Check bucket metric ages point to a multi bucket agg (#26215)

* Check bucket metric ages point to a multi bucket agg

This adds a validation step to the BucketMetricsPipelineAggregationBuilder which ensure that the first aggregation in the `buckets_path` is a multi-bucket aggregation. It does this using a new `MultiBucketAggregationBuilder` marker interface.

The change also moves the validate of pipeline aggregations to the `AggregatorFactories.build()` method so the validate can inspect sibling `AggregatorBuilder` objects rather than `AggregatorFactory` objects. Further it removes the validate from `AggregatorFactory` since this was never implemented and since aggregators only depend on their own internal state and not on other aggregators they should be validated ideally at setter time but in rare case where this is not possible the validation should be done in the `AggregationBuilder.build()` step.

Closes #25775

Move validate stage to happen during AggregatorFactories.Builder.build

Also removes validate method from normal aggs since it was never used.

* review comment fix

core/src/main/java/org/elasticsearch/search/SearchService.java

@@ -101,7 +101,6 @@ import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.Objects;
 import java.util.Optional;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.atomic.AtomicLong;
@@ -710,7 +709,6 @@ public class SearchService extends AbstractLifecycleComponent implements IndexEv
         if (source.aggregations() != null) {
             try {
                 AggregatorFactories factories = source.aggregations().build(context, null);
-                factories.validate();
                 context.aggregations(new SearchContextAggregations(factories));
             } catch (IOException e) {
                 throw new AggregationInitializationException("Failed to create aggregators", e);

core/src/main/java/org/elasticsearch/search/aggregations/AggregatorFactories.java

@@ -238,15 +238,6 @@ public class AggregatorFactories {
         return pipelineAggregatorFactories.size();
     }
 
-    public void validate() {
-        for (AggregatorFactory<?> factory : factories) {
-            factory.validate();
-        }
-        for (PipelineAggregationBuilder factory : pipelineAggregatorFactories) {
-            factory.validate(parent, factories, pipelineAggregatorFactories);
-        }
-    }
-
     public static class Builder implements Writeable, ToXContentObject {
         private final Set<String> names = new HashSet<>();
         private final List<AggregationBuilder> aggregationBuilders = new ArrayList<>();
@@ -330,7 +321,8 @@ public class AggregatorFactories {
             if (skipResolveOrder) {
                 orderedpipelineAggregators = new ArrayList<>(pipelineAggregatorBuilders);
             } else {
-                orderedpipelineAggregators = resolvePipelineAggregatorOrder(this.pipelineAggregatorBuilders, this.aggregationBuilders);
+                orderedpipelineAggregators = resolvePipelineAggregatorOrder(this.pipelineAggregatorBuilders, this.aggregationBuilders,
+                        parent);
             }
             AggregatorFactory<?>[] aggFactories = new AggregatorFactory<?>[aggregationBuilders.size()];
             for (int i = 0; i < aggregationBuilders.size(); i++) {
@@ -340,7 +332,8 @@ public class AggregatorFactories {
         }
 
         private List<PipelineAggregationBuilder> resolvePipelineAggregatorOrder(
-                List<PipelineAggregationBuilder> pipelineAggregatorBuilders, List<AggregationBuilder> aggBuilders) {
+                List<PipelineAggregationBuilder> pipelineAggregatorBuilders, List<AggregationBuilder> aggBuilders,
+                AggregatorFactory<?> parent) {
             Map<String, PipelineAggregationBuilder> pipelineAggregatorBuildersMap = new HashMap<>();
             for (PipelineAggregationBuilder builder : pipelineAggregatorBuilders) {
                 pipelineAggregatorBuildersMap.put(builder.getName(), builder);
@@ -354,6 +347,7 @@ public class AggregatorFactories {
             Set<PipelineAggregationBuilder> temporarilyMarked = new HashSet<>();
             while (!unmarkedBuilders.isEmpty()) {
                 PipelineAggregationBuilder builder = unmarkedBuilders.get(0);
+                builder.validate(parent, aggBuilders, pipelineAggregatorBuilders);
                 resolvePipelineAggregatorOrder(aggBuildersMap, pipelineAggregatorBuildersMap, orderedPipelineAggregatorrs, unmarkedBuilders,
                         temporarilyMarked, builder);
             }

core/src/main/java/org/elasticsearch/search/aggregations/AggregatorFactory.java

@@ -188,15 +188,6 @@ public abstract class AggregatorFactory<AF extends AggregatorFactory<AF>> {
         return name;
     }
 
-    /**
-     * Validates the state of this factory (makes sure the factory is properly
-     * configured)
-     */
-    public final void validate() {
-        doValidate();
-        factories.validate();
-    }
-
     public void doValidate() {
     }
 

core/src/main/java/org/elasticsearch/search/aggregations/PipelineAggregationBuilder.java

@@ -68,7 +68,7 @@ public abstract class PipelineAggregationBuilder implements NamedWriteable, Base
      * Internal: Validates the state of this factory (makes sure the factory is properly
      * configured)
      */
-    protected abstract void validate(AggregatorFactory<?> parent, AggregatorFactory<?>[] factories,
+    protected abstract void validate(AggregatorFactory<?> parent, List<AggregationBuilder> factories,
             List<PipelineAggregationBuilder> pipelineAggregatorFactories);
 
