Add lifetime to field::Visit

Partially an exercise in "how bad would it be?" This allows the removal
of the unsafety in tracing-log's LogVisitor (see next commit), as well
as generalization of NormalizeEvent to more RecordField containers.

examples/examples/counters.rs

@@ -29,7 +29,7 @@ struct Count<'a> {
     counters: RwLockReadGuard<'a, HashMap<String, AtomicUsize>>,
 }
 
-impl<'a> Visit for Count<'a> {
+impl<'a> Visit<'_> for Count<'a> {
     fn record_i64(&mut self, field: &Field, value: i64) {
         if let Some(counter) = self.counters.get(field.name()) {
             if value > 0 {

examples/examples/sloggish/sloggish_collector.rs

@@ -101,13 +101,13 @@ impl Span {
     }
 }
 
-impl Visit for Span {
+impl Visit<'_> for Span {
     fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug) {
         self.kvs.push((field.name(), format!("{:?}", value)))
     }
 }
 
-impl<'a> Visit for Event<'a> {
+impl<'a> Visit<'_> for Event<'a> {
     fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug) {
         write!(
             &mut self.stderr,

tracing-core/src/event.rs

@@ -83,7 +83,7 @@ impl<'a> Event<'a> {
     ///
     /// [visitor]: super::field::Visit
     #[inline]
-    pub fn record(&self, visitor: &mut dyn field::Visit) {
+    pub fn record(&self, visitor: &mut dyn field::Visit<'a>) {
         self.fields.record(visitor);
     }
 

tracing-core/src/field.rs

@@ -114,7 +114,7 @@ pub struct Iter {
 ///     string: &'a mut String,
 /// }
 ///
-/// impl<'a> Visit for StringVisitor<'a> {
+/// impl<'a> Visit<'_> for StringVisitor<'a> {
 ///     fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug) {
 ///         write!(self.string, "{} = {:?}; ", field.name(), value).unwrap();
 ///     }
@@ -145,7 +145,7 @@ pub struct Iter {
 ///     sum: i64,
 /// }
 ///
-/// impl Visit for SumVisitor {
+/// impl Visit<'_> for SumVisitor {
 ///     fn record_i64(&mut self, _field: &Field, value: i64) {
 ///        self.sum += value;
 ///     }
@@ -178,7 +178,7 @@ pub struct Iter {
 /// [records an `Event`]: super::collect::Collect::event
 /// [set of `Value`s added to a `Span`]: super::collect::Collect::record
 /// [`Event`]: super::event::Event
-pub trait Visit {
+pub trait Visit<'a> {
     /// Visit a double-precision floating point value.
     fn record_f64(&mut self, field: &Field, value: f64) {
         self.record_debug(field, &value)
@@ -200,7 +200,7 @@ pub trait Visit {
     }
 
     /// Visit a string value.
-    fn record_str(&mut self, field: &Field, value: &str) {
+    fn record_str(&mut self, field: &Field, value: &'a str) {
         self.record_debug(field, &value)
     }
 
@@ -230,7 +230,7 @@ pub trait Visit {
 /// [visitor]: Visit
 pub trait Value: crate::sealed::Sealed {
     /// Visits this value with the given `Visitor`.
-    fn record(&self, key: &Field, visitor: &mut dyn Visit);
+    fn record<'a>(&'a self, key: &Field, visitor: &mut dyn Visit<'a>);
 }
 
 /// A `Value` which serializes using `fmt::Display`.
@@ -264,19 +264,19 @@ where
 
 // ===== impl Visit =====
 
-impl<'a, 'b> Visit for fmt::DebugStruct<'a, 'b> {
+impl<'a, 'b> Visit<'_> for fmt::DebugStruct<'a, 'b> {
     fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug) {
         self.field(field.name(), value);
     }
 }
 
-impl<'a, 'b> Visit for fmt::DebugMap<'a, 'b> {
+impl<'a, 'b> Visit<'_> for fmt::DebugMap<'a, 'b> {
     fn record_debug(&mut self, field: &Field, value: &dyn fmt::Debug) {
         self.entry(&format_args!("{}", field), value);
     }
 }
 
-impl<F> Visit for F
+impl<F> Visit<'_> for F
 where
     F: FnMut(&Field, &dyn fmt::Debug),
 {
@@ -351,7 +351,11 @@ macro_rules! impl_one_value {
     (normal, $value_ty:tt, $op:expr, $record:ident) => {
         impl $crate::sealed::Sealed for $value_ty {}
         impl $crate::field::Value for $value_ty {
-            fn record(&self, key: &$crate::field::Field, visitor: &mut dyn $crate::field::Visit) {
+            fn record(
+                &self,
+                key: &$crate::field::Field,
+                visitor: &mut dyn $crate::field::Visit<'_>,
+            ) {
                 visitor.$record(key, $op(*self))
             }
         }
@@ -366,7 +370,11 @@ macro_rules! impl_one_value {
         use num::*;
         impl $crate::sealed::Sealed for ty_to_nonzero!($value_ty) {}
         impl $crate::field::Value for ty_to_nonzero!($value_ty) {
-            fn record(&self, key: &$crate::field::Field, visitor: &mut dyn $crate::field::Visit) {
+            fn record(
+                &self,
+                key: &$crate::field::Field,
+                visitor: &mut dyn $crate::field::Visit<'_>,
+            ) {
                 visitor.$record(key, $op(self.get()))
             }
         }
@@ -399,15 +407,15 @@ impl_values! {
 
