Use default view if instrument does not match any pipeline view

CHANGELOG.md

@@ -19,6 +19,10 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Upgrade `golang.org/x/sys/unix` from `v0.0.0-20210423185535-09eb48e85fd7` to `v0.0.0-20220919091848-fb04ddd9f9c8`.
   This addresses [GO-2022-0493](https://pkg.go.dev/vuln/GO-2022-0493). (#3235)
 
+### Fixed
+
+- Use default view if instrument does not match any registered view of a reader. (#3224, #3237)
+
 ## [0.32.1] Metric SDK (Alpha) - 2022-09-22
 
 ### Changed

sdk/metric/config.go

@@ -126,10 +126,6 @@ func WithReader(r Reader, views ...view.View) Option {
 		if cfg.readers == nil {
 			cfg.readers = make(map[Reader][]view.View)
 		}
-		if len(views) == 0 {
-			views = []view.View{{}}
-		}
-
 		cfg.readers[r] = views
 		return cfg
 	})

sdk/metric/pipeline.go

@@ -188,31 +188,23 @@ func newInserter[N int64 | float64](p *pipeline) *inserter[N] {
 // Instrument inserts instrument inst with instUnit returning the Aggregators
 // that need to be updated with measurments for that instrument.
 func (i *inserter[N]) Instrument(inst view.Instrument, instUnit unit.Unit) ([]internal.Aggregator[N], error) {
+	var matched bool
 	seen := map[instrumentID]struct{}{}
 	var aggs []internal.Aggregator[N]
 	errs := &multierror{wrapped: errCreatingAggregators}
 	for _, v := range i.pipeline.views {
 		inst, match := v.TransformInstrument(inst)
+		if !match {
+			continue
+		}
+		matched = true
 
 		id := instrumentID{
 			scope:       inst.Scope,
 			name:        inst.Name,
 			description: inst.Description,
 		}
-
-		if _, ok := seen[id]; ok || !match {
-			continue
-		}
-
-		if inst.Aggregation == nil {
-			inst.Aggregation = i.pipeline.reader.aggregation(inst.Kind)
-		} else if _, ok := inst.Aggregation.(aggregation.Default); ok {
-			inst.Aggregation = i.pipeline.reader.aggregation(inst.Kind)
-		}
-
-		if err := isAggregatorCompatible(inst.Kind, inst.Aggregation); err != nil {
-			err = fmt.Errorf("creating aggregator with instrumentKind: %d, aggregation %v: %w", inst.Kind, inst.Aggregation, err)
-			errs.append(err)
+		if _, ok := seen[id]; ok {
 			continue
 		}
 
@@ -224,25 +216,55 @@ func (i *inserter[N]) Instrument(inst view.Instrument, instUnit unit.Unit) ([]in
 		if agg == nil { // Drop aggregator.
 			continue
 		}
+		err = i.pipeline.addAggregator(inst.Scope, inst.Name, inst.Description, instUnit, agg)
+		if err != nil {
+			errs.append(err)
+			// Do not return the aggregator to be updated if the pipeline will
+			// never produce from it.
+			continue
+		}
 		// TODO (#3011): If filtering is done at the instrument level add here.
 		// This is where the aggregator and the view are both in scope.
 		aggs = append(aggs, agg)
 		seen[id] = struct{}{}
-		err = i.pipeline.addAggregator(inst.Scope, inst.Name, inst.Description, instUnit, agg)
+	}
+
+	if !matched { // Apply implicit default view if no explicit matched.
+		a, err := i.aggregator(inst)
 		if err != nil {
 			errs.append(err)
 		}
+		if a != nil {
+			err = i.pipeline.addAggregator(inst.Scope, inst.Name, inst.Description, instUnit, a)
+			if err != nil {
+				// Do not return the aggregator to be updated if the pipeline
+				// will never produce from it.
+				errs.append(err)
+			} else {
+				aggs = append(aggs, a)
+			}
+		}
 	}
-	// TODO(#3224): handle when no views match. Default should be reader
-	// aggregation returned.
+
 	return aggs, errs.errorOrNil()
 }
 