     /**

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

@@ -0,0 +1,30 @@
+/*
+ * 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 {
+
+}

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

@@ -32,6 +32,7 @@ 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 org.elasticsearch.search.internal.SearchContext;
 import org.elasticsearch.search.query.QueryPhaseExecutionException;
@@ -46,7 +47,8 @@ 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 = "&";

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

@@ -31,8 +31,9 @@ import org.elasticsearch.index.query.Rewriteable;
 import org.elasticsearch.search.aggregations.AbstractAggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregatorFactories.Builder;
-import org.elasticsearch.search.aggregations.bucket.filter.FiltersAggregator.KeyedFilter;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
+import org.elasticsearch.search.aggregations.bucket.MultiBucketAggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.filter.FiltersAggregator.KeyedFilter;
 import org.elasticsearch.search.internal.SearchContext;
 
 import java.io.IOException;
@@ -44,7 +45,8 @@ 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");

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

@@ -38,6 +38,7 @@ import org.elasticsearch.index.fielddata.SortedNumericDoubleValues;
 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.ValueType;
 import org.elasticsearch.search.aggregations.support.ValuesSource;
 import org.elasticsearch.search.aggregations.support.ValuesSourceAggregationBuilder;
@@ -50,7 +51,8 @@ import org.elasticsearch.search.internal.SearchContext;
 import java.io.IOException;
 import java.util.Objects;
 
-public class GeoGridAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource.GeoPoint, GeoGridAggregationBuilder> {
+public class GeoGridAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource.GeoPoint, GeoGridAggregationBuilder>
+        implements MultiBucketAggregationBuilder {
     public static final String NAME = "geohash_grid";
     public static final int DEFAULT_PRECISION = 5;
     public static final int DEFAULT_MAX_NUM_CELLS = 10000;

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

@@ -32,6 +32,7 @@ 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.ValueType;
 import org.elasticsearch.search.aggregations.support.ValuesSource;
 import org.elasticsearch.search.aggregations.support.ValuesSource.Numeric;
@@ -53,8 +54,8 @@ import static java.util.Collections.unmodifiableMap;
 /**
  * A builder for histograms on date fields.
  */
-public class DateHistogramAggregationBuilder
+public class DateHistogramAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource.Numeric, DateHistogramAggregationBuilder>
-        extends ValuesSourceAggregationBuilder<ValuesSource.Numeric, DateHistogramAggregationBuilder> {
+        implements MultiBucketAggregationBuilder {
     public static final String NAME = "date_histogram";
 
     public static final Map<String, DateTimeUnit> DATE_FIELD_UNITS;

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

@@ -30,6 +30,7 @@ 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.ValueType;
 import org.elasticsearch.search.aggregations.support.ValuesSource;
 import org.elasticsearch.search.aggregations.support.ValuesSource.Numeric;
@@ -47,8 +48,8 @@ import java.util.Objects;
 /**
  * A builder for histograms on numeric fields.
  */
-public class HistogramAggregationBuilder
+public class HistogramAggregationBuilder extends ValuesSourceAggregationBuilder<ValuesSource.Numeric, HistogramAggregationBuilder>
-        extends ValuesSourceAggregationBuilder<ValuesSource.Numeric, HistogramAggregationBuilder> {
+        implements MultiBucketAggregationBuilder {
     public static final String NAME = "histogram";
 
     private static final ObjectParser<double[], Void> EXTENDED_BOUNDS_PARSER = new ObjectParser<>(

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

@@ -24,6 +24,7 @@ import org.elasticsearch.common.io.stream.StreamInput;
 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.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;
@@ -35,7 +36,7 @@ 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> {
+        extends ValuesSourceAggregationBuilder<ValuesSource.Numeric, AB> implements MultiBucketAggregationBuilder {
 
     protected final InternalRange.Factory<?, ?> rangeFactory;
     protected List<R> ranges = new ArrayList<>();

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

@@ -30,6 +30,7 @@ import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.Aggregator;
 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.significant.heuristics.SignificanceHeuristicParser;
@@ -51,7 +52,8 @@ 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");

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

@@ -31,6 +31,7 @@ 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.ValueType;
 import org.elasticsearch.search.aggregations.support.ValuesSource;
@@ -45,7 +46,8 @@ import java.io.IOException;
 import java.util.List;
 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");

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/AbstractPipelineAggregationBuilder.java

@@ -22,6 +22,7 @@ import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.PipelineAggregationBuilder;
 
@@ -80,7 +81,7 @@ public abstract class AbstractPipelineAggregationBuilder<PAB extends AbstractPip
      * configured)
      */
     @Override
-    public final void validate(AggregatorFactory<?> parent, AggregatorFactory<?>[] factories,
+    public final void validate(AggregatorFactory<?> parent, List<AggregationBuilder> factories,
             List<PipelineAggregationBuilder> pipelineAggregatorFactories) {
         doValidate(parent, factories, pipelineAggregatorFactories);
     }
@@ -98,7 +99,7 @@ public abstract class AbstractPipelineAggregationBuilder<PAB extends AbstractPip
         return aggregator;
     }
 
-    public void doValidate(AggregatorFactory<?> parent, AggregatorFactory<?>[] factories,
+    public void doValidate(AggregatorFactory<?> parent, List<AggregationBuilder> factories,
             List<PipelineAggregationBuilder> pipelineAggregatorFactories) {
     }
 

