Restore cluster leaf names to a List

Author: larry-safran

xds/src/main/java/io/grpc/xds/XdsConfig.java

@@ -26,9 +26,9 @@
 import io.grpc.xds.XdsRouteConfigureResource.RdsUpdate;
 import java.io.Closeable;
 import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.Objects;
-import java.util.Set;
 
 /**
  * Represents the xDS configuration tree for a specified Listener.
@@ -206,9 +206,9 @@ public String toString() {
 
     // The list of leaf clusters for an aggregate cluster.
     static final class AggregateConfig implements ClusterChild {
-      private final Set<String> leafNames;
+      private final List<String> leafNames;
 
-      public AggregateConfig(Set<String> leafNames) {
+      public AggregateConfig(List<String> leafNames) {
         this.leafNames = checkNotNull(leafNames, "leafNames");
       }
 

xds/src/main/java/io/grpc/xds/XdsDependencyManager.java

@@ -472,7 +472,7 @@ private Set<String> addTopLevelClustersToBuilder(
       XdsConfig.XdsClusterConfig.ClusterChild child;
       switch (cdsUpdate.clusterType()) {
         case AGGREGATE:
-          Set<String> leafNames = new HashSet<>();
+          List<String> leafNames = new ArrayList<>();
           addLeafNames(leafNames, cdsUpdate);
           child = new AggregateConfig(leafNames);
           leafClusterNames.addAll(leafNames);
@@ -508,15 +508,27 @@ private Set<String> addTopLevelClustersToBuilder(
     return leafClusterNames;
   }
 
-  private void addLeafNames(Set<String> leafNames, XdsClusterResource.CdsUpdate cdsUpdate) {
+  /**
+   * Recursively adds the leaf names of the clusters in the aggregate cluster to the list.
+   * @param leafNames priority ordered list of leaf names we will add to
+   * @param cdsUpdate the cluster config being processed
+   */
+  private void addLeafNames(List<String> leafNames, XdsClusterResource.CdsUpdate cdsUpdate) {
     for (String cluster : cdsUpdate.prioritizedClusterNames()) {
       if (leafNames.contains(cluster)) {
         continue;
       }
+
       StatusOr<XdsClusterResource.CdsUpdate> data = getCluster(cluster).getData();
-      if (data == null || !data.hasValue() || data.getValue() == null) {
+      if (data == null) {
         continue;
       }
+      if (!data.hasValue()) {
+        leafNames.add(cluster);
+        continue;
+      }
+      assert data.getValue() != null;
+
       if (data.getValue().clusterType() == ClusterType.AGGREGATE) {
         addLeafNames(leafNames, data.getValue());
       } else {