 // aggregator returns the Aggregator for an instrument configuration. If the
 // instrument defines an unknown aggregation, an error is returned.
 func (i *inserter[N]) aggregator(inst view.Instrument) (internal.Aggregator[N], error) {
-	// TODO (#3011): If filtering is done by the Aggregator it should be passed
-	// here.
+	switch inst.Aggregation.(type) {
+	case nil, aggregation.Default:
+		// Undefined, nil, means to use the default from the reader.
+		inst.Aggregation = i.pipeline.reader.aggregation(inst.Kind)
+	}
+
+	if err := isAggregatorCompatible(inst.Kind, inst.Aggregation); err != nil {
+		return nil, fmt.Errorf(
+			"creating aggregator with instrumentKind: %d, aggregation %v: %w",
+			inst.Kind, inst.Aggregation, err,
+		)
+	}
+
 	var (
 		temporality = i.pipeline.reader.temporality(inst.Kind)
 		monotonic   bool

sdk/metric/pipeline_test.go

@@ -25,7 +25,10 @@ import (
 	"go.opentelemetry.io/otel/attribute"
 	"go.opentelemetry.io/otel/metric/unit"
 	"go.opentelemetry.io/otel/sdk/instrumentation"
+	"go.opentelemetry.io/otel/sdk/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/metricdata"
+	"go.opentelemetry.io/otel/sdk/metric/metricdata/metricdatatest"
+	"go.opentelemetry.io/otel/sdk/metric/view"
 	"go.opentelemetry.io/otel/sdk/resource"
 )
 
@@ -211,3 +214,61 @@ func TestPipelineConcurrency(t *testing.T) {
 	}
 	wg.Wait()
 }
+
+func TestDefaultViewImplicit(t *testing.T) {
+	t.Run("Int64", testDefaultViewImplicit[int64]())
+	t.Run("Float64", testDefaultViewImplicit[float64]())
+}
+
+func testDefaultViewImplicit[N int64 | float64]() func(t *testing.T) {
+	inst := view.Instrument{
+		Scope:       instrumentation.Scope{Name: "testing/lib"},
+		Name:        "requests",
+		Description: "count of requests received",
+		Kind:        view.SyncCounter,
+		Aggregation: aggregation.Sum{},
+	}
+	return func(t *testing.T) {
+		reader := NewManualReader()
+		v, err := view.New(view.MatchInstrumentName("foo"), view.WithRename("bar"))
+		require.NoError(t, err)
+
+		tests := []struct {
+			name string
+			pipe *pipeline
+		}{
+			{
+				name: "NoView",
+				pipe: newPipeline(nil, reader, nil),
+			},
+			{
+				name: "NoMatchingView",
+				pipe: newPipeline(nil, reader, []view.View{v}),
+			},
+		}
+
+		for _, test := range tests {
+			t.Run(test.name, func(t *testing.T) {
+				i := newInserter[N](test.pipe)
+				got, err := i.Instrument(inst, unit.Dimensionless)
+				require.NoError(t, err)
+				assert.Len(t, got, 1, "default view not applied")
+
+				out, err := test.pipe.produce(context.Background())
+				require.NoError(t, err)
+				require.Len(t, out.ScopeMetrics, 1, "Aggregator not registered with pipeline")
+				sm := out.ScopeMetrics[0]
+				require.Len(t, sm.Metrics, 1, "metrics not produced from default view")
+				metricdatatest.AssertEqual(t, metricdata.Metrics{
+					Name:        inst.Name,
+					Description: inst.Description,
+					Unit:        unit.Dimensionless,
+					Data: metricdata.Sum[N]{
+						Temporality: metricdata.CumulativeTemporality,
+						IsMonotonic: true,
+					},
+				}, sm.Metrics[0], metricdatatest.IgnoreTimestamp())
+			})
+		}
+	}
+}