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/BucketMetricsPipelineAggregationBuilder.java

@@ -23,16 +23,19 @@ import org.elasticsearch.common.io.stream.StreamInput;
 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.AggregatorFactory;
 import org.elasticsearch.search.aggregations.PipelineAggregationBuilder;
-import org.elasticsearch.search.aggregations.pipeline.BucketHelpers.GapPolicy;
+import org.elasticsearch.search.aggregations.bucket.MultiBucketAggregationBuilder;
 import org.elasticsearch.search.aggregations.pipeline.AbstractPipelineAggregationBuilder;
+import org.elasticsearch.search.aggregations.pipeline.BucketHelpers.GapPolicy;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 
 import java.io.IOException;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Optional;
 
 public abstract class BucketMetricsPipelineAggregationBuilder<AF extends BucketMetricsPipelineAggregationBuilder<AF>>
         extends AbstractPipelineAggregationBuilder<AF> {
@@ -106,12 +109,29 @@ public abstract class BucketMetricsPipelineAggregationBuilder<AF extends BucketM
     protected abstract PipelineAggregator createInternal(Map<String, Object> metaData) throws IOException;
 
     @Override
-    public void doValidate(AggregatorFactory<?> parent, AggregatorFactory<?>[] aggFactories,
+    public void doValidate(AggregatorFactory<?> parent, List<AggregationBuilder> aggBuilders,
             List<PipelineAggregationBuilder> pipelineAggregatorFactories) {
         if (bucketsPaths.length != 1) {
             throw new IllegalStateException(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
                     + " must contain a single entry for aggregation [" + name + "]");
         }
+        // Need to find the first agg name in the buckets path to check its a
+        // multi bucket agg: aggs are split with '>' and can optionally have a
+        // metric name after them by using '.' so need to split on both to get
+        // just the agg name
+        final String firstAgg = bucketsPaths[0].split("[>\\.]")[0];
+        Optional<AggregationBuilder> aggBuilder = aggBuilders.stream().filter((builder) -> builder.getName().equals(firstAgg))
+                .findAny();
+        if (aggBuilder.isPresent()) {
+            if ((aggBuilder.get() instanceof MultiBucketAggregationBuilder) == false) {
+                throw new IllegalArgumentException("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]);
+            }
+        } else {
+            throw new IllegalArgumentException(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                    + " aggregation does not exist for aggregation [" + name + "]: " + bucketsPaths[0]);
+        }
     }
 
     @Override

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/avg/AvgBucketPipelineAggregationBuilder.java

@@ -22,14 +22,11 @@ package org.elasticsearch.search.aggregations.pipeline.bucketmetrics.avg;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.XContentBuilder;
-import org.elasticsearch.search.aggregations.AggregatorFactory;
-import org.elasticsearch.search.aggregations.PipelineAggregationBuilder;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.BucketMetricsParser;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.BucketMetricsPipelineAggregationBuilder;
 
 import java.io.IOException;
-import java.util.List;
 import java.util.Map;
 
 public class AvgBucketPipelineAggregationBuilder extends BucketMetricsPipelineAggregationBuilder<AvgBucketPipelineAggregationBuilder> {
@@ -56,15 +53,6 @@ public class AvgBucketPipelineAggregationBuilder extends BucketMetricsPipelineAg
         return new AvgBucketPipelineAggregator(name, bucketsPaths, gapPolicy(), formatter(), metaData);
     }
 
-    @Override
-    public void doValidate(AggregatorFactory<?> parent, AggregatorFactory<?>[] aggFactories,
-            List<PipelineAggregationBuilder> pipelineAggregatorFactories) {
-        if (bucketsPaths.length != 1) {
-            throw new IllegalStateException(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
-                    + " must contain a single entry for aggregation [" + name + "]");
-        }
-    }
-
     @Override
     protected XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
         return builder;

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/max/MaxBucketPipelineAggregationBuilder.java

@@ -22,14 +22,11 @@ package org.elasticsearch.search.aggregations.pipeline.bucketmetrics.max;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.XContentBuilder;
-import org.elasticsearch.search.aggregations.AggregatorFactory;
-import org.elasticsearch.search.aggregations.PipelineAggregationBuilder;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.BucketMetricsParser;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.BucketMetricsPipelineAggregationBuilder;
 
 import java.io.IOException;
-import java.util.List;
 import java.util.Map;
 
 public class MaxBucketPipelineAggregationBuilder extends BucketMetricsPipelineAggregationBuilder<MaxBucketPipelineAggregationBuilder> {
@@ -56,15 +53,6 @@ public class MaxBucketPipelineAggregationBuilder extends BucketMetricsPipelineAg
         return new MaxBucketPipelineAggregator(name, bucketsPaths, gapPolicy(), formatter(), metaData);
     }
 
-    @Override
-    public void doValidate(AggregatorFactory<?> parent, AggregatorFactory<?>[] aggFactories,
-            List<PipelineAggregationBuilder> pipelineAggregatorFactories) {
-        if (bucketsPaths.length != 1) {
-            throw new IllegalStateException(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
-                    + " must contain a single entry for aggregation [" + name + "]");
-        }
-    }
-
     @Override
     protected XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
         return builder;

