[processor/metricstransform] Fix silent data loss for single Summary metric in combine action

Author: himanshu130700

.chloggen/49693-metricstransform-combine-summary-single.yaml

@@ -0,0 +1,9 @@
+change_type: bug_fix
+
+component: processor/metrics_transform
+
+note: combine action no longer silently drops data points when a single Summary metric matches the transform. The operation is now skipped with a warning log instead.
+
+issues: [49693]
+
+change_logs: [user]

processor/metricstransformprocessor/metrics_transform_processor_otlp.go

@@ -324,15 +324,18 @@ func initResourceMetrics(dest pmetric.ResourceMetrics, resource pcommon.Resource
 
 // canBeCombined returns true if all the provided metrics share the same type, unit, and labels
 func canBeCombined(metrics []pmetric.Metric) error {
+	for _, metric := range metrics {
+		if metric.Type() == pmetric.MetricTypeSummary {
+			return fmt.Errorf("Summary metrics cannot be combined: %v ", metric.Name())
+		}
+	}
+
 	if len(metrics) <= 1 {
 		return nil
 	}
 
 	var firstMetric pmetric.Metric
 	for _, metric := range metrics {
-		if metric.Type() == pmetric.MetricTypeSummary {
-			return fmt.Errorf("Summary metrics cannot be combined: %v ", metric.Name())
-		}
 
 		if firstMetric == (pmetric.Metric{}) {
 			firstMetric = metric

processor/metricstransformprocessor/metrics_transform_processor_testcases_test.go

@@ -1440,6 +1440,29 @@ var standardTests = []metricsTransformTest{
 			metricBuilder(pmetric.MetricTypeGauge, "metric3").addIntDatapoint(1, 1, 3).build(),
 		},
 	},
+	{
+		name: "combine_error_summary_single_match",
+		transforms: []internalTransform{
+			{
+				MetricIncludeFilter: internalFilterRegexp{include: regexp.MustCompile("^metric1$")},
+				Action:              Combine,
+				NewName:             "new",
+				AggregationType:     aggregateutil.Sum,
+			},
+		},
+		in: []pmetric.Metric{
+			metricBuilder(pmetric.MetricTypeSummary, "metric1", "label1").
+				addSummaryDatapoint(1, 2, 10, 100.0, "label1-value1").
+				addSummaryDatapoint(1, 2, 20, 200.0, "label1-value2").build(),
+			metricBuilder(pmetric.MetricTypeGauge, "metric2").addIntDatapoint(1, 1, 2).build(),
+		},
+		out: []pmetric.Metric{
+			metricBuilder(pmetric.MetricTypeSummary, "metric1", "label1").
+				addSummaryDatapoint(1, 2, 10, 100.0, "label1-value1").
+				addSummaryDatapoint(1, 2, 20, 200.0, "label1-value2").build(),
+			metricBuilder(pmetric.MetricTypeGauge, "metric2").addIntDatapoint(1, 1, 2).build(),
+		},
+	},
 	// Toggle Data Type
 	{
 		name: "metric_toggle_scalar_data_type_int64_to_double",