Add specific QueryRuleRankDoc for better explain support

server/src/main/java/org/elasticsearch/TransportVersions.java

@@ -178,6 +178,7 @@ static TransportVersion def(int id) {
     public static final TransportVersion REVERT_REMOVE_MIN_COMPATIBLE_SHARD_NODE = def(8_774_00_0);
     public static final TransportVersion ESQL_FIELD_ATTRIBUTE_PARENT_SIMPLIFIED = def(8_775_00_0);
     public static final TransportVersion INFERENCE_DONT_PERSIST_ON_READ = def(8_776_00_0);
+    public static final TransportVersion QUERY_RULES_RETRIEVER = def(8_777_00_0);
 
     /*
      * STOP! READ THIS FIRST! No, really,

x-pack/plugin/ent-search/qa/rest/src/yamlRestTest/resources/rest-api-spec/test/entsearch/rules/80_query_rules_retriever.yml

@@ -281,8 +281,8 @@ setup:
           explain: true
 
   - match: { hits.hits.0._id: foo }
-  - match: { hits.hits.0._explanation.value: 1 }
-  - match: { hits.hits.0._explanation.description: "doc [0] with an original score of [1.7014124E38] is at rank [1] from the following source queries." }
+  - match: { hits.hits.0._explanation.value: 1.7014124430769804E38 }
+  - match: { hits.hits.0._explanation.description: "query rules evaluated rules from rulesets [test-ruleset] and match criteria {bar=bar, foo=foo}" }
   - match: { hits.hits.0._explanation.details.0.value: 1 }
   - match: { hits.hits.0._explanation.details.0.description: "doc [0] with an original score of [1.7014124E38] is at rank [1] from the following source queries." }
   - match: { hits.hits.0._explanation.details.0.details.0.description: "sum of:" }

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

@@ -0,0 +1,102 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+package org.elasticsearch.xpack.application.rules.retriever;
+
+import org.apache.lucene.search.Explanation;
+import org.elasticsearch.TransportVersion;
+import org.elasticsearch.TransportVersions;
+import org.elasticsearch.common.io.stream.StreamInput;
+import org.elasticsearch.common.io.stream.StreamOutput;
+import org.elasticsearch.search.rank.RankDoc;
+import org.elasticsearch.xcontent.XContentBuilder;
+
+import java.io.IOException;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+
+public class QueryRuleRankDoc extends RankDoc {
+
+    public static final String NAME = "query_rule_rank_doc";
+
+    public final List<String> rulesetIds;
+    public final Map<String, Object> matchCriteria;
+
+    public QueryRuleRankDoc(int doc, float score, int shardIndex, List<String> rulesetIds, Map<String, Object> matchCriteria) {
+        super(doc, score, shardIndex);
+        this.rulesetIds = rulesetIds;
+        this.matchCriteria = matchCriteria;
+    }
+
+    public QueryRuleRankDoc(StreamInput in) throws IOException {
+        super(in);
+        rulesetIds = in.readStringCollectionAsImmutableList();
+        matchCriteria = in.readGenericMap();
+    }
+
+    @Override
+    public Explanation explain(Explanation[] sources, String[] queryNames) {
+
+        return Explanation.match(
+            score,
+            "query rules evaluated rules from rulesets " + rulesetIds + " and match criteria " + matchCriteria,
+            sources
+        );
+    }
+
+    @Override
+    public void doWriteTo(StreamOutput out) throws IOException {
+        out.writeStringCollection(rulesetIds);
+        out.writeGenericMap(matchCriteria);
+    }
+
+    @Override
+    public boolean doEquals(RankDoc rd) {
+        QueryRuleRankDoc qrrd = (QueryRuleRankDoc) rd;
+        return Objects.equals(rulesetIds, qrrd.rulesetIds) && Objects.equals(matchCriteria, qrrd.matchCriteria);
+    }
+
+    @Override
+    public int doHashCode() {
+        return Objects.hash(rulesetIds, matchCriteria);
+    }
+
+    @Override
+    public String toString() {
+        return "QueryRuleRankDoc{"
+            + "doc="
+            + doc
+            + ", shardIndex="
+            + shardIndex
+            + ", score="
+            + score
+            + ", rulesetIds="
+            + rulesetIds
+            + ", matchCriteria="
+            + matchCriteria
+            + "}";
+    }
+
+    @Override
+    public String getWriteableName() {
+        return NAME;
+    }
+
+    @Override
+    protected void doToXContent(XContentBuilder builder, Params params) throws IOException {
+        builder.array("rulesetIds", rulesetIds.toArray());
+        builder.startObject("matchCriteria");
+        builder.mapContents(matchCriteria);
+        builder.endObject();
+    }
+
+    @Override
+    public TransportVersion getMinimalSupportedVersion() {
+        return TransportVersions.QUERY_RULES_RETRIEVER;
+    }
+}

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

@@ -160,10 +160,10 @@ protected QueryRuleRetrieverBuilder clone(List<RetrieverSource> newChildRetrieve
     protected RankDoc[] combineInnerRetrieverResults(List<ScoreDoc[]> rankResults) {
         assert rankResults.size() == 1;
         ScoreDoc[] scoreDocs = rankResults.getFirst();
-        RankDoc[] rankDocs = new RankDoc[scoreDocs.length];
+        RankDoc[] rankDocs = new QueryRuleRankDoc[scoreDocs.length];
         for (int i = 0; i < scoreDocs.length; i++) {
             ScoreDoc scoreDoc = scoreDocs[i];
-            rankDocs[i] = new RankDoc(scoreDoc.doc, scoreDoc.score, scoreDoc.shardIndex);
+            rankDocs[i] = new QueryRuleRankDoc(scoreDoc.doc, scoreDoc.score, scoreDoc.shardIndex, rulesetIds, matchCriteria);
             rankDocs[i].rank = i + 1;
         }
         return rankDocs;