Clean up how pipeline aggs check for multi-bucket (backport of #54161) (#54379)

Pipeline aggregations like `stats_bucket`, `sum_bucket`, and
`percentiles_bucket` only operate on buckets that have multiple buckets.
This adds support for those aggregations to `geo_distance`, `ip_range`,
`auto_date_histogram`, and `rare_terms`.

This all happened because we used a marker interface to mark compatible
aggs, `MultiBucketAggregationBuilder` and it was fairly easy to forget
to implement the interface.

This replaces the marker interface with an abstract method in
`AggregationBuilder`, `bucketCardinality` which makes you return `NONE`,
`ONE`, or `MANY`. The `bucket` aggregations can check for `MANY`. At
this point `ONE` and `NONE` amount to about the same thing, but I
suspect that'll be a useful distinction when validating bucket sorts.

Closes #53215

client/rest-high-level/src/main/java/org/elasticsearch/client/analytics/StringStatsAggregationBuilder.java

@@ -86,6 +86,11 @@ public class StringStatsAggregationBuilder extends ValuesSourceAggregationBuilde
         throw new UnsupportedOperationException();
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.NONE;
+    }
+
     @Override
     protected ValuesSourceAggregatorFactory<Bytes> innerBuild(QueryShardContext queryShardContext, ValuesSourceConfig<Bytes> config,
             AggregatorFactory parent, Builder subFactoriesBuilder) throws IOException {

client/rest-high-level/src/main/java/org/elasticsearch/client/analytics/TopMetricsAggregationBuilder.java

@@ -94,6 +94,11 @@ public class TopMetricsAggregationBuilder extends AbstractAggregationBuilder<Top
         throw new UnsupportedOperationException();
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.NONE;
+    }
+
     @Override
     protected AggregatorFactory doBuild(QueryShardContext queryShardContext, AggregatorFactory parent, Builder subfactoriesBuilder)
             throws IOException {

modules/aggs-matrix-stats/src/main/java/org/elasticsearch/search/aggregations/matrix/stats/MatrixStatsAggregationBuilder.java

@@ -38,7 +38,7 @@ import java.io.IOException;
 import java.util.Map;
 
 public class MatrixStatsAggregationBuilder
-    extends ArrayValuesSourceAggregationBuilder.LeafOnly<ValuesSource.Numeric, MatrixStatsAggregationBuilder> {
+        extends ArrayValuesSourceAggregationBuilder.LeafOnly<ValuesSource.Numeric, MatrixStatsAggregationBuilder> {
     public static final String NAME = "matrix_stats";
 
     private MultiValueMode multiValueMode = MultiValueMode.AVG;

modules/aggs-matrix-stats/src/main/java/org/elasticsearch/search/aggregations/support/ArrayValuesSourceAggregationBuilder.java

@@ -84,6 +84,11 @@ public abstract class ArrayValuesSourceAggregationBuilder<VS extends ValuesSourc
             throw new AggregationInitializationException("Aggregator [" + name + "] of type [" +
                 getType() + "] cannot accept sub-aggregations");
         }
+
+        @Override
+        public final BucketCardinality bucketCardinality() {
+            return BucketCardinality.NONE;
+        }
     }
 
     private final ValuesSourceType valuesSourceType;

modules/parent-join/src/main/java/org/elasticsearch/join/aggregations/ChildrenAggregationBuilder.java

@@ -94,11 +94,16 @@ public class ChildrenAggregationBuilder
         out.writeString(childType);
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.ONE;
+    }
+
     @Override
     protected ValuesSourceAggregatorFactory<WithOrdinals> innerBuild(QueryShardContext queryShardContext,
-                                                                     ValuesSourceConfig<WithOrdinals> config,
+                                    ValuesSourceConfig<WithOrdinals> config,
-                                                                     AggregatorFactory parent,
+                                    AggregatorFactory parent,
-                                                                     Builder subFactoriesBuilder) throws IOException {
+                                    Builder subFactoriesBuilder) throws IOException {
         return new ChildrenAggregatorFactory(name, config, childFilter, parentFilter, queryShardContext, parent,
                 subFactoriesBuilder, metaData);
     }

modules/parent-join/src/main/java/org/elasticsearch/join/aggregations/ParentAggregationBuilder.java

@@ -94,11 +94,16 @@ public class ParentAggregationBuilder
         out.writeString(childType);
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.ONE;
+    }
+
     @Override
     protected ValuesSourceAggregatorFactory<WithOrdinals> innerBuild(QueryShardContext queryShardContext,
-                                                                     ValuesSourceConfig<WithOrdinals> config,
+                                ValuesSourceConfig<WithOrdinals> config,
-                                                                     AggregatorFactory parent,
+                                AggregatorFactory parent,
-                                                                     Builder subFactoriesBuilder) throws IOException {
+                                Builder subFactoriesBuilder) throws IOException {
         return new ParentAggregatorFactory(name, config, childFilter, parentFilter, queryShardContext, parent,
                 subFactoriesBuilder, metaData);
     }

rest-api-spec/src/main/resources/rest-api-spec/test/search.aggregation/280_rare_terms.yml

@@ -360,3 +360,64 @@ setup:
   - is_false: aggregations.str_terms.buckets.0.key_as_string
   - match: { aggregations.str_terms.buckets.0.doc_count: 1 }
   - match: { aggregations.str_terms.buckets.0.max_n.value: 3.0 }
+
+---
+"avg_bucket":
+  - skip:
+      version: " - 7.7.99"
+      reason: Fixed in 7.8.0
+  - do:
+      indices.create:
+          index: test
+          body:
+            settings:
+              number_of_replicas: 0
+            mappings:
+              properties:
+                str:
+                   type: keyword
+  - do:
+      bulk:
+        index: test
+        refresh: true
+        body:
+          - '{"index": {}}'
+          - '{"str": "foo", "v": 1}'
+          - '{"index": {}}'
+          - '{"str": "foo", "v": 2}'
+          - '{"index": {}}'
+          - '{"str": "foo", "v": 3}'
+          - '{"index": {}}'
+          - '{"str": "bar", "v": 4}'
+          - '{"index": {}}'
+          - '{"str": "bar", "v": 5}'
+          - '{"index": {}}'
+          - '{"str": "baz", "v": 6}'
+
+  - do:
+      search:
+        index: test
+        body:
+          size: 0
+          aggs:
+            str_terms:
+              rare_terms:
+                field: str
+                max_doc_count: 2
+              aggs:
+                v:
+                  sum:
+                    field: v
+            str_terms_avg_v:
+              avg_bucket:
+                buckets_path: str_terms.v
+
+  - match: { hits.total.value: 6 }
+  - length: { aggregations.str_terms.buckets: 2 }
+  - match: { aggregations.str_terms.buckets.0.key: baz }
+  - match: { aggregations.str_terms.buckets.0.doc_count: 1 }
+  - match: { aggregations.str_terms.buckets.0.v.value: 6 }
+  - match: { aggregations.str_terms.buckets.1.key: bar }
+  - match: { aggregations.str_terms.buckets.1.doc_count: 2 }
+  - match: { aggregations.str_terms.buckets.1.v.value: 9 }
+  - match: { aggregations.str_terms_avg_v.value: 7.5 }

