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[tracing-subscriber][tracing] improve duplciate tracing situation a bit #3319

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[tracing-subscriber][tracing] improve duplciate tracing situation a bit #3319

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969e82c
no longer use Deref for FormattedFields in tracing-subscriber to prep…
xMAC94x Jun 18, 2025
1fa67da
warn users of a bug in `tracing-subscriber` which is there for some t…
xMAC94x Jun 19, 2025
24f7012
fix a spelling mistake. change position to the end of the description…
xMAC94x Jun 19, 2025
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4 changes: 2 additions & 2 deletions tracing-subscriber/src/fmt/fmt_layer.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -797,6 +797,7 @@ impl<E: ?Sized> fmt::Display for FormattedFields<E> {
}
}

// TODO: Evaluate removing Deref in future versions, as its a powerful tool and barely useful (consumers can just call `.fields` directly)
impl<E: ?Sized> Deref for FormattedFields<E> {
type Target = String;
fn deref(&self) -> &Self::Target {
Expand Down Expand Up @@ -1631,8 +1632,7 @@ mod test {
.with_timer(MockTime)
.with_span_events(FmtSpan::ACTIVE);

let (reloadable_layer, reload_handle) =
crate::reload::Layer::new(inner_layer);
let (reloadable_layer, reload_handle) = crate::reload::Layer::new(inner_layer);
let reload = reloadable_layer.with_subscriber(Registry::default());

with_default(reload, || {
Expand Down
4 changes: 2 additions & 2 deletions tracing-subscriber/src/fmt/format/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -969,7 +969,7 @@ where

let ext = span.extensions();
if let Some(fields) = &ext.get::<FormattedFields<N>>() {
if !fields.is_empty() {
if !fields.fields.is_empty() {
write!(writer, "{}{}{}", bold.paint("{"), fields, bold.paint("}"))?;
}
}
Expand Down Expand Up @@ -1146,7 +1146,7 @@ where
{
let exts = span.extensions();
if let Some(fields) = exts.get::<FormattedFields<N>>() {
if !fields.is_empty() {
if !fields.fields.is_empty() {
write!(writer, " {}", dimmed.paint(&fields.fields))?;
}
}
Expand Down
4 changes: 2 additions & 2 deletions tracing-subscriber/src/fmt/format/pretty.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -324,7 +324,7 @@ where
let fields = &ext
.get::<FormattedFields<N>>()
.expect("Unable to find FormattedFields in extensions; this is a bug");
if !fields.is_empty() {
if !fields.fields.is_empty() {
write!(writer, " {} {}", dimmed.paint("with"), fields)?;
}
writer.write_char('\n')?;
Expand All @@ -346,7 +346,7 @@ impl<'writer> FormatFields<'writer> for Pretty {
current: &'writer mut FormattedFields<Self>,
fields: &span::Record<'_>,
) -> fmt::Result {
let empty = current.is_empty();
let empty = current.fields.is_empty();
let writer = current.as_writer();
let mut v = PrettyVisitor::new(writer, empty);
fields.record(&mut v);
Expand Down
5 changes: 5 additions & 0 deletions tracing/src/span.rs
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Expand Up @@ -1187,6 +1187,11 @@ impl Span {
/// **Note**: To record several values in just one call, see the [`record_all!`](crate::record_all!) macro.
/// </pre></div>
///
/// <pre class="ignore" style="white-space:normal;font:inherit;">
/// <strong>Note</strong>: <a href="https://docs.rs/tracing-subscriber/latest/tracing_subscriber/fmt/struct.Subscriber.html"><code>FmtSubscriber</code></a> has a bug
/// where it might duplicates span fields because of its implementation. See details at: <a href="https://github.com/tokio-rs/tracing/issues/1372">Github</a>
/// </pre>
///
/// [`field::Empty`]: super::field::Empty
/// [`Metadata`]: super::Metadata
pub fn record<Q: field::AsField + ?Sized, V: field::Value>(
Expand Down