Delegate rangeIntoBitSet in SingletonSortedNumericDocValues (#16295)

SingletonSortedNumericDocValues did not override rangeIntoBitSet,
causing single-valued sorted numeric fields queried via
SortedNumericDocValuesField.newSlowRangeQuery to fall back to
per-doc scalar evaluation even when the underlying NumericDocValues
has an optimized override.

Author: costin

lucene/CHANGES.txt

@@ -325,7 +325,10 @@ Optimizations
 
 Bug Fixes
 ---------------------
-(No changes)
+
+* GITHUB#16295: SingletonSortedNumericDocValues now delegates rangeIntoBitSet
+  to the wrapped NumericDocValues, enabling optimized range evaluation for
+  single-valued sorted numeric fields. (Costin Leau)
 
 Other
 ---------------------

lucene/core/src/java/org/apache/lucene/index/SingletonSortedNumericDocValues.java

@@ -73,6 +73,13 @@ public int docIDRunEnd() throws IOException {
     return in.docIDRunEnd();
   }
 
+  @Override
+  public void rangeIntoBitSet(
+      int fromDoc, int toDoc, long minValue, long maxValue, FixedBitSet bitSet, int offset)
+      throws IOException {
+    in.rangeIntoBitSet(fromDoc, toDoc, minValue, maxValue, bitSet, offset);
+  }
+
   @Override
   public long cost() {
     return in.cost();

lucene/core/src/test/org/apache/lucene/search/TestSkipBlockRangeIteratorIntoBitSet.java

@@ -16,6 +16,7 @@
  */
 package org.apache.lucene.search;
 
+import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Random;
@@ -25,11 +26,13 @@
 import org.apache.lucene.document.NumericDocValuesField;
 import org.apache.lucene.document.SortedNumericDocValuesField;
 import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.DocValues;
 import org.apache.lucene.index.DocValuesSkipper;
 import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.index.IndexWriterConfig;
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.NumericDocValues;
+import org.apache.lucene.index.SortedNumericDocValues;
 import org.apache.lucene.search.BooleanClause.Occur;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.FixedBitSet;
@@ -818,6 +821,62 @@ private void doTestSortedNumericRangeIntoBitSet(
     }
   }
 
+  public void testSingletonDelegatesRangeIntoBitSet() throws Exception {
+    int maxDoc = 100;
+    boolean[] delegated = {false};
+    NumericDocValues spy =
+        new NumericDocValues() {
+          private int doc = -1;
+
+          @Override
+          public long longValue() {
+            return doc;
+          }
+
+          @Override
+          public boolean advanceExact(int target) {
+            doc = target;
+            return true;
+          }
+
+          @Override
+          public int docID() {
+            return doc;
+          }
+
+          @Override
+          public int nextDoc() {
+            return ++doc < maxDoc ? doc : NO_MORE_DOCS;
+          }
+
+          @Override
+          public int advance(int target) {
+            doc = target;
+            return doc < maxDoc ? doc : NO_MORE_DOCS;
+          }
+
+          @Override
+          public long cost() {
+            return maxDoc;
+          }
+
+          @Override
+          public void rangeIntoBitSet(
+              int fromDoc, int toDoc, long minValue, long maxValue, FixedBitSet bitSet, int offset)
+              throws IOException {
+            delegated[0] = true;
+            super.rangeIntoBitSet(fromDoc, toDoc, minValue, maxValue, bitSet, offset);
+          }
+        };
+
+    SortedNumericDocValues singleton = DocValues.singleton(spy);
+    FixedBitSet bitSet = new FixedBitSet(maxDoc);
+    singleton.rangeIntoBitSet(0, maxDoc, 20, 40, bitSet, 0);
+
+    assertTrue("Expected delegation to NumericDocValues.rangeIntoBitSet", delegated[0]);
+    assertTrue("Expected some bits set", bitSet.cardinality() > 0);
+  }
+
   private static long[] rangeValues(int numDocs, LongUnaryOperator valueFunction) {
     long[] values = new long[numDocs];
     for (int i = 0; i < numDocs; i++) {