rest-api-spec/src/main/resources/rest-api-spec/test/search.aggregation/330_auto_date_histogram.yml

@@ -0,0 +1,76 @@
+setup:
+  - do:
+      indices.create:
+          index: test
+          body:
+            settings:
+              number_of_replicas: 0
+            mappings:
+              properties:
+                date:
+                  type: date
+  - do:
+      bulk:
+        refresh: true
+        index: test
+        body:
+            - '{"index": {}}'
+            - '{"date": "2020-03-01", "v": 1}'
+            - '{"index": {}}'
+            - '{"date": "2020-03-02", "v": 2}'
+            - '{"index": {}}'
+            - '{"date": "2020-03-08", "v": 3}'
+            - '{"index": {}}'
+            - '{"date": "2020-03-09", "v": 4}'
+
+---
+"basic":
+  - skip:
+      version: " - 7.7.99"
+      reason: Tracked in https://github.com/elastic/elasticsearch/issues/54382
+  - do:
+      search:
+        body:
+          size: 0
+          aggs:
+            histo:
+              auto_date_histogram:
+                field: date
+                buckets: 2
+  - match: { hits.total.value: 4 }
+  - length: { aggregations.histo.buckets: 2 }
+  - match: { aggregations.histo.buckets.0.key_as_string: "2020-03-01T00:00:00.000Z" }
+  - match: { aggregations.histo.buckets.0.doc_count: 2 }
+  - match: { aggregations.histo.buckets.1.key_as_string: "2020-03-08T00:00:00.000Z" }
+  - match: { aggregations.histo.buckets.1.doc_count: 2 }
+
+---
+"avg_bucket":
+  - skip:
+      version: " - 7.7.99"
+      reason: Fixed in 7.8.0
+  - do:
+      search:
+        body:
+          size: 0
+          aggs:
+            histo:
+              auto_date_histogram:
+                field: date
+                buckets: 2
+              aggs:
+                v:
+                  sum:
+                    field: v
+            histo_avg_v:
+              avg_bucket:
+                buckets_path: histo.v
+  - match: { hits.total.value: 4 }
+  - length: { aggregations.histo.buckets: 2 }
+  - match: { aggregations.histo.buckets.0.key_as_string: "2020-03-01T00:00:00.000Z" }
+  - match: { aggregations.histo.buckets.0.doc_count: 2 }
+  - match: { aggregations.histo.buckets.0.v.value: 3 }
+  - match: { aggregations.histo.buckets.1.key_as_string: "2020-03-08T00:00:00.000Z" }
+  - match: { aggregations.histo.buckets.1.doc_count: 2 }
+  - match: { aggregations.histo.buckets.1.v.value: 7 }
+  - match: { aggregations.histo_avg_v.value: 5 }

rest-api-spec/src/main/resources/rest-api-spec/test/search.aggregation/340_geo_distance.yml

@@ -0,0 +1,85 @@
+setup:
+  - do:
+      indices.create:
+        index: test
+        body:
+          mappings:
+            properties:
+              location:
+                type: geo_point
+  - do:
+      bulk:
+        index: test
+        refresh: true
+        body:
+          - '{"index": {}}'
+          - '{"location": {"lat" : 40.7128, "lon" : -74.0060}, "name": "New York", "population": 8623000}'
+          - '{"index": {}}'
+          - '{"location": {"lat" : 34.0522, "lon" : -118.2437}, "name": "Los Angeles", "population": 4000000}'
+          - '{"index": {}}'
+          - '{"location": {"lat" : 41.8781, "lon" : -87.6298}, "name": "Chicago", "population": 2716000}'
+
+---
+"basic":
+  - do:
+      search:
+        rest_total_hits_as_int: true
+        body:
+          size: 0
+          aggs:
+            distance:
+              geo_distance:
+                field: location
+                origin: "35.7796, -78.6382"
+                ranges:
+                  - to: 1000000
+                  - from: 1000000
+                    to: 5000000
+                  - from: 5000000
+  - match: { hits.total: 3 }
+  - length: { aggregations.distance.buckets: 3 }
+  - match: { aggregations.distance.buckets.0.key: "*-1000000.0" }
+  - match: { aggregations.distance.buckets.0.doc_count: 1 }
+  - match: { aggregations.distance.buckets.1.key: "1000000.0-5000000.0" }
+  - match: { aggregations.distance.buckets.1.doc_count: 2 }
+  - match: { aggregations.distance.buckets.2.key: "5000000.0-*" }
+  - match: { aggregations.distance.buckets.2.doc_count: 0 }
+
+---
+"avg_bucket":
+  - skip:
+      version: " - 7.7.99"
+      reason: Fixed in 7.8.0
+  - do:
+      search:
+        body:
+          size: 0
+          aggs:
+            distance:
+              geo_distance:
+                field: location
+                origin: "35.7796, -78.6382"
+                ranges:
+                  - to: 1000000
+                  - from: 1000000
+                    to: 5000000
+                  - from: 5000000
+              aggs:
+                total_population:
+                  sum:
+                    field: population
+            avg_total_population:
+              avg_bucket:
+                buckets_path: distance.total_population
+  - match: { hits.total.value: 3 }
+  - length: { aggregations.distance.buckets: 3 }
+  - match: { aggregations.distance.buckets.0.key: "*-1000000.0" }
+  - match: { aggregations.distance.buckets.0.doc_count: 1 }
+  - match: { aggregations.distance.buckets.0.total_population.value: 8623000.0 }
+  - match: { aggregations.distance.buckets.1.key: "1000000.0-5000000.0" }
+  - match: { aggregations.distance.buckets.1.doc_count: 2 }
+  - match: { aggregations.distance.buckets.1.total_population.value: 6716000.0 }
+  - match: { aggregations.distance.buckets.2.key: "5000000.0-*" }
+  - match: { aggregations.distance.buckets.2.doc_count: 0 }
+  - match: { aggregations.distance.buckets.2.total_population.value: 0 }
+  - match: { aggregations.avg_total_population.value: 7669500.0 }

rest-api-spec/src/main/resources/rest-api-spec/test/search.aggregation/40_range.yml

