Add superset size to Significant Term REST response (#24865)

This commit adds a new bg_count field to the REST response of
SignificantTerms aggregations. Similarly to the bg_count that already
exists in significant terms buckets, this new bg_count field is set at
the aggregation level and is populated with the superset size value.

5 files changed, 53 insertions, 11 deletions

diff --git a/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/InternalMappedSignificantTerms.java b/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/InternalMappedSignificantTerms.java
index da346a8a1e..e1bd4defd3 100644
--- a/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/InternalMappedSignificantTerms.java
+++ b/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/InternalMappedSignificantTerms.java
@@ -128,6 +128,7 @@ public abstract class InternalMappedSignificantTerms<
     @Override
     public XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
         builder.field(CommonFields.DOC_COUNT.getPreferredName(), subsetSize);
+        builder.field(BG_COUNT, supersetSize);
         builder.startArray(CommonFields.BUCKETS.getPreferredName());
         for (Bucket bucket : buckets) {
             //There is a condition (presumably when only one shard has a bucket?) where reduce is not called
diff --git a/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/ParsedSignificantLongTerms.java b/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/ParsedSignificantLongTerms.java
index 2d512632f5..9592d80c77 100644
--- a/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/ParsedSignificantLongTerms.java
+++ b/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/ParsedSignificantLongTerms.java
@@ -39,9 +39,7 @@ public class ParsedSignificantLongTerms extends ParsedSignificantTerms {
     }
 
     public static ParsedSignificantLongTerms fromXContent(XContentParser parser, String name) throws IOException {
-        ParsedSignificantLongTerms aggregation = PARSER.parse(parser, null);
-        aggregation.setName(name);
-        return aggregation;
+        return parseSignificantTermsXContent(() -> PARSER.parse(parser, null), name);
     }
 
     public static class ParsedBucket extends ParsedSignificantTerms.ParsedBucket {
diff --git a/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/ParsedSignificantStringTerms.java b/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/ParsedSignificantStringTerms.java
index fb1c7728e0..008a5a28e5 100644
--- a/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/ParsedSignificantStringTerms.java
+++ b/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/ParsedSignificantStringTerms.java
@@ -40,9 +40,7 @@ public class ParsedSignificantStringTerms extends ParsedSignificantTerms {
     }
 
     public static ParsedSignificantStringTerms fromXContent(XContentParser parser, String name) throws IOException {
-        ParsedSignificantStringTerms aggregation = PARSER.parse(parser, null);
-        aggregation.setName(name);
-        return aggregation;
+        return parseSignificantTermsXContent(() -> PARSER.parse(parser, null), name);
     }
 
     public static class ParsedBucket extends ParsedSignificantTerms.ParsedBucket {
diff --git a/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/ParsedSignificantTerms.java b/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/ParsedSignificantTerms.java
index 56be0aa607..8991ca0993 100644
--- a/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/ParsedSignificantTerms.java
+++ b/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/ParsedSignificantTerms.java
@@ -21,6 +21,8 @@ package org.elasticsearch.search.aggregations.bucket.significant;
 
 import org.elasticsearch.common.CheckedBiConsumer;
 import org.elasticsearch.common.CheckedFunction;
+import org.elasticsearch.common.CheckedSupplier;
+import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.xcontent.ObjectParser;
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentParser;
@@ -42,11 +44,16 @@ public abstract class ParsedSignificantTerms extends ParsedMultiBucketAggregatio
 
     private Map<String, ParsedBucket> bucketMap;
     protected long subsetSize;
+    protected long supersetSize;
 
