Code refactoring so we are using _termStatistics reserved variable.

modules/lang-expression/src/main/java/org/elasticsearch/script/expression/ExpressionScoreScript.java

@@ -42,6 +42,11 @@ public boolean needs_score() {
         return needsScores;
     }
 
+    @Override
+    public boolean needs_termStatistics() {
+        return false;
+    }
+
     @Override
     public ScoreScript newInstance(final DocReader reader) throws IOException {
         // Use DocReader to get the leaf context while transitioning to DocReader for Painless. DocReader for expressions should follow.

modules/lang-painless/src/main/resources/org/elasticsearch/painless/org.elasticsearch.script.score.txt

@@ -13,6 +13,21 @@ class org.elasticsearch.script.ScoreScript @no_import {
 class org.elasticsearch.script.ScoreScript$Factory @no_import {
 }
 
+class org.apache.lucene.index.Term {
+    String field()
+    String text()
+}
+
+class org.elasticsearch.script.TermStatsReader {
+    Set terms()
+    long uniqueTermsCount()
+    long matchedTermsCount()
+    DoubleSummaryStatistics docFreq()
+    DoubleSummaryStatistics totalTermFreq()
+    DoubleSummaryStatistics termFreq()
+    DoubleSummaryStatistics termPositions()
+}
+
 static_import {
     double saturation(double, double) from_class org.elasticsearch.script.ScoreScriptUtils
     double sigmoid(double, double, double) from_class org.elasticsearch.script.ScoreScriptUtils
@@ -31,7 +46,5 @@ static_import {
     double l2norm(org.elasticsearch.script.ScoreScript, List, String) bound_to org.elasticsearch.script.VectorScoreScriptUtils$L2Norm
     double cosineSimilarity(org.elasticsearch.script.ScoreScript, List, String) bound_to org.elasticsearch.script.VectorScoreScriptUtils$CosineSimilarity
     double dotProduct(org.elasticsearch.script.ScoreScript, List, String) bound_to org.elasticsearch.script.VectorScoreScriptUtils$DotProduct
-    java.util.DoubleSummaryStatistics documentFrequencyStatistics(org.elasticsearch.script.ScoreScript) bound_to org.elasticsearch.script.TermStatsScriptUtils$DocumentFrequencyStatistics
-    java.util.DoubleSummaryStatistics termFrequencyStatistics(org.elasticsearch.script.ScoreScript) bound_to org.elasticsearch.script.TermStatsScriptUtils$TermFrequencyStatistics
 }
 

server/src/main/java/org/elasticsearch/common/lucene/search/function/ScriptScoreQuery.java

@@ -10,7 +10,6 @@
 
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.Term;
-import org.apache.lucene.index.TermStates;
 import org.apache.lucene.search.BooleanClause;
 import org.apache.lucene.search.BulkScorer;
 import org.apache.lucene.search.DocIdSetIterator;
@@ -31,13 +30,10 @@
 import org.elasticsearch.script.ScoreScript;
 import org.elasticsearch.script.ScoreScript.ExplanationHolder;
 import org.elasticsearch.script.Script;
-import org.elasticsearch.script.TermStatsReader;
 import org.elasticsearch.search.lookup.SearchLookup;
 
 import java.io.IOException;
-import java.util.HashMap;
 import java.util.HashSet;
-import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
 
@@ -93,10 +89,17 @@ public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float bo
             return subQuery.createWeight(searcher, scoreMode, boost);
         }
         boolean needsScore = scriptBuilder.needs_score();
-        ScoreMode subQueryScoreMode = needsScore ? ScoreMode.COMPLETE : ScoreMode.COMPLETE_NO_SCORES;
+        boolean needsTermStatistics = scriptBuilder.needs_termStatistics();
+
+        ScoreMode subQueryScoreMode = needsScore || needsTermStatistics ? ScoreMode.COMPLETE : ScoreMode.COMPLETE_NO_SCORES;
         Weight subQueryWeight = subQuery.createWeight(searcher, subQueryScoreMode, 1.0f);
 
-        TermStatsReader termStatsReader = createTermStatsReader(searcher);
+        // We collect the different terms used in the child query.
+        final Set<Term> terms = new HashSet<>();
+
+        if (needsTermStatistics) {
+            this.visit(QueryVisitor.termCollector(terms));
+        }
 
         return new Weight(this) {
             @Override
@@ -173,9 +176,12 @@ public Explanation explain(LeafReaderContext context, int doc) throws IOExceptio
             }
 
             private ScoreScript makeScoreScript(LeafReaderContext context) throws IOException {
-                final ScoreScript scoreScript = scriptBuilder.newInstance(new DocValuesDocReader(lookup, context, termStatsReader));
+                final ScoreScript scoreScript = scriptBuilder.newInstance(new DocValuesDocReader(lookup, context));
                 scoreScript._setIndexName(indexName);
                 scoreScript._setShard(shardId);
+                if (needsTermStatistics) {
+                    scoreScript._setTerms(terms);
+                }
                 return scoreScript;
             }
 