@@ -224,6 +224,58 @@ setup:
   - match: { aggregations.ip_range.buckets.1.key: "192.168.0.0-192.169.0.0" }
   - match: { aggregations.ip_range.buckets.2.key: "192.169.0.0-*" }
 
+---
+"IP Range avg_bucket":
+  - skip:
+      version: " - 7.7.99"
+      reason: Fixed in 7.8.0
+  - do:
+      bulk:
+        refresh: true
+        index: test
+        body:
+            - '{"index": {}}'
+            - '{"ip": "::1", "v": 1}'
+            - '{"index": {}}'
+            - '{"ip": "192.168.0.1", "v": 2}'
+            - '{"index": {}}'
+            - '{"ip": "192.168.0.7", "v": 3}'
+
+  - do:
+      search:
+        index: test
+        body:
+          size: 0
+          aggs:
+            range:
+              ip_range:
+                field: ip
+                ranges:
+                  - to: 192.168.0.0
+                  - from: 192.168.0.0
+                    to: 192.169.0.0
+                  - from: 192.169.0.0
+              aggs:
+                v:
+                  sum:
+                    field: v
+            range_avg_v:
+              avg_bucket:
+                buckets_path: range.v
+
+  - match: { hits.total.value: 3 }
+  - length: { aggregations.range.buckets: 3 }
+  - match: { aggregations.range.buckets.0.key: "*-192.168.0.0" }
+  - match: { aggregations.range.buckets.0.doc_count: 1 }
+  - match: { aggregations.range.buckets.0.v.value: 1 }
+  - match: { aggregations.range.buckets.1.key: "192.168.0.0-192.169.0.0" }
+  - match: { aggregations.range.buckets.1.doc_count: 2 }
+  - match: { aggregations.range.buckets.1.v.value: 5 }
+  - match: { aggregations.range.buckets.2.key: "192.169.0.0-*" }
+  - match: { aggregations.range.buckets.2.doc_count: 0 }
+  - match: { aggregations.range.buckets.2.v.value: 0 }
+  - match: { aggregations.range_avg_v.value: 3 }
+
 ---
 "Date range":
   - do:

server/src/main/java/org/elasticsearch/search/aggregations/AggregationBuilder.java

@@ -154,6 +154,19 @@ public abstract class AggregationBuilder
         return factoriesBuilder.buildPipelineTree();
     }
 
+    /**
+     * Rough measure of how many buckets this aggregation can return. Just
+     * "zero", "one", and "many".
+     */
+    public enum BucketCardinality {
+        NONE, ONE, MANY;
+    }
+    /**
+     * Do aggregations built by this builder contain buckets? If so, do they
+     * contain *always* contain a single bucket?
+     */
+    public abstract BucketCardinality bucketCardinality();
+
     /** Common xcontent fields shared among aggregator builders */
     public static final class CommonFields extends ParseField.CommonFields {
         public static final ParseField VALUE_TYPE = new ParseField("value_type");

server/src/main/java/org/elasticsearch/search/aggregations/bucket/MultiBucketAggregationBuilder.java

@@ -1,30 +0,0 @@
-/*
- * Licensed to Elasticsearch under one or more contributor
- * license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright
- * ownership. Elasticsearch licenses this file to you under
- * the Apache License, Version 2.0 (the "License"); you may
- * not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *    http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied.  See the License for the
- * specific language governing permissions and limitations
- * under the License.
- */
-
-package org.elasticsearch.search.aggregations.bucket;
-
-import org.elasticsearch.search.aggregations.AggregationBuilder;
-
-/**
- * Marker interface to indicate that the {@link AggregationBuilder} is for a
- * multi-bucket aggregation.
- */
-public interface MultiBucketAggregationBuilder {
-
-}

server/src/main/java/org/elasticsearch/search/aggregations/bucket/adjacency/AdjacencyMatrixAggregationBuilder.java

@@ -33,7 +33,6 @@ import org.elasticsearch.search.aggregations.AbstractAggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregatorFactories.Builder;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
-import org.elasticsearch.search.aggregations.bucket.MultiBucketAggregationBuilder;
 import org.elasticsearch.search.aggregations.bucket.adjacency.AdjacencyMatrixAggregator.KeyedFilter;
 
 import java.io.IOException;
@@ -46,8 +45,7 @@ import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Objects;
 
-public class AdjacencyMatrixAggregationBuilder extends AbstractAggregationBuilder<AdjacencyMatrixAggregationBuilder>
+public class AdjacencyMatrixAggregationBuilder extends AbstractAggregationBuilder<AdjacencyMatrixAggregationBuilder> {
-        implements MultiBucketAggregationBuilder {
     public static final String NAME = "adjacency_matrix";
 
     private static final String DEFAULT_SEPARATOR = "&";
@@ -215,6 +213,11 @@ public class AdjacencyMatrixAggregationBuilder extends AbstractAggregationBuilde
                 subFactoriesBuilder, metaData);
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.MANY;
+    }
+
     @Override
     protected XContentBuilder internalXContent(XContentBuilder builder, Params params) throws IOException {
         builder.startObject();

server/src/main/java/org/elasticsearch/search/aggregations/bucket/composite/CompositeAggregationBuilder.java

