Add unit test & address comments

Signed-off-by: sjs004 <simarjeet.singh004@gmail.com>

Author: sjs004

CHANGELOG.md

@@ -47,35 +47,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Fix file-based ingestion consumer to handle start point beyond max line number([#19757])(https://github.com/opensearch-project/OpenSearch/pull/19757))
 - Fix IndexOutOfBoundsException when running include/exclude on non-existent prefix in terms aggregations ([#19637](https://github.com/opensearch-project/OpenSearch/pull/19637))
 - Fixed assertion unsafe use of ClusterService.state() in ResourceUsageCollectorService ([#19775])(https://github.com/opensearch-project/OpenSearch/pull/19775))
-- Add S3Repository.LEGACY_MD5_CHECKSUM_CALCULATION to list of repository-s3 settings ([#19788](https://github.com/opensearch-project/OpenSearch/pull/19788))
-- Fix unnecessary refreshes on update preparation failures ([#15261](https://github.com/opensearch-project/OpenSearch/issues/15261))
-- Fix NullPointerException in segment replicator ([#18997](https://github.com/opensearch-project/OpenSearch/pull/18997))
-- Ensure that plugins that utilize dumpCoverage can write to jacoco.dir when tests.security.manager is enabled ([#18983](https://github.com/opensearch-project/OpenSearch/pull/18983))
-- Fix OOM due to large number of shard result buffering ([#19066](https://github.com/opensearch-project/OpenSearch/pull/19066))
-- Fix flaky tests in CloseIndexIT by addressing cluster state synchronization issues ([#18878](https://github.com/opensearch-project/OpenSearch/issues/18878))
-- [Tiered Caching] Handle  query execution exception ([#19000](https://github.com/opensearch-project/OpenSearch/issues/19000))
-- Grant access to testclusters dir for tests ([#19085](https://github.com/opensearch-project/OpenSearch/issues/19085))
-- Fix assertion error when collapsing search results with concurrent segment search enabled ([#19053](https://github.com/opensearch-project/OpenSearch/pull/19053))
-- Fix skip_unavailable setting changing to default during node drop issue ([#18766](https://github.com/opensearch-project/OpenSearch/pull/18766))
-- Fix issue with s3-compatible repositories due to missing checksum trailing headers ([#19220](https://github.com/opensearch-project/OpenSearch/pull/19220))
-- Add reference count control in NRTReplicationEngine#acquireLastIndexCommit ([#19214](https://github.com/opensearch-project/OpenSearch/pull/19214))
-- Fix pull-based ingestion pause state initialization during replica promotion ([#19212](https://github.com/opensearch-project/OpenSearch/pull/19212))
-- Fix QueryPhaseResultConsumer incomplete callback loops ([#19231](https://github.com/opensearch-project/OpenSearch/pull/19231))
-- Fix the `scaled_float` precision issue ([#19188](https://github.com/opensearch-project/OpenSearch/pull/19188))
-- Fix Using an excessively large reindex slice can lead to a JVM OutOfMemoryError on coordinator.([#18964](https://github.com/opensearch-project/OpenSearch/pull/18964))
-- Add alias write index policy to control writeIndex during restore([#1511](https://github.com/opensearch-project/OpenSearch/pull/19368))
-- [Flaky Test] Fix flaky test in SecureReactorNetty4HttpServerTransportTests with reproducible seed ([#19327](https://github.com/opensearch-project/OpenSearch/pull/19327))
-- Remove unnecessary looping in field data cache clear ([#19116](https://github.com/opensearch-project/OpenSearch/pull/19116))
-- [Flaky Test] Fix flaky test IngestFromKinesisIT.testAllActiveIngestion ([#19380](https://github.com/opensearch-project/OpenSearch/pull/19380))
-- Fix lag metric for pull-based ingestion when streaming source is empty ([#19393](https://github.com/opensearch-project/OpenSearch/pull/19393))
-- Fix IntervalQuery flaky test ([#19332](https://github.com/opensearch-project/OpenSearch/pull/19332))
-- Fix ingestion state xcontent serialization in IndexMetadata and fail fast on mapping errors([#19320](https://github.com/opensearch-project/OpenSearch/pull/19320))
-- Fix updated keyword field params leading to stale responses from request cache ([#19385](https://github.com/opensearch-project/OpenSearch/pull/19385))
-- Fix cardinality agg pruning optimization by self collecting ([#19473](https://github.com/opensearch-project/OpenSearch/pull/19473))
-- Implement SslHandler retrieval logic for transport-reactor-netty4 plugin ([#19458](https://github.com/opensearch-project/OpenSearch/pull/19458))
-- Cache serialised cluster state based on cluster state version and node version.([#19307](https://github.com/opensearch-project/OpenSearch/pull/19307))
-- Handle negative search request nodes stats ([#19340](https://github.com/opensearch-project/OpenSearch/pull/19340))
 - Fix Unified highlighter for nested fields when using matchPhrasePrefixQuery ([#19442](https://github.com/opensearch-project/OpenSearch/pull/19442))
+- Add S3Repository.LEGACY_MD5_CHECKSUM_CALCULATION to list of repository-s3 settings ([#19788](https://github.com/opensearch-project/OpenSearch/pull/19788))
 
