Fix phrase_slop in query_string query (#35533)

This change ensures that custom `phrase_slop`s are correctly handled
in the `query_string` query.

Fixes #35125

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

@@ -160,6 +160,12 @@ public class QueryStringQueryParser extends XQueryParser {
         queryBuilder.setOccur(op == Operator.AND ? BooleanClause.Occur.MUST : BooleanClause.Occur.SHOULD);
     }
 
+    @Override
+    public void setPhraseSlop(int phraseSlop) {
+        super.setPhraseSlop(phraseSlop);
+        queryBuilder.setPhraseSlop(phraseSlop);
+    }
+
     /**
      * @param type Sets how multiple fields should be combined to build textual part queries.
      */

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

@@ -1387,6 +1387,44 @@ public class QueryStringQueryBuilderTests extends AbstractQueryTestCase<QueryStr
         }
     }
 
+    public void testPhraseSlop() throws Exception {
+        Query query = new QueryStringQueryBuilder("quick fox")
+            .field(STRING_FIELD_NAME)
+            .type(MultiMatchQueryBuilder.Type.PHRASE)
+            .toQuery(createShardContext());
+
+        PhraseQuery expected = new PhraseQuery.Builder()
+            .add(new Term(STRING_FIELD_NAME, "quick"))
+            .add(new Term(STRING_FIELD_NAME, "fox"))
+            .build();
+        assertEquals(expected, query);
+
+        query = new QueryStringQueryBuilder("quick fox")
+            .field(STRING_FIELD_NAME)
+            .type(MultiMatchQueryBuilder.Type.PHRASE)
+            .phraseSlop(2)
+            .toQuery(createShardContext());
+
+        expected = new PhraseQuery.Builder()
+            .add(new Term(STRING_FIELD_NAME, "quick"))
+            .add(new Term(STRING_FIELD_NAME, "fox"))
+            .setSlop(2)
+            .build();
+        assertEquals(expected, query);
+
+        query = new QueryStringQueryBuilder("\"quick fox\"")
+            .field(STRING_FIELD_NAME)
+            .phraseSlop(2)
+            .toQuery(createShardContext());
+        assertEquals(expected, query);
+
+        query = new QueryStringQueryBuilder("\"quick fox\"~2")
+            .field(STRING_FIELD_NAME)
+            .phraseSlop(10)
+            .toQuery(createShardContext());
+        assertEquals(expected, query);
+    }
+
     private static IndexMetaData newIndexMeta(String name, Settings oldIndexSettings, Settings indexSettings) {
         Settings build = Settings.builder().put(oldIndexSettings)
             .put(indexSettings)