[hotfix] Fix FlinkKafkaConsumerBaseTest.testClosePartitionDiscovererWithCancellation

Make a copy of AbstractPartitionDiscoverer#getAllTopics before modifying it.

Author: AHeise

flink-connector-kafka/src/main/java/org/apache/flink/streaming/connectors/kafka/internals/AbstractPartitionDiscoverer.java

@@ -19,8 +19,8 @@
 
 import org.apache.flink.annotation.Internal;
 
+import java.util.ArrayList;
 import java.util.HashSet;
-import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
 
@@ -130,21 +130,18 @@ public List<KafkaTopicPartition> discoverPartitions() throws WakeupException, Cl
                 // topics or a topic pattern
                 if (topicsDescriptor.isFixedTopics()) {
                     newDiscoveredPartitions =
-                            getAllPartitionsForTopics(topicsDescriptor.getFixedTopics());
+                            new ArrayList<>(
+                                    getAllPartitionsForTopics(topicsDescriptor.getFixedTopics()));
                 } else {
-                    List<String> matchedTopics = getAllTopics();
+                    List<String> matchedTopics = new ArrayList<>(getAllTopics());
 
                     // retain topics that match the pattern
-                    Iterator<String> iter = matchedTopics.iterator();
-                    while (iter.hasNext()) {
-                        if (!topicsDescriptor.isMatchingTopic(iter.next())) {
-                            iter.remove();
-                        }
-                    }
+                    matchedTopics.removeIf(s -> !topicsDescriptor.isMatchingTopic(s));
 
-                    if (matchedTopics.size() != 0) {
+                    if (!matchedTopics.isEmpty()) {
                         // get partitions only for matched topics
-                        newDiscoveredPartitions = getAllPartitionsForTopics(matchedTopics);
+                        newDiscoveredPartitions =
+                                new ArrayList<>(getAllPartitionsForTopics(matchedTopics));
                     } else {
                         newDiscoveredPartitions = null;
                     }
@@ -157,14 +154,8 @@ public List<KafkaTopicPartition> discoverPartitions() throws WakeupException, Cl
                             "Unable to retrieve any partitions with KafkaTopicsDescriptor: "
                                     + topicsDescriptor);
                 } else {
-                    Iterator<KafkaTopicPartition> iter = newDiscoveredPartitions.iterator();
-                    KafkaTopicPartition nextPartition;
-                    while (iter.hasNext()) {
-                        nextPartition = iter.next();
-                        if (!setAndCheckDiscoveredPartition(nextPartition)) {
-                            iter.remove();
-                        }
-                    }
+                    newDiscoveredPartitions.removeIf(
+                            nextPartition -> !setAndCheckDiscoveredPartition(nextPartition));
                 }
 
                 return newDiscoveredPartitions;