Validate compatible handlers have correct version (#58304)

Validating if registered compatible rest handlers are overriding
compatibleWith method and specify the right compatible version
("197 błędów / +197")

modules/rest-compatibility/src/main/java/org/elasticsearch/compat/RestCompatPlugin.java

@@ -44,6 +44,7 @@
 
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 import java.util.function.Supplier;
 
 public class RestCompatPlugin extends Plugin implements ActionPlugin {
@@ -59,7 +60,8 @@ public List<RestHandler> getRestHandlers(
         Supplier<DiscoveryNodes> nodesInCluster
     ) {
         if (Version.CURRENT.major == 8) {
-            return List.of(
+            return validateCompatibleHandlers(
+                7,
                 new RestDeleteByQueryActionV7(),
                 new RestUpdateByQueryActionV7(),
                 new RestCreateIndexActionV7(),
@@ -77,4 +79,20 @@ public List<RestHandler> getRestHandlers(
         }
         return Collections.emptyList();
     }
+
+    // default scope for testing
+    List<RestHandler> validateCompatibleHandlers(int expectedVersion, RestHandler... handlers) {
+        for (RestHandler handler : handlers) {
+            if (handler.compatibleWithVersion().major != expectedVersion) {
+                String msg = String.format(
+                    Locale.ROOT,
+                    "Handler %s is of incorrect version %s.",
+                    handler.getClass().getSimpleName(),
+                    handler.compatibleWithVersion()
+                );
+                throw new IllegalStateException(msg);
+            }
+        }
+        return List.of(handlers);
+    }
 }

modules/rest-compatibility/src/test/java/org/elasticsearch/compat/RestCompatPluginTests.java

@@ -0,0 +1,59 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch licenses this file to you under
+ * the Apache License, Version 2.0 (the "License"); you may
+ * not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.elasticsearch.compat;
+
+import org.elasticsearch.Version;
+import org.elasticsearch.client.node.NodeClient;
+import org.elasticsearch.rest.RestChannel;
+import org.elasticsearch.rest.RestHandler;
+import org.elasticsearch.rest.RestRequest;
+import org.elasticsearch.test.ESTestCase;
+import org.hamcrest.Matchers;
+
+import java.util.List;
+
+public class RestCompatPluginTests extends ESTestCase {
+
+    public void testRestHandlersValidation() {
+        RestCompatPlugin restCompatPlugin = new RestCompatPlugin();
+        Version prevVersion = Version.fromString("7.0.0");
+        expectThrows(
+            IllegalStateException.class,
+            () -> restCompatPlugin.validateCompatibleHandlers(7, restHandler(prevVersion), restHandler(Version.fromString("8.0.0")))
+        );
+
+        List<RestHandler> restHandlers = restCompatPlugin.validateCompatibleHandlers(7, restHandler(prevVersion), restHandler(prevVersion));
+        assertThat(restHandlers, Matchers.hasSize(2));
+    }
+
+    private RestHandler restHandler(final Version version) {
+        return new RestHandler() {
+            @Override
+            public Version compatibleWithVersion() {
+                return version;
+            }
+
+            @Override
+            public void handleRequest(RestRequest request, RestChannel channel, NodeClient client) throws Exception {
+
+            }
+        };
+    }
+}