Retrievers - Fix rank_window_size validation

server/src/main/java/org/elasticsearch/search/retriever/CompoundRetrieverBuilder.java

@@ -247,6 +247,13 @@ public ActionRequestValidationException validate(
         if (isScroll) {
             validationException = addValidationError("cannot specify [" + getName() + "] and [scroll]", validationException);
         }
+        if (rankWindowSize < 0) {
+            validationException = addValidationError(
+                "[" + getRankWindowSizeField().getPreferredName() + "] parameter cannot be negative, found [" + rankWindowSize + "]",
+                validationException
+            );
+        }
+
         for (RetrieverSource innerRetriever : innerRetrievers) {
             validationException = innerRetriever.retriever().validate(source, validationException, isScroll, allowPartialSearchResults);
             if (innerRetriever.retriever() instanceof CompoundRetrieverBuilder<?> compoundChild) {
@@ -279,6 +286,10 @@ public int doHashCode() {
         return Objects.hash(innerRetrievers);
     }
 
+    public int rankWindowSize() {
+        return rankWindowSize;
+    }
+
     protected final SearchSourceBuilder createSearchSourceBuilder(PointInTimeBuilder pit, RetrieverBuilder retrieverBuilder) {
         var sourceBuilder = new SearchSourceBuilder().pointInTimeBuilder(pit)
             .trackTotalHits(false)

server/src/main/java/org/elasticsearch/search/retriever/RetrieversFeatures.java

@@ -19,9 +19,15 @@
  * retrievers can be added individually with additional functionality.
  */
 public class RetrieversFeatures implements FeatureSpecification {
+    public static final NodeFeature NEGATIVE_RANK_WINDOW_SIZE_FIX = new NodeFeature("retriever.negative_rank_window_size_fix");
 
     @Override
     public Set<NodeFeature> getFeatures() {
         return Set.of();
     }
+
+    @Override
+    public Set<NodeFeature> getTestFeatures() {
+        return Set.of(NEGATIVE_RANK_WINDOW_SIZE_FIX);
+    }
 }

x-pack/plugin/ent-search/src/main/java/org/elasticsearch/xpack/application/rules/retriever/QueryRuleRetrieverBuilder.java

@@ -119,10 +119,6 @@ public String getName() {
         return NAME;
     }
 
-    public int rankWindowSize() {
-        return rankWindowSize;
-    }
-
     @Override
     protected SearchSourceBuilder finalizeSourceBuilder(SearchSourceBuilder source) {
         checkValidSort(source.sorts());

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

@@ -193,10 +193,6 @@ public String inferenceId() {
         return inferenceId;
     }
 
-    public int rankWindowSize() {
-        return rankWindowSize;
-    }
-
     public boolean failuresAllowed() {
         return failuresAllowed;
     }

x-pack/plugin/rank-rrf/src/yamlRestTest/resources/rest-api-spec/test/linear/10_linear_retriever.yml

@@ -1063,3 +1063,42 @@ setup:
   - close_to: { hits.hits.0._score: { value: 10.5, error: 0.001 } }
   - match: { hits.hits.1._id: "1" }
   - match: { hits.hits.1._score: 10 }
+
+---
+"should throw when rank_window_size is negative":
+  - requires:
+      cluster_features: [ "retriever.negative_rank_window_size_fix" ]
+      reason: "Fix for negative rank_window_size error message"
+  - do:
+      catch: /\[rank_window_size\] parameter cannot be negative, found \[-10\]/
+      search:
+        index: test
+        body:
+          retriever:
+            linear:
+              retrievers: [
+                {
+                  retriever: {
+                    standard: {
+                      query: {
+                        match_all: { }
+                      }
+                    }
+                  },
+                  weight: 10.0,
+                  normalizer: "minmax"
+                },
+                {
+                  retriever: {
+                    knn: {
+                      field: "vector",
+                      query_vector: [ 4 ],
+                      k: 1,
+                      num_candidates: 1
+                    }
+                  },
+                  weight: 2.0
+                }
+              ]
+              rank_window_size: -10
+  - match: { status: 400 }

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

@@ -151,10 +151,6 @@ public String getName() {
         return NAME;
     }
 
-    public int rankWindowSize() {
-        return rankWindowSize;
-    }
-
     /**
      * Creates a PinnedQueryBuilder with the appropriate pinned documents.
      *