Maintain existing sort order on failure

Author: thecoop

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/rank/textsimilarity/TextSimilarityRankFeaturePhaseRankCoordinatorContext.java

@@ -134,8 +134,7 @@ protected void computeScores(RankFeatureDoc[] featureDocs, ActionListener<float[
     @Override
     protected RankFeatureDoc[] preprocess(RankFeatureDoc[] originalDocs, boolean rerankedScores) {
         if (rerankedScores == false) {
-            // just do a sort, don't normalize or apply minScore to scores that haven't been modified
-            Arrays.sort(originalDocs);
+            // just return, don't normalize or apply minScore to scores that haven't been modified
             return originalDocs;
         }
         List<RankFeatureDoc> docs = new ArrayList<>(originalDocs.length);

x-pack/plugin/inference/src/yamlRestTest/resources/rest-api-spec/test/inference/70_text_similarity_rank_retriever.yml

@@ -172,6 +172,36 @@ setup:
               field: text
           size: 10
 
+---
+"Text similarity reranking with allowed failure maintains custom sorting":
+
+  - do:
+      search:
+        index: test-index
+        body:
+          track_total_hits: true
+          fields: [ "text", "topic" ]
+          retriever:
+            text_similarity_reranker:
+              retriever:
+                standard:
+                  query:
+                    term:
+                      topic: "science"
+                  sort:
+                    - "subtopic"
+              rank_window_size: 10
+              inference_id: failing-rerank-model
+              inference_text: "science"
+              field: text
+              allow_rerank_failures: true
+          size: 10
+
+  - match: { hits.total.value: 2 }
+  - length: { hits.hits: 2 }
+
+  - match: { hits.hits.0._id: "doc_2" }
+  - match: { hits.hits.1._id: "doc_1" }
 
 ---
 "text similarity reranking with explain":