Expand description
This library provides wallee::Error
, a trait object based error
type for easy idiomatic error handling in Rust applications.
This crate is a fork of anyhow
with support for
caller location tracking. This is useful when debug information is not included in the build.
The caller location attached to wallee::Error
includes the file, line and
column where the error originated.
§Details
-
Use
Result<T, wallee::Error>
, or equivalentlywallee::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 wallee::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) }
-
Attach context 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 debug without more context about what higher level step the application was in the middle of.
use wallee::{Context, Result}; fn main() -> Result<()> { ... it.detach().context("Failed to detach the important thing")?; let content = std::fs::read(path) .with_context(|| 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), }
-
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
.
- If you want panics and errors to both have backtraces, set
-
Wallee 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
wallee!
macro, which supports string interpolation and produces awallee::Error
.return Err(wallee!("Missing attribute: {}", missing));
A
bail!
macro is provided as a shorthand for the same early return.bail!("Missing attribute: {}", missing);
Re-exports§
pub use wallee as format_err;
Macros§
- bail
- Return early with an error.
- ensure
- Return early with an error if a condition is not satisfied.
- wallee
- Construct an ad-hoc error from a string or existing non-
wallee
error value.
Structs§
- Chain
- Iterator of a chain of source errors.
- Error
- The
Error
type, a wrapper around a dynamic error type.
Traits§
- Context
- Provides the
context
method forResult
.
Functions§
- Ok
- Equivalent to Ok::<_, wallee::Error>(value).
Type Aliases§
- Result
Result<T, Error>