add WithProducer to the prometheus exporter (#4473)

CHANGELOG.md

@@ -8,6 +8,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 
 ## [Unreleased]
 
+### Added
+
+- Add `WithProducer` option in `go.opentelemetry.op/otel/exporters/prometheus` to restore the ability to register producers on the prometheus exporter's manual reader. (#4473)
+
 ### Deprecated
 
 - The `NewMetricExporter` in `go.opentelemetry.io/otel/bridge/opencensus` was deprecated in `v0.35.0` (#3541).

exporters/prometheus/config.go

@@ -28,7 +28,7 @@ type config struct {
 	disableTargetInfo      bool
 	withoutUnits           bool
 	withoutCounterSuffixes bool
-	aggregation            metric.AggregationSelector
+	readerOpts             []metric.ManualReaderOption
 	disableScopeInfo       bool
 	namespace              string
 }
@@ -47,14 +47,6 @@ func newConfig(opts ...Option) config {
 	return cfg
 }
 
-func (cfg config) manualReaderOptions() []metric.ManualReaderOption {
-	opts := []metric.ManualReaderOption{}
-	if cfg.aggregation != nil {
-		opts = append(opts, metric.WithAggregationSelector(cfg.aggregation))
-	}
-	return opts
-}
-
 // Option sets exporter option values.
 type Option interface {
 	apply(config) config
@@ -81,7 +73,16 @@ func WithRegisterer(reg prometheus.Registerer) Option {
 // used.
 func WithAggregationSelector(agg metric.AggregationSelector) Option {
 	return optionFunc(func(cfg config) config {
-		cfg.aggregation = agg
+		cfg.readerOpts = append(cfg.readerOpts, metric.WithAggregationSelector(agg))
+		return cfg
+	})
+}
+
+// WithProducer configure the metric Producer the exporter will use as a source
+// of external metric data.
+func WithProducer(producer metric.Producer) Option {
+	return optionFunc(func(cfg config) config {
+		cfg.readerOpts = append(cfg.readerOpts, metric.WithProducer(producer))
 		return cfg
 	})
 }

exporters/prometheus/config_test.go

@@ -15,18 +15,21 @@
 package prometheus // import "go.opentelemetry.io/otel/exporters/prometheus"
 
 import (
+	"context"
 	"testing"
 
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/stretchr/testify/assert"
 
 	"go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/metric/metricdata"
 )
 
 func TestNewConfig(t *testing.T) {
 	registry := prometheus.NewRegistry()
 
 	aggregationSelector := func(metric.InstrumentKind) metric.Aggregation { return nil }
+	producer := &noopProducer{}
 
 	testCases := []struct {
 		name       string
@@ -56,17 +59,33 @@ func TestNewConfig(t *testing.T) {
 			},
 			wantConfig: config{
 				registerer: prometheus.DefaultRegisterer,
+				readerOpts: []metric.ManualReaderOption{metric.WithAggregationSelector(aggregationSelector)},
+			},
+		},
+		{
+			name: "WithProducer",
+			options: []Option{
+				WithProducer(producer),
+			},
+			wantConfig: config{
+				registerer: prometheus.DefaultRegisterer,
+				readerOpts: []metric.ManualReaderOption{metric.WithProducer(producer)},
 			},
 		},
 		{
 			name: "With Multiple Options",
 			options: []Option{
 				WithRegisterer(registry),
 				WithAggregationSelector(aggregationSelector),
+				WithProducer(producer),
 			},
 
 			wantConfig: config{
 				registerer: registry,
+				readerOpts: []metric.ManualReaderOption{
+					metric.WithAggregationSelector(aggregationSelector),
+					metric.WithProducer(producer),
+				},
 			},
 		},
 		{
@@ -132,38 +151,18 @@ func TestNewConfig(t *testing.T) {
 	for _, tt := range testCases {
 		t.Run(tt.name, func(t *testing.T) {
 			cfg := newConfig(tt.options...)
-			// tested by TestConfigManualReaderOptions
-			cfg.aggregation = nil
+			// only check the length of readerOpts, since they are not compareable
+			assert.Equal(t, len(tt.wantConfig.readerOpts), len(cfg.readerOpts))
+			cfg.readerOpts = nil
+			tt.wantConfig.readerOpts = nil
 
 			assert.Equal(t, tt.wantConfig, cfg)
 		})
 	}
 }
 
-func TestConfigManualReaderOptions(t *testing.T) {
-	aggregationSelector := func(metric.InstrumentKind) metric.Aggregation { return nil }
-
-	testCases := []struct {
-		name            string
-		config          config
-		wantOptionCount int
-	}{
-		{
-			name:            "Default",
-			config:          config{},
-			wantOptionCount: 0,
-		},
+type noopProducer struct{}
 
-		{
-			name:            "WithAggregationSelector",
-			config:          config{aggregation: aggregationSelector},
-			wantOptionCount: 1,
-		},
-	}
-	for _, tt := range testCases {
-		t.Run(tt.name, func(t *testing.T) {
-			opts := tt.config.manualReaderOptions()
-			assert.Len(t, opts, tt.wantOptionCount)
-		})
-	}
+func (*noopProducer) Produce(ctx context.Context) ([]metricdata.ScopeMetrics, error) {
+	return nil, nil
 }

exporters/prometheus/exporter.go

@@ -101,7 +101,7 @@ func New(opts ...Option) (*Exporter, error) {
 	// this assumes that the default temporality selector will always return cumulative.
 	// we only support cumulative temporality, so building our own reader enforces this.
 	// TODO (#3244): Enable some way to configure the reader, but not change temporality.
-	reader := metric.NewManualReader(cfg.manualReaderOptions()...)
+	reader := metric.NewManualReader(cfg.readerOpts...)
 
 	collector := &collector{
 		reader:                 reader,