Wait for UI plugins to load

If a screen is registered by a plugin this registration needs to be
completed before the dispatcher tries to parse the token.  Wait for
plugin scripts to finish loading and evaluating.  The old method of
injecting a script tag was not waiting correctly, especially for GWT
based plugins.

JavaScript plugins are now required to use Gerrit.install() as this
method updates internal Gerrit state tracking the script.  Not using
install() will eventually cause the UI to report the plugin as failing
to load.

GWT plugins must override onPluginLoad() not onModuleLoad().  All
plugins must recompile with the new glue code, as there is now a
handshake between the GWT plugin and the main Gerrit code.

All plugins must load within 5 seconds, otherwise the page marks them
as failed and reports loading errors.  During loading a glass pane is
used to prevent the user from interacting with a partial initialized
UI.  Plugins may be making critical contributions that need to be
registered before use.

A chunk of the API glue code was moved around to make each JSNI block
smaller, and better isolate purpose.  Plugin is now declared in its
own Java class.

Plugin instances are now tracked in the map $wnd.Gerrit.plugins.
This allows the main code to later figure out if any instance failed
to load. Any loading errors are usually reported on the JavaScript
console as script failures, and may include stack traces.

Change-Id: Id03581437ae1010cf995ef7ba8626ece37dfc2f4

Documentation/dev-plugins.txt

@@ -1353,10 +1353,13 @@ driven plugins:
 </manifestEntries>
 ----
 
-It is important that the module name that is provided to the
-`GwtPlugin` matches the GWT module contained in the plugin. The name
-of the GWT module can be explicitly set in the GWT module file by
-specifying the `rename-to` attribute on the module.
+The name that is provided to the `GwtPlugin` must match the GWT
+module name compiled into the plugin. The name of the GWT module
+can be explicitly set in the GWT module XML file by specifying
+the `rename-to` attribute on the module. It is important that the
+module name be unique across all plugins installed on the server,
+as the module name determines the JavaScript namespace used by the
+compiled plugin code.
 
 [source,xml]
 ----
@@ -1364,14 +1367,14 @@ specifying the `rename-to` attribute on the module.
 ----
 
 The actual GWT code must be implemented in a class that extends
-`com.google.gerrit.plugin.client.Plugin`:
+`com.google.gerrit.plugin.client.PluginEntryPoint`:
 
 [source,java]
 ----
-public class HelloPlugin extends Plugin {
+public class HelloPlugin extends PluginEntryPoint {
 
   @Override
-  public void onModuleLoad() {
+  public void onPluginLoad() {
     // Create the dialog box
     final DialogBox dialogBox = new DialogBox();
 

gerrit-gwtui/src/main/java/com/google/gerrit/client/Gerrit.java

@@ -22,6 +22,7 @@ import com.google.gerrit.client.account.AccountCapabilities;
 import com.google.gerrit.client.account.AccountInfo;
 import com.google.gerrit.client.admin.ProjectScreen;
 import com.google.gerrit.client.api.ApiGlue;
+import com.google.gerrit.client.api.PluginLoader;
 import com.google.gerrit.client.changes.ChangeConstants;
 import com.google.gerrit.client.changes.ChangeListScreen;
 import com.google.gerrit.client.config.ConfigServerApi;
@@ -49,12 +50,8 @@ import com.google.gerrit.reviewdb.client.AccountGeneralPreferences;
 import com.google.gerrit.reviewdb.client.AuthType;
 import com.google.gerrit.reviewdb.client.Project;
 import com.google.gwt.aria.client.Roles;
-import com.google.gwt.core.client.Callback;
-import com.google.gwt.core.client.CodeDownloadException;
 import com.google.gwt.core.client.EntryPoint;
 import com.google.gwt.core.client.GWT;
-import com.google.gwt.core.client.JavaScriptObject;
-import com.google.gwt.core.client.ScriptInjector;
 import com.google.gwt.dom.client.AnchorElement;
 import com.google.gwt.dom.client.Document;
 import com.google.gwt.event.dom.client.ClickEvent;
@@ -84,12 +81,9 @@ import com.google.gwt.user.client.ui.RootPanel;
 import com.google.gwtexpui.clippy.client.CopyableLabel;
 import com.google.gwtexpui.user.client.UserAgent;
 import com.google.gwtexpui.user.client.ViewSite;
-import com.google.gwtjsonrpc.client.CallbackHandle;
 import com.google.gwtjsonrpc.client.JsonDefTarget;
 import com.google.gwtjsonrpc.client.JsonUtil;
 import com.google.gwtjsonrpc.client.XsrfManager;
-import com.google.gwtjsonrpc.client.impl.ResultDeserializer;
-import com.google.gwtjsonrpc.common.AsyncCallback;
 import com.google.gwtorm.client.KeyUtil;
 
