Fix: Allow non-score sorts in pinned retriever sub-retrievers

docs/changelog/128323.yaml

@@ -0,0 +1,5 @@
+pr: 128323
+summary: "Fix: Allow non-score sorts in pinned retriever sub-retrievers"
+area: Relevance
+type: bug
+issues: []

x-pack/plugin/search-business-rules/src/main/java/org/elasticsearch/xpack/searchbusinessrules/retriever/PinnedRetrieverBuilder.java

@@ -18,9 +18,7 @@
 import org.elasticsearch.search.retriever.RetrieverBuilder;
 import org.elasticsearch.search.retriever.RetrieverBuilderWrapper;
 import org.elasticsearch.search.retriever.RetrieverParserContext;
-import org.elasticsearch.search.sort.FieldSortBuilder;
 import org.elasticsearch.search.sort.ScoreSortBuilder;
-import org.elasticsearch.search.sort.ShardDocSortField;
 import org.elasticsearch.search.sort.SortBuilder;
 import org.elasticsearch.xcontent.ConstructingObjectParser;
 import org.elasticsearch.xcontent.ParseField;
@@ -106,16 +104,9 @@ private void validateSort(SearchSourceBuilder source) {
         if (sorts == null || sorts.isEmpty()) {
             return;
         }
-        for (SortBuilder<?> sort : sorts) {
-            if (sort instanceof ScoreSortBuilder) {
-                continue;
-            }
-            if (sort instanceof FieldSortBuilder) {
-                FieldSortBuilder fieldSort = (FieldSortBuilder) sort;
-                if (ShardDocSortField.NAME.equals(fieldSort.getFieldName())) {
-                    continue;
-                }
-            }
+
+        SortBuilder<?> sort = sorts.get(0);
+        if (!(sort instanceof ScoreSortBuilder)) {
             throw new IllegalArgumentException(
                 "[" + NAME + "] retriever only supports sorting by score, invalid sort criterion: " + sort.toString()
             );

x-pack/plugin/search-business-rules/src/test/java/org/elasticsearch/xpack/searchbusinessrules/retriever/PinnedRetrieverBuilderTests.java

@@ -209,7 +209,18 @@ public void testValidateSort() {
         multipleSortsSource.query(dummyQuery);
         multipleSortsSource.sort("_score");
         multipleSortsSource.sort("field1");
-        e = expectThrows(IllegalArgumentException.class, () -> builder.finalizeSourceBuilder(multipleSortsSource));
+        builder.finalizeSourceBuilder(multipleSortsSource);
+        assertThat(multipleSortsSource.sorts().size(), equalTo(2));
+        assertThat(multipleSortsSource.sorts().get(0).getField(), equalTo("_score"));
+        assertThat(multipleSortsSource.sorts().get(0).getOrder(), equalTo(SortOrder.DESC));
+        assertThat(multipleSortsSource.sorts().get(1).getField(), equalTo("field1"));
+        assertThat(multipleSortsSource.sorts().get(1).getOrder(), equalTo(SortOrder.ASC));
+
+        SearchSourceBuilder fieldFirstSource = new SearchSourceBuilder();
+        fieldFirstSource.query(dummyQuery);
+        fieldFirstSource.sort("field1");
+        fieldFirstSource.sort("_score");
+        e = expectThrows(IllegalArgumentException.class, () -> builder.finalizeSourceBuilder(fieldFirstSource));
         assertThat(
             e.getMessage(),
             equalTo(