Add error for both consumer filter fields specified

Signed-off-by: Tomasz Pietrek <tomasz@nats.io>

server/consumer.go

@@ -495,6 +495,13 @@ func checkConsumerCfg(
 		}
 	}
 
+	// Do not allow specifying both FilterSubject and FilterSubjects,
+	// as that's probably unintentional wihout any difference from passing
+	// all filters in FilterSubjects.
+	if config.FilterSubject != _EMPTY_ && len(config.FilterSubjects) > 0 {
+		return NewJSConsumerDuplicateFilterSubjectsError()
+	}
+
 	if config.FilterSubject != _EMPTY_ && !IsValidSubject(config.FilterSubject) {
 		return NewJSStreamInvalidConfigError(ErrBadSubject)
 	}

server/jetstream_test.go

@@ -19228,6 +19228,31 @@ func TestJetStreamConsumerOverlappingSubjects(t *testing.T) {
 	}
 }
 
+func TestJetStreamBothFiltersSet(t *testing.T) {
+	s := RunBasicJetStreamServer(t)
+	if config := s.JetStreamConfig(); config != nil {
+		defer removeDir(t, config.StoreDir)
+	}
+	defer s.Shutdown()
+
+	nc, _ := jsClientConnect(t, s)
+	defer nc.Close()
+	acc := s.GlobalAccount()
+
+	_, err := acc.addStream(&StreamConfig{
+		Subjects: []string{"events.>"},
+		Name:     "deliver",
+	})
+	require_NoError(t, err)
+
+	resp := createConsumer(t, nc, "deliver", ConsumerConfig{
+		FilterSubjects: []string{"events.one", "events.two"},
+		FilterSubject:  "events.three",
+		Durable:        "name",
+	})
+	require_True(t, resp.Error.ErrCode == 10136)
+}
+
 func TestJetStreamMultipleSubjectsPushBasic(t *testing.T) {
 	s := RunBasicJetStreamServer(t)
 	if config := s.JetStreamConfig(); config != nil {