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https://github.com/tokio-rs/tracing.git
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06daa9512b
## Motivation
The `tracing-fmt` crate crate currently uses a `NewVisitor` trait to
abstract over constructing field visitors of different types or with
different configurations:
d51d4d69d8/tracing-fmt/src/lib.rs (L192-L196)
There have been other use-cases where having this abstraction seems
valuable. For example, issue #73 is a proposal for adding utilities for
wrapping a visitor to skip a set of excluded field names. A `MakeVisitor`
abstraction would allow us to provide much more ergonomic APIs for
composing this kind of visitor behaviour.
Additionally, the current trait in `tracing-fmt` is tied pretty closely
to `tracing-fmt- specific behaviour. A generalized version of this trait
should be generic over the input type used to build the visitor.
## Solution
This PR adds a new `MakeVisitor` trait in `tracing-subscriber`.
`MakeVisitor` generalizes the `NewVisitor` trait in `tracing-fmt` to
represent constructing visitors for arbitrary targets. In addition, I've
added some additional traits representing common patterns for visitors,
such as those that format to a `fmt::Write` instance or write to an IO
stream, or those that produce output once a set of fields have been
visited. I've also added some extension traits & combinators to make
composing visitors easier, and to demonstrate that the trait in this
branch can be used for implementing this kind of wrapper.
I've also rewritten the `tracing-fmt` crate to use the new
`tracing-subscriber::MakeVisitor` trait rather than its homegrown
`fmt`-specifc version.
Closes: #240
Signed-off-by: Eliza Weisman <eliza@buoyant.io>
71 lines
1.9 KiB
Rust
71 lines
1.9 KiB
Rust
#![deny(rust_2018_idioms)]
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use tracing::{debug, error, info, span, trace, warn, Level};
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#[tracing::instrument]
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fn shave(yak: usize) -> bool {
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debug!(
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message = "hello! I'm gonna shave a yak.",
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excitement = "yay!"
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);
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if yak == 3 {
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warn!(target: "yak_events", "could not locate yak!");
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false
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} else {
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trace!(target: "yak_events", "yak shaved successfully");
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true
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}
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}
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fn shave_all(yaks: usize) -> usize {
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let span = span!(Level::TRACE, "shaving_yaks", yaks_to_shave = yaks);
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let _enter = span.enter();
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info!("shaving yaks");
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let mut num_shaved = 0;
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for yak in 1..=yaks {
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let shaved = shave(yak);
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trace!(target: "yak_events", yak, shaved);
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if !shaved {
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error!(message = "failed to shave yak!", yak);
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} else {
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num_shaved += 1;
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}
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trace!(target: "yak_events", yaks_shaved = num_shaved);
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}
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num_shaved
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}
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fn main() {
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use tracing_fmt::format;
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use tracing_subscriber::prelude::*;
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let formatter =
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// Construct a custom formatter for `Debug` fields
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format::debug_fn(|writer, field, value| write!(writer, "{}: {:?}", field, value))
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// Use `tracing-subscriber`'s extension traits to add delimiters
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// between fields, and ensure that fields named "message" are
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// formatted using fmt::Display.
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.display_messages()
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.delimited(", ");
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let subscriber = tracing_fmt::FmtSubscriber::builder()
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.fmt_fields(formatter)
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.finish();
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tracing::subscriber::with_default(subscriber, || {
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let number_of_yaks = 3;
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debug!("preparing to shave {} yaks", number_of_yaks);
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let number_shaved = shave_all(number_of_yaks);
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debug!(
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message = "yak shaving completed.",
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all_yaks_shaved = number_shaved == number_of_yaks,
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);
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});
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}
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