 impl<T: crate::sealed::Sealed> crate::sealed::Sealed for Wrapping<T> {}
 impl<T: crate::field::Value> crate::field::Value for Wrapping<T> {
-    fn record(&self, key: &crate::field::Field, visitor: &mut dyn crate::field::Visit) {
+    fn record<'a>(&'a self, key: &crate::field::Field, visitor: &mut dyn crate::field::Visit<'a>) {
         self.0.record(key, visitor)
     }
 }
 
 impl crate::sealed::Sealed for str {}
 
 impl Value for str {
-    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
+    fn record<'a>(&'a self, key: &Field, visitor: &mut dyn Visit<'a>) {
         visitor.record_str(key, self)
     }
 }
@@ -418,7 +426,7 @@ impl crate::sealed::Sealed for dyn std::error::Error + 'static {}
 #[cfg(feature = "std")]
 #[cfg_attr(docsrs, doc(cfg(feature = "std")))]
 impl Value for dyn std::error::Error + 'static {
-    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
+    fn record<'a>(&'a self, key: &Field, visitor: &mut dyn Visit<'a>) {
         visitor.record_error(key, self)
     }
 }
@@ -429,7 +437,7 @@ impl<'a, T: ?Sized> Value for &'a T
 where
     T: Value + 'a,
 {
-    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
+    fn record<'visit>(&'visit self, key: &Field, visitor: &mut dyn Visit<'visit>) {
         (*self).record(key, visitor)
     }
 }
@@ -440,7 +448,7 @@ impl<'a, T: ?Sized> Value for &'a mut T
 where
     T: Value + 'a,
 {
-    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
+    fn record<'visit>(&'visit self, key: &Field, visitor: &mut dyn Visit<'visit>) {
         // Don't use `(*self).record(key, visitor)`, otherwise would
         // cause stack overflow due to `unconditional_recursion`.
         T::record(self, key, visitor)
@@ -450,7 +458,7 @@ where
 impl<'a> crate::sealed::Sealed for fmt::Arguments<'a> {}
 
 impl<'a> Value for fmt::Arguments<'a> {
-    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
+    fn record<'visit>(&'visit self, key: &Field, visitor: &mut dyn Visit<'visit>) {
         visitor.record_debug(key, self)
     }
 }
@@ -498,7 +506,7 @@ impl<T> Value for DisplayValue<T>
 where
     T: fmt::Display,
 {
-    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
+    fn record(&self, key: &Field, visitor: &mut dyn Visit<'_>) {
         visitor.record_debug(key, self)
     }
 }
@@ -523,7 +531,7 @@ impl<T: fmt::Debug> Value for DebugValue<T>
 where
     T: fmt::Debug,
 {
-    fn record(&self, key: &Field, visitor: &mut dyn Visit) {
+    fn record(&self, key: &Field, visitor: &mut dyn Visit<'_>) {
         visitor.record_debug(key, &self.0)
     }
 }
@@ -537,7 +545,7 @@ impl<T: fmt::Debug> fmt::Debug for DebugValue<T> {
 impl crate::sealed::Sealed for Empty {}
 impl Value for Empty {
     #[inline]
-    fn record(&self, _: &Field, _: &mut dyn Visit) {}
+    fn record(&self, _: &Field, _: &mut dyn Visit<'_>) {}
 }
 
 // ===== impl Field =====
@@ -748,7 +756,7 @@ impl<'a> ValueSet<'a> {
     /// Visits all the fields in this `ValueSet` with the provided [visitor].
     ///
     /// [visitor]: Visit
-    pub fn record(&self, visitor: &mut dyn Visit) {
+    pub fn record(&self, visitor: &mut dyn Visit<'a>) {
         let my_callsite = self.callsite();
         for (field, value) in self.values {
             if field.callsite() != my_callsite {
@@ -943,7 +951,7 @@ mod test {
         ];
 
         struct MyVisitor;
-        impl Visit for MyVisitor {
+        impl Visit<'_> for MyVisitor {
             fn record_debug(&mut self, field: &Field, _: &dyn (core::fmt::Debug)) {
                 assert_eq!(field.callsite(), TEST_META_1.callsite())
             }
@@ -962,7 +970,7 @@ mod test {
         ];
 
         struct MyVisitor;
-        impl Visit for MyVisitor {
+        impl Visit<'_> for MyVisitor {
             fn record_debug(&mut self, field: &Field, _: &dyn (core::fmt::Debug)) {
                 assert_eq!(field.name(), "bar")
             }

tracing-core/src/span.rs

@@ -180,7 +180,7 @@ impl<'a> Attributes<'a> {
     /// [Visitor].
     ///
     /// [visitor]: super::field::Visit
-    pub fn record(&self, visitor: &mut dyn field::Visit) {
+    pub fn record(&self, visitor: &mut dyn field::Visit<'a>) {
         self.values.record(visitor)
     }
 