@@ -187,25 +193,6 @@ public boolean isCacheable(LeafReaderContext ctx) {
         };
     }
 
-    private TermStatsReader createTermStatsReader(IndexSearcher searcher) throws IOException {
-        // We collect the different terms used in the child query.
-        final Set<Term> terms = new HashSet<>();
-        this.visit(QueryVisitor.termCollector(terms));
-
-        // For each terms build the term states.
-        final Map<Term, TermStates> termContexts = new HashMap<>();
-
-        for (Term term: terms) {
-            TermStates termStates = TermStates.build(searcher, term, true);
-            if (termStates != null && termStates.docFreq() > 0) {
-                termContexts.put(term, termStates);
-                searcher.termStatistics(term, termStates.docFreq(), termStates.totalTermFreq());
-            }
-        }
-
-        return new TermStatsReader(searcher, terms, termContexts);
-    }
-
     @Override
     public void visit(QueryVisitor visitor) {
         // Highlighters must visit the child query to extract terms

server/src/main/java/org/elasticsearch/index/query/SearchExecutionContext.java

@@ -51,6 +51,7 @@
 import org.elasticsearch.script.ScriptCompiler;
 import org.elasticsearch.script.ScriptContext;
 import org.elasticsearch.script.ScriptFactory;
+import org.elasticsearch.script.TermStatsReader;
 import org.elasticsearch.search.NestedDocuments;
 import org.elasticsearch.search.aggregations.support.ValuesSourceRegistry;
 import org.elasticsearch.search.lookup.LeafFieldLookupProvider;
@@ -508,7 +509,8 @@ public void setLookupProviders(
                 new FieldDataContext(getFullyQualifiedIndex().getName(), searchLookup, this::sourcePath, fielddataOperation)
             ),
             sourceProvider,
-            fieldLookupProvider
+            fieldLookupProvider,
+            (leafReaderContext, docIdSupplier) -> new TermStatsReader(searcher, docIdSupplier, leafReaderContext)
         );
     }
 

server/src/main/java/org/elasticsearch/script/DocReader.java

@@ -8,9 +8,6 @@
 
 package org.elasticsearch.script;
 
-import org.apache.lucene.index.PostingsEnum;
-import org.apache.lucene.index.Term;
-import org.apache.lucene.search.TermStatistics;
 import org.elasticsearch.index.fielddata.ScriptDocValues;
 import org.elasticsearch.script.field.Field;
 import org.elasticsearch.search.lookup.Source;
@@ -26,26 +23,35 @@
  * only reads doc-values.
  */
 public interface DocReader {
-    /** New-style field access */
+    /**
+     * New-style field access
+     */
     Field<?> field(String fieldName);
 
-    /** New-style field iterator */
+    /**
+     * New-style field iterator
+     */
     Stream<Field<?>> fields(String fieldGlob);
 
-    /** Set the underlying docId */
+    /**
+     * Set the underlying docId
+     */
     void setDocument(int docID);
 
     // Compatibility APIS
-    /** Old-style doc access for contexts that map some doc contents in params */
+
+    /**
+     * Old-style doc access for contexts that map some doc contents in params
+     */
     Map<String, Object> docAsMap();
 
-    /** Old-style doc['field'] access */
+    /**
+     * Old-style doc['field'] access
+     */
     Map<String, ScriptDocValues<?>> doc();
 
-    /** Helper for source access */
+    /**
+     * Helper for source access
+     */
     Supplier<Source> source();
-
-    Map<Term, TermStatistics> termStatistics();
-
-    Map<Term, PostingsEnum> postings(int flags);
 }

server/src/main/java/org/elasticsearch/script/DocValuesDocReader.java

@@ -9,9 +9,6 @@
 package org.elasticsearch.script;
 
 import org.apache.lucene.index.LeafReaderContext;
-import org.apache.lucene.index.PostingsEnum;
-import org.apache.lucene.index.Term;
-import org.apache.lucene.search.TermStatistics;
 import org.elasticsearch.index.fielddata.ScriptDocValues;
 import org.elasticsearch.script.field.EmptyField;
 import org.elasticsearch.script.field.Field;
@@ -20,7 +17,6 @@
 import org.elasticsearch.search.lookup.SearchLookup;
 import org.elasticsearch.search.lookup.Source;
 