 ### Dependencies
 - Update to Gradle 9.1 ([#19575](https://github.com/opensearch-project/OpenSearch/pull/19575))

server/src/main/java/org/opensearch/lucene/search/uhighlight/CustomUnifiedHighlighter.java

@@ -229,8 +229,7 @@ protected Collection<Query> preSpanQueryRewrite(Query query) {
      * Translate custom queries in queries that are supported by the unified highlighter.
      */
     private Collection<Query> rewriteCustomQuery(Query query) {
-        if (query instanceof MultiPhrasePrefixQuery) {
-            MultiPhrasePrefixQuery mpq = (MultiPhrasePrefixQuery) query;
+        if (query instanceof MultiPhrasePrefixQuery mpq) {
             Term[][] terms = mpq.getTerms();
             int[] positions = mpq.getPositions();
             SpanQuery[] positionSpanQueries = new SpanQuery[positions.length];
@@ -263,13 +262,14 @@ private Collection<Query> rewriteCustomQuery(Query query) {
             // if original slop is 0 then require inOrder
             boolean inorder = (mpq.getSlop() == 0);
             return Collections.singletonList(new SpanNearQuery(positionSpanQueries, mpq.getSlop() + positionGaps, inorder));
-        } else if (query instanceof OpenSearchToParentBlockJoinQuery) {
-            return Collections.singletonList(((OpenSearchToParentBlockJoinQuery) query).getChildQuery());
+        } else if (query instanceof OpenSearchToParentBlockJoinQuery parentQuery) {
+            return Collections.singletonList(parentQuery.getChildQuery());
         } else {
             return null;
         }
     }
 
+
     /**
      * Forces the offset source for this highlighter
      */

server/src/test/java/org/opensearch/lucene/search/uhighlight/CustomUnifiedHighlighterTests.java

@@ -44,6 +44,7 @@
 import org.apache.lucene.index.IndexOptions;
 import org.apache.lucene.index.IndexWriterConfig;
 import org.apache.lucene.index.Term;
+import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.queries.CommonTermsQuery;
 import org.apache.lucene.search.BooleanClause;
 import org.apache.lucene.search.BooleanQuery;
@@ -56,13 +57,19 @@
 import org.apache.lucene.search.TermQuery;
 import org.apache.lucene.search.TopDocs;
 import org.apache.lucene.search.highlight.DefaultEncoder;
+import org.apache.lucene.search.join.BitSetProducer;
+import org.apache.lucene.search.join.ScoreMode;
 import org.apache.lucene.search.uhighlight.UnifiedHighlighter;
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.tests.index.RandomIndexWriter;
+import org.apache.lucene.util.BitSet;
+import org.apache.lucene.util.FixedBitSet;
 import org.opensearch.common.lucene.search.MultiPhrasePrefixQuery;
 import org.opensearch.core.common.Strings;
+import org.opensearch.index.search.OpenSearchToParentBlockJoinQuery;
 import org.opensearch.test.OpenSearchTestCase;
 
+import java.io.IOException;
 import java.text.BreakIterator;
 import java.util.Locale;
 
@@ -335,4 +342,34 @@ public void testOverlappingTerms() throws Exception {
         assertHighlightOneDoc("text", inputs, analyzer, query, Locale.ROOT, BreakIterator.getSentenceInstance(Locale.ROOT), 0, outputs);
     }
 
+    public void testOpenSearchToParentBlockJoinQuery() throws Exception {
+        final String[] inputs = { "Nested highlighting query." };
+        final String[] outputs = { "Nested <b>highlighting</b> query." };
+
+        Query childQuery = new TermQuery(new Term("text", "highlighting"));
+        BitSetProducer parentsFilter = new BitSetProducer() {
+            @Override
+            public BitSet getBitSet(LeafReaderContext context) throws IOException {
+                FixedBitSet bits = new FixedBitSet(context.reader().maxDoc());
+                for (int i = 0; i < context.reader().maxDoc(); i++) {
+                    bits.set(i);
+                }
+                return bits;
+            }
+        };
+
+        Query parentQuery = new OpenSearchToParentBlockJoinQuery(childQuery, parentsFilter, ScoreMode.None, "foo");
+        assertHighlightOneDoc(
+            "text",
+            inputs,
+            new StandardAnalyzer(),
+            parentQuery,
+            Locale.ROOT,
+            BreakIterator.getSentenceInstance(Locale.ROOT),
+            0,
+            outputs
+        );
+    }
+
+
 }