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Tracking Issue for error::Report #90172
Description
Feature gate: #![feature(error_reporter)]
This is a tracking issue for a Report type that wraps an error, allowing the entire error chain to be printed in either single- or multi-line format.
Implementation PR: #91938
Public API
pub struct Report<E = Box<dyn Error>> {
error: E,
show_backtrace: bool,
pretty: bool,
}
impl<E> Report<E>
where
Report<E>: From<E>,
{
pub fn new(error: E) -> Report<E>;
}
impl<E> Report<E> {
pub fn pretty(mut self, pretty: bool) -> Self;
pub fn show_backtrace(mut self, show_backtrace: bool) -> Self;
}
impl<E> From<E> for Report<E>
where
E: Error;
impl<'a, E> From<E> for Report<Box<dyn Error + 'a>>
where
E: Error + 'a;
impl<E> fmt::Display for Report<E>
where
E: Error;
impl fmt::Display for Report<Box<dyn Error>>;
impl<E> fmt::Debug for Report<E>
where
Report<E>: fmt::Display;Unresolved Questions
- There exists an
impl<E> From<E> for Report<E> where E: Errorthat converts an error into a report. Is it possible to make this work for types that convert into the inner error type?
Edit(yaahc):
show_backtracecurrently has no effect if theprettyformat isn't enabled, we won't display backtraces ever in the single line format. I dislike this aspect, and am wondering if settingshow_backtraceshould implicitly also enablepretty, which isn't necessarily much better, but at least it's less error prone.- I don't like the name of
pretty, in the docs we refer to it as the multi-line format, should it just bemultiline? - I dislike how requiring the boolean for
pretty/show_backtracemeans you can't write something likelet val = my_result.map_err(Report::new).map_err(Report::pretty).unwrap();, though I'm leaning towards this being the lesser evil compared to the issues with lifetimes and if statements on alternative builder API styles. It's not that big of a deal to introduce a closure like.map_err(|r| r.pretty(should_be_pretty))
Reacted by Raimundo Saona, Brooks, John Bernard, Brooke Lew, rkeulemans, kennytm, Rob Ede, Simon Ruggier and sekun
Activity
yaahc commentedon Jan 7, 2022
Regarding the first unresolved issue about making it convert the inner type, I don't think its possible to do it generally, but I was able to add a special case for
Box<dyn Error>https://github.com/rust-lang/rust/pull/91938/files#diff-6605ea65189fd18a801464d4718ad307bb93be455d1592603ebf9382063902b2R1388 so that it boxes and wraps the error at the same time, which should make it work nicely as the return type formain.[-]Tracking Issue for error::Reporter[/-][+]Tracking Issue for `error::Report`[/+]yaahc commentedon Mar 28, 2022
I want to raise a concern on this related to naming. I think it's not unlikely that we may want to have a
Box<dyn Error>equivalent type instdat some point for storing errors which are only meant to be reported, similar toanyhow::Errororeyre::Report. If we do introduce such a type in the future it might make more sense for that type to be the one namedReport, or something else that clearly communicates that it semantically represents an error which is no longer expected to be handled anymore other than via reporting.It might make more sense to call this
std::error::Reporteror something along those lines. For now though I think it's fine to leave it as is. I'm in no rush to stabilize this interface.HTGAzureX1212 commentedon Sep 3, 2022
Not sure whether it would be in scope of this issue, but would it be possible for a
impl<E, F> From<Report<F>> for Report<E> where E: Error + From<F>, F: Errorbe added such thatReport<E>can be used with the?operator if I had to change error types when creating a report from an error?HTGAzureX1212 commentedon Sep 4, 2022
After some brief investigation, such an implementation would not work due to a conflicting blanket implementation in core.
HTGAzureX1212 commentedon Sep 4, 2022
A little bit more context for the rationale, I encountered this error when trying to convert a
Reoprt<F>to aReport<E>givenE: From<F>:map_reportis a trait extension function I added toResult<T, E>that does this:maxwase commentedon May 15, 2026
Hey, I've started building something with a similar concept that this discussion may benefit from: https://github.com/maxwase/errortools
Currently I see 2 requirements:
?and get a nice message for usability (no intermediatefn run)There are of course problems with trait Termiation, its impl for Result and Exit code, but if we're just talking about the default printing strategy, then this can be quite useful