Remove __name__ from alerts sent to AM.

Fixes #1861

rules/alerting.go

@@ -198,6 +198,7 @@ func (r *AlertingRule) eval(ts model.Time, engine *promql.Engine, externalURLPat
 			return model.LabelValue(result)
 		}
 
+		delete(smpl.Metric, model.MetricNameLabel)
 		labels := make(model.LabelSet, len(smpl.Metric)+len(r.labels)+1)
 		for ln, lv := range smpl.Metric {
 			labels[ln] = lv
@@ -219,8 +220,6 @@ func (r *AlertingRule) eval(ts model.Time, engine *promql.Engine, externalURLPat
 			continue
 		}
 
-		delete(smpl.Metric, model.MetricNameLabel)
-
 		r.active[fp] = &Alert{
 			Labels:      labels,
 			Annotations: annotations,

rules/manager_test.go

@@ -136,6 +136,12 @@ func TestAlertingRule(t *testing.T) {
 			t.Errorf("%d. Expected and actual outputs don't match:", i)
 			t.Fatalf("Expected:\n%v\n----\nActual:\n%v", strings.Join(expected, "\n"), strings.Join(actual, "\n"))
 		}
+
+		for _, aa := range rule.ActiveAlerts() {
+			if _, ok := aa.Labels[model.MetricNameLabel]; ok {
+				t.Fatalf("%s label set on active alert: %s", model.MetricNameLabel, aa.Labels)
+			}
+		}
 	}
 }