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subscriber: add set_span_events to fmt::Subscriber #2962

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May 25, 2024
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69 changes: 69 additions & 0 deletions tracing-subscriber/src/fmt/fmt_subscriber.rs
Original file line number Diff line number Diff line change
Expand Up @@ -240,6 +240,27 @@ impl<C, N, E, W> Subscriber<C, N, E, W> {
self.is_ansi = ansi;
}

/// Modifies how synthesized events are emitted at points in the [span
/// lifecycle][lifecycle].
///
/// See [`Self::with_span_events`] for documentation on the [`FmtSpan`]
///
/// This method is primarily expected to be used with the
/// [`reload::Handle::modify`](crate::reload::Handle::modify) method
///
/// Note that using this method modifies the span configuration instantly and does not take into
/// account any current spans. If the previous configuration was set to capture
/// `FmtSpan::ALL`, for example, using this method to change to `FmtSpan::NONE` will cause an
/// exit event for currently entered events not to be formatted
///
/// [lifecycle]: mod@tracing::span#the-span-lifecycle
pub fn set_span_events(&mut self, kind: FmtSpan) {
self.fmt_span = format::FmtSpanConfig {
kind,
fmt_timing: self.fmt_span.fmt_timing,
}
}

/// Configures the subscriber to support [`libtest`'s output capturing][capturing] when used in
/// unit tests.
///
Expand Down Expand Up @@ -1590,4 +1611,52 @@ mod test {
// dropping `_saved_no_color` will restore the previous value of
// `NO_COLOR`.
}

// Validates that span event configuration can be modified with a reload handle
#[test]
fn modify_span_events() {
let make_writer = MockMakeWriter::default();

let inner_subscriber = fmt::Subscriber::default()
.with_writer(make_writer.clone())
.with_level(false)
.with_ansi(false)
.with_timer(MockTime)
.with_span_events(FmtSpan::ACTIVE);

let (reloadable_subscriber, reload_handle) =
crate::reload::Subscriber::new(inner_subscriber);
let reload = reloadable_subscriber.with_collector(Registry::default());

with_default(reload, || {
{
let span1 = tracing::info_span!("span1", x = 42);
let _e = span1.enter();
}

let _ = reload_handle.modify(|s| s.set_span_events(FmtSpan::NONE));

// this span should not be logged at all!
{
let span2 = tracing::info_span!("span2", x = 100);
let _e = span2.enter();
}

{
let span3 = tracing::info_span!("span3", x = 42);
let _e = span3.enter();

// The span config was modified after span3 was already entered.
// We should only see an exit
let _ = reload_handle.modify(|s| s.set_span_events(FmtSpan::ACTIVE));
}
});
let actual = sanitize_timings(make_writer.get_string());
assert_eq!(
"fake time span1{x=42}: tracing_subscriber::fmt::fmt_subscriber::test: enter\n\
fake time span1{x=42}: tracing_subscriber::fmt::fmt_subscriber::test: exit\n\
fake time span3{x=42}: tracing_subscriber::fmt::fmt_subscriber::test: exit\n",
actual.as_str()
);
}
}
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