@@ -147,6 +147,16 @@ public class CompositeAggregationBuilder extends AbstractAggregationBuilder<Comp
         return size;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        /*
+         * Cardinality *does* have buckets so MULTI might be appropriate here.
+         * But the buckets can't be used with the composite agg so we're
+         * going to pretend that it doesn't have buckets.
+         */
+        return BucketCardinality.NONE;
+    }
+
     /**
      * Returns null if the provided factory and his parents are compatible with
      * this aggregator or the instance of the parent's factory that is incompatible with

server/src/main/java/org/elasticsearch/search/aggregations/bucket/filter/FilterAggregationBuilder.java

@@ -83,6 +83,11 @@ public class FilterAggregationBuilder extends AbstractAggregationBuilder<FilterA
         out.writeNamedWriteable(filter);
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.ONE;
+    }
+
     @Override
     protected AggregationBuilder doRewrite(QueryRewriteContext queryShardContext) throws IOException {
         QueryBuilder result = Rewriteable.rewrite(filter, queryShardContext);

server/src/main/java/org/elasticsearch/search/aggregations/bucket/filter/FiltersAggregationBuilder.java

@@ -33,7 +33,6 @@ import org.elasticsearch.search.aggregations.AbstractAggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregatorFactories.Builder;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
-import org.elasticsearch.search.aggregations.bucket.MultiBucketAggregationBuilder;
 import org.elasticsearch.search.aggregations.bucket.filter.FiltersAggregator.KeyedFilter;
 
 import java.io.IOException;
@@ -47,8 +46,7 @@ import java.util.Objects;
 
 import static org.elasticsearch.index.query.AbstractQueryBuilder.parseInnerQueryBuilder;
 
-public class FiltersAggregationBuilder extends AbstractAggregationBuilder<FiltersAggregationBuilder>
+public class FiltersAggregationBuilder extends AbstractAggregationBuilder<FiltersAggregationBuilder> {
-    implements MultiBucketAggregationBuilder {
     public static final String NAME = "filters";
 
     private static final ParseField FILTERS_FIELD = new ParseField("filters");
@@ -198,6 +196,11 @@ public class FiltersAggregationBuilder extends AbstractAggregationBuilder<Filter
         return otherBucketKey;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.MANY;
+    }
+
     @Override
     protected AggregationBuilder doRewrite(QueryRewriteContext queryShardContext) throws IOException {
         List<KeyedFilter> rewrittenFilters = new ArrayList<>(filters.size());

server/src/main/java/org/elasticsearch/search/aggregations/bucket/geogrid/GeoGridAggregationBuilder.java

@@ -19,11 +19,6 @@
 
 package org.elasticsearch.search.aggregations.bucket.geogrid;
 
-import java.io.IOException;
-import java.util.Map;
-import java.util.Objects;
-import java.util.function.Function;
-
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.Version;
 import org.elasticsearch.common.ParseField;
@@ -38,7 +33,6 @@ import org.elasticsearch.index.query.QueryShardContext;
 import org.elasticsearch.search.aggregations.AggregatorFactories.Builder;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.bucket.BucketUtils;
-import org.elasticsearch.search.aggregations.bucket.MultiBucketAggregationBuilder;
 import org.elasticsearch.search.aggregations.support.CoreValuesSourceType;
 import org.elasticsearch.search.aggregations.support.ValueType;
 import org.elasticsearch.search.aggregations.support.ValuesSource;
@@ -47,8 +41,12 @@ import org.elasticsearch.search.aggregations.support.ValuesSourceAggregatorFacto
 import org.elasticsearch.search.aggregations.support.ValuesSourceConfig;
 import org.elasticsearch.search.aggregations.support.ValuesSourceParserHelper;
 
-public abstract class GeoGridAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource.GeoPoint, GeoGridAggregationBuilder>
+import java.io.IOException;
-        implements MultiBucketAggregationBuilder {
+import java.util.Map;
+import java.util.Objects;
+import java.util.function.Function;
+
+public abstract class GeoGridAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource.GeoPoint, GeoGridAggregationBuilder> {
     /* recognized field names in JSON */
     static final ParseField FIELD_PRECISION = new ParseField("precision");
     static final ParseField FIELD_SIZE = new ParseField("size");
@@ -171,11 +169,15 @@ public abstract class GeoGridAggregationBuilder extends ValuesSourceAggregationB
         return geoBoundingBox;
     }
 
+    @Override
+    public final BucketCardinality bucketCardinality() {
+        return BucketCardinality.MANY;
+    }
+
     @Override
     protected ValuesSourceAggregatorFactory<ValuesSource.GeoPoint> innerBuild(QueryShardContext queryShardContext,
-                                                                                ValuesSourceConfig<ValuesSource.GeoPoint> config,
+                                        ValuesSourceConfig<ValuesSource.GeoPoint> config,
-                                                                                AggregatorFactory parent, Builder subFactoriesBuilder)
+                                        AggregatorFactory parent, Builder subFactoriesBuilder) throws IOException {
-                    throws IOException {
         int shardSize = this.shardSize;
 
         int requiredSize = this.requiredSize;

server/src/main/java/org/elasticsearch/search/aggregations/bucket/geogrid/GeoHashGridAggregationBuilder.java

@@ -19,9 +19,6 @@
 
 package org.elasticsearch.search.aggregations.bucket.geogrid;
 
-import java.io.IOException;
-import java.util.Map;
-
 import org.elasticsearch.common.geo.GeoBoundingBox;
 import org.elasticsearch.common.geo.GeoUtils;
 import org.elasticsearch.common.io.stream.StreamInput;
@@ -34,6 +31,9 @@ import org.elasticsearch.search.aggregations.support.ValuesSource;
 import org.elasticsearch.search.aggregations.support.ValuesSourceAggregatorFactory;
 import org.elasticsearch.search.aggregations.support.ValuesSourceConfig;
 
+import java.io.IOException;
+import java.util.Map;
+
 public class GeoHashGridAggregationBuilder extends GeoGridAggregationBuilder {
     public static final String NAME = "geohash_grid";
     public static final int DEFAULT_PRECISION = 5;

server/src/main/java/org/elasticsearch/search/aggregations/bucket/global/GlobalAggregationBuilder.java