-import java.util.HashMap;
 import java.util.Map;
 import java.util.function.Supplier;
 import java.util.stream.Stream;
@@ -34,20 +30,14 @@ public class DocValuesDocReader implements DocReader, LeafReaderContextSupplier
 
     // provide access to the leaf context reader for expressions
     protected final LeafReaderContext leafReaderContext;
-    private final TermStatsReader termStatsReader;
 
     /** A leaf lookup for the bound segment this proxy will operate on. */
     protected LeafSearchLookup leafSearchLookup;
 
     public DocValuesDocReader(SearchLookup searchLookup, LeafReaderContext leafContext) {
-        this(searchLookup, leafContext, null);
-    }
-
-    public DocValuesDocReader(SearchLookup searchLookup, LeafReaderContext leafContext, TermStatsReader termStatsReader) {
         this.searchLookup = searchLookup;
         this.leafReaderContext = leafContext;
         this.leafSearchLookup = searchLookup.getLeafSearchLookup(leafReaderContext);
-        this.termStatsReader = termStatsReader;
     }
 
     @Override
@@ -90,22 +80,4 @@ public LeafReaderContext getLeafReaderContext() {
     public Supplier<Source> source() {
         return leafSearchLookup.source();
     }
-
-    @Override
-    public Map<Term, TermStatistics> termStatistics() {
-        Map<Term, TermStatistics> termStatistics = new HashMap<>();
-        for (Term term: termStatsReader.terms()) {
-            termStatistics.put(term, termStatsReader.termStatistics(term));
-        }
-        return termStatistics;
-    }
-
-    @Override
-    public Map<Term, PostingsEnum> postings(int flags) {
-        Map<Term, PostingsEnum> postings = new HashMap<>();
-        for (Term term: termStatsReader.terms()) {
-            postings.put(term, termStatsReader.postings(leafReaderContext, term, flags));
-        }
-        return postings;
-    }
 }

server/src/main/java/org/elasticsearch/script/ScoreScript.java

@@ -7,11 +7,10 @@
  */
 package org.elasticsearch.script;
 
-import org.apache.lucene.index.PostingsEnum;
+import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.Term;
 import org.apache.lucene.search.Explanation;
 import org.apache.lucene.search.Scorable;
-import org.apache.lucene.search.TermStatistics;
 import org.elasticsearch.common.logging.DeprecationCategory;
 import org.elasticsearch.common.logging.DeprecationLogger;
 import org.elasticsearch.search.lookup.SearchLookup;
@@ -21,6 +20,7 @@
 import java.io.UncheckedIOException;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Set;
 import java.util.function.DoubleSupplier;
 import java.util.function.Function;
 import java.util.function.Supplier;
@@ -85,6 +85,8 @@ public Explanation get(double score, Explanation subQueryExplanation) {
     private int shardId = -1;
     private String indexName = null;
 
+    private final TermStatsReader termStatsReader;
+
     public ScoreScript(Map<String, Object> params, SearchLookup searchLookup, DocReader docReader) {
         // searchLookup parameter is ignored but part of the ScriptFactory contract. It is part of that contract because it's required
         // for expressions. Expressions should eventually be transitioned to using DocReader.
@@ -95,11 +97,15 @@ public ScoreScript(Map<String, Object> params, SearchLookup searchLookup, DocRea
             this.params = null;
             ;
             this.docBase = 0;
+            this.termStatsReader = null;
         } else {
             params = new HashMap<>(params);
             params.putAll(docReader.docAsMap());
             this.params = new DynamicMap(params, PARAMS_FUNCTIONS);
-            this.docBase = ((DocValuesDocReader) docReader).getLeafReaderContext().docBase;
+            LeafReaderContext leafReaderContext = ((DocValuesDocReader) docReader).getLeafReaderContext();
+            this.docBase = leafReaderContext.docBase;
+            this.termStatsReader = searchLookup.getTermStatsReader(leafReaderContext, this::_getDocId);
+
         }
     }
 
@@ -192,13 +198,12 @@ public void _setIndexName(String indexName) {
         this.indexName = indexName;
     }
 
-
-    public Map<Term, TermStatistics> _termStatistics() {
-        return  this.docReader.termStatistics();
+    public void _setTerms(Set<Term> terms) {
+        this.termStatsReader._setTerms(terms);
     }
 
-    public Map<Term, PostingsEnum> _postings(int flags) {
-        return  this.docReader.postings(flags);
+    public TermStatsReader get_termStatistics() {
+        return termStatsReader;
     }
 
 
@@ -210,6 +215,8 @@ public interface LeafFactory {
          */
         boolean needs_score();
 
+        boolean needs_termStatistics();
+
         ScoreScript newInstance(DocReader reader) throws IOException;
     }