pub enum Error {
UsualCase {
backtrace: Backtrace,
},
UsedInTightLoop {
backtrace: Option<Backtrace>,
},
SnafuErrorAsSource {
source: ConfigFileError,
},
SourceErrorDoesNotHaveBacktrace {
source: Error,
backtrace: Backtrace,
},
}Expand description
Rust 1.65 stabilized the std::backtrace::Backtrace type, but
there’s not yet a stable abstraction for accessing a backtrace
from an arbitrary error value. SNAFU provides a stable-compatible
way of accessing backtraces on a SNAFU-created error type. SNAFU
also supports environments where backtraces are not available,
such as no_std projects.
When defining error types which include backtraces, it’s
recommended to start with a Backtrace field on every leaf
error variant (those without a source). Backtraces are only
captured on failure.
Certain errors are used for flow control. These don’t need a
backtrace as they don’t represent actual failures. However,
sometimes an error is mostly used for flow control but might
also indicate an error. In those cases, you can use
Option<Backtrace> to avoid capturing a backtrace unless an
environment variable is set by the end user to provide additional
debugging.
For variants that do have a source, you need to evaluate if the source error provides a backtrace of some kind. If it is another SNAFU error, for example, you can delegate retrieval of the backtrace to the source error. If the source error doesn’t provide its own backtrace, you should capture your own backtrace. This backtrace will not be as useful as one captured by the source error, but it’s as useful as you can get.
When you wish to display the backtrace of an error, you can use
the ErrorCompat::backtrace method. It’s recommended to always
use this in the fully-qualified form so it will be easy to find
and replace when there’s a stable way to access backtraces.
use snafu::ErrorCompat;
fn inner_process() -> Result<(), Error> {
// Complicated logic
}
fn main() {
if let Err(e) = inner_process() {
eprintln!("An error occurred: {}", e);
if let Some(bt) = ErrorCompat::backtrace(&e) {
eprintln!("{:?}", bt);
}
}
}Variants§
UsualCase
The most common case: leaf errors should always include a backtrace field.
UsedInTightLoop
When an error is expected to be created frequently but the
backtrace is rarely needed, you can wrap it in an
Option. See the instructions on how to access the
backtrace in this case.
SnafuErrorAsSource
Fields
source: ConfigFileErrorThis error wraps another error that already has a backtrace. Instead of capturing our own, we forward the request for the backtrace to the inner error. This gives a more accurate backtrace.
SourceErrorDoesNotHaveBacktrace
This error wraps another error that does not expose a backtrace. We capture our own backtrace to provide something useful.
Trait Implementations§
source§impl Error for Error
impl Error for Error
source§fn description(&self) -> &str
fn description(&self) -> &str
source§fn cause(&self) -> Option<&dyn Error>
fn cause(&self) -> Option<&dyn Error>
source§impl ErrorCompat for Error
impl ErrorCompat for Error
source§fn iter_chain(&self) -> ChainCompat<'_, '_> ⓘwhere
Self: AsErrorSource,
fn iter_chain(&self) -> ChainCompat<'_, '_> ⓘwhere
Self: AsErrorSource,
Error::source. Read more