Fixed bug when non percolator docs end up in the search hits.

In the case that a document with a percolator field is matched when using the `percolate` query then
the fetch phase can fail due to the fact that the percolator can't resolve any query from that document.

Closes #29429

modules/percolator/src/main/java/org/elasticsearch/percolator/PercolatorMatchedSlotSubFetchPhase.java

@@ -57,7 +57,11 @@ final class PercolatorMatchedSlotSubFetchPhase implements FetchSubPhase {
 
     @Override
     public void hitsExecute(SearchContext context, SearchHit[] hits) throws IOException {
-        List<PercolateQuery> percolateQueries = locatePercolatorQuery(context.query());
+        innerHitsExecute(context.query(), context.searcher(), hits);
+    }
+
+    static void innerHitsExecute(Query mainQuery, IndexSearcher indexSearcher, SearchHit[] hits) throws IOException {
+        List<PercolateQuery> percolateQueries = locatePercolatorQuery(mainQuery);
         if (percolateQueries.isEmpty()) {
             return;
         }
@@ -81,11 +85,15 @@ final class PercolatorMatchedSlotSubFetchPhase implements FetchSubPhase {
             }
 
             PercolateQuery.QueryStore queryStore = percolateQuery.getQueryStore();
-            List<LeafReaderContext> ctxs = context.searcher().getIndexReader().leaves();
+            List<LeafReaderContext> ctxs = indexSearcher.getIndexReader().leaves();
             for (SearchHit hit : hits) {
                 LeafReaderContext ctx = ctxs.get(ReaderUtil.subIndex(hit.docId(), ctxs));
                 int segmentDocId = hit.docId() - ctx.docBase;
                 Query query = queryStore.getQueries(ctx).apply(segmentDocId);
+                if (query == null) {
+                    // This is not a document with a percolator field.
+                    continue;
+                }
 
                 TopDocs topDocs = percolatorIndexSearcher.search(query, memoryIndexMaxDoc, new Sort(SortField.FIELD_DOC));
                 if (topDocs.totalHits == 0) {

modules/percolator/src/test/java/org/elasticsearch/percolator/PercolatorMatchedSlotSubFetchPhaseTests.java

@@ -18,15 +18,82 @@
  */
 package org.elasticsearch.percolator;
 
+import org.apache.lucene.analysis.core.WhitespaceAnalyzer;
+import org.apache.lucene.document.Document;
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.RandomIndexWriter;
+import org.apache.lucene.index.Term;
+import org.apache.lucene.index.memory.MemoryIndex;
+import org.apache.lucene.search.IndexSearcher;
+import org.apache.lucene.search.MatchAllDocsQuery;
+import org.apache.lucene.search.MatchNoDocsQuery;
 import org.apache.lucene.search.ScoreDoc;
+import org.apache.lucene.search.TermQuery;
 import org.apache.lucene.search.TopDocs;
+import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.FixedBitSet;
+import org.elasticsearch.search.SearchHit;
 import org.elasticsearch.test.ESTestCase;
 
+import java.util.Collections;
 import java.util.stream.IntStream;
 
 public class PercolatorMatchedSlotSubFetchPhaseTests extends ESTestCase {
 
+    public void testHitsExecute() throws Exception {
+        try (Directory directory = newDirectory()) {
+            // Need a one doc index:
+            try (RandomIndexWriter indexWriter = new RandomIndexWriter(random(), directory)) {
+                Document document = new Document();
+                indexWriter.addDocument(document);
+            }
+
+            try (DirectoryReader reader = DirectoryReader.open(directory)) {
+                IndexSearcher indexSearcher = new IndexSearcher(reader);
+
+                // A match:
+                {
+                    SearchHit[] hits = new SearchHit[]{new SearchHit(0)};
+                    PercolateQuery.QueryStore queryStore = ctx -> docId -> new TermQuery(new Term("field", "value"));
+                    MemoryIndex memoryIndex = new MemoryIndex();
+                    memoryIndex.addField("field", "value", new WhitespaceAnalyzer());
+                    PercolateQuery percolateQuery =  new PercolateQuery("_name", queryStore, Collections.emptyList(),
+                        new MatchAllDocsQuery(), memoryIndex.createSearcher(), new MatchNoDocsQuery());
+
+                    PercolatorMatchedSlotSubFetchPhase.innerHitsExecute(percolateQuery, indexSearcher, hits);
+                    assertNotNull(hits[0].field(PercolatorMatchedSlotSubFetchPhase.FIELD_NAME_PREFIX));
+                    assertEquals(0, (int) hits[0].field(PercolatorMatchedSlotSubFetchPhase.FIELD_NAME_PREFIX).getValue());
+                }
+
+                // No match:
+                {
+                    SearchHit[] hits = new SearchHit[]{new SearchHit(0)};
+                    PercolateQuery.QueryStore queryStore = ctx -> docId -> new TermQuery(new Term("field", "value"));
+                    MemoryIndex memoryIndex = new MemoryIndex();
+                    memoryIndex.addField("field", "value1", new WhitespaceAnalyzer());
+                    PercolateQuery percolateQuery =  new PercolateQuery("_name", queryStore, Collections.emptyList(),
+                        new MatchAllDocsQuery(), memoryIndex.createSearcher(), new MatchNoDocsQuery());
+
+                    PercolatorMatchedSlotSubFetchPhase.innerHitsExecute(percolateQuery, indexSearcher, hits);
+                    assertNull(hits[0].field(PercolatorMatchedSlotSubFetchPhase.FIELD_NAME_PREFIX));
+                }
+
+                // No query:
+                {
+                    SearchHit[] hits = new SearchHit[]{new SearchHit(0)};
+                    PercolateQuery.QueryStore queryStore = ctx -> docId -> null;
+                    MemoryIndex memoryIndex = new MemoryIndex();
+                    memoryIndex.addField("field", "value", new WhitespaceAnalyzer());
+                    PercolateQuery percolateQuery =  new PercolateQuery("_name", queryStore, Collections.emptyList(),
+                        new MatchAllDocsQuery(), memoryIndex.createSearcher(), new MatchNoDocsQuery());
+
+                    PercolatorMatchedSlotSubFetchPhase.innerHitsExecute(percolateQuery, indexSearcher, hits);
+                    assertNull(hits[0].field(PercolatorMatchedSlotSubFetchPhase.FIELD_NAME_PREFIX));
+                }
+            }
+        }
+    }
+
     public void testConvertTopDocsToSlots() {
         ScoreDoc[] scoreDocs = new ScoreDoc[randomInt(128)];
         for (int i = 0; i < scoreDocs.length; i++) {