@@ -65,6 +65,11 @@ public class GlobalAggregationBuilder extends AbstractAggregationBuilder<GlobalA
         // Nothing to write
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.ONE;
+    }
+
     @Override
     protected AggregatorFactory doBuild(QueryShardContext queryShardContext, AggregatorFactory parent, Builder subFactoriesBuilder)
             throws IOException {

server/src/main/java/org/elasticsearch/search/aggregations/bucket/histogram/AutoDateHistogramAggregationBuilder.java

@@ -178,9 +178,14 @@ public class AutoDateHistogramAggregationBuilder
         return numBuckets;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.MANY;
+    }
+
     @Override
     protected ValuesSourceAggregatorFactory<Numeric> innerBuild(QueryShardContext queryShardContext, ValuesSourceConfig<Numeric> config,
-                                                                AggregatorFactory parent, Builder subFactoriesBuilder) throws IOException {
+            AggregatorFactory parent, Builder subFactoriesBuilder) throws IOException {
         RoundingInfo[] roundings = buildRoundings(timeZone(), getMinimumIntervalExpression());
         int maxRoundingInterval = Arrays.stream(roundings,0, roundings.length-1)
             .map(rounding -> rounding.innerIntervals)

server/src/main/java/org/elasticsearch/search/aggregations/bucket/histogram/DateHistogramAggregationBuilder.java

@@ -43,7 +43,6 @@ import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.BucketOrder;
 import org.elasticsearch.search.aggregations.InternalOrder;
 import org.elasticsearch.search.aggregations.InternalOrder.CompoundOrder;
-import org.elasticsearch.search.aggregations.bucket.MultiBucketAggregationBuilder;
 import org.elasticsearch.search.aggregations.support.CoreValuesSourceType;
 import org.elasticsearch.search.aggregations.support.ValueType;
 import org.elasticsearch.search.aggregations.support.ValuesSource;
@@ -69,8 +68,7 @@ import static java.util.Collections.unmodifiableMap;
  * A builder for histograms on date fields.
  */
 public class DateHistogramAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource, DateHistogramAggregationBuilder>
-        implements MultiBucketAggregationBuilder, DateIntervalConsumer {
+        implements DateIntervalConsumer {
-
     public static final String NAME = "date_histogram";
 
     public static final Map<String, Rounding.DateTimeUnit> DATE_FIELD_UNITS;
@@ -376,6 +374,11 @@ public class DateHistogramAggregationBuilder extends ValuesSourceAggregationBuil
         return this;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.MANY;
+    }
+
     @Override
     protected XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
 

server/src/main/java/org/elasticsearch/search/aggregations/bucket/histogram/HistogramAggregationBuilder.java

@@ -19,11 +19,6 @@
 
 package org.elasticsearch.search.aggregations.bucket.histogram;
 
-import java.io.IOException;
-import java.util.List;
-import java.util.Map;
-import java.util.Objects;
-
 import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -37,7 +32,6 @@ import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.BucketOrder;
 import org.elasticsearch.search.aggregations.InternalOrder;
 import org.elasticsearch.search.aggregations.InternalOrder.CompoundOrder;
-import org.elasticsearch.search.aggregations.bucket.MultiBucketAggregationBuilder;
 import org.elasticsearch.search.aggregations.support.CoreValuesSourceType;
 import org.elasticsearch.search.aggregations.support.ValueType;
 import org.elasticsearch.search.aggregations.support.ValuesSource;
@@ -47,12 +41,16 @@ import org.elasticsearch.search.aggregations.support.ValuesSourceConfig;
 import org.elasticsearch.search.aggregations.support.ValuesSourceParserHelper;
 import org.elasticsearch.search.aggregations.support.ValuesSourceType;
 
+import java.io.IOException;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+
 /**
  * A builder for histograms on numeric fields.  This builder can operate on either base numeric fields, or numeric range fields.  IP range
  * fields are unsupported, and will throw at the factory layer.
  */
-public class HistogramAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource, HistogramAggregationBuilder>
+public class HistogramAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource, HistogramAggregationBuilder> {
-        implements MultiBucketAggregationBuilder {
     public static final String NAME = "histogram";
 
     private static final ObjectParser<double[], Void> EXTENDED_BOUNDS_PARSER = new ObjectParser<>(
@@ -263,6 +261,11 @@ public class HistogramAggregationBuilder extends ValuesSourceAggregationBuilder<
         return this;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.MANY;
+    }
+
     @Override
     protected XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
 

server/src/main/java/org/elasticsearch/search/aggregations/bucket/missing/MissingAggregationBuilder.java

@@ -78,11 +78,16 @@ public class MissingAggregationBuilder extends ValuesSourceAggregationBuilder<Va
         return true;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.ONE;
+    }
+
     @Override
     protected ValuesSourceAggregatorFactory<ValuesSource> innerBuild(QueryShardContext queryShardContext,
-                                                                        ValuesSourceConfig<ValuesSource> config,
+                                ValuesSourceConfig<ValuesSource> config,
-                                                                        AggregatorFactory parent,
+                                AggregatorFactory parent,
-                                                                        Builder subFactoriesBuilder) throws IOException {
+                                Builder subFactoriesBuilder) throws IOException {
         return new MissingAggregatorFactory(name, config, queryShardContext, parent, subFactoriesBuilder, metaData);
     }
 

server/src/main/java/org/elasticsearch/search/aggregations/bucket/nested/NestedAggregationBuilder.java

@@ -86,6 +86,11 @@ public class NestedAggregationBuilder extends AbstractAggregationBuilder<NestedA
         return path;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.ONE;
+    }
+
     @Override
     protected AggregatorFactory doBuild(QueryShardContext queryShardContext,
                                             AggregatorFactory parent,

server/src/main/java/org/elasticsearch/search/aggregations/bucket/nested/ReverseNestedAggregationBuilder.java

@@ -90,6 +90,11 @@ public class ReverseNestedAggregationBuilder extends AbstractAggregationBuilder<
         return path;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.ONE;
+    }
+
     @Override
     protected AggregatorFactory doBuild(QueryShardContext queryShardContext, AggregatorFactory parent, Builder subFactoriesBuilder)
             throws IOException {

server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/AbstractRangeBuilder.java

@@ -25,7 +25,6 @@ import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.search.aggregations.AggregatorFactories;
-import org.elasticsearch.search.aggregations.bucket.MultiBucketAggregationBuilder;
 import org.elasticsearch.search.aggregations.bucket.range.RangeAggregator.Range;
 import org.elasticsearch.search.aggregations.support.ValuesSource;
 import org.elasticsearch.search.aggregations.support.ValuesSourceAggregationBuilder;
@@ -38,8 +37,7 @@ import java.util.Objects;
 import java.util.function.Function;
 
 public abstract class AbstractRangeBuilder<AB extends AbstractRangeBuilder<AB, R>, R extends Range>
-        extends ValuesSourceAggregationBuilder<ValuesSource.Numeric, AB> implements MultiBucketAggregationBuilder {
+        extends ValuesSourceAggregationBuilder<ValuesSource.Numeric, AB> {
-
     protected final InternalRange.Factory<?, ?> rangeFactory;
     protected List<R> ranges = new ArrayList<>();
     protected boolean keyed = false;
@@ -132,6 +130,11 @@ public abstract class AbstractRangeBuilder<AB extends AbstractRangeBuilder<AB, R
         return keyed;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.MANY;
+    }
+
     @Override
     protected XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
         builder.field(RangeAggregator.RANGES_FIELD.getPreferredName(), ranges);

server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/GeoDistanceAggregationBuilder.java

@@ -410,11 +410,16 @@ public class GeoDistanceAggregationBuilder extends ValuesSourceAggregationBuilde
         return keyed;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.MANY;
+    }
+
     @Override
     protected ValuesSourceAggregatorFactory<ValuesSource.GeoPoint> innerBuild(QueryShardContext queryShardContext,
-                                                                                ValuesSourceConfig<ValuesSource.GeoPoint> config,
+                            ValuesSourceConfig<ValuesSource.GeoPoint> config,
-                                                                                AggregatorFactory parent,
+                            AggregatorFactory parent,
-                                                                                Builder subFactoriesBuilder) throws IOException {
+                            Builder subFactoriesBuilder) throws IOException {
         Range[] ranges = this.ranges.toArray(new Range[this.range().size()]);
         if (ranges.length == 0) {
             throw new IllegalArgumentException("No [ranges] specified for the [" + this.getName() + "] aggregation");

server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/IpRangeAggregationBuilder.java

@@ -18,15 +18,6 @@
  */
 package org.elasticsearch.search.aggregations.bucket.range;
 
-import java.io.IOException;
-import java.net.InetAddress;
-import java.net.UnknownHostException;
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.List;
-import java.util.Map;
-import java.util.Objects;
-
 import org.apache.lucene.document.InetAddressPoint;
 import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.common.ParseField;
@@ -53,6 +44,15 @@ import org.elasticsearch.search.aggregations.support.ValuesSourceAggregatorFacto
 import org.elasticsearch.search.aggregations.support.ValuesSourceConfig;
 import org.elasticsearch.search.aggregations.support.ValuesSourceParserHelper;
 
+import java.io.IOException;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+
 
 public final class IpRangeAggregationBuilder
         extends ValuesSourceAggregationBuilder<ValuesSource.Bytes, IpRangeAggregationBuilder> {
@@ -359,11 +359,15 @@ public final class IpRangeAggregationBuilder
         return new BytesRef(bytes);
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.MANY;
+    }
+
     @Override
     protected ValuesSourceAggregatorFactory<ValuesSource.Bytes> innerBuild(
-        QueryShardContext queryShardContext, ValuesSourceConfig<ValuesSource.Bytes> config,
+                QueryShardContext queryShardContext, ValuesSourceConfig<ValuesSource.Bytes> config,
-        AggregatorFactory parent, Builder subFactoriesBuilder)
+                AggregatorFactory parent, Builder subFactoriesBuilder) throws IOException {
-                    throws IOException {
         List<BinaryRangeAggregator.Range> ranges = new ArrayList<>();
         if(this.ranges.size() == 0){
             throw new IllegalArgumentException("No [ranges] specified for the [" + this.getName() + "] aggregation");

server/src/main/java/org/elasticsearch/search/aggregations/bucket/sampler/DiversifiedAggregationBuilder.java

@@ -142,11 +142,16 @@ public class DiversifiedAggregationBuilder extends ValuesSourceAggregationBuilde
         return executionHint;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.ONE;
+    }
+
     @Override
     protected ValuesSourceAggregatorFactory<ValuesSource> innerBuild(QueryShardContext queryShardContext,
-                                                                        ValuesSourceConfig<ValuesSource> config,
+                            ValuesSourceConfig<ValuesSource> config,
-                                                                        AggregatorFactory parent,
+                            AggregatorFactory parent,
-                                                                        Builder subFactoriesBuilder) throws IOException {
+                            Builder subFactoriesBuilder) throws IOException {
         return new DiversifiedAggregatorFactory(name, config, shardSize, maxDocsPerValue, executionHint, queryShardContext, parent,
                 subFactoriesBuilder, metaData);
     }

server/src/main/java/org/elasticsearch/search/aggregations/bucket/sampler/SamplerAggregationBuilder.java

@@ -83,6 +83,11 @@ public class SamplerAggregationBuilder extends AbstractAggregationBuilder<Sample
         return shardSize;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.ONE;
+    }
+
     @Override
     protected SamplerAggregatorFactory doBuild(QueryShardContext queryShardContext, AggregatorFactory parent, Builder subFactoriesBuilder)
             throws IOException {

server/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/SignificantTermsAggregationBuilder.java

@@ -31,7 +31,6 @@ import org.elasticsearch.index.query.QueryShardContext;
 import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregatorFactories.Builder;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
-import org.elasticsearch.search.aggregations.bucket.MultiBucketAggregationBuilder;
 import org.elasticsearch.search.aggregations.bucket.significant.heuristics.JLHScore;
 import org.elasticsearch.search.aggregations.bucket.significant.heuristics.SignificanceHeuristic;
 import org.elasticsearch.search.aggregations.bucket.terms.IncludeExclude;
@@ -52,8 +51,7 @@ import java.util.Objects;
 
 import static org.elasticsearch.index.query.AbstractQueryBuilder.parseInnerQueryBuilder;
 
-public class SignificantTermsAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource, SignificantTermsAggregationBuilder>
+public class SignificantTermsAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource, SignificantTermsAggregationBuilder> {
-        implements MultiBucketAggregationBuilder {
     public static final String NAME = "significant_terms";
 
     static final ParseField BACKGROUND_FILTER = new ParseField("background_filter");
@@ -282,11 +280,16 @@ public class SignificantTermsAggregationBuilder extends ValuesSourceAggregationB
         return significanceHeuristic;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.MANY;
+    }
+
     @Override
     protected ValuesSourceAggregatorFactory<ValuesSource> innerBuild(QueryShardContext queryShardContext,
-                                                                        ValuesSourceConfig<ValuesSource> config,
+                                                                    ValuesSourceConfig<ValuesSource> config,
-                                                                        AggregatorFactory parent,
+                                                                    AggregatorFactory parent,
-                                                                        Builder subFactoriesBuilder) throws IOException {
+                                                                    Builder subFactoriesBuilder) throws IOException {
         SignificanceHeuristic executionHeuristic = this.significanceHeuristic.rewrite(queryShardContext);
         return new SignificantTermsAggregatorFactory(name, config, includeExclude, executionHint, filterBuilder,
                 bucketCountThresholds, executionHeuristic, queryShardContext, parent, subFactoriesBuilder, metaData);

server/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/SignificantTextAggregationBuilder.java

@@ -321,6 +321,11 @@ public class SignificantTextAggregationBuilder extends AbstractAggregationBuilde
         out.writeOptionalStringArray(sourceFieldNames);
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.MANY;
+    }
+
     @Override
     protected AggregatorFactory doBuild(QueryShardContext queryShardContext, AggregatorFactory parent,
                                         Builder subFactoriesBuilder) throws IOException {

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/RareTermsAggregationBuilder.java

@@ -156,11 +156,16 @@ public class RareTermsAggregationBuilder extends ValuesSourceAggregationBuilder<
         this.precision = precision;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.MANY;
+    }
+
     @Override
     protected ValuesSourceAggregatorFactory<ValuesSource> innerBuild(QueryShardContext queryShardContext,
-                                                                     ValuesSourceConfig<ValuesSource> config,
+                                ValuesSourceConfig<ValuesSource> config,
-                                                                     AggregatorFactory parent,
+                                AggregatorFactory parent,
-                                                                     Builder subFactoriesBuilder) throws IOException {
+                                Builder subFactoriesBuilder) throws IOException {
         return new RareTermsAggregatorFactory(name, config, includeExclude,
             queryShardContext, parent, subFactoriesBuilder, metaData, maxDocCount, precision);
     }

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/TermsAggregationBuilder.java

@@ -34,7 +34,6 @@ import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.BucketOrder;
 import org.elasticsearch.search.aggregations.InternalOrder;
 import org.elasticsearch.search.aggregations.InternalOrder.CompoundOrder;
-import org.elasticsearch.search.aggregations.bucket.MultiBucketAggregationBuilder;
 import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregator.BucketCountThresholds;
 import org.elasticsearch.search.aggregations.support.CoreValuesSourceType;
 import org.elasticsearch.search.aggregations.support.ValueType;
@@ -49,8 +48,7 @@ import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 
-public class TermsAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource, TermsAggregationBuilder>
+public class TermsAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource, TermsAggregationBuilder> {
-        implements MultiBucketAggregationBuilder {
     public static final String NAME = "terms";
 
     public static final ParseField EXECUTION_HINT_FIELD_NAME = new ParseField("execution_hint");
@@ -329,11 +327,16 @@ public class TermsAggregationBuilder extends ValuesSourceAggregationBuilder<Valu
         return this;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.MANY;
+    }
+
     @Override
     protected ValuesSourceAggregatorFactory<ValuesSource> innerBuild(QueryShardContext queryShardContext,
-                                                                        ValuesSourceConfig<ValuesSource> config,
+                                                                ValuesSourceConfig<ValuesSource> config,
-                                                                        AggregatorFactory parent,
+                                                                AggregatorFactory parent,
-                                                                        Builder subFactoriesBuilder) throws IOException {
+                                                                Builder subFactoriesBuilder) throws IOException {
         return new TermsAggregatorFactory(name, config, order, includeExclude, executionHint, collectMode,
                 bucketCountThresholds, showTermDocCountError, queryShardContext, parent, subFactoriesBuilder, metaData);
     }

server/src/main/java/org/elasticsearch/search/aggregations/metrics/GeoBoundsAggregationBuilder.java

@@ -19,10 +19,6 @@
 
 package org.elasticsearch.search.aggregations.metrics;
 
-import java.io.IOException;
-import java.util.Map;
-import java.util.Objects;
-
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.ObjectParser;
@@ -38,6 +34,10 @@ import org.elasticsearch.search.aggregations.support.ValuesSourceAggregationBuil
 import org.elasticsearch.search.aggregations.support.ValuesSourceConfig;
 import org.elasticsearch.search.aggregations.support.ValuesSourceParserHelper;
 
+import java.io.IOException;
+import java.util.Map;
+import java.util.Objects;
+
 public class GeoBoundsAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource.GeoPoint, GeoBoundsAggregationBuilder> {
     public static final String NAME = "geo_bounds";
 
@@ -92,6 +92,11 @@ public class GeoBoundsAggregationBuilder extends ValuesSourceAggregationBuilder<
         return wrapLongitude;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.NONE;
+    }
+
     @Override
     protected GeoBoundsAggregatorFactory innerBuild(QueryShardContext queryShardContext, ValuesSourceConfig<ValuesSource.GeoPoint> config,
                                                     AggregatorFactory parent, Builder subFactoriesBuilder) throws IOException {

server/src/main/java/org/elasticsearch/search/aggregations/metrics/ScriptedMetricAggregationBuilder.java

@@ -206,6 +206,11 @@ public class ScriptedMetricAggregationBuilder extends AbstractAggregationBuilder
         return params;
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.NONE;
+    }
+
     @Override
     protected ScriptedMetricAggregatorFactory doBuild(QueryShardContext queryShardContext, AggregatorFactory parent,
                                                       Builder subfactoriesBuilder) throws IOException {

server/src/main/java/org/elasticsearch/search/aggregations/metrics/TopHitsAggregationBuilder.java

@@ -575,6 +575,11 @@ public class TopHitsAggregationBuilder extends AbstractAggregationBuilder<TopHit
                 + getType() + "] cannot accept sub-aggregations");
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.NONE;
+    }
+
     @Override
     protected TopHitsAggregatorFactory doBuild(QueryShardContext queryShardContext, AggregatorFactory parent, Builder subfactoriesBuilder)
             throws IOException {

server/src/main/java/org/elasticsearch/search/aggregations/metrics/WeightedAvgAggregationBuilder.java

@@ -92,12 +92,17 @@ public class WeightedAvgAggregationBuilder extends MultiValuesSourceAggregationB
         // Do nothing, no extra state to write to stream
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.NONE;
+    }
+
     @Override
     protected MultiValuesSourceAggregatorFactory<Numeric> innerBuild(QueryShardContext queryShardContext,
-                                                                     Map<String, ValuesSourceConfig<Numeric>> configs,
+                                                                    Map<String, ValuesSourceConfig<Numeric>> configs,
-                                                                     DocValueFormat format,
+                                                                    DocValueFormat format,
-                                                                     AggregatorFactory parent,
+                                                                    AggregatorFactory parent,
-                                                                     Builder subFactoriesBuilder) throws IOException {
+                                                                    Builder subFactoriesBuilder) throws IOException {
         return new WeightedAvgAggregatorFactory(name, configs, format, queryShardContext, parent, subFactoriesBuilder, metaData);
     }
 

server/src/main/java/org/elasticsearch/search/aggregations/pipeline/BucketMetricsPipelineAggregationBuilder.java

@@ -24,7 +24,6 @@ import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.search.DocValueFormat;
 import org.elasticsearch.search.aggregations.AggregationBuilder;
-import org.elasticsearch.search.aggregations.bucket.MultiBucketAggregationBuilder;
 import org.elasticsearch.search.aggregations.pipeline.BucketHelpers.GapPolicy;
 
 import java.io.IOException;
@@ -121,7 +120,7 @@ public abstract class BucketMetricsPipelineAggregationBuilder<AF extends BucketM
             context.addBucketPathValidationError("aggregation does not exist for aggregation [" + name + "]: " + bucketsPaths[0]);
             return;
         }
-        if ((aggBuilder.get() instanceof MultiBucketAggregationBuilder) == false) {
+        if (aggBuilder.get().bucketCardinality() != AggregationBuilder.BucketCardinality.MANY) {
             context.addValidationError("The first aggregation in " + PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
                     + " must be a multi-bucket aggregation for aggregation [" + name + "] found :"
                     + aggBuilder.get().getClass().getName() + " for buckets path: " + bucketsPaths[0]);

server/src/main/java/org/elasticsearch/search/aggregations/support/ValuesSourceAggregationBuilder.java

@@ -73,6 +73,11 @@ public abstract class ValuesSourceAggregationBuilder<VS extends ValuesSource, AB
             throw new AggregationInitializationException("Aggregator [" + name + "] of type ["
                     + getType() + "] cannot accept sub-aggregations");
         }
+
+        @Override
+        public final BucketCardinality bucketCardinality() {
+            return BucketCardinality.NONE;
+        }
     }
 
     private final ValuesSourceType valuesSourceType;

server/src/test/java/org/elasticsearch/search/SearchModuleTests.java

@@ -396,11 +396,16 @@ public class SearchModuleTests extends ESTestCase {
         protected void innerWriteTo(StreamOutput out) throws IOException {
         }
 
+        @Override
+        public BucketCardinality bucketCardinality() {
+            return BucketCardinality.NONE;
+        }
+
         @Override
         protected ValuesSourceAggregatorFactory<ValuesSource> innerBuild(QueryShardContext queryShardContext,
-                                                                            ValuesSourceConfig<ValuesSource> config,
+                                    ValuesSourceConfig<ValuesSource> config,
-                                                                            AggregatorFactory parent,
+                                    AggregatorFactory parent,
-                                                                            Builder subFactoriesBuilder) throws IOException {
+                                    Builder subFactoriesBuilder) throws IOException {
             return null;
         }
 

x-pack/plugin/analytics/src/main/java/org/elasticsearch/xpack/analytics/stringstats/StringStatsAggregationBuilder.java

@@ -65,6 +65,11 @@ public class StringStatsAggregationBuilder extends ValuesSourceAggregationBuilde
         out.writeBoolean(showDistribution);
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.NONE;
+    }
+
     @Override
     protected StringStatsAggregatorFactory innerBuild(QueryShardContext queryShardContext,
                                                       ValuesSourceConfig<ValuesSource.Bytes> config,

x-pack/plugin/analytics/src/main/java/org/elasticsearch/xpack/analytics/topmetrics/TopMetricsAggregationBuilder.java

@@ -113,6 +113,11 @@ public class TopMetricsAggregationBuilder extends AbstractAggregationBuilder<Top
         return new TopMetricsAggregationBuilder(this, factoriesBuilder, metaData);
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.NONE;
+    }
+
     @Override
     protected AggregatorFactory doBuild(QueryShardContext queryShardContext, AggregatorFactory parent, Builder subFactoriesBuilder)
             throws IOException {

x-pack/plugin/async-search/src/test/java/org/elasticsearch/xpack/search/CancellingAggregationBuilder.java

@@ -99,4 +99,9 @@ public class CancellingAggregationBuilder extends AbstractAggregationBuilder<Can
             }
         };
     }
+
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.NONE;
+    }
 }

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/transform/transforms/MockDeprecatedAggregationBuilder.java

@@ -64,11 +64,16 @@ public class MockDeprecatedAggregationBuilder extends ValuesSourceAggregationBui
     protected void innerWriteTo(StreamOutput out) throws IOException {
     }
 
+    @Override
+    public BucketCardinality bucketCardinality() {
+        return BucketCardinality.NONE;
+    }
+
     @Override
     protected ValuesSourceAggregatorFactory<ValuesSource> innerBuild(QueryShardContext queryShardContext,
-                                                                        ValuesSourceConfig<ValuesSource> config,
+            ValuesSourceConfig<ValuesSource> config,
-                                                                        AggregatorFactory parent,
+            AggregatorFactory parent,
-                                                                        Builder subFactoriesBuilder) throws IOException {
+            Builder subFactoriesBuilder) throws IOException {
         return null;
     }