Add helper classes to determine if aggs have a value (#36020)

This adds a set of helper classes to determine if an agg "has a value". 
This is needed because InternalAggs represent "empty" in different 
manners according to convention. Some use `NaN`, `+/- Inf`, `0.0`, etc.

A user can pass the Internal agg type to one of these helper methods
and it will report if the agg contains a value or not, which allows the
user to differentiate "empty" from a real `NaN`.

These helpers are best-effort in some cases.  For example, several
pipeline aggs share a single return class but use different conventions
to mark "empty", so the helper uses the loosest definition that applies
to all the aggs that use the class.

Sums in particular are unreliable.  The InternalSum simply returns 0.0
if the agg is empty (which is correct, no values == sum of zero).  But this
also means the helper cannot differentiate from "empty" and `+1 + -1`.

Author: polyfractal

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

@@ -0,0 +1,29 @@
+/*
+ * 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.matrix.stats;
+
+/**
+ * Counterpart to {@link org.elasticsearch.search.aggregations.support.AggregationInspectionHelper}, providing
+ * helpers for some aggs in the MatrixStats package
+ */
+public class MatrixAggregationInspectionHelper {
+    public static boolean hasValue(InternalMatrixStats agg) {
+        return agg.getResults() != null;
+    }
+}

modules/aggs-matrix-stats/src/test/java/org/elasticsearch/search/aggregations/matrix/stats/MatrixStatsAggregatorTests.java

@@ -53,10 +53,12 @@ public void testNoData() throws Exception {
                     .fields(Collections.singletonList("field"));
                 InternalMatrixStats stats = search(searcher, new MatchAllDocsQuery(), aggBuilder, ft);
                 assertNull(stats.getStats());
+                assertFalse(MatrixAggregationInspectionHelper.hasValue(stats));
             }
         }
     }
 
+    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/37587")
     public void testTwoFields() throws Exception {
         String fieldA = "a";
         MappedFieldType ftA = new NumberFieldMapper.NumberFieldType(NumberFieldMapper.NumberType.DOUBLE);
@@ -87,8 +89,9 @@ public void testTwoFields() throws Exception {
                 IndexSearcher searcher = new IndexSearcher(reader);
                 MatrixStatsAggregationBuilder aggBuilder = new MatrixStatsAggregationBuilder("my_agg")
                     .fields(Arrays.asList(fieldA, fieldB));
-                InternalMatrixStats stats = search(searcher, new MatchAllDocsQuery(), aggBuilder, ftA, ftB);
+                InternalMatrixStats stats = searchAndReduce(searcher, new MatchAllDocsQuery(), aggBuilder, ftA, ftB);
                 multiPassStats.assertNearlyEqual(new MatrixStatsResults(stats.getStats()));
+                assertTrue(MatrixAggregationInspectionHelper.hasValue(stats));
             }
         }
     }

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

@@ -0,0 +1,34 @@
+/*
+ * 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.join.aggregations;
+
+/**
+ * Counterpart to {@link org.elasticsearch.search.aggregations.support.AggregationInspectionHelper}, providing
+ * helpers for some aggs in the Join package
+ */
+public class JoinAggregationInspectionHelper {
+
+    public static boolean hasValue(InternalParent agg) {
+        return agg.getDocCount() > 0;
+    }
+
+    public static boolean hasValue(InternalChildren agg) {
+        return agg.getDocCount() > 0;
+    }
+}

modules/parent-join/src/test/java/org/elasticsearch/join/aggregations/ChildrenToParentAggregatorTests.java

@@ -90,6 +90,7 @@ public void testNoDocs() throws IOException {
             assertEquals(0, childrenToParent.getDocCount());
             assertNotNull("Aggregations: " + childrenToParent.getAggregations().asMap(), parentAggregation);
             assertEquals(Double.POSITIVE_INFINITY, ((InternalMin) parentAggregation).getValue(), Double.MIN_VALUE);
+            assertFalse(JoinAggregationInspectionHelper.hasValue(childrenToParent));
         });
         indexReader.close();
         directory.close();
@@ -119,6 +120,7 @@ public void testParentChild() throws IOException {
                     parent.getAggregations().asMap(),
                 expectedTotalParents, parent.getDocCount());
             assertEquals(expectedMinValue, ((InternalMin) parent.getAggregations().get("in_parent")).getValue(), Double.MIN_VALUE);
+            assertTrue(JoinAggregationInspectionHelper.hasValue(parent));
         });
 
         // verify for each children
@@ -170,6 +172,7 @@ public void testParentChildTerms() throws IOException {
         // verify a terms-aggregation inside the parent-aggregation
         testCaseTerms(new MatchAllDocsQuery(), indexSearcher, parent -> {
             assertNotNull(parent);
+            assertTrue(JoinAggregationInspectionHelper.hasValue(parent));
             LongTerms valueTerms = parent.getAggregations().get("value_terms");
             assertNotNull(valueTerms);
 

modules/parent-join/src/test/java/org/elasticsearch/join/aggregations/ParentToChildrenAggregatorTests.java

@@ -105,6 +105,7 @@ public void testParentChild() throws IOException {
                 expectedMinValue = Math.min(expectedMinValue, expectedValues.v2());
             }
             assertEquals(expectedTotalChildren, child.getDocCount());
+            assertTrue(JoinAggregationInspectionHelper.hasValue(child));
             assertEquals(expectedMinValue, ((InternalMin) child.getAggregations().get("in_child")).getValue(), Double.MIN_VALUE);
         });
 

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

@@ -226,7 +226,7 @@ InternalBucket next() {
         }
     }
 
-    static class InternalBucket extends InternalMultiBucketAggregation.InternalBucket
+    public static class InternalBucket extends InternalMultiBucketAggregation.InternalBucket
         implements CompositeAggregation.Bucket, KeyComparable<InternalBucket> {
 
         private final CompositeKey key;

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

@@ -50,4 +50,4 @@ public String getWriteableName() {
     protected InternalSingleBucketAggregation newAggregation(String name, long docCount, InternalAggregations subAggregations) {
         return new InternalFilter(name, docCount, subAggregations, pipelineAggregators(), getMetaData());
     }
-}
+}

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

@@ -34,7 +34,7 @@
 import java.util.List;
 import java.util.Objects;
 
-class GeoGridBucket extends InternalMultiBucketAggregation.InternalBucket implements GeoHashGrid.Bucket, Comparable<GeoGridBucket> {
+public class GeoGridBucket extends InternalMultiBucketAggregation.InternalBucket implements GeoHashGrid.Bucket, Comparable<GeoGridBucket> {
 
     protected long geohashAsLong;
     protected long docCount;

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

@@ -59,4 +59,4 @@ protected InternalSingleBucketAggregation newAggregation(String name, long docCo
             InternalAggregations subAggregations) {
         return new InternalSampler(name, docCount, subAggregations, pipelineAggregators(), metaData);
     }
-}
+}

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

@@ -98,6 +98,10 @@ public long getEstimatedMemoryFootprint() {
         return state.getEstimatedFootprintInBytes();
     }
 
+    DoubleHistogram getState() {
+        return state;
+    }
+
     @Override
     public AbstractInternalHDRPercentiles doReduce(List<InternalAggregation> aggregations, ReduceContext reduceContext) {
         DoubleHistogram merged = null;