[−][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
.
[dependencies]
eyre = "0.4"
Custom Contexts
The heart of this crate is it's ability to swap out the Context 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 custom context crates and short summaries of what features they provide.
stable-eyre
: Switches the backtrace type fromstd
's tobacktrace-rs
's so that it can be captured on stable. The report format is identical toDefaultContext
's report format.color-eyre
: Captures abacktrace::Backtrace
and atracing_error::SpanTrace
. Provides aHelp
trait for attaching warnings and suggestions to error reports. The end report is then pretty printed with the help ofcolor-backtrace
,color-spantrace
, andansi_term
. Check out the README oncolor-eyre
for screenshots of the report format.simple-eyre
: A minimalEyreContext
that captures no additional information, for when you do not wish to captureBacktrace
s with errors.jane-eyre
: A custom context type that exists purely for the pun. Currently just re-exportscolor-eyre
.
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
.
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 forOption
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:
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 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.
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:
use anyhow::Context; let opt: Option<()> = None; let result = opt.context("new error message");
With eyre
we want users to write:
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.
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
ContextCompat | Provides the |
EyreContext | Context trait for customizing |
WrapErr | Provides the |
Type Definitions
Result |
|