Always use DisjunctionMaxQuery to build cross fields disjunction (#25115)

This commit modifies query_string, simple_query_string and multi_match queries to always use a DisjunctionMaxQuery when a disjunction over multiple fields is built. The tiebreaker is set to 1 in order to behave like the boolean query in terms of scoring.
The removal of the coord factor in Lucene 7 made this change mandatory to correctly handle minimum_should_match.

Closes #23966

1 files changed, 9 insertions, 0 deletions

diff --git a/test/framework/src/main/java/org/elasticsearch/test/hamcrest/ElasticsearchAssertions.java b/test/framework/src/main/java/org/elasticsearch/test/hamcrest/ElasticsearchAssertions.java
index 9a36a0c3a3..c1facb772c 100644
--- a/test/framework/src/main/java/org/elasticsearch/test/hamcrest/ElasticsearchAssertions.java
+++ b/test/framework/src/main/java/org/elasticsearch/test/hamcrest/ElasticsearchAssertions.java
@@ -19,6 +19,7 @@
 package org.elasticsearch.test.hamcrest;
 
 import org.apache.lucene.search.BooleanQuery;
+import org.apache.lucene.search.DisjunctionMaxQuery;
 import org.apache.lucene.search.Query;
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.ExceptionsHelper;
@@ -515,6 +516,14 @@ public class ElasticsearchAssertions {
         return subqueryType.cast(q.clauses().get(i).getQuery());
     }
 
+    public static <T extends Query> T assertDisjunctionSubQuery(Query query, Class<T> subqueryType, int i) {
+        assertThat(query, instanceOf(DisjunctionMaxQuery.class));
+        DisjunctionMaxQuery q = (DisjunctionMaxQuery) query;
+        assertThat(q.getDisjuncts().size(), greaterThan(i));
+        assertThat(q.getDisjuncts().get(i), instanceOf(subqueryType));
+        return subqueryType.cast(q.getDisjuncts().get(i));
+    }
+
     /**
      * Run the request from a given builder and check that it throws an exception of the right type
      */