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/min/MinBucketPipelineAggregationBuilder.java

@@ -22,14 +22,11 @@ package org.elasticsearch.search.aggregations.pipeline.bucketmetrics.min;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.XContentBuilder;
-import org.elasticsearch.search.aggregations.AggregatorFactory;
-import org.elasticsearch.search.aggregations.PipelineAggregationBuilder;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.BucketMetricsParser;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.BucketMetricsPipelineAggregationBuilder;
 
 import java.io.IOException;
-import java.util.List;
 import java.util.Map;
 
 public class MinBucketPipelineAggregationBuilder extends BucketMetricsPipelineAggregationBuilder<MinBucketPipelineAggregationBuilder> {
@@ -56,15 +53,6 @@ public class MinBucketPipelineAggregationBuilder extends BucketMetricsPipelineAg
         return new MinBucketPipelineAggregator(name, bucketsPaths, gapPolicy(), formatter(), metaData);
     }
 
-    @Override
-    public void doValidate(AggregatorFactory<?> parent, AggregatorFactory<?>[] aggFactories,
-            List<PipelineAggregationBuilder> pipelineAggregatorFactories) {
-        if (bucketsPaths.length != 1) {
-            throw new IllegalStateException(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
-                    + " must contain a single entry for aggregation [" + name + "]");
-        }
-    }
-
     @Override
     protected XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
         return builder;

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/percentile/PercentilesBucketPipelineAggregationBuilder.java

@@ -26,6 +26,7 @@ import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentParser;
+import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.PipelineAggregationBuilder;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
@@ -42,7 +43,7 @@ public class PercentilesBucketPipelineAggregationBuilder
         extends BucketMetricsPipelineAggregationBuilder<PercentilesBucketPipelineAggregationBuilder> {
     public static final String NAME = "percentiles_bucket";
 
-    private static final ParseField PERCENTS_FIELD = new ParseField("percents");
+    public static final ParseField PERCENTS_FIELD = new ParseField("percents");
 
     private double[] percents = new double[] { 1.0, 5.0, 25.0, 50.0, 75.0, 95.0, 99.0 };
 
@@ -94,12 +95,9 @@ public class PercentilesBucketPipelineAggregationBuilder
     }
 
     @Override
-    public void doValidate(AggregatorFactory<?> parent, AggregatorFactory<?>[] aggFactories,
+    public void doValidate(AggregatorFactory<?> parent, List<AggregationBuilder> aggFactories,
             List<PipelineAggregationBuilder> pipelineAggregatorFactories) {
-        if (bucketsPaths.length != 1) {
+        super.doValidate(parent, aggFactories, pipelineAggregatorFactories);
-            throw new IllegalStateException(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
-                    + " must contain a single entry for aggregation [" + name + "]");
-        }
 
         for (Double p : percents) {
             if (p == null || p < 0.0 || p > 100.0) {

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/stats/StatsBucketPipelineAggregationBuilder.java

@@ -22,15 +22,11 @@ package org.elasticsearch.search.aggregations.pipeline.bucketmetrics.stats;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.XContentBuilder;
-import org.elasticsearch.search.aggregations.AggregatorFactory;
-import org.elasticsearch.search.aggregations.PipelineAggregationBuilder;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
-import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator.Parser;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.BucketMetricsParser;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.BucketMetricsPipelineAggregationBuilder;
 
 import java.io.IOException;
-import java.util.List;
 import java.util.Map;
 
 public class StatsBucketPipelineAggregationBuilder extends BucketMetricsPipelineAggregationBuilder<StatsBucketPipelineAggregationBuilder> {
@@ -58,15 +54,6 @@ public class StatsBucketPipelineAggregationBuilder extends BucketMetricsPipeline
         return new StatsBucketPipelineAggregator(name, bucketsPaths, gapPolicy(), formatter(), metaData);
     }
 
-    @Override
-    public void doValidate(AggregatorFactory<?> parent, AggregatorFactory<?>[] aggFactories,
-            List<PipelineAggregationBuilder> pipelineAggregatorFactories) {
-        if (bucketsPaths.length != 1) {
-            throw new IllegalStateException(Parser.BUCKETS_PATH.getPreferredName()
-                    + " must contain a single entry for aggregation [" + name + "]");
-        }
-    }
-
     @Override
     protected XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
         return builder;

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/stats/extended/ExtendedStatsBucketPipelineAggregationBuilder.java

@@ -22,10 +22,10 @@ package org.elasticsearch.search.aggregations.pipeline.bucketmetrics.stats.exten
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.PipelineAggregationBuilder;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
-import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator.Parser;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.BucketMetricsPipelineAggregationBuilder;
 
 import java.io.IOException;
@@ -82,12 +82,9 @@ public class ExtendedStatsBucketPipelineAggregationBuilder
     }
 
     @Override
-    public void doValidate(AggregatorFactory<?> parent, AggregatorFactory<?>[] aggFactories,
+    public void doValidate(AggregatorFactory<?> parent, List<AggregationBuilder> aggBuilders,
             List<PipelineAggregationBuilder> pipelineAggregatorFactories) {
-        if (bucketsPaths.length != 1) {
+        super.doValidate(parent, aggBuilders, pipelineAggregatorFactories);
-            throw new IllegalStateException(Parser.BUCKETS_PATH.getPreferredName()
-                    + " must contain a single entry for aggregation [" + name + "]");
-        }
 
         if (sigma < 0.0 ) {
             throw new IllegalStateException(ExtendedStatsBucketParser.SIGMA.getPreferredName()

