Fix cross fields mode of the query_string query (#34216)

This change fixes a bug in the cross fields mode of the `query_string`
query. The multi fields query builder must be reseted before parsing
in order to clear the list of expanded fields coming from the previous text block.

Closes #34215

server/src/main/java/org/elasticsearch/index/search/MultiMatchQuery.java

@@ -67,7 +67,9 @@ public class MultiMatchQuery extends MatchQuery {
     }
 
     public Query parse(MultiMatchQueryBuilder.Type type, Map<String, Float> fieldNames, Object value, String minimumShouldMatch) throws IOException {
-        Query result;
+        final Query result;
+        // reset query builder
+        queryBuilder = null;
         if (fieldNames.size() == 1) {
             Map.Entry<String, Float> fieldBoost = fieldNames.entrySet().iterator().next();
             Float boostValue = fieldBoost.getValue();

server/src/test/java/org/elasticsearch/index/query/QueryStringQueryBuilderTests.java

@@ -21,6 +21,7 @@ package org.elasticsearch.index.query;
 
 import org.apache.lucene.analysis.MockSynonymAnalyzer;
 import org.apache.lucene.index.Term;
+import org.apache.lucene.queries.BlendedTermQuery;
 import org.apache.lucene.search.BooleanClause;
 import org.apache.lucene.search.BooleanClause.Occur;
 import org.apache.lucene.search.BooleanQuery;
@@ -1195,6 +1196,7 @@ public class QueryStringQueryBuilderTests extends AbstractQueryTestCase<QueryStr
             newIndexMeta("index", context.getIndexSettings().getSettings(), Settings.builder().putList("index.query.default_field",
                 STRING_FIELD_NAME, STRING_FIELD_NAME_2 + "^5").build())
         );
+        try {
             Query query = new QueryStringQueryBuilder("hello")
                 .toQuery(context);
             Query expected = new DisjunctionMaxQuery(
@@ -1204,12 +1206,14 @@ public class QueryStringQueryBuilderTests extends AbstractQueryTestCase<QueryStr
                 ), 0.0f
             );
             assertEquals(expected, query);
+        } finally {
             // Reset the default value
             context.getIndexSettings().updateIndexMetaData(
                 newIndexMeta("index",
                     context.getIndexSettings().getSettings(), Settings.builder().putList("index.query.default_field", "*").build())
             );
         }
+    }
 
     /**
      * the quote analyzer should overwrite any other forced analyzer in quoted parts of the query
@@ -1345,6 +1349,44 @@ public class QueryStringQueryBuilderTests extends AbstractQueryTestCase<QueryStr
         assertEquals(expected, query);
     }
 
+    public void testCrossFields() throws Exception {
+        final QueryShardContext context = createShardContext();
+        context.getIndexSettings().updateIndexMetaData(
+            newIndexMeta("index", context.getIndexSettings().getSettings(),
+                Settings.builder().putList("index.query.default_field",
+                    STRING_FIELD_NAME, STRING_FIELD_NAME_2).build())
+        );
+        try {
+            Term[] blendedTerms = new Term[2];
+            blendedTerms[0] = new Term(STRING_FIELD_NAME, "foo");
+            blendedTerms[1] = new Term(STRING_FIELD_NAME_2, "foo");
+
+            Query query = new QueryStringQueryBuilder("foo")
+                .analyzer("whitespace")
+                .type(MultiMatchQueryBuilder.Type.CROSS_FIELDS)
+                .toQuery(createShardContext());
+            Query expected = BlendedTermQuery.dismaxBlendedQuery(blendedTerms, 1.0f);
+            assertEquals(expected, query);
+
+            query = new QueryStringQueryBuilder("foo mapped_string:10")
+                .analyzer("whitespace")
+                .type(MultiMatchQueryBuilder.Type.CROSS_FIELDS)
+                .toQuery(createShardContext());
+            expected = new BooleanQuery.Builder()
+                .add(BlendedTermQuery.dismaxBlendedQuery(blendedTerms, 1.0f), Occur.SHOULD)
+                .add(new TermQuery(new Term(STRING_FIELD_NAME, "10")), Occur.SHOULD)
+                .build();
+            assertEquals(expected, query);
+        } finally {
+            // Reset the default value
+            context.getIndexSettings().updateIndexMetaData(
+                newIndexMeta("index",
+                    context.getIndexSettings().getSettings(),
+                    Settings.builder().putList("index.query.default_field", "*").build())
+            );
+        }
+    }
+
     private static IndexMetaData newIndexMeta(String name, Settings oldIndexSettings, Settings indexSettings) {
         Settings build = Settings.builder().put(oldIndexSettings)
             .put(indexSettings)