 import java.util.HashMap;
@@ -571,7 +565,7 @@ public class Gerrit implements EntryPoint {
     }
 
     saveDefaultTheme();
-    loadPlugins(hpd, token);
+    PluginLoader.load(hpd.plugins, token);
   }
 
   private void saveDefaultTheme() {
@@ -580,53 +574,6 @@ public class Gerrit implements EntryPoint {
         Document.get().getElementById("gerrit_footer"));
   }
 
-  private void loadPlugins(HostPageData hpd, final String token) {
-    if (hpd.plugins != null && !hpd.plugins.isEmpty()) {
-      for (final String url : hpd.plugins) {
-        ScriptInjector.fromUrl(url)
-            .setWindow(ScriptInjector.TOP_WINDOW)
-            .setCallback(new Callback<Void, Exception>() {
-              @Override
-              public void onSuccess(Void result) {
-              }
-
-              @Override
-              public void onFailure(Exception reason) {
-                ErrorDialog d;
-                if (reason instanceof CodeDownloadException) {
-                  d = new ErrorDialog(M.cannotDownloadPlugin(url));
-                } else {
-                  d = new ErrorDialog(M.pluginFailed(url));
-                }
-                d.center();
-              }
-            }).inject();
-      }
-    }
-
-    CallbackHandle<Void> cb = new CallbackHandle<Void>(
-        new ResultDeserializer<Void>() {
-          @Override
-          public Void fromResult(JavaScriptObject responseObject) {
-            return null;
-          }
-        },
-        new AsyncCallback<Void>() {
-          @Override
-          public void onFailure(Throwable caught) {
-          }
-
-          @Override
-          public void onSuccess(Void result) {
-            display(token);
-          }
-        });
-    cb.install();
-    ScriptInjector.fromString(cb.getFunctionName() + "();")
-        .setWindow(ScriptInjector.TOP_WINDOW)
-        .inject();
-  }
-
   public static void refreshMenuBar() {
     menuLeft.clear();
     menuRight.clear();

gerrit-gwtui/src/main/java/com/google/gerrit/client/GerritConstants.java

@@ -20,6 +20,7 @@ public interface GerritConstants extends Constants {
   String menuSignIn();
   String menuRegister();
   String reportBug();
+  String loadingPlugins();
 
   String signInDialogTitle();
   String signInDialogClose();

gerrit-gwtui/src/main/java/com/google/gerrit/client/GerritConstants.properties

@@ -1,6 +1,7 @@
 menuSignIn = Sign In
 menuRegister = Register
 reportBug = Report Bug
+loadingPlugins = Loading plugins ...
 
 signInDialogTitle = Code Review - Sign In
 signInDialogClose = Close

gerrit-gwtui/src/main/java/com/google/gerrit/client/GerritCss.java

@@ -116,6 +116,7 @@ public interface GerritCss extends CssResource {
   String errorDialogGlass();
   String errorDialogText();
   String errorDialogTitle();
+  String loadingPluginsDialog();
   String fileColumnHeader();
   String fileCommentBorder();
   String fileLine();

gerrit-gwtui/src/main/java/com/google/gerrit/client/GerritMessages.properties

@@ -13,7 +13,7 @@ branchCreationNotAllowedUnderRefnamePrefix = Branch creation is not allowed unde
 branchAlreadyExists = A branch with the name {0} already exists.
 branchCreationConflict = Cannot create branch {0} since it conflicts with branch {1}.
 
