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Add #[must_use] to Span. #3477

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e821257
Add must use annotation to `Span` as in #3234.
raldone01 May 16, 2025
2496332
Bless test that changed due to different rust compiler version.
raldone01 Feb 12, 2026
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28 changes: 13 additions & 15 deletions tracing-attributes/tests/ui/async_instrument.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -14,15 +14,17 @@ error[E0308]: mismatched types
--> tests/ui/async_instrument.rs:10:5
|
10 | ""
| ^^- help: try using a conversion method: `.to_string()`
| |
| expected `String`, found `&str`
| ^^ expected `String`, found `&str`
|
note: return type inferred to be `String` here
--> tests/ui/async_instrument.rs:9:31
|
9 | async fn simple_mismatch() -> String {
9 | async fn simple_mismatch() -> String {
| ^^^^^^
help: try using a conversion method
|
10 | "".to_string()
| ++++++++++++

error[E0277]: `(&str,)` doesn't implement `std::fmt::Display`
--> tests/ui/async_instrument.rs:14:57
Expand All @@ -33,20 +35,14 @@ error[E0277]: `(&str,)` doesn't implement `std::fmt::Display`
16 | | }
| | ^
| | |
| |_`(&str,)` cannot be formatted with the default formatter
| |_the trait `std::fmt::Display` is not implemented for `(&str,)`
| return type was inferred to be `(&str,)` here
|
= help: the trait `std::fmt::Display` is not implemented for `(&str,)`
= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead

error[E0277]: `(&str,)` doesn't implement `std::fmt::Display`
--> tests/ui/async_instrument.rs:14:34
|
14 | async fn opaque_unsatisfied() -> impl std::fmt::Display {
| ^^^^^^^^^^^^^^^^^^^^^^ `(&str,)` cannot be formatted with the default formatter
|
= help: the trait `std::fmt::Display` is not implemented for `(&str,)`
= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
| ^^^^^^^^^^^^^^^^^^^^^^ the trait `std::fmt::Display` is not implemented for `(&str,)`

error[E0308]: mismatched types
--> tests/ui/async_instrument.rs:22:5
Expand Down Expand Up @@ -82,15 +78,17 @@ error[E0308]: mismatched types
--> tests/ui/async_instrument.rs:35:16
|
35 | return "";
| ^^- help: try using a conversion method: `.to_string()`
| |
| expected `String`, found `&str`
| ^^ expected `String`, found `&str`
|
note: return type inferred to be `String` here
--> tests/ui/async_instrument.rs:33:28
|
33 | async fn early_return() -> String {
| ^^^^^^
help: try using a conversion method
|
35 | return "".to_string();
| ++++++++++++

error[E0308]: mismatched types
--> tests/ui/async_instrument.rs:40:1
Expand Down
4 changes: 2 additions & 2 deletions tracing-core/src/field.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1114,7 +1114,7 @@ mod test {

struct MyVisitor;
impl Visit for MyVisitor {
fn record_debug(&mut self, field: &Field, _: &dyn (core::fmt::Debug)) {
fn record_debug(&mut self, field: &Field, _: &dyn core::fmt::Debug) {
assert_eq!(field.callsite(), TEST_META_1.callsite())
}
}
Expand All @@ -1133,7 +1133,7 @@ mod test {

struct MyVisitor;
impl Visit for MyVisitor {
fn record_debug(&mut self, field: &Field, _: &dyn (core::fmt::Debug)) {
fn record_debug(&mut self, field: &Field, _: &dyn core::fmt::Debug) {
assert_eq!(field.name(), "bar")
}
}
Expand Down
46 changes: 23 additions & 23 deletions tracing-mock/tests/span_ancestry.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,7 @@ fn contextual_parent() {

with_default(collector, || {
let _guard = tracing::info_span!("contextual parent").entered();
tracing::info_span!("span");
let _ = tracing::info_span!("span");
});

handle.assert_finished();
Expand All @@ -45,7 +45,7 @@ fn contextual_parent_wrong_name() {

with_default(collector, || {
let _guard = tracing::info_span!("another parent").entered();
tracing::info_span!("span");
let _ = tracing::info_span!("span");
});

handle.assert_finished();
Expand All @@ -70,7 +70,7 @@ fn contextual_parent_wrong_id() {
with_default(collector, || {
let _span = tracing::info_span!("contextual parent");
let _guard = tracing::info_span!("another parent").entered();
tracing::info_span!("span");
let _ = tracing::info_span!("span");
});

handle.assert_finished();
Expand All @@ -94,7 +94,7 @@ fn contextual_parent_wrong_level() {

with_default(collector, || {
let _guard = tracing::debug_span!("contextual parent").entered();
tracing::info_span!("span");
let _ = tracing::info_span!("span");
});

handle.assert_finished();
Expand All @@ -111,7 +111,7 @@ fn expect_contextual_parent_actual_contextual_root() {
let (collector, handle) = collector::mock().new_span(span).run_with_handle();

