Add WithExplicitBucketBoundaries Histogram option to the metric api (#4603)

* Add WithExplicitBucketBoundaries Histogram option to the metric api

* Add note that the option is advisory

---------

Co-authored-by: Robert Pająk <pellared@hotmail.com>
Co-authored-by: Aaron Clawson <3766680+MadVikingGod@users.noreply.github.com>

CHANGELOG.md

@@ -16,6 +16,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Add the `go.opentelemetry.io/otel/trace/noop` package as a default no-op implementation of the trace API. (#4620)
 - Add context propagation in `go.opentelemetry.io/otel/example/dice`. (#4644)
 - Add view configuration to `go.opentelemetry.io/otel/example/prometheus`. (#4649)
+- Add `go.opentelemetry.io/otel/metric.WithExplicitBucketBoundaries`, which allows defining default explicit bucket boundaries when creating histogram instruments. (#4603)
 - Add `Version` function in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetricgrpc`. (#4660)
 - Add `Version` function in `go.opentelemetry.io/otel/exporters/otlp/otlpmetric/otlpmetrichttp`. (#4660)
 - Add Summary, SummaryDataPoint, and QuantileValue to `go.opentelemetry.io/sdk/metric/metricdata`. (#4622)

metric/example_test.go

@@ -161,6 +161,7 @@ func ExampleMeter_histogram() {
 		"task.duration",
 		metric.WithDescription("The duration of task execution."),
 		metric.WithUnit("s"),
+		metric.WithExplicitBucketBoundaries(.005, .01, .025, .05, .075, .1, .25, .5, .75, 1, 2.5, 5, 7.5, 10),
 	)
 	if err != nil {
 		panic(err)

metric/instrument.go

@@ -39,6 +39,12 @@ type InstrumentOption interface {
 	Float64ObservableGaugeOption
 }
 
+// HistogramOption applies options to histogram instruments.
+type HistogramOption interface {
+	Int64HistogramOption
+	Float64HistogramOption
+}
+
 type descOpt string
 
 func (o descOpt) applyFloat64Counter(c Float64CounterConfig) Float64CounterConfig {
@@ -171,6 +177,23 @@ func (o unitOpt) applyInt64ObservableGauge(c Int64ObservableGaugeConfig) Int64Ob
 // The unit u should be defined using the appropriate [UCUM](https://ucum.org) case-sensitive code.
 func WithUnit(u string) InstrumentOption { return unitOpt(u) }
 
+// WithExplicitBucketBoundaries sets the instrument explicit bucket boundaries.
+//
+// This option is considered "advisory", and may be ignored by API implementations.
+func WithExplicitBucketBoundaries(bounds ...float64) HistogramOption { return bucketOpt(bounds) }
+
+type bucketOpt []float64
+
+func (o bucketOpt) applyFloat64Histogram(c Float64HistogramConfig) Float64HistogramConfig {
+	c.explicitBucketBoundaries = o
+	return c
+}
+
+func (o bucketOpt) applyInt64Histogram(c Int64HistogramConfig) Int64HistogramConfig {
+	c.explicitBucketBoundaries = o
+	return c
+}
+
 // AddOption applies options to an addition measurement. See
 // [MeasurementOption] for other options that can be used as an AddOption.
 type AddOption interface {

metric/syncfloat64.go

@@ -147,8 +147,9 @@ type Float64Histogram interface {
 // Float64HistogramConfig contains options for synchronous counter instruments
 // that record int64 values.
 type Float64HistogramConfig struct {
-	description string
+	description              string
-	unit        string
+	unit                     string
+	explicitBucketBoundaries []float64
 }
 
 // NewFloat64HistogramConfig returns a new [Float64HistogramConfig] with all
@@ -171,6 +172,11 @@ func (c Float64HistogramConfig) Unit() string {
 	return c.unit
 }
 
+// ExplicitBucketBoundaries returns the configured explicit bucket boundaries.
+func (c Float64HistogramConfig) ExplicitBucketBoundaries() []float64 {
+	return c.explicitBucketBoundaries
+}
+
 // Float64HistogramOption applies options to a [Float64HistogramConfig]. See
 // [InstrumentOption] for other options that can be used as a
 // Float64HistogramOption.

metric/syncfloat64_test.go

@@ -51,3 +51,9 @@ type float64Config interface {
 	Description() string
 	Unit() string
 }
+
+func TestFloat64ExplicitBucketHistogramConfiguration(t *testing.T) {
+	bounds := []float64{0.1, 0.5, 1.0}
+	got := NewFloat64HistogramConfig(WithExplicitBucketBoundaries(bounds...))
+	assert.Equal(t, bounds, got.ExplicitBucketBoundaries(), "boundaries")
+}

metric/syncint64.go

@@ -147,8 +147,9 @@ type Int64Histogram interface {
 // Int64HistogramConfig contains options for synchronous counter instruments
 // that record int64 values.
 type Int64HistogramConfig struct {
-	description string
+	description              string
-	unit        string
+	unit                     string
+	explicitBucketBoundaries []float64
 }
 
 // NewInt64HistogramConfig returns a new [Int64HistogramConfig] with all opts
@@ -171,6 +172,11 @@ func (c Int64HistogramConfig) Unit() string {
 	return c.unit
 }
 
+// ExplicitBucketBoundaries returns the configured explicit bucket boundaries.
+func (c Int64HistogramConfig) ExplicitBucketBoundaries() []float64 {
+	return c.explicitBucketBoundaries
+}
+
 // Int64HistogramOption applies options to a [Int64HistogramConfig]. See
 // [InstrumentOption] for other options that can be used as an
 // Int64HistogramOption.

metric/syncint64_test.go

@@ -51,3 +51,9 @@ type int64Config interface {
 	Description() string
 	Unit() string
 }
+
+func TestInt64ExplicitBucketHistogramConfiguration(t *testing.T) {
+	bounds := []float64{0.1, 0.5, 1.0}
+	got := NewInt64HistogramConfig(WithExplicitBucketBoundaries(bounds...))
+	assert.Equal(t, bounds, got.ExplicitBucketBoundaries(), "boundaries")
+}