Trial integrating spantrace extraction with tracing-subscriber via generic member access #1861
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…neric member access
yaahc
commented
Jan 26, 2022
| @@ -58,16 +58,6 @@ where | |||
| span.extensions_mut().insert(fields); | |||
| } | |||
| } | |||
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| unsafe fn downcast_raw(&self, id: TypeId) -> Option<NonNull<()>> { | |||
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this appears to be dead code but doesn't produce a lint????!?
yaahc
commented
Jan 26, 2022
| } else { | ||
| self.record_debug(field, &format_args!("{}", value)) | ||
| let source = value.source(); | ||
| let spantrace = value.chain().find_map(|value| value.request_ref::<tracing::Span>()); |
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this would be tracing_error::SpanTrace if it weren't for the circular dependency issue that I will need to navigate later if I ever want this to actually be a thing.
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Motivation
I'd like to be able to log errors that have captured a
SpanTraceto gather context on the state of the world when the error was constructed. Right now this is possible but the only way to get this spantrace info back into tracing logs is to either include the info in your error message's display output or separately extract and log the spantrace in the tracing event alongside the error. I feel that the first option ends up looking bad, and the second option is error prone / easy to forget. I'd like to make this automatic in a way that formats well.Solution
This PR uses generic member access to request an arbitrary type through a
&dyn Errortrait object. For now I'm only printing aSpanbecauseSpanTraceis defined in a downstream crate and would have to be moved intotracing-subscriberto name it directly sincetracing-errordepends ontracing-subscriber.This PR only compiles when using a custom rustc toolchain based on rust-lang/rust#90328