     protected long getSubsetSize() {
         return subsetSize;
     }
 
+    protected long getSupersetSize() {
+        return supersetSize;
+    }
+
     @Override
     public List<? extends SignificantTerms.Bucket> getBuckets() {
         return buckets;
@@ -68,6 +75,7 @@ public abstract class ParsedSignificantTerms extends ParsedMultiBucketAggregatio
     @Override
     protected XContentBuilder doXContentBody(XContentBuilder builder, Params params) throws IOException {
         builder.field(CommonFields.DOC_COUNT.getPreferredName(), subsetSize);
+        builder.field(InternalMappedSignificantTerms.BG_COUNT, supersetSize);
         builder.startArray(CommonFields.BUCKETS.getPreferredName());
         for (SignificantTerms.Bucket bucket : buckets) {
             bucket.toXContent(builder, params);
@@ -76,16 +84,31 @@ public abstract class ParsedSignificantTerms extends ParsedMultiBucketAggregatio
         return builder;
     }
 
+    static <T extends ParsedSignificantTerms> T parseSignificantTermsXContent(final CheckedSupplier<T, IOException> aggregationSupplier,
+                                                                              final String name) throws IOException {
+        T aggregation = aggregationSupplier.get();
+        aggregation.setName(name);
+        for (ParsedBucket bucket : aggregation.buckets) {
+            bucket.subsetSize = aggregation.subsetSize;
+            bucket.supersetSize = aggregation.supersetSize;
+        }
+        return aggregation;
+    }
+
     static void declareParsedSignificantTermsFields(final ObjectParser<? extends ParsedSignificantTerms, Void> objectParser,
                                      final CheckedFunction<XContentParser, ParsedSignificantTerms.ParsedBucket, IOException> bucketParser) {
         declareMultiBucketAggregationFields(objectParser, bucketParser::apply, bucketParser::apply);
         objectParser.declareLong((parsedTerms, value) -> parsedTerms.subsetSize = value , CommonFields.DOC_COUNT);
+        objectParser.declareLong((parsedTerms, value) -> parsedTerms.supersetSize = value ,
+                new ParseField(InternalMappedSignificantTerms.BG_COUNT));
     }
 
     public abstract static class ParsedBucket extends ParsedMultiBucketAggregation.ParsedBucket implements SignificantTerms.Bucket {
 
         protected long subsetDf;
+        protected long subsetSize;
         protected long supersetDf;
+        protected long supersetSize;
         protected double score;
 
         @Override
@@ -110,12 +133,12 @@ public abstract class ParsedSignificantTerms extends ParsedMultiBucketAggregatio
 
         @Override
         public long getSupersetSize() {
-            throw new UnsupportedOperationException();
+            return supersetSize;
         }
 
         @Override
         public long getSubsetSize() {
-            throw new UnsupportedOperationException();
+            return subsetSize;
         }
 
         @Override
diff --git a/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/SignificantTerms.java b/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/SignificantTerms.java
index 8c0da8b890..61cb4a9ca0 100644
--- a/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/SignificantTerms.java
+++ b/core/src/main/java/org/elasticsearch/search/aggregations/bucket/significant/SignificantTerms.java
@@ -29,17 +29,39 @@ public interface SignificantTerms extends MultiBucketsAggregation, Iterable<Sign
 
     interface Bucket extends MultiBucketsAggregation.Bucket {
 
+        /**
+         * @return The significant score for the subset
+         */
         double getSignificanceScore();
 
-        Number getKeyAsNumber();
-
+        /**
+         * @return The number of docs in the subset containing a particular term.
+         * This number is equal to the document count of the bucket.
+         */
         long getSubsetDf();
 
+        /**
+         * @return The numbers of docs in the subset (also known as "foreground set").
+         * This number is equal to the document count of the containing aggregation.
+         */
+        long getSubsetSize();
+
+        /**
+         * @return The number of docs in the superset containing a particular term (also
+         * known as the "background count" of the bucket)
+         */
         long getSupersetDf();
 
+        /**
+         * @return The numbers of docs in the superset (ordinarily the background count
+         * of the containing aggregation).
+         */
         long getSupersetSize();
 
-        long getSubsetSize();
+        /**
+         * @return The key, expressed as a number
+         */
+        Number getKeyAsNumber();
     }
 
     @Override