[−][src]Crate eyre
This library provides eyre::Report
, a trait object based error
type for easy idiomatic error handling 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::EyreContext
. For an example on how
to implement a custom context check out [stable-eyre
] which implements a minimal custom
context for capturing backtraces on stable.
[dependencies]
eyre = "0.4"
Details
-
Use
Result<T, eyre::Report>
, or equivalentlyeyre::Result<T>
, as the return type of any fallible function.Within the function, use
?
to easily propagate any error that implements thestd::error::Report
trait.use eyre::Result; fn get_cluster_info() -> Result<ClusterMap> { let config = std::fs::read_to_string("cluster.json")?; let map: ClusterMap = serde_json::from_str(&config)?; Ok(map) }
-
Create new errors from messages to help the person troubleshooting the error understand where things went wrong. A low-level error like "No such file or directory" can be annoying to directly and often benefit from being wrapped with higher level error messages.
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))?; ... }
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.
// If the error was caused by redaction, then return a // tombstone instead of the content. match root_cause.downcast_ref::<DataStoreError>() { 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
andRUST_LIB_BACKTRACE=0
.
The tracking issue for this feature is rust-lang/rust#53487.
- If you want panics and errors to both have backtraces, set
-
Eyre works with any error type that has an impl of
std::error::Error
, including ones defined in your crate. We do not bundle aderive(Error)
macro but you can write the impls yourself or use a standalone macro like thiserror.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 aneyre::Report
.return Err(eyre!("Missing attribute: {}", missing));
No-std support
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.
[dependencies]
eyre = { version = "0.4", default-features = false }
Since the ?
-based error conversions would normally rely on the
std::error::Report
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.
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
.
It is not 100% compatible because there are some cases where eyre
encounters
type inference errors but it should mostly work as a drop in replacement.
Specifically, the following works in anyhow:
// Works let val = get_optional_val.ok_or_else(|| anyhow!("failed to get value")).unwrap();
Where as with eyre!
this will fail due to being unable to infer the type for
the Context 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.
// 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();
Re-exports
pub use eyre as format_err; |
pub use eyre as anyhow; |
pub use Report as Error; |
pub use WrapErr as Context; |
Macros
bail | Return early with an error. |
ensure | Return early with an error if a condition is not satisfied. |
eyre | Construct an ad-hoc error from a string. |
Structs
Chain | Iterator of a chain of source errors. |
DefaultContext | The default provided context for |
Report | The core error reporting type of the library, a wrapper around a dynamic error reporting type. |
Traits
EyreContext | Context trait for customizing |
WrapErr | Provides the |
Type Definitions
Result |
|