promql: info function: fix series without identifying labels not being returned (#17898)

* promql: info function: fix series without identifying labels not being returned

---------

Signed-off-by: Jeanette Tan <jeanette.tan@grafana.com>

promql/info.go

@@ -143,6 +143,23 @@ func (ev *evaluator) fetchInfoSeries(ctx context.Context, mat Matrix, ignoreSeri
 		}
 	}
 	if len(idLblValues) == 0 {
+		// Even when returning early, we need to remove __name__ from dataLabelMatchers
+		// since it's not a data label selector (it's used to select which info metrics
+		// to consider). Without this, combineWithInfoVector would incorrectly exclude
+		// series when only __name__ is specified in the selector.
+		for name, ms := range dataLabelMatchers {
+			for i, m := range ms {
+				if m.Name == labels.MetricName {
+					ms = slices.Delete(ms, i, i+1)
+					break
+				}
+			}
+			if len(ms) > 0 {
+				dataLabelMatchers[name] = ms
+			} else {
+				delete(dataLabelMatchers, name)
+			}
+		}
 		return nil, nil, nil
 	}
 

promql/promqltest/testdata/info.test

@@ -166,3 +166,35 @@ eval range from 0 to 2m step 1m info({job="work"}, {__name__="info_metric"})
 	data_metric{instance="a", job="work", state="running", label="new"} _ _ 30
 	info_metric{instance="b", job="work", state="stopped"} 1 1 1
 	info_metric{instance="a", job="work", state="running"} 1 1 1
+
+clear
+
+load 1m
+	data_metric{} 1 2 3
+
+eval range from 0 to 2m step 1m info(data_metric, {__name__="info_metric"})
+	data_metric{} 1 2 3
+
+clear
+
+load 1m
+	data_metric{} 1 2 3
+	data_metric{instance="a"} 4 5 6
+
+eval range from 0 to 2m step 1m info(data_metric, {__name__="info_metric"})
+	data_metric{} 1 2 3
+	data_metric{instance="a"} 4 5 6
+
+clear
+
+load 1m
+	data_metric{} 1 2 3
+	data_metric{instance="a"} 4 5 6
+	data_metric{job="1"} 7 8 9
+	data_metric{instance="a", job="1"} 10 20 30
+
+eval range from 0 to 2m step 1m info(data_metric, {__name__="info_metric"})
+	data_metric{} 1 2 3
+	data_metric{instance="a"} 4 5 6
+	data_metric{job="1"} 7 8 9
+	data_metric{instance="a", job="1"} 10 20 30