Fix a potential issue in the ResourceChangeSnapshot.

helix-core/src/main/java/org/apache/helix/controller/changedetector/ResourceChangeSnapshot.java

@@ -24,8 +24,10 @@
 import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
+import java.util.stream.Collectors;
 
 import org.apache.helix.HelixConstants;
+import org.apache.helix.ZNRecord;
 import org.apache.helix.controller.dataproviders.ResourceControllerDataProvider;
 import org.apache.helix.model.ClusterConfig;
 import org.apache.helix.model.IdealState;
@@ -130,18 +132,22 @@ private IdealState trimIdealState(IdealState originalIdealState) {
     // Clone the IdealState to avoid modifying the objects in the Cluster Data Cache, which might
     // be used by the other stages in the pipeline.
     IdealState trimmedIdealState = new IdealState(originalIdealState.getRecord());
+    ZNRecord trimmedIdealStateRecord = trimmedIdealState.getRecord();
     switch (originalIdealState.getRebalanceMode()) {
+      // WARNING: the IdealState copy constructor is not really deep copy. So we should not modify
+      // the values directly or the cached values will be changed.
       case FULL_AUTO:
         // For FULL_AUTO resources, both map fields and list fields are not considered as data input
         // for the controller. The controller will write to these two types of fields for persisting
         // the assignment mapping.
-        trimmedIdealState.getRecord().setListFields(Collections.emptyMap());
-        trimmedIdealState.getRecord().setMapFields(Collections.emptyMap());
-        break;
+        trimmedIdealStateRecord.setListFields(trimmedIdealStateRecord.getListFields().keySet().stream().collect(
+            Collectors.toMap(partition -> partition, partition -> Collections.emptyList())));
+        // Continue to clean up map fields in the SEMI_AUTO case.
       case SEMI_AUTO:
         // For SEMI_AUTO resources, map fields are not considered as data input for the controller.
         // The controller will write to the map fields for persisting the assignment mapping.
-        trimmedIdealState.getRecord().setMapFields(Collections.emptyMap());
+        trimmedIdealStateRecord.setMapFields(trimmedIdealStateRecord.getMapFields().keySet().stream().collect(
+            Collectors.toMap(partition -> partition, partition -> Collections.emptyMap())));
         break;
       default:
         break;

helix-core/src/test/java/org/apache/helix/controller/changedetector/TestResourceChangeDetector.java

@@ -359,22 +359,21 @@ public void testIgnoreControllerGeneratedFields() {
         .addResource(CLUSTER_NAME, resourceName, NUM_PARTITIONS, STATE_MODEL);
     IdealState idealState = _dataAccessor.getProperty(_keyBuilder.idealStates(resourceName));
     idealState.setRebalanceMode(IdealState.RebalanceMode.FULL_AUTO);
+    idealState.getRecord().getMapFields().put("Partition1", new HashMap<>());
     _dataAccessor.updateProperty(_keyBuilder.idealStates(resourceName), idealState);
-
     _dataProvider.notifyDataChange(ChangeType.CLUSTER_CONFIG);
     _dataProvider.notifyDataChange(ChangeType.IDEAL_STATE);
     _dataProvider.refresh(_dataAccessor);
 
+    // Test with ignore option to be true
     ResourceChangeDetector changeDetector = new ResourceChangeDetector(true);
     changeDetector.updateSnapshots(_dataProvider);
-
-    // Now, modify the field that is modifying by Helix logic
-    idealState.getRecord().getMapFields().put("Extra_Change", new HashMap<>());
-    _dataAccessor.updateProperty(_keyBuilder.idealStates(NEW_RESOURCE_NAME), idealState);
+    // Now, modify the field
+    idealState.getRecord().getMapFields().put("Partition1", Collections.singletonMap("foo", "bar"));
+    _dataAccessor.updateProperty(_keyBuilder.idealStates(resourceName), idealState);
     _dataProvider.notifyDataChange(ChangeType.IDEAL_STATE);
     _dataProvider.refresh(_dataAccessor);
     changeDetector.updateSnapshots(_dataProvider);
-
     Assert.assertEquals(changeDetector.getChangeTypes(),
         Collections.singleton(ChangeType.IDEAL_STATE));
     Assert.assertEquals(