@@ -222,7 +222,7 @@ impl<'a> Record<'a> {
     /// Records all the fields in this `Record` with the provided [Visitor].
     ///
     /// [visitor]: super::field::Visit
-    pub fn record(&self, visitor: &mut dyn field::Visit) {
+    pub fn record(&self, visitor: &mut dyn field::Visit<'a>) {
         self.values.record(visitor)
     }
 

tracing-error/src/subscriber.rs

@@ -39,7 +39,7 @@ pub(crate) struct WithContext(
 impl<C, F> Subscribe<C> for ErrorSubscriber<C, F>
 where
     C: Collect + for<'span> LookupSpan<'span>,
-    F: for<'writer> FormatFields<'writer> + 'static,
+    F: for<'visit, 'writer> FormatFields<'visit, 'writer> + 'static,
 {
     /// Notifies this subscriber that a new span was constructed with the given
     /// `Attributes` and `Id`.
@@ -72,7 +72,7 @@ where
 
 impl<C, F> ErrorSubscriber<C, F>
 where
-    F: for<'writer> FormatFields<'writer> + 'static,
+    F: for<'visit, 'writer> FormatFields<'visit, 'writer> + 'static,
     C: Collect + for<'span> LookupSpan<'span>,
 {
     /// Returns a new `ErrorSubscriber` with the provided [field formatter].

tracing-journald/src/lib.rs

@@ -290,7 +290,7 @@ impl SpanVisitor<'_> {
     }
 }
 
-impl Visit for SpanVisitor<'_> {
+impl Visit<'_> for SpanVisitor<'_> {
     fn record_str(&mut self, field: &Field, value: &str) {
         self.put_span_prefix();
         put_field_length_encoded(self.buf, field.name(), |buf| {
@@ -329,7 +329,7 @@ impl<'a> EventVisitor<'a> {
     }
 }
 
-impl Visit for EventVisitor<'_> {
+impl Visit<'_> for EventVisitor<'_> {
     fn record_str(&mut self, field: &Field, value: &str) {
         self.put_prefix(field);
         put_field_length_encoded(self.buf, field.name(), |buf| {

tracing-log/src/lib.rs

@@ -516,7 +516,7 @@ impl<'a> LogVisitor<'a> {
     }
 }
 
-impl<'a> Visit for LogVisitor<'a> {
+impl<'a> Visit<'_> for LogVisitor<'a> {
     fn record_debug(&mut self, _field: &Field, _value: &dyn fmt::Debug) {}
 
     fn record_u64(&mut self, field: &Field, value: u64) {

tracing-mock/src/field.rs

@@ -175,7 +175,7 @@ pub struct CheckVisitor<'a> {
     collector_name: &'a str,
 }
 
-impl<'a> Visit for CheckVisitor<'a> {
+impl<'a> Visit<'_> for CheckVisitor<'a> {
     fn record_f64(&mut self, field: &Field, value: f64) {
         self.expect
             .compare_or_panic(field.name(), &value, self.ctx, self.collector_name)
@@ -229,7 +229,7 @@ impl<'a> From<&'a dyn Value> for MockValue {
             value: Option<MockValue>,
         }
 
-        impl Visit for MockValueBuilder {
+        impl Visit<'_> for MockValueBuilder {
             fn record_f64(&mut self, _: &Field, value: f64) {
                 self.value = Some(MockValue::F64(value));
             }

tracing-opentelemetry/src/subscriber.rs

@@ -108,7 +108,7 @@ fn str_to_status_code(s: &str) -> Option<otel::StatusCode> {
 
 struct SpanEventVisitor<'a>(&'a mut otel::Event);
 
-impl<'a> field::Visit for SpanEventVisitor<'a> {
+impl<'a> field::Visit<'_> for SpanEventVisitor<'a> {
     /// Record events on the underlying OpenTelemetry [`Span`] from `bool` values.
     ///
     /// [`Span`]: opentelemetry::trace::Span
@@ -201,7 +201,7 @@ impl<'a> SpanAttributeVisitor<'a> {
     }
 }
 
-impl<'a> field::Visit for SpanAttributeVisitor<'a> {
+impl<'a> field::Visit<'_> for SpanAttributeVisitor<'a> {
     /// Set attributes on the underlying OpenTelemetry [`Span`] from `bool` values.
     ///
     /// [`Span`]: opentelemetry::trace::Span

tracing-serde/src/lib.rs

@@ -371,7 +371,7 @@ where
     }
 }
 
-impl<S> Visit for SerdeMapVisitor<S>
+impl<S> Visit<'_> for SerdeMapVisitor<S>
 where
     S: SerializeMap,
 {
@@ -423,7 +423,7 @@ pub struct SerdeStructVisitor<S: SerializeStruct> {
     state: Result<(), S::Error>,
 }
 
-impl<S> Visit for SerdeStructVisitor<S>
+impl<S> Visit<'_> for SerdeStructVisitor<S>
 where
     S: SerializeStruct,
 {