trace: Add arguments struct to subscriber::Record (#955)

This branch changes the `Subscriber::record` method to take a new
arguments struct, `span::Record`. The `field::Record` trait was renamed
to `field::Visit` to prevent name conflicts.

In addition, the `ValueSet::is_empty`, `ValueSet::contains`, and
`ValueSet::record` methods were made crate-private, as they are exposed
on the `Attributes` and `Record` types. 

Signed-off-by: Eliza Weisman <[email protected]>

tokio-trace/examples/counters.rs

@@ -2,7 +2,7 @@
 extern crate tokio_trace;
 
 use tokio_trace::{
-    field::{self, Field, Record},
+    field::{self, Field, Visit},
     span,
     subscriber::{self, Subscriber},
     Event, Id, Metadata,
@@ -29,7 +29,7 @@ struct Count<'a> {
     counters: RwLockReadGuard<'a, HashMap<String, AtomicUsize>>,
 }
 
-impl<'a> Record 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 {
@@ -52,7 +52,7 @@ impl<'a> Record for Count<'a> {
 }
 
 impl CounterSubscriber {
-    fn recorder(&self) -> Count {
+    fn visitor(&self) -> Count {
         Count {
             counters: self.counters.0.read().unwrap(),
         }
@@ -78,7 +78,7 @@ impl Subscriber for CounterSubscriber {
     }
 
     fn new_span(&self, new_span: &span::Attributes) -> Id {
-        new_span.values().record(&mut self.recorder());
+        new_span.record(&mut self.visitor());
         let id = self.ids.fetch_add(1, Ordering::SeqCst);
         Id::from_u64(id as u64)
     }
@@ -87,12 +87,12 @@ impl Subscriber for CounterSubscriber {
         // unimplemented
     }
 
-    fn record(&self, _: &Id, values: &field::ValueSet) {
-        values.record(&mut self.recorder())
+    fn record(&self, _: &Id, values: &span::Record) {
+        values.record(&mut self.visitor())
     }
 
     fn event(&self, event: &Event) {
-        event.record(&mut self.recorder())
+        event.record(&mut self.visitor())
     }
 
     fn enabled(&self, metadata: &Metadata) -> bool {

tokio-trace/examples/sloggish/sloggish_subscriber.rs

@@ -15,7 +15,7 @@ extern crate humantime;
 use self::ansi_term::{Color, Style};
 use super::tokio_trace::{
     self,
-    field::{Field, Record},
+    field::{Field, Visit},
     Id, Level, Subscriber,
 };
 
@@ -103,27 +103,23 @@ impl<'a> fmt::Display for ColorLevel<'a> {
 }
 
 impl Span {
-    fn new(
-        parent: Option<Id>,
-        _meta: &tokio_trace::Metadata,
-        values: &tokio_trace::field::ValueSet,
-    ) -> Self {
+    fn new(parent: Option<Id>, attrs: &tokio_trace::span::Attributes) -> Self {
         let mut span = Self {
             parent,
             kvs: Vec::new(),
         };
-        values.record(&mut span);
+        attrs.record(&mut span);
         span
     }
 }
 
-impl Record for Span {
+impl Visit for Span {
     fn record_debug(&mut self, field: &Field, value: &fmt::Debug) {
         self.kvs.push((field.name(), format!("{:?}", value)))
     }
 }
 
-impl<'a> Record for Event<'a> {
+impl<'a> Visit for Event<'a> {
     fn record_debug(&mut self, field: &Field, value: &fmt::Debug) {
         write!(
             &mut self.stderr,
@@ -207,16 +203,14 @@ impl Subscriber for SloggishSubscriber {
     }
 
     fn new_span(&self, span: &tokio_trace::span::Attributes) -> tokio_trace::Id {
-        let meta = span.metadata();
-        let values = span.values();
         let next = self.ids.fetch_add(1, Ordering::SeqCst) as u64;
         let id = tokio_trace::Id::from_u64(next);
-        let span = Span::new(self.current.id(), meta, values);
+        let span = Span::new(self.current.id(), span);
         self.spans.lock().unwrap().insert(id.clone(), span);
         id
     }
 
-    fn record(&self, span: &tokio_trace::Id, values: &tokio_trace::field::ValueSet) {
+    fn record(&self, span: &tokio_trace::Id, values: &tokio_trace::span::Record) {
         let mut spans = self.spans.lock().expect("mutex poisoned!");
         if let Some(span) = spans.get_mut(span) {
             values.record(span);
@@ -271,12 +265,12 @@ impl Subscriber for SloggishSubscriber {
             target = &event.metadata().target(),
         )
         .unwrap();
-        let mut recorder = Event {
+        let mut visitor = Event {
             stderr,
             comma: false,
         };
-        event.record(&mut recorder);
-        write!(&mut recorder.stderr, "\n").unwrap();
+        event.record(&mut visitor);
+        write!(&mut visitor.stderr, "\n").unwrap();
     }
 
     #[inline]