Add with_unit method for metrics API (#431)

Add `with_unit` method to `CounterBuilder`, `SumObserverBuilder`,
`UpDownSumObserverBuilder`, `ValueObserverBuilder` structs

opentelemetry/src/metrics/counter.rs

@@ -3,7 +3,7 @@ use crate::{
         sync_instrument::{SyncBoundInstrument, SyncInstrument},
         Descriptor, InstrumentKind, Measurement, Meter, Number, NumberKind, Result,
     },
-    KeyValue,
+    KeyValue, Unit,
 };
 use std::marker;
 
@@ -84,6 +84,12 @@ impl<'a, T> CounterBuilder<'a, T> {
         self
     }
 
+    /// Set the unit for this counter.
+    pub fn with_unit(mut self, unit: Unit) -> Self {
+        self.descriptor.config.unit = Some(unit);
+        self
+    }
+
     /// Creates a new counter instrument.
     pub fn try_init(self) -> Result<Counter<T>> {
         let instrument = self.meter.new_sync_instrument(self.descriptor)?;

opentelemetry/src/metrics/descriptor.rs

@@ -10,7 +10,7 @@ pub struct Descriptor {
     name: String,
     instrument_kind: InstrumentKind,
     number_kind: NumberKind,
-    config: InstrumentConfig,
+    pub(crate) config: InstrumentConfig,
     attribute_hash: u64,
 }
 

opentelemetry/src/metrics/observer.rs

@@ -2,6 +2,7 @@ use crate::metrics::{
     sdk_api, AsyncRunner, Descriptor, InstrumentKind, Meter, Number, NumberKind, Observation,
     Result,
 };
+use crate::Unit;
 use std::sync::Arc;
 
 /// An Observer callback that can report observations for multiple instruments.
@@ -127,6 +128,12 @@ impl<'a, T> SumObserverBuilder<'a, T> {
         self
     }
 
+    /// Set the unit for this `SumObserver`.
+    pub fn with_unit(mut self, unit: Unit) -> Self {
+        self.descriptor.config.unit = Some(unit);
+        self
+    }
+
     /// Create a `SumObserver` from this configuration.
     pub fn try_init(self) -> Result<SumObserver<T>> {
         let instrument = self
@@ -214,6 +221,12 @@ impl<'a, T> UpDownSumObserverBuilder<'a, T> {
         self
     }
 
+    /// Set the unit for this `UpDownSumObserver`.
+    pub fn with_unit(mut self, unit: Unit) -> Self {
+        self.descriptor.config.unit = Some(unit);
+        self
+    }
+
     /// Create a `UpDownSumObserver` from this configuration.
     pub fn try_init(self) -> Result<UpDownSumObserver<T>> {
         let instrument = self
@@ -299,6 +312,12 @@ impl<'a, T> ValueObserverBuilder<'a, T> {
         self
     }
 
+    /// Set the unit for this `ValueObserver`.
+    pub fn with_unit(mut self, unit: Unit) -> Self {
+        self.descriptor.config.unit = Some(unit);
+        self
+    }
+
     /// Create a `ValueObserver` from this configuration.
     pub fn try_init(self) -> Result<ValueObserver<T>> {
         let instrument = self

opentelemetry/src/metrics/up_down_counter.rs

@@ -3,7 +3,7 @@ use crate::{
         sync_instrument::{SyncBoundInstrument, SyncInstrument},
         Descriptor, InstrumentKind, Measurement, Meter, Number, NumberKind, Result,
     },
-    KeyValue,
+    KeyValue, Unit,
 };
 use std::marker;
 
@@ -84,6 +84,12 @@ impl<'a, T> UpDownCounterBuilder<'a, T> {
         self
     }
 
+    /// Set the unit for this counter.
+    pub fn with_unit(mut self, unit: Unit) -> Self {
+        self.descriptor.config.unit = Some(unit);
+        self
+    }
+
     /// Creates a new counter instrument.
     pub fn try_init(self) -> Result<UpDownCounter<T>> {
         let instrument = self.meter.new_sync_instrument(self.descriptor)?;

opentelemetry/src/metrics/value_recorder.rs

@@ -3,6 +3,7 @@ use crate::metrics::{
     Descriptor, InstrumentKind, Measurement, Meter, Number, NumberKind, Result,
 };
 use crate::KeyValue;
+use crate::Unit;
 use std::marker;
 
 /// ValueRecorder is a metric that records per-request non-additive values.
@@ -84,6 +85,12 @@ impl<'a, T> ValueRecorderBuilder<'a, T> {
         self
     }
 
+    /// Set the unit for this `ValueRecorder`.
+    pub fn with_unit(mut self, unit: Unit) -> Self {
+        self.descriptor.config.unit = Some(unit);
+        self
+    }
+
     /// Creates a new value recorder.
     pub fn try_init(self) -> Result<ValueRecorder<T>> {
         let instrument = self.meter.new_sync_instrument(self.descriptor)?;