; // Broken let val = get_optional_val().ok_or_else(|| eyre!("failed to get value")).unwrap(); // Works let val: Report = get_optional_val().ok_or_else(|| eyre!("failed to get value")).unwrap(); ``` #### `Context` and `Option` As part of renaming `Context` to `WrapErr` we also intentionally do not implement `WrapErr` for `Option`. This decision was made because `wrap_err` implies that you're creating a new error that saves the old error as its `source`. With `Option` there is no source error to wrap, so `wrap_err` ends up being somewhat meaningless. Instead `eyre` intends for users to use the combinator functions provided by `std` for converting `Option`s to `Result`s. So where you would write this with anyhow: ```rust use anyhow::Context; let opt: Option<()> = None; let result = opt.context("new error message"); ``` With `eyre` we want users to write: ```rust use eyre::{eyre, Result}; let opt: Option<()> = None; let result: Result<()> = opt.ok_or_else(|| eyre!("new error message")); ``` However, to help with porting we do provide a `ContextCompat` trait which implements `context` for options which you can import to make existing `.context` calls compile. [Report]: https://docs.rs/eyre/*/eyre/struct.Report.html [`eyre::EyreHandler`]: https://docs.rs/eyre/*/eyre/trait.EyreHandler.html [`eyre::WrapErr`]: https://docs.rs/eyre/*/eyre/trait.WrapErr.html [`anyhow::Context`]: https://docs.rs/anyhow/*/anyhow/trait.Context.html [`anyhow`]: https://github.com/dtolnay/anyhow [`tracing_error::SpanTrace`]: https://docs.rs/tracing-error/*/tracing_error/struct.SpanTrace.html [`stable-eyre`]: https://github.com/yaahc/stable-eyre [`color-eyre`]: https://github.com/yaahc/color-eyre [`jane-eyre`]: https://github.com/yaahc/jane-eyre [`simple-eyre`]: https://github.com/yaahc/simple-eyre [`color-spantrace`]: https://github.com/yaahc/color-spantrace [`color-backtrace`]: https://github.com/athre0z/color-backtrace #### License Licensed under either of Apache License, Version 2.0 or MIT license at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.