Auto register static/init.js as JavaScript plugin

When plugin does not expose Guice Modules explicitly,
auto discover and register static/init.js as WebUi extension
if found by the plugin content scanner.
This simplify JavaScript development from now on
no Java (or other scripting) code/classes are
required to extend Gerrit WebUi.

(based on the idea and initial patch by Dariusz: Ia5b3cb63f62)

Change-Id: I8c793764ac1876dc62d740d28c0d4cf6b9409b10

gerrit-httpd/src/main/java/com/google/gerrit/httpd/plugins/HttpAutoRegisterModuleGenerator.java

@@ -14,14 +14,18 @@
 
 package com.google.gerrit.httpd.plugins;
 
+import static com.google.common.base.Preconditions.checkState;
 import static com.google.gerrit.server.plugins.AutoRegisterUtil.calculateBindAnnotation;
 
 import com.google.common.collect.LinkedListMultimap;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Multimap;
 import com.google.gerrit.extensions.annotations.Export;
+import com.google.gerrit.extensions.registration.DynamicSet;
+import com.google.gerrit.extensions.webui.JavaScriptPlugin;
+import com.google.gerrit.extensions.webui.WebUiPlugin;
+import com.google.gerrit.server.plugins.HttpModuleGenerator;
 import com.google.gerrit.server.plugins.InvalidPluginException;
-import com.google.gerrit.server.plugins.ModuleGenerator;
 import com.google.inject.Module;
 import com.google.inject.Scopes;
 import com.google.inject.TypeLiteral;
@@ -33,9 +37,10 @@ import java.util.Map;
 import javax.servlet.http.HttpServlet;
 
 class HttpAutoRegisterModuleGenerator extends ServletModule
-    implements ModuleGenerator {
+    implements HttpModuleGenerator {
   private final Map<String, Class<HttpServlet>> serve = Maps.newHashMap();
   private final Multimap<TypeLiteral<?>, Class<?>> listeners = LinkedListMultimap.create();
+  private String javascript;
 
   @Override
   protected void configureServlets() {
@@ -53,6 +58,10 @@ class HttpAutoRegisterModuleGenerator extends ServletModule
       Annotation n = calculateBindAnnotation(impl);
       bind(type).annotatedWith(n).to(impl);
     }
+    if (javascript != null) {
+      DynamicSet.bind(binder(), WebUiPlugin.class).toInstance(
+          new JavaScriptPlugin(javascript));
+    }
   }
 
   @Override
@@ -79,6 +88,14 @@ class HttpAutoRegisterModuleGenerator extends ServletModule
     }
   }
 
+  @Override
+  public void export(String javascript) {
+    checkState(this.javascript == null,
+        "Multiple JavaScript plugins detected: %s, %s", this.javascript,
+        javascript);
+    this.javascript = javascript;
+  }
+
   @Override
   public void listen(TypeLiteral<?> tl, Class<?> clazz) {
     listeners.put(tl, clazz);

gerrit-httpd/src/main/java/com/google/gerrit/httpd/plugins/HttpPluginModule.java

@@ -15,6 +15,7 @@
 package com.google.gerrit.httpd.plugins;
 
 import com.google.gerrit.server.cache.CacheModule;
+import com.google.gerrit.server.plugins.HttpModuleGenerator;
 import com.google.gerrit.server.plugins.ModuleGenerator;
 import com.google.gerrit.server.plugins.ReloadPluginListener;
 import com.google.gerrit.server.plugins.StartPluginListener;
@@ -37,7 +38,7 @@ public class HttpPluginModule extends ServletModule {
       .annotatedWith(UniqueAnnotations.create())
       .to(HttpPluginServlet.class);
 
-    bind(ModuleGenerator.class)
+    bind(HttpModuleGenerator.class)
       .to(HttpAutoRegisterModuleGenerator.class);
 
     install(new CacheModule() {