The `top_hits` aggregation should compile scripts only once. (#20738)

Today it compiles when creating the aggregator, meaning that scripts will be
compiled as many times as there are buckets. Instead it should compile when
creating the factory so that scripts are compiled only once regardless of the
number of buckets.

core/src/main/java/org/elasticsearch/search/aggregations/metrics/tophits/TopHitsAggregationBuilder.java

@@ -28,6 +28,8 @@ import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.index.query.QueryParseContext;
 import org.elasticsearch.script.Script;
+import org.elasticsearch.script.ScriptContext;
+import org.elasticsearch.script.SearchScript;
 import org.elasticsearch.search.aggregations.AbstractAggregationBuilder;
 import org.elasticsearch.search.aggregations.AggregationInitializationException;
 import org.elasticsearch.search.aggregations.AggregatorFactories.Builder;
@@ -39,6 +41,7 @@ import org.elasticsearch.search.builder.SearchSourceBuilder;
 import org.elasticsearch.search.builder.SearchSourceBuilder.ScriptField;
 import org.elasticsearch.search.fetch.StoredFieldsContext;
 import org.elasticsearch.search.fetch.subphase.FetchSourceContext;
+import org.elasticsearch.search.fetch.subphase.ScriptFieldsContext;
 import org.elasticsearch.search.fetch.subphase.highlight.HighlightBuilder;
 import org.elasticsearch.search.sort.ScoreSortBuilder;
 import org.elasticsearch.search.sort.SortBuilder;
@@ -527,6 +530,18 @@ public class TopHitsAggregationBuilder extends AbstractAggregationBuilder<TopHit
     @Override
     protected TopHitsAggregatorFactory doBuild(AggregationContext context, AggregatorFactory<?> parent, Builder subfactoriesBuilder)
             throws IOException {
+        List<ScriptFieldsContext.ScriptField> scriptFields = null;
+        if (this.scriptFields != null) {
+            scriptFields = new ArrayList<>();
+            for (ScriptField field : this.scriptFields) {
+                SearchScript searchScript = context.searchContext().scriptService().search(
+                        context.searchContext().lookup(), field.script(), ScriptContext.Standard.SEARCH, Collections.emptyMap());
+                scriptFields.add(new ScriptFieldsContext.ScriptField(
+                        field.fieldName(), searchScript, field.ignoreFailure()));
+            }
+        } else {
+            scriptFields = Collections.emptyList();
+        }
         return new TopHitsAggregatorFactory(name, type, from, size, explain, version, trackScores, sorts, highlightBuilder,
             storedFieldsContext, fieldDataFields, scriptFields, fetchSourceContext, context,
             parent, subfactoriesBuilder, metaData);

core/src/main/java/org/elasticsearch/search/aggregations/metrics/tophits/TopHitsAggregatorFactory.java

@@ -19,29 +19,25 @@
 
 package org.elasticsearch.search.aggregations.metrics.tophits;
 
-import org.elasticsearch.script.ScriptContext;
-import org.elasticsearch.script.SearchScript;
 import org.elasticsearch.search.aggregations.Aggregator;
 import org.elasticsearch.search.aggregations.AggregatorFactories;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.InternalAggregation.Type;
 import org.elasticsearch.search.aggregations.pipeline.PipelineAggregator;
 import org.elasticsearch.search.aggregations.support.AggregationContext;
-import org.elasticsearch.search.builder.SearchSourceBuilder.ScriptField;
 import org.elasticsearch.search.fetch.StoredFieldsContext;
 import org.elasticsearch.search.fetch.subphase.DocValueFieldsContext;
 import org.elasticsearch.search.fetch.subphase.FetchSourceContext;
+import org.elasticsearch.search.fetch.subphase.ScriptFieldsContext;
 import org.elasticsearch.search.fetch.subphase.highlight.HighlightBuilder;
 import org.elasticsearch.search.internal.SubSearchContext;
 import org.elasticsearch.search.sort.SortAndFormats;
 import org.elasticsearch.search.sort.SortBuilder;
 
 import java.io.IOException;
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
-import java.util.Set;
 
 public class TopHitsAggregatorFactory extends AggregatorFactory<TopHitsAggregatorFactory> {
 
@@ -54,12 +50,12 @@ public class TopHitsAggregatorFactory extends AggregatorFactory<TopHitsAggregato
     private final HighlightBuilder highlightBuilder;
     private final StoredFieldsContext storedFieldsContext;
     private final List<String> docValueFields;
-    private final Set<ScriptField> scriptFields;
+    private final List<ScriptFieldsContext.ScriptField> scriptFields;
     private final FetchSourceContext fetchSourceContext;
 
     public TopHitsAggregatorFactory(String name, Type type, int from, int size, boolean explain, boolean version, boolean trackScores,
             List<SortBuilder<?>> sorts, HighlightBuilder highlightBuilder, StoredFieldsContext storedFieldsContext,
-            List<String> docValueFields, Set<ScriptField> scriptFields, FetchSourceContext fetchSourceContext,
+            List<String> docValueFields, List<ScriptFieldsContext.ScriptField> scriptFields, FetchSourceContext fetchSourceContext,
             AggregationContext context, AggregatorFactory<?> parent, AggregatorFactories.Builder subFactories,
             Map<String, Object> metaData) throws IOException {
         super(name, type, context, parent, subFactories, metaData);
@@ -98,13 +94,8 @@ public class TopHitsAggregatorFactory extends AggregatorFactory<TopHitsAggregato
         if (docValueFields != null) {
             subSearchContext.docValueFieldsContext(new DocValueFieldsContext(docValueFields));
         }
-        if (scriptFields != null) {
+        for (ScriptFieldsContext.ScriptField field : scriptFields) {
-            for (ScriptField field : scriptFields) {
+            subSearchContext.scriptFields().add(field);
-                SearchScript searchScript = subSearchContext.scriptService().search(subSearchContext.lookup(), field.script(),
-                        ScriptContext.Standard.SEARCH, Collections.emptyMap());
-                subSearchContext.scriptFields().add(new org.elasticsearch.search.fetch.subphase.ScriptFieldsContext.ScriptField(
-                        field.fieldName(), searchScript, field.ignoreFailure()));
-            }
         }
         if (fetchSourceContext != null) {
             subSearchContext.fetchSourceContext(fetchSourceContext);