-pluginFailed = Plugin JavaScript {0} failed to load
-cannotDownloadPlugin = Cannot download JavaScript plugin from: {0}.
+pluginFailed = Plugin "{0}" failed to load
+cannotDownloadPlugin = Cannot load plugin from {0}
 
 parentUpdateFailed = Setting parent project failed: {0}

gerrit-gwtui/src/main/java/com/google/gerrit/client/api/ApiGlue.java

@@ -15,6 +15,8 @@
 package com.google.gerrit.client.api;
 
 import com.google.gerrit.client.Gerrit;
+import com.google.gerrit.client.rpc.NativeString;
+import com.google.gwt.core.client.GWT;
 import com.google.gwt.core.client.JavaScriptObject;
 import com.google.gwt.core.client.JsArray;
 import com.google.gwt.user.client.History;
@@ -24,29 +26,36 @@ public class ApiGlue {
   private static String pluginName;
 
   public static void init() {
-    init0();
+    init0(GWT.getHostPageBaseURL(), NativeString.TYPE);
     ActionContext.init();
+    Plugin.init();
     addHistoryHook();
   }
 
-  private static native void init0() /*-{
-    var serverUrl = @com.google.gwt.core.client.GWT::getHostPageBaseURL()();
-    var Plugin = function (name){this.name = name};
-    var Gerrit = {
+  private static native void init0(String serverUrl, JavaScriptObject JsonString) /*-{
+    $wnd.Gerrit = {
+      JsonString: JsonString,
+      events: {},
+      plugins: {},
+      change_actions: {},
+      revision_actions: {},
+      project_actions: {},
+
       getPluginName: @com.google.gerrit.client.api.ApiGlue::getPluginName(),
       install: function (f) {
-        var p = new Plugin(this.getPluginName());
-        @com.google.gerrit.client.api.ApiGlue::install(Lcom/google/gwt/core/client/JavaScriptObject;Lcom/google/gerrit/client/api/JsUiPlugin;)(f,p);
+        var p = this._getPluginByUrl(@com.google.gerrit.client.api.PluginName::getCallerUrl()());
+        @com.google.gerrit.client.api.ApiGlue::install(Lcom/google/gwt/core/client/JavaScriptObject;Lcom/google/gerrit/client/api/Plugin;)(f,p);
+      },
+      installGwt: function(u){return this._getPluginByUrl(u)},
+      _getPluginByUrl: function(u) {
+        return u.indexOf(serverUrl) == 0
+          ? this.plugins[u.substring(serverUrl.length)]
+          : this.plugins[u]
       },
 
       go: @com.google.gerrit.client.api.ApiGlue::go(Ljava/lang/String;),
       refresh: @com.google.gerrit.client.api.ApiGlue::refresh(),
 
-      events: {},
-      change_actions: {},
-      revision_actions: {},
-      project_actions: {},
-
       on: function (e,f){(this.events[e] || (this.events[e]=[])).push(f)},
       onAction: function (t,n,c){this._onAction(this.getPluginName(),t,n,c)},
       _onAction: function (p,t,n,c) {
@@ -81,34 +90,7 @@ public class ApiGlue {
         }
       },
       'delete': function(u,b){@com.google.gerrit.client.api.ActionContext::delete(Lcom/google/gerrit/client/rpc/RestApi;Lcom/google/gwt/core/client/JavaScriptObject;)(this._api(u),b)},
-      JsonString: @com.google.gerrit.client.rpc.NativeString::TYPE,
     };
-
-    Plugin.prototype = {
-      getPluginName: function(){return this.name},
-      go: @com.google.gerrit.client.api.ApiGlue::go(Ljava/lang/String;),
-      refresh: Gerrit.refresh,
-      onAction: function(t,n,c) {Gerrit._onAction(this.name,t,n,c)},
-
-      url: function (d) {
-        var u = serverUrl + 'plugins/' + this.name + '/';
-        if (d && d.length > 0) u += d.charAt(0)=='/' ? d.substring(1) : d;
-        return u;
-      },
-
-      _api: function(d) {
-        var u = 'plugins/' + this.name + '/';
-        if (d && d.length > 0) u += d.charAt(0)=='/' ? d.substring(1) : d;
-        return @com.google.gerrit.client.rpc.RestApi::new(Ljava/lang/String;)(u);
-      },
-
-      get: function(u,b){@com.google.gerrit.client.api.ActionContext::get(Lcom/google/gerrit/client/rpc/RestApi;Lcom/google/gwt/core/client/JavaScriptObject;)(this._api(u),b)},
-      post: function(u,i,b){@com.google.gerrit.client.api.ActionContext::post(Lcom/google/gerrit/client/rpc