Apply suggestions from code review

Co-authored-by: Ivan <2103732+codebien@users.noreply.github.com>

output/cloud/expv2/flush.go

@@ -74,7 +74,7 @@ func (f *metricsFlusher) push(msb metricSetBuilder) error {
 		}
 
 		f.discardedLabels[key] = struct{}{}
-		f.logger.Warnf("Label %s was discarded since it can't be used with the cloud output", key)
+		f.logger.Warnf("Tag %s has been discarded since it is reserved for Cloud operations.", key)
 	}
 
 	return f.client.push(msb.MetricSet)
@@ -107,7 +107,7 @@ type metricSetBuilder struct {
 	seriesIndex map[metrics.TimeSeries]uint
 
 	// discardedLabels tracks the labels that have been discarded
-	// because they are not supported by the remote service.
+	// since they are reserved for internal usage by the Cloud service.
 	discardedLabels map[string]struct{}
 }
 
@@ -157,12 +157,16 @@ func (msb *metricSetBuilder) addTimeBucket(bucket timeBucket) {
 	}
 }
 
-func (msb *metricSetBuilder) recordDiscardedLabels(labels map[string]struct{}) {
+func (msb *metricSetBuilder) recordDiscardedLabels(labels []string) {
+	if len(labels) == 0 {
+		return
+	}
+
 	if msb.discardedLabels == nil {
 		msb.discardedLabels = make(map[string]struct{})
 	}
 
-	for key := range labels {
+	for _, key := range labels {
 		if _, ok := msb.discardedLabels[key]; ok {
 			continue
 		}

output/cloud/expv2/flush_test.go

@@ -224,8 +224,8 @@ func TestFlushWithReservedLabels(t *testing.T) {
 
 	// check that warnings sown only once per label
 	require.Len(t, loglines, 2)
-	testutils.LogContains(loglines, logrus.WarnLevel, "Label __name__ was discarded since it can't be used with the cloud output")
-	testutils.LogContains(loglines, logrus.WarnLevel, "Label test_run_id was discarded since it can't be used with the cloud output")
+	testutils.LogContains(loglines, logrus.WarnLevel, "Tag __name__ has been discarded since it is reserved for Cloud operations.")
+	testutils.LogContains(loglines, logrus.WarnLevel, "Tag test_run_id has been discarded since it is reserved for Cloud operations.")
 
 	// check that flusher is not sending labels with reserved names
 	require.Len(t, collected[0].Metrics, 1)

output/cloud/expv2/mapping.go

@@ -11,9 +11,9 @@ import (
 )
 
 // TODO: unit test
-func mapTimeSeriesLabelsProto(tags *metrics.TagSet) ([]*pbcloud.Label, map[string]struct{}) {
+func mapTimeSeriesLabelsProto(tags *metrics.TagSet) ([]*pbcloud.Label, []string) {
 	labels := make([]*pbcloud.Label, 0, ((*atlas.Node)(tags)).Len())
-	var discardedLabels map[string]struct{}
+	var discardedLabels []string
 
 	// TODO: move this as a shared func
 	// https://github.com/grafana/k6/issues/2764
@@ -31,10 +31,10 @@ func mapTimeSeriesLabelsProto(tags *metrics.TagSet) ([]*pbcloud.Label, map[strin
 		}
 
 		if discardedLabels == nil {
-			discardedLabels = make(map[string]struct{})
+			discardedLabels = make([]string, 0, 1)
 		}
 
-		discardedLabels[key] = struct{}{}
+		discardedLabels = append(discardedLabels, key)
 	}
 	return labels, discardedLabels
 }