with_default(collector, || {
tracing::info_span!("span");
let _ = tracing::info_span!("span");
});

handle.assert_finished();
Expand All @@ -132,7 +132,7 @@ fn expect_contextual_parent_actual_explicit_parent() {

with_default(collector, || {
let span = tracing::info_span!("explicit parent");
tracing::info_span!(parent: span.id(), "span");
let _ = tracing::info_span!(parent: span.id(), "span");
});

handle.assert_finished();
Expand All @@ -153,7 +153,7 @@ fn expect_contextual_parent_actual_explicit_root() {

with_default(collector, || {
let _guard = tracing::info_span!("contextual parent").entered();
tracing::info_span!(parent: None, "span");
let _ = tracing::info_span!(parent: None, "span");
});

handle.assert_finished();
Expand All @@ -168,7 +168,7 @@ fn contextual_root() {
let (collector, handle) = collector::mock().new_span(span).run_with_handle();

with_default(collector, || {
tracing::info_span!("span");
let _ = tracing::info_span!("span");
});

handle.assert_finished();
Expand All @@ -188,7 +188,7 @@ fn expect_contextual_root_actual_contextual_parent() {

with_default(collector, || {
let _guard = tracing::info_span!("contextual parent").entered();
tracing::info_span!("span");
let _ = tracing::info_span!("span");
});

handle.assert_finished();
Expand All @@ -208,7 +208,7 @@ fn expect_contextual_root_actual_explicit_parent() {

with_default(collector, || {
let span = tracing::info_span!("explicit parent");
tracing::info_span!(parent: span.id(), "span");
let _ = tracing::info_span!(parent: span.id(), "span");
});

handle.assert_finished();
Expand All @@ -228,7 +228,7 @@ fn expect_contextual_root_actual_explicit_root() {

with_default(collector, || {
let _guard = tracing::info_span!("contextual parent").entered();
tracing::info_span!(parent: None, "span");
let _ = tracing::info_span!(parent: None, "span");
});

handle.assert_finished();
Expand All @@ -247,7 +247,7 @@ fn explicit_parent() {

with_default(collector, || {
let span = tracing::info_span!("explicit parent");
tracing::info_span!(parent: span.id(), "span");
let _ = tracing::info_span!(parent: span.id(), "span");
});

handle.assert_finished();
Expand All @@ -270,7 +270,7 @@ fn explicit_parent_wrong_name() {

with_default(collector, || {
let span = tracing::info_span!("another parent");
tracing::info_span!(parent: span.id(), "span");
let _ = tracing::info_span!(parent: span.id(), "span");
});

handle.assert_finished();
Expand All @@ -294,7 +294,7 @@ fn explicit_parent_wrong_id() {
with_default(collector, || {
let _span = tracing::info_span!("explicit parent");
let another_span = tracing::info_span!("another parent");
tracing::info_span!(parent: another_span.id(), "span");
let _ = tracing::info_span!(parent: another_span.id(), "span");
});

handle.assert_finished();
Expand All @@ -316,7 +316,7 @@ fn explicit_parent_wrong_level() {

with_default(collector, || {
let span = tracing::debug_span!("explicit parent");
tracing::info_span!(parent: span.id(), "span");
let _ = tracing::info_span!(parent: span.id(), "span");
});

handle.assert_finished();
Expand All @@ -337,7 +337,7 @@ fn expect_explicit_parent_actual_contextual_parent() {

with_default(collector, || {
let _guard = tracing::info_span!("contextual parent").entered();
tracing::info_span!("span");
let _ = tracing::info_span!("span");
});

handle.assert_finished();
Expand All @@ -354,7 +354,7 @@ fn expect_explicit_parent_actual_contextual_root() {
let (collector, handle) = collector::mock().new_span(span).run_with_handle();

with_default(collector, || {
tracing::info_span!("span");
let _ = tracing::info_span!("span");
});

handle.assert_finished();
Expand All @@ -375,7 +375,7 @@ fn expect_explicit_parent_actual_explicit_root() {

with_default(collector, || {
let _guard = tracing::info_span!("contextual parent").entered();
tracing::info_span!(parent: None, "span");
let _ = tracing::info_span!(parent: None, "span");
});

handle.assert_finished();
Expand All @@ -395,7 +395,7 @@ fn explicit_root() {

with_default(collector, || {
let _guard = tracing::info_span!("contextual parent").entered();
tracing::info_span!(parent: None, "span");
let _ = tracing::info_span!(parent: None, "span");
});

handle.assert_finished();
Expand All @@ -415,7 +415,7 @@ fn expect_explicit_root_actual_contextual_parent() {

with_default(collector, || {
let _guard = tracing::info_span!("contextual parent").entered();
tracing::info_span!("span");
let _ = tracing::info_span!("span");
});

handle.assert_finished();
Expand All @@ -431,7 +431,7 @@ fn expect_explicit_root_actual_contextual_root() {
let (collector, handle) = collector::mock().new_span(span).run_with_handle();

