Enable testing for ExtensiblePlugins using classpath plugins

server/src/internalClusterTest/java/org/opensearch/plugins/ClasspathPluginIT.java

@@ -0,0 +1,52 @@
+/*
+ * SPDX-License-Identifier: Apache-2.0
+ *
+ * The OpenSearch Contributors require contributions made to
+ * this file be licensed under the Apache-2.0 license or a
+ * compatible open source license.
+ */
+
+package org.opensearch.plugins;
+
+import org.opensearch.test.OpenSearchIntegTestCase;
+
+import java.io.IOException;
+import java.util.Collection;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static org.hamcrest.Matchers.equalTo;
+
+@OpenSearchIntegTestCase.ClusterScope(scope = OpenSearchIntegTestCase.Scope.TEST, numDataNodes = 0)
+public class ClasspathPluginIT extends OpenSearchIntegTestCase {
+
+    public interface SampleExtension {}
+
+    public static class SampleExtensiblePlugin extends Plugin implements ExtensiblePlugin {
+        public SampleExtensiblePlugin() {}
+
+        @Override
+        public void loadExtensions(ExtensiblePlugin.ExtensionLoader loader) {
+            int nLoaded = 0;
+            for (SampleExtension e : loader.loadExtensions(SampleExtension.class)) {
+                nLoaded++;
+            }
+
+            assertThat(nLoaded, equalTo(1));
+        }
+    }
+
+    public static class SampleExtendingPlugin extends Plugin implements SampleExtension {
+        public SampleExtendingPlugin() {}
+    };
+
+    @Override
+    protected Collection<Class<? extends Plugin>> nodePlugins() {
+        return Stream.concat(super.nodePlugins().stream(), Stream.of(SampleExtensiblePlugin.class, SampleExtendingPlugin.class))
+            .collect(Collectors.toList());
+    }
+
+    public void testPluginExtensionWithClasspathPlugins() throws IOException {
+        internalCluster().startNode();
+    }
+}

server/src/internalClusterTest/resources/META-INF/services/org.opensearch.plugins.ClasspathPluginIT$SampleExtension

@@ -0,0 +1,8 @@
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+# The OpenSearch Contributors require contributions made to
+# this file be licensed under the Apache-2.0 license or a
+# compatible open source license.
+
+org.opensearch.plugins.ClasspathPluginIT$SampleExtendingPlugin

server/src/main/java/org/opensearch/plugins/PluginsService.java

@@ -150,7 +150,7 @@ public PluginsService(
                 "1.8",
                 pluginClass.getName(),
                 null,
-                Collections.emptyList(),
+                classpathPlugins.stream().map(Class::getName).filter(cp -> !pluginClass.getName().equals(cp)).collect(Collectors.toList()),
                 false
             );
             if (logger.isTraceEnabled()) {
@@ -160,6 +160,7 @@ public PluginsService(
             pluginsList.add(pluginInfo);
             pluginsNames.add(pluginInfo.getName());
         }
+        loadExtensions(pluginsLoaded);
 
         Set<Bundle> seenBundles = new LinkedHashSet<>();
         List<PluginInfo> modulesList = new ArrayList<>();
@@ -569,9 +570,17 @@ private static void loadExtensionsForPlugin(ExtensiblePlugin extensiblePlugin, L
         ExtensiblePlugin.ExtensionLoader extensionLoader = new ExtensiblePlugin.ExtensionLoader() {
             @Override
             public <T> List<T> loadExtensions(Class<T> extensionPointType) {
+                Set<Class<?>> seenClasses = new LinkedHashSet<>();
                 List<T> result = new ArrayList<>();
+
                 for (Plugin extendingPlugin : extendingPlugins) {
-                    result.addAll(createExtensions(extensionPointType, extendingPlugin));
+                    List<? extends T> extensions = createExtensions(extensionPointType, extendingPlugin);
+                    for (T extension : extensions) {
+                        // Only add if we haven't seen this class before, needed for classpath extensions for testing
+                        if (seenClasses.add(extension.getClass())) {
+                            result.add(extension);
+                        }
+                    }
                 }
                 return Collections.unmodifiableList(result);
             }