Eyre
This library provides eyre::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::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.
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::Error
trait.use Result;
-
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.
use ;
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.
-
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 Error;
-
One-off error messages can be constructed using the
eyre!
macro, which supports string interpolation and produces aneyre::Report
.return Err;
No-std support
NOTE: tests are currently broken for no_std
so I cannot guaruntee 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.
[]
= { = "0.3", = 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.
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.
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.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.unwrap;
// Works
let val: Report = get_optional_val.ok_or_else.unwrap;