with_default(collector, || {
tracing::info_span!("span");
let _ = tracing::info_span!("span");
});

handle.assert_finished();
Expand All @@ -451,7 +451,7 @@ fn expect_explicit_root_actual_explicit_parent() {

with_default(collector, || {
let span = tracing::info_span!("explicit parent");
tracing::info_span!(parent: span.id(), "span");
let _ = tracing::info_span!(parent: span.id(), "span");
});

handle.assert_finished();
Expand All @@ -466,7 +466,7 @@ fn explicit_and_contextual_root_is_explicit() {
let (collector, handle) = collector::mock().new_span(span).run_with_handle();

with_default(collector, || {
tracing::info_span!(parent: None, "span");
let _ = tracing::info_span!(parent: None, "span");
});

handle.assert_finished();
Expand Down
18 changes: 9 additions & 9 deletions tracing-subscriber/tests/env_filter/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -53,8 +53,8 @@ fn same_name_spans() {
.run_with_handle();
let subscriber = subscriber.with(filter);
with_default(subscriber, || {
tracing::trace_span!("foo", bar = 1);
tracing::trace_span!("foo", baz = 1);
let _ = tracing::trace_span!("foo", bar = 1);
let _ = tracing::trace_span!("foo", baz = 1);
});

finished.assert_finished();
Expand Down Expand Up @@ -343,9 +343,9 @@ fn more_specific_dynamic_filter_more_verbose() {
let subscriber = collector.with(filter);

with_default(subscriber, || {
tracing::info_span!("enabled info");
tracing::debug_span!("disabled debug");
tracing::debug_span!("enabled debug", hello = &4_u64);
let _ = tracing::info_span!("enabled info");
let _ = tracing::debug_span!("disabled debug");
let _ = tracing::debug_span!("enabled debug", hello = &4_u64);

// .only() doesn't work when we don't enter/exit spans
tracing::info!("marker");
Expand Down Expand Up @@ -391,10 +391,10 @@ fn more_specific_dynamic_filter_less_verbose() {
let subscriber = collector.with(filter);

with_default(subscriber, || {
tracing::info_span!("enabled info");
tracing::warn_span!("enabled hello=100 warn", hello = &100_u64);
tracing::info_span!("disabled hello=4 info", hello = &4_u64);
tracing::warn_span!("enabled hello=4 warn", hello = &4_u64);
let _ = tracing::info_span!("enabled info");
let _ = tracing::warn_span!("enabled hello=100 warn", hello = &100_u64);
let _ = tracing::info_span!("disabled hello=4 info", hello = &4_u64);
let _ = tracing::warn_span!("enabled hello=4 warn", hello = &4_u64);

// .only() doesn't work when we don't enter/exit spans
tracing::info!("marker");
Expand Down
4 changes: 2 additions & 2 deletions tracing-subscriber/tests/env_filter/per_subscriber.rs
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Expand Up @@ -52,8 +52,8 @@ fn same_name_spans() {
.with(subscriber.with_filter(filter))
.set_default();

tracing::trace_span!("foo", bar = 1);
tracing::trace_span!("foo", baz = 1);
let _ = tracing::trace_span!("foo", bar = 1);
let _ = tracing::trace_span!("foo", baz = 1);

handle.assert_finished();
}
Expand Down
4 changes: 2 additions & 2 deletions tracing-subscriber/tests/same_len_filters.rs
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Expand Up @@ -73,8 +73,8 @@ fn same_num_fields_and_name_len() {
.run_with_handle();
let subscriber = subscriber.with(filter);
with_default(subscriber, || {
tracing::trace_span!("foo", bar = 1);
tracing::trace_span!("baz", boz = 1);
let _ = tracing::trace_span!("foo", bar = 1);
let _ = tracing::trace_span!("baz", boz = 1);
});

finished.assert_finished();
Expand Down
6 changes: 3 additions & 3 deletions tracing-subscriber/tests/subscriber_filters/main.rs
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Expand Up @@ -71,9 +71,9 @@ fn basic_subscriber_filters_spans() {
.with(info_subscriber.with_filter(LevelFilter::INFO))
.set_default();

tracing::trace_span!("hello trace");
tracing::debug_span!("hello debug");
tracing::info_span!("hello info");
let _ = tracing::trace_span!("hello trace");
let _ = tracing::debug_span!("hello debug");
let _ = tracing::info_span!("hello info");

trace_handle.assert_finished();
debug_handle.assert_finished();
Expand Down
1 change: 1 addition & 0 deletions tracing/src/span.rs
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Expand Up @@ -328,6 +328,7 @@ pub trait AsId: crate::sealed::Sealed {
/// span will silently do nothing. Thus, the handle can be used in the same
/// manner regardless of whether or not the trace is currently being collected.
#[derive(Clone)]
#[must_use = "Once a span has been created, it should be entered."]
pub struct Span {
/// A handle used to enter the span when it is not executing.
///
Expand Down
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