Add support for exists queries for rank_features

docs/changelog/110876.yaml

@@ -0,0 +1,6 @@
+pr: 110876
+summary: Add support for exists queries for `rank_features`
+area: Search
+type: enhancement
+issues:
+ - 98096

modules/mapper-extras/src/main/java/org/elasticsearch/index/mapper/extras/RankFeaturesFieldMapper.java

@@ -12,6 +12,7 @@
 import org.apache.lucene.search.Query;
 import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.common.lucene.Lucene;
+import org.elasticsearch.index.IndexVersions;
 import org.elasticsearch.index.analysis.NamedAnalyzer;
 import org.elasticsearch.index.fielddata.FieldDataContext;
 import org.elasticsearch.index.fielddata.IndexFieldData;
@@ -91,7 +92,10 @@ public String typeName() {
 
         @Override
         public Query existsQuery(SearchExecutionContext context) {
-            throw new IllegalArgumentException("[rank_features] fields do not support [exists] queries");
+            if (context.getIndexSettings().getIndexVersionCreated().before(IndexVersions.RANK_FEATURES_IN_FIELD_NAMES_SUPPORT)) {
+                throw new IllegalArgumentException("[rank_features] fields do not support [exists] queries");
+            }
+            return super.existsQuery(context);
         }
 
         @Override
@@ -196,6 +200,9 @@ public void parse(DocumentParserContext context) throws IOException {
                     );
                 }
             }
+            if (context.indexSettings().getIndexVersionCreated().onOrAfter(IndexVersions.RANK_FEATURES_IN_FIELD_NAMES_SUPPORT)) {
+                context.addToFieldNames(fieldType().name());
+            }
         } finally {
             context.path().setWithinLeafObject(false);
         }

modules/mapper-extras/src/test/java/org/elasticsearch/index/mapper/extras/RankFeaturesFieldMapperTests.java

@@ -15,7 +15,6 @@
 import org.elasticsearch.index.mapper.DocumentParsingException;
 import org.elasticsearch.index.mapper.MappedFieldType;
 import org.elasticsearch.index.mapper.MapperParsingException;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.mapper.MapperTestCase;
 import org.elasticsearch.index.mapper.ParsedDocument;
 import org.elasticsearch.plugins.Plugin;
@@ -43,12 +42,6 @@ protected Object getSampleObjectForDocument() {
         return getSampleValueForDocument();
     }
 
-    @Override
-    protected void assertExistsQuery(MapperService mapperService) {
-        IllegalArgumentException iae = expectThrows(IllegalArgumentException.class, () -> super.assertExistsQuery(mapperService));
-        assertEquals("[rank_features] fields do not support [exists] queries", iae.getMessage());
-    }
-
     @Override
     protected Collection<? extends Plugin> getPlugins() {
         return List.of(new MapperExtrasPlugin());

modules/mapper-extras/src/yamlRestTest/resources/rest-api-spec/test/rank_features/10_basic.yml

@@ -39,6 +39,13 @@ setup:
             1star: 1
             2star: 10
 
+  - do:
+      index:
+        index: test
+        id: "3"
+        body:
+          text: "doc with no rank_features fields available"
+
   - do:
       indices.refresh: {}
 
@@ -181,3 +188,19 @@ setup:
           negative_reviews:
             1star: 1
             2star: 10
+
+---
+"Exists queries":
+
+  - requires:
+      cluster_features: [ "gte_v8.16.0" ]
+      reason: "Support for exists queries was introduced in 8.16.0"
+  - do:
+      search:
+        rest_total_hits_as_int: true
+        index: test
+        body:
+          query:
+            exists:
+              field: tags
+  - match: { hits.total: 2 }

server/src/internalClusterTest/java/org/elasticsearch/search/query/ExistsIT.java

@@ -72,6 +72,9 @@ public void testExists() throws Exception {
             .startObject("vec")
             .field("type", "sparse_vector")
             .endObject()
+            .startObject("rank_feats")
+            .field("type", "rank_features")
+            .endObject()
             .endObject()
             .endObject()
             .endObject();
@@ -91,6 +94,10 @@ public void testExists() throws Exception {
             singletonMap("vec", emptyMap()),
             // sparse_vector field non-empty
             singletonMap("vec", singletonMap("1", 100)),
+            // rank features field empty
+            singletonMap("rank_feats", emptyMap()),
+            // rank_features field non-empty
+            singletonMap("rank_feats", singletonMap("foo", 100)),
             // empty doc
             emptyMap() };
         List<IndexRequestBuilder> reqs = new ArrayList<>();
@@ -112,6 +119,7 @@ public void testExists() throws Exception {
         expected.put("bar.bar.bar", 1);
         expected.put("foobar", 0);
         expected.put("vec", 2);
+        expected.put("rank_feats", 2);
 
         final long numDocs = sources.length;
         assertNoFailuresAndResponse(prepareSearch("idx").setSize(sources.length), allDocs -> {

server/src/main/java/org/elasticsearch/index/IndexVersions.java

@@ -112,6 +112,7 @@ private static IndexVersion def(int id, Version luceneVersion) {
     public static final IndexVersion ADD_SECURITY_MIGRATION = def(8_510_00_0, Version.LUCENE_9_11_0);
     public static final IndexVersion UPGRADE_TO_LUCENE_9_11_1 = def(8_511_00_0, Version.LUCENE_9_11_1);
     public static final IndexVersion INDEX_SORTING_ON_NESTED = def(8_512_00_0, Version.LUCENE_9_11_1);
+    public static final IndexVersion RANK_FEATURES_IN_FIELD_NAMES_SUPPORT = def(8_513_00_0, Version.LUCENE_9_11_1);
     /*
      * STOP! READ THIS FIRST! No, really,
      *        ____ _____ ___  ____  _        ____  _____    _    ____    _____ _   _ ___ ____    _____ ___ ____  ____ _____ _