Short circuited to MatchNone for non-participating slice (#51207)

In case of numSlices = numShards, use a MatchNone query 
instead of boolean with a MatchNone - MUST clause

server/src/main/java/org/elasticsearch/search/DefaultSearchContext.java

@@ -23,6 +23,7 @@ import org.apache.lucene.search.BooleanClause.Occur;
 import org.apache.lucene.search.BooleanQuery;
 import org.apache.lucene.search.Collector;
 import org.apache.lucene.search.FieldDoc;
+import org.apache.lucene.search.MatchNoDocsQuery;
 import org.apache.lucene.search.Query;
 import org.elasticsearch.action.search.SearchShardTask;
 import org.elasticsearch.action.search.SearchType;
@@ -274,7 +275,12 @@ final class DefaultSearchContext extends SearchContext {
         }
 
         if (sliceBuilder != null) {
-            filters.add(sliceBuilder.toFilter(clusterService, request, queryShardContext));
+            Query slicedQuery = sliceBuilder.toFilter(clusterService, request, queryShardContext);
+            if (slicedQuery instanceof MatchNoDocsQuery) {
+                return slicedQuery;
+            } else {
+                filters.add(slicedQuery);
+            }
         }
 
         if (filters.isEmpty()) {

server/src/test/java/org/elasticsearch/search/DefaultSearchContextTests.java

@@ -22,6 +22,8 @@ package org.elasticsearch.search;
 import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.RandomIndexWriter;
 import org.apache.lucene.search.IndexSearcher;
+import org.apache.lucene.search.MatchNoDocsQuery;
+import org.apache.lucene.search.Query;
 import org.apache.lucene.search.QueryCachingPolicy;
 import org.apache.lucene.search.Sort;
 import org.apache.lucene.store.Directory;
@@ -39,6 +41,7 @@ import org.elasticsearch.index.IndexSettings;
 import org.elasticsearch.index.cache.IndexCache;
 import org.elasticsearch.index.cache.query.QueryCache;
 import org.elasticsearch.index.engine.Engine;
+import org.elasticsearch.index.mapper.MappedFieldType;
 import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.query.AbstractQueryBuilder;
 import org.elasticsearch.index.query.ParsedQuery;
@@ -178,6 +181,19 @@ public class DefaultSearchContextTests extends ESTestCase {
             ParsedQuery parsedQuery = ParsedQuery.parsedMatchAllQuery();
             context3.sliceBuilder(null).parsedQuery(parsedQuery).preProcess(false);
             assertEquals(context3.query(), context3.buildFilteredQuery(parsedQuery.query()));
+
+            when(queryShardContext.getIndexSettings()).thenReturn(indexSettings);
+            when(queryShardContext.fieldMapper(anyString())).thenReturn(mock(MappedFieldType.class));
+            when(shardSearchRequest.indexRoutings()).thenReturn(new String[0]);
+
+            DefaultSearchContext context4 = new DefaultSearchContext(4L, shardSearchRequest, target, searcher, null,
+                indexService, indexShard, bigArrays, null, timeout, null);
+            context4.sliceBuilder(new SliceBuilder(1,2)).parsedQuery(parsedQuery).preProcess(false);
+            Query query1 = context4.query();
+            context4.sliceBuilder(new SliceBuilder(0,2)).parsedQuery(parsedQuery).preProcess(false);
+            Query query2 = context4.query();
+            assertTrue(query1 instanceof MatchNoDocsQuery || query2 instanceof MatchNoDocsQuery);
+
         }
     }
 }