Fix Name field in template processor (#7258)

(cherry picked from commit 3dab845)

plugins/processors/template/template_metric.go

@@ -1,16 +1,17 @@
 package template
 
 import (
-	"github.com/influxdata/telegraf"
 	"time"
+
+	"github.com/influxdata/telegraf"
 )
 
 type TemplateMetric struct {
 	metric telegraf.Metric
 }
 
-func (m *TemplateMetric) Measurement() string {
-	return m.Measurement()
+func (m *TemplateMetric) Name() string {
+	return m.metric.Name()
 }
 
 func (m *TemplateMetric) Tag(key string) string {

plugins/processors/template/template_test.go

@@ -7,8 +7,45 @@ import (
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/testutil"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
+func TestName(t *testing.T) {
+	plugin := TemplateProcessor{
+		Tag:      "measurement",
+		Template: "{{ .Name }}",
+	}
+
+	err := plugin.Init()
+	require.NoError(t, err)
+
+	input := []telegraf.Metric{
+		testutil.MustMetric(
+			"cpu",
+			map[string]string{},
+			map[string]interface{}{
+				"time_idle": 42,
+			},
+			time.Unix(0, 0),
+		),
+	}
+
+	actual := plugin.Apply(input...)
+	expected := []telegraf.Metric{
+		testutil.MustMetric(
+			"cpu",
+			map[string]string{
+				"measurement": "cpu",
+			},
+			map[string]interface{}{
+				"time_idle": 42,
+			},
+			time.Unix(0, 0),
+		),
+	}
+	testutil.RequireMetricsEqual(t, expected, actual)
+}
+
 func TestTagTemplateConcatenate(t *testing.T) {
 	now := time.Now()