Log an error for an empty view criteria

CHANGELOG.md

@@ -33,6 +33,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 ### Fixed
 
 - Correctly format log messages from the `go.opentelemetry.io/otel/exporters/zipkin` exporter. (#4143)
+- Log an error for calls to `NewView` in `go.opentelemetry.io/otel/sdk/metric` that have empty criteria. (#4307)
 
 ## [1.16.0/0.39.0] 2023-05-18
 

sdk/metric/view.go

@@ -25,6 +25,7 @@ import (
 
 var (
 	errMultiInst = errors.New("name replacement for multiple instruments")
+	errEmptyView = errors.New("no criteria provided for view")
 
 	emptyView = func(Instrument) (Stream, bool) { return Stream{}, false }
 )
@@ -55,6 +56,10 @@ type View func(Instrument) (Stream, bool)
 // View, create a View directly.
 func NewView(criteria Instrument, mask Stream) View {
 	if criteria.empty() {
+		global.Error(
+			errEmptyView, "dropping view",
+			"mask", mask,
+		)
 		return emptyView
 	}
 

sdk/metric/view_test.go

@@ -20,6 +20,7 @@ import (
 	"testing"
 
 	"github.com/go-logr/logr"
+	"github.com/go-logr/logr/funcr"
 	"github.com/go-logr/logr/testr"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -466,6 +467,16 @@ func TestNewViewAggregationErrorLogged(t *testing.T) {
 	assert.Equal(t, 1, l.ErrorN())
 }
 
+func TestNewViewEmptyViewErrorLogged(t *testing.T) {
+	var got string
+	otel.SetLogger(funcr.New(func(_, args string) {
+		got = args
+	}, funcr.Options{Verbosity: 6}))
+
+	_ = NewView(Instrument{}, Stream{})
+	assert.Contains(t, got, errEmptyView.Error())
+}
+
 func ExampleNewView() {
 	// Create a view that renames the "latency" instrument from the v0.34.0
 	// version of the "http" instrumentation library as "request.latency".