Fix name of combining filtered aggregator factory. (#16224)

The name of the combining filtered aggregator factory should be the same
as the name of the original factory. However, it wasn't the same in the
case where the original factory's name and the original delegate aggregator
were inconsistently named. In this scenario, we should use the name of
the original filtered aggregator, not the name of the original delegate
aggregator.

processing/src/main/java/org/apache/druid/query/aggregation/FilteredAggregatorFactory.java

@@ -139,7 +139,14 @@ public AggregateCombiner makeAggregateCombiner()
   @Override
   public AggregatorFactory getCombiningFactory()
   {
-    return delegate.getCombiningFactory();
+    final AggregatorFactory delegateCombiningFactory = delegate.getCombiningFactory();
+    final String myName = getName();
+
+    if (myName.equals(delegateCombiningFactory.getName())) {
+      return delegateCombiningFactory;
+    } else {
+      return delegateCombiningFactory.withName(myName);
+    }
   }
 
   @Override

processing/src/test/java/org/apache/druid/query/aggregation/FilteredAggregatorFactoryTest.java

@@ -48,6 +48,26 @@ public void testSimpleNaming()
     ).getName());
   }
 
+  @Test
+  public void testNameOfCombiningFactory()
+  {
+    Assert.assertEquals("overrideName", new FilteredAggregatorFactory(
+        new CountAggregatorFactory("foo"),
+        TrueDimFilter.instance(),
+        "overrideName"
+    ).getCombiningFactory().getName());
+    Assert.assertEquals("delegateName", new FilteredAggregatorFactory(
+        new CountAggregatorFactory("delegateName"),
+        TrueDimFilter.instance(),
+        ""
+    ).getCombiningFactory().getName());
+    Assert.assertEquals("delegateName", new FilteredAggregatorFactory(
+        new CountAggregatorFactory("delegateName"),
+        TrueDimFilter.instance(),
+        null
+    ).getCombiningFactory().getName());
+  }
+
   @Test
   public void testRequiredFields()
   {