ES|QL: Replace RRF with FUSE

x-pack/plugin/esql/qa/server/src/main/java/org/elasticsearch/xpack/esql/qa/rest/generative/GenerativeForkRestTest.java

@@ -46,8 +46,8 @@ protected void shouldSkipTest(String testName) throws IOException {
         super.shouldSkipTest(testName);
 
         assumeFalse(
-            "Tests using FORK or RRF already are skipped since we don't support multiple FORKs",
-            testCase.requiredCapabilities.contains(FORK_V9.capabilityName()) || testCase.requiredCapabilities.contains(RRF.capabilityName())
+            "Tests using FORK are skipped since we don't support multiple FORKs",
+            testCase.requiredCapabilities.contains(FORK_V9.capabilityName())
         );
 
         assumeFalse(

x-pack/plugin/esql/qa/testFixtures/src/main/resources/rerank.csv-spec

@@ -143,16 +143,16 @@ book_no:keyword | title:text                                            | author
 ;
 
 
-reranker after RRF
+reranker after FUSE
 required_capability: fork_v9
-required_capability: rrf
+required_capability: fuse
 required_capability: match_operator_colon
 required_capability: rerank
 
 FROM books METADATA _id, _index, _score
 | FORK ( WHERE title:"Tolkien" | SORT _score, _id DESC | LIMIT 3 )
        ( WHERE author:"Tolkien" | SORT _score, _id DESC | LIMIT 3 )
-| RRF
+| FUSE
 | RERANK "Tolkien" ON title WITH inferenceId=test_reranker
 | EVAL _score=ROUND(_score, 2)
 | SORT _score DESC, book_no ASC

x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/RrfIT.java → x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/FuseIT.java

@@ -20,26 +20,27 @@
 import static org.elasticsearch.xpack.esql.EsqlTestUtils.getValuesList;
 import static org.hamcrest.Matchers.equalTo;
 
-public class RrfIT extends AbstractEsqlIntegTestCase {
+public class FuseIT extends AbstractEsqlIntegTestCase {
     @Override
     protected Collection<Class<? extends Plugin>> nodePlugins() {
         return List.of(EsqlPluginWithEnterpriseOrTrialLicense.class);
     }
 
     @Before
     public void setupIndex() {
-        assumeTrue("requires RRF capability", EsqlCapabilities.Cap.RRF.isEnabled());
+        assumeTrue("requires FUSE capability", EsqlCapabilities.Cap.FUSE.isEnabled());
         createAndPopulateIndex();
     }
 
-    public void testRrf() {
+    public void testFuseWithRrf() throws Exception {
         var query = """
             FROM test METADATA _score, _id, _index
             | WHERE id > 2
             | FORK
                ( WHERE content:"fox" | SORT _score, _id DESC )
                ( WHERE content:"dog" | SORT _score, _id DESC )
-            | RRF
+            | FUSE
+            | SORT _score DESC, _id, _index
             | EVAL _fork = mv_sort(_fork)
             | EVAL _score = round(_score, 4)
             | KEEP id, content, _score, _fork

x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/RrfWithInvalidLicenseIT.java → x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/FuseWithInvalidLicenseIT.java

@@ -21,8 +21,8 @@
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertAcked;
 import static org.hamcrest.Matchers.containsString;
 
-public class RrfWithInvalidLicenseIT extends AbstractEsqlIntegTestCase {
-    private static final String LICENSE_ERROR_MESSAGE = "current license is non-compliant for [RRF]";
+public class FuseWithInvalidLicenseIT extends AbstractEsqlIntegTestCase {
+    private static final String LICENSE_ERROR_MESSAGE = "current license is non-compliant for [FUSE]";
 
     @Override
     protected Collection<Class<? extends Plugin>> nodePlugins() {
@@ -31,7 +31,7 @@ protected Collection<Class<? extends Plugin>> nodePlugins() {
 
     @Before
     public void setupIndex() {
-        assumeTrue("requires RRF capability", EsqlCapabilities.Cap.RRF.isEnabled());
+        assumeTrue("requires FUSE capability", EsqlCapabilities.Cap.FUSE.isEnabled());
         var indexName = "test";
         var client = client().admin().indices();
         var CreateRequest = client.prepareCreate(indexName)
@@ -52,7 +52,7 @@ public void testRrf() {
             | FORK
                ( WHERE content:"fox" )
                ( WHERE content:"dog" )
-            | RRF
+            | FUSE
             """;
 
         ElasticsearchException e = expectThrows(VerificationException.class, () -> run(query));

x-pack/plugin/esql/src/main/antlr/EsqlBaseLexer.g4

@@ -65,7 +65,6 @@ import ChangePoint,
        Lookup,
        MvExpand,
        Project,
-       Rrf,
        Rename,
        Show,
        UnknownCommand;