sdk/metric: Log empty meter name (#4153)

* sdk/metric: Log empty meter name

* Avoid magic numbers

* Lint

* Apply suggestions from code review

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update log message

* Apply suggestion

---------

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

sdk/metric/provider.go

@@ -17,6 +17,7 @@ package metric // import "go.opentelemetry.io/otel/sdk/metric"
 import (
 	"context"
 
+	"go.opentelemetry.io/otel/internal/global"
 	"go.opentelemetry.io/otel/metric"
 	"go.opentelemetry.io/otel/metric/embedded"
 	"go.opentelemetry.io/otel/sdk/instrumentation"
@@ -65,6 +66,10 @@ func NewMeterProvider(options ...Option) *MeterProvider {
 //
 // This method is safe to call concurrently.
 func (mp *MeterProvider) Meter(name string, options ...metric.MeterOption) metric.Meter {
+	if name == "" {
+		global.Warn("Invalid Meter name.", "name", name)
+	}
+
 	c := metric.NewMeterConfig(options...)
 	s := instrumentation.Scope{
 		Name:      name,

sdk/metric/provider_test.go

@@ -16,9 +16,14 @@ package metric
 
 import (
 	"context"
+	"fmt"
+	"strings"
 	"testing"
 
+	"github.com/go-logr/logr/funcr"
 	"github.com/stretchr/testify/assert"
+
+	"go.opentelemetry.io/otel"
 )
 
 func TestMeterConcurrentSafe(t *testing.T) {
@@ -74,3 +79,17 @@ func TestMeterProviderReturnsSameMeter(t *testing.T) {
 	assert.Same(t, mtr, mp.Meter(""))
 	assert.NotSame(t, mtr, mp.Meter("diff"))
 }
+
+func TestEmptyMeterName(t *testing.T) {
+	var buf strings.Builder
+	warnLevel := 1
+	l := funcr.New(func(prefix, args string) {
+		_, _ = buf.WriteString(fmt.Sprint(prefix, args))
+	}, funcr.Options{Verbosity: warnLevel})
+	otel.SetLogger(l)
+	mp := NewMeterProvider()
+
+	mp.Meter("")
+
+	assert.Contains(t, buf.String(), `"level"=1 "msg"="Invalid Meter name." "name"=""`)
+}