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/sum/SumBucketPipelineAggregationBuilder.java

@@ -22,14 +22,11 @@ package org.elasticsearch.search.aggregations.pipeline.bucketmetrics.sum;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.XContentBuilder;
-import org.elasticsearch.search.aggregations.AggregatorFactory;
-import org.elasticsearch.search.aggregations.PipelineAggregationBuilder;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.BucketMetricsParser;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.BucketMetricsPipelineAggregationBuilder;
 
 import java.io.IOException;
-import java.util.List;
 import java.util.Map;
 
 public class SumBucketPipelineAggregationBuilder extends BucketMetricsPipelineAggregationBuilder<SumBucketPipelineAggregationBuilder> {
@@ -56,15 +53,6 @@ public class SumBucketPipelineAggregationBuilder extends BucketMetricsPipelineAg
         return new SumBucketPipelineAggregator(name, bucketsPaths, gapPolicy(), formatter(), metaData);
     }
 
-    @Override
-    public void doValidate(AggregatorFactory<?> parent, AggregatorFactory<?>[] aggFactories,
-            List<PipelineAggregationBuilder> pipelineAggregatorFactories) {
-        if (bucketsPaths.length != 1) {
-            throw new IllegalStateException(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
-                    + " must contain a single entry for aggregation [" + name + "]");
-        }
-    }
-
     @Override
     protected XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
         return builder;

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/cumulativesum/CumulativeSumPipelineAggregationBuilder.java

@@ -25,6 +25,7 @@ import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.PipelineAggregationBuilder;
 import org.elasticsearch.search.aggregations.bucket.histogram.DateHistogramAggregatorFactory;
@@ -96,7 +97,7 @@ public class CumulativeSumPipelineAggregationBuilder extends AbstractPipelineAgg
     }
 
     @Override
-    public void doValidate(AggregatorFactory<?> parent, AggregatorFactory<?>[] aggFactories,
+    public void doValidate(AggregatorFactory<?> parent, List<AggregationBuilder> aggFactories,
             List<PipelineAggregationBuilder> pipelineAggregatorFactories) {
         if (bucketsPaths.length != 1) {
             throw new IllegalStateException(BUCKETS_PATH.getPreferredName()

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/derivative/DerivativePipelineAggregationBuilder.java

@@ -28,6 +28,7 @@ import org.elasticsearch.common.unit.TimeValue;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.PipelineAggregationBuilder;
 import org.elasticsearch.search.aggregations.bucket.histogram.DateHistogramAggregationBuilder;
@@ -155,7 +156,7 @@ public class DerivativePipelineAggregationBuilder extends AbstractPipelineAggreg
     }
 
     @Override
-    public void doValidate(AggregatorFactory<?> parent, AggregatorFactory<?>[] aggFactories,
+    public void doValidate(AggregatorFactory<?> parent, List<AggregationBuilder> aggFactories,
             List<PipelineAggregationBuilder> pipelineAggregatoractories) {
         if (bucketsPaths.length != 1) {
             throw new IllegalStateException(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()

core/src/main/java/org/elasticsearch/search/aggregations/pipeline/movavg/MovAvgPipelineAggregationBuilder.java

@@ -27,6 +27,7 @@ import org.elasticsearch.common.xcontent.ParseFieldRegistry;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.search.DocValueFormat;
+import org.elasticsearch.search.aggregations.AggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.PipelineAggregationBuilder;
 import org.elasticsearch.search.aggregations.bucket.histogram.DateHistogramAggregatorFactory;
@@ -255,7 +256,7 @@ public class MovAvgPipelineAggregationBuilder extends AbstractPipelineAggregatio
     }
 
     @Override
-    public void doValidate(AggregatorFactory<?> parent, AggregatorFactory<?>[] aggFactories,
+    public void doValidate(AggregatorFactory<?> parent, List<AggregationBuilder> aggFactories,
             List<PipelineAggregationBuilder> pipelineAggregatoractories) {
         if (minimize != null && minimize && !model.canBeMinimized()) {
             // If the user asks to minimize, but this model doesn't support

core/src/test/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/AvgBucketTests.java

@@ -19,7 +19,16 @@
 
 package org.elasticsearch.search.aggregations.pipeline.bucketmetrics;
 
+import org.elasticsearch.search.aggregations.AggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.global.GlobalAggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
+import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.avg.AvgBucketPipelineAggregationBuilder;
+import org.elasticsearch.search.aggregations.support.ValueType;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 
 public class AvgBucketTests extends AbstractBucketMetricsTestCase<AvgBucketPipelineAggregationBuilder> {
 
@@ -28,5 +37,31 @@ public class AvgBucketTests extends AbstractBucketMetricsTestCase<AvgBucketPipel
         return new AvgBucketPipelineAggregationBuilder(name, bucketsPath);
     }
 
+    public void testValidate() {
+        AggregationBuilder singleBucketAgg = new GlobalAggregationBuilder("global");
+        AggregationBuilder multiBucketAgg = new TermsAggregationBuilder("terms", ValueType.STRING);
+        final List<AggregationBuilder> aggBuilders = new ArrayList<>();
+        aggBuilders.add(singleBucketAgg);
+        aggBuilders.add(multiBucketAgg);
+
+        // First try to point to a non-existent agg
+        final AvgBucketPipelineAggregationBuilder builder = new AvgBucketPipelineAggregationBuilder("name", "invalid_agg>metric");
+        IllegalArgumentException ex = expectThrows(IllegalArgumentException.class,
+                () -> builder.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " aggregation does not exist for aggregation [name]: invalid_agg>metric", ex.getMessage());
+        
+        // Now try to point to a single bucket agg
+        AvgBucketPipelineAggregationBuilder builder2 = new AvgBucketPipelineAggregationBuilder("name", "global>metric");
+        ex = expectThrows(IllegalArgumentException.class, () -> builder2.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals("The first aggregation in " + PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " must be a multi-bucket aggregation for aggregation [name] found :" + GlobalAggregationBuilder.class.getName()
+                + " for buckets path: global>metric", ex.getMessage());
+        
+        // Now try to point to a valid multi-bucket agg (no exception should be thrown)
+        AvgBucketPipelineAggregationBuilder builder3 = new AvgBucketPipelineAggregationBuilder("name", "terms>metric");
+        builder3.validate(null, aggBuilders, Collections.emptyList());
+        
+    }
 
 }

core/src/test/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/ExtendedStatsBucketTests.java

@@ -21,7 +21,16 @@ package org.elasticsearch.search.aggregations.pipeline.bucketmetrics;
 
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentFactory;
+import org.elasticsearch.search.aggregations.AggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.global.GlobalAggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
+import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.stats.extended.ExtendedStatsBucketPipelineAggregationBuilder;
+import org.elasticsearch.search.aggregations.support.ValueType;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 
 import static org.hamcrest.Matchers.equalTo;
 
@@ -52,4 +61,32 @@ public class ExtendedStatsBucketTests extends AbstractBucketMetricsTestCase<Exte
 
         assertThat(builder.sigma(), equalTo(5.0));
     }
+
+    public void testValidate() {
+        AggregationBuilder singleBucketAgg = new GlobalAggregationBuilder("global");
+        AggregationBuilder multiBucketAgg = new TermsAggregationBuilder("terms", ValueType.STRING);
+        final List<AggregationBuilder> aggBuilders = new ArrayList<>();
+        aggBuilders.add(singleBucketAgg);
+        aggBuilders.add(multiBucketAgg);
+
+        // First try to point to a non-existent agg
+        final ExtendedStatsBucketPipelineAggregationBuilder builder = new ExtendedStatsBucketPipelineAggregationBuilder("name",
+                "invalid_agg>metric");
+        IllegalArgumentException ex = expectThrows(IllegalArgumentException.class,
+                () -> builder.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " aggregation does not exist for aggregation [name]: invalid_agg>metric", ex.getMessage());
+
+        // Now try to point to a single bucket agg
+        ExtendedStatsBucketPipelineAggregationBuilder builder2 = new ExtendedStatsBucketPipelineAggregationBuilder("name", "global>metric");
+        ex = expectThrows(IllegalArgumentException.class, () -> builder2.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals("The first aggregation in " + PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " must be a multi-bucket aggregation for aggregation [name] found :" + GlobalAggregationBuilder.class.getName()
+                + " for buckets path: global>metric", ex.getMessage());
+
+        // Now try to point to a valid multi-bucket agg (no exception should be
+        // thrown)
+        ExtendedStatsBucketPipelineAggregationBuilder builder3 = new ExtendedStatsBucketPipelineAggregationBuilder("name", "terms>metric");
+        builder3.validate(null, aggBuilders, Collections.emptyList());
+    }
 }

core/src/test/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/MaxBucketTests.java

@@ -19,7 +19,16 @@
 
 package org.elasticsearch.search.aggregations.pipeline.bucketmetrics;
 
+import org.elasticsearch.search.aggregations.AggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.global.GlobalAggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
+import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.max.MaxBucketPipelineAggregationBuilder;
+import org.elasticsearch.search.aggregations.support.ValueType;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 
 public class MaxBucketTests extends AbstractBucketMetricsTestCase<MaxBucketPipelineAggregationBuilder> {
 
@@ -28,5 +37,31 @@ public class MaxBucketTests extends AbstractBucketMetricsTestCase<MaxBucketPipel
         return new MaxBucketPipelineAggregationBuilder(name, bucketsPath);
     }
 
+    public void testValidate() {
+        AggregationBuilder singleBucketAgg = new GlobalAggregationBuilder("global");
+        AggregationBuilder multiBucketAgg = new TermsAggregationBuilder("terms", ValueType.STRING);
+        final List<AggregationBuilder> aggBuilders = new ArrayList<>();
+        aggBuilders.add(singleBucketAgg);
+        aggBuilders.add(multiBucketAgg);
+
+        // First try to point to a non-existent agg
+        final MaxBucketPipelineAggregationBuilder builder = new MaxBucketPipelineAggregationBuilder("name", "invalid_agg>metric");
+        IllegalArgumentException ex = expectThrows(IllegalArgumentException.class,
+                () -> builder.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " aggregation does not exist for aggregation [name]: invalid_agg>metric", ex.getMessage());
+
+        // Now try to point to a single bucket agg
+        MaxBucketPipelineAggregationBuilder builder2 = new MaxBucketPipelineAggregationBuilder("name", "global>metric");
+        ex = expectThrows(IllegalArgumentException.class, () -> builder2.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals("The first aggregation in " + PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " must be a multi-bucket aggregation for aggregation [name] found :" + GlobalAggregationBuilder.class.getName()
+                + " for buckets path: global>metric", ex.getMessage());
+
+        // Now try to point to a valid multi-bucket agg (no exception should be
+        // thrown)
+        MaxBucketPipelineAggregationBuilder builder3 = new MaxBucketPipelineAggregationBuilder("name", "terms>metric");
+        builder3.validate(null, aggBuilders, Collections.emptyList());
+    }
 
 }

core/src/test/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/MinBucketTests.java

@@ -19,7 +19,16 @@
 
 package org.elasticsearch.search.aggregations.pipeline.bucketmetrics;
 
+import org.elasticsearch.search.aggregations.AggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.global.GlobalAggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
+import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.min.MinBucketPipelineAggregationBuilder;
+import org.elasticsearch.search.aggregations.support.ValueType;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 
 public class MinBucketTests extends AbstractBucketMetricsTestCase<MinBucketPipelineAggregationBuilder> {
 
@@ -28,5 +37,31 @@ public class MinBucketTests extends AbstractBucketMetricsTestCase<MinBucketPipel
         return new MinBucketPipelineAggregationBuilder(name, bucketsPath);
     }
 
+    public void testValidate() {
+        AggregationBuilder singleBucketAgg = new GlobalAggregationBuilder("global");
+        AggregationBuilder multiBucketAgg = new TermsAggregationBuilder("terms", ValueType.STRING);
+        final List<AggregationBuilder> aggBuilders = new ArrayList<>();
+        aggBuilders.add(singleBucketAgg);
+        aggBuilders.add(multiBucketAgg);
+
+        // First try to point to a non-existent agg
+        final MinBucketPipelineAggregationBuilder builder = new MinBucketPipelineAggregationBuilder("name", "invalid_agg>metric");
+        IllegalArgumentException ex = expectThrows(IllegalArgumentException.class,
+                () -> builder.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " aggregation does not exist for aggregation [name]: invalid_agg>metric", ex.getMessage());
+
+        // Now try to point to a single bucket agg
+        MinBucketPipelineAggregationBuilder builder2 = new MinBucketPipelineAggregationBuilder("name", "global>metric");
+        ex = expectThrows(IllegalArgumentException.class, () -> builder2.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals("The first aggregation in " + PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " must be a multi-bucket aggregation for aggregation [name] found :" + GlobalAggregationBuilder.class.getName()
+                + " for buckets path: global>metric", ex.getMessage());
+
+        // Now try to point to a valid multi-bucket agg (no exception should be
+        // thrown)
+        MinBucketPipelineAggregationBuilder builder3 = new MinBucketPipelineAggregationBuilder("name", "terms>metric");
+        builder3.validate(null, aggBuilders, Collections.emptyList());
+    }
 
 }

core/src/test/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/PercentilesBucketTests.java

@@ -21,7 +21,16 @@ package org.elasticsearch.search.aggregations.pipeline.bucketmetrics;
 
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentFactory;
+import org.elasticsearch.search.aggregations.AggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.global.GlobalAggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
+import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.percentile.PercentilesBucketPipelineAggregationBuilder;
+import org.elasticsearch.search.aggregations.support.ValueType;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 
 import static org.hamcrest.Matchers.equalTo;
 
@@ -56,4 +65,32 @@ public class PercentilesBucketTests extends AbstractBucketMetricsTestCase<Percen
 
         assertThat(builder.percents(), equalTo(new double[]{0.0, 20.0, 50.0, 75.99}));
     }
+
+    public void testValidate() {
+        AggregationBuilder singleBucketAgg = new GlobalAggregationBuilder("global");
+        AggregationBuilder multiBucketAgg = new TermsAggregationBuilder("terms", ValueType.STRING);
+        final List<AggregationBuilder> aggBuilders = new ArrayList<>();
+        aggBuilders.add(singleBucketAgg);
+        aggBuilders.add(multiBucketAgg);
+
+        // First try to point to a non-existent agg
+        final PercentilesBucketPipelineAggregationBuilder builder = new PercentilesBucketPipelineAggregationBuilder("name",
+                "invalid_agg>metric");
+        IllegalArgumentException ex = expectThrows(IllegalArgumentException.class,
+                () -> builder.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " aggregation does not exist for aggregation [name]: invalid_agg>metric", ex.getMessage());
+
+        // Now try to point to a single bucket agg
+        PercentilesBucketPipelineAggregationBuilder builder2 = new PercentilesBucketPipelineAggregationBuilder("name", "global>metric");
+        ex = expectThrows(IllegalArgumentException.class, () -> builder2.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals("The first aggregation in " + PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " must be a multi-bucket aggregation for aggregation [name] found :" + GlobalAggregationBuilder.class.getName()
+                + " for buckets path: global>metric", ex.getMessage());
+
+        // Now try to point to a valid multi-bucket agg (no exception should be
+        // thrown)
+        PercentilesBucketPipelineAggregationBuilder builder3 = new PercentilesBucketPipelineAggregationBuilder("name", "terms>metric");
+        builder3.validate(null, aggBuilders, Collections.emptyList());
+    }
 }

core/src/test/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/StatsBucketTests.java

@@ -19,7 +19,16 @@
 
 package org.elasticsearch.search.aggregations.pipeline.bucketmetrics;
 
+import org.elasticsearch.search.aggregations.AggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.global.GlobalAggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
+import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.stats.StatsBucketPipelineAggregationBuilder;
+import org.elasticsearch.search.aggregations.support.ValueType;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 
 public class StatsBucketTests extends AbstractBucketMetricsTestCase<StatsBucketPipelineAggregationBuilder> {
 
@@ -29,5 +38,31 @@ public class StatsBucketTests extends AbstractBucketMetricsTestCase<StatsBucketP
         return new StatsBucketPipelineAggregationBuilder(name, bucketsPath);
     }
 
+    public void testValidate() {
+        AggregationBuilder singleBucketAgg = new GlobalAggregationBuilder("global");
+        AggregationBuilder multiBucketAgg = new TermsAggregationBuilder("terms", ValueType.STRING);
+        final List<AggregationBuilder> aggBuilders = new ArrayList<>();
+        aggBuilders.add(singleBucketAgg);
+        aggBuilders.add(multiBucketAgg);
+
+        // First try to point to a non-existent agg
+        final StatsBucketPipelineAggregationBuilder builder = new StatsBucketPipelineAggregationBuilder("name", "invalid_agg>metric");
+        IllegalArgumentException ex = expectThrows(IllegalArgumentException.class,
+                () -> builder.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " aggregation does not exist for aggregation [name]: invalid_agg>metric", ex.getMessage());
+
+        // Now try to point to a single bucket agg
+        StatsBucketPipelineAggregationBuilder builder2 = new StatsBucketPipelineAggregationBuilder("name", "global>metric");
+        ex = expectThrows(IllegalArgumentException.class, () -> builder2.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals("The first aggregation in " + PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " must be a multi-bucket aggregation for aggregation [name] found :" + GlobalAggregationBuilder.class.getName()
+                + " for buckets path: global>metric", ex.getMessage());
+
+        // Now try to point to a valid multi-bucket agg (no exception should be
+        // thrown)
+        StatsBucketPipelineAggregationBuilder builder3 = new StatsBucketPipelineAggregationBuilder("name", "terms>metric");
+        builder3.validate(null, aggBuilders, Collections.emptyList());
+    }
 
 }

core/src/test/java/org/elasticsearch/search/aggregations/pipeline/bucketmetrics/SumBucketTests.java

@@ -19,7 +19,16 @@
 
 package org.elasticsearch.search.aggregations.pipeline.bucketmetrics;
 
+import org.elasticsearch.search.aggregations.AggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.global.GlobalAggregationBuilder;
+import org.elasticsearch.search.aggregations.bucket.terms.TermsAggregationBuilder;
+import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.pipeline.bucketmetrics.sum.SumBucketPipelineAggregationBuilder;
+import org.elasticsearch.search.aggregations.support.ValueType;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 
 public class SumBucketTests extends AbstractBucketMetricsTestCase<SumBucketPipelineAggregationBuilder> {
 
@@ -28,5 +37,31 @@ public class SumBucketTests extends AbstractBucketMetricsTestCase<SumBucketPipel
         return new SumBucketPipelineAggregationBuilder(name, bucketsPath);
     }
 
+    public void testValidate() {
+        AggregationBuilder singleBucketAgg = new GlobalAggregationBuilder("global");
+        AggregationBuilder multiBucketAgg = new TermsAggregationBuilder("terms", ValueType.STRING);
+        final List<AggregationBuilder> aggBuilders = new ArrayList<>();
+        aggBuilders.add(singleBucketAgg);
+        aggBuilders.add(multiBucketAgg);
+
+        // First try to point to a non-existent agg
+        final SumBucketPipelineAggregationBuilder builder = new SumBucketPipelineAggregationBuilder("name", "invalid_agg>metric");
+        IllegalArgumentException ex = expectThrows(IllegalArgumentException.class,
+                () -> builder.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals(PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " aggregation does not exist for aggregation [name]: invalid_agg>metric", ex.getMessage());
+
+        // Now try to point to a single bucket agg
+        SumBucketPipelineAggregationBuilder builder2 = new SumBucketPipelineAggregationBuilder("name", "global>metric");
+        ex = expectThrows(IllegalArgumentException.class, () -> builder2.validate(null, aggBuilders, Collections.emptyList()));
+        assertEquals("The first aggregation in " + PipelineAggregator.Parser.BUCKETS_PATH.getPreferredName()
+                + " must be a multi-bucket aggregation for aggregation [name] found :" + GlobalAggregationBuilder.class.getName()
+                + " for buckets path: global>metric", ex.getMessage());
+
+        // Now try to point to a valid multi-bucket agg (no exception should be
+        // thrown)
+        SumBucketPipelineAggregationBuilder builder3 = new SumBucketPipelineAggregationBuilder("name", "terms>metric");
+        builder3.validate(null, aggBuilders, Collections.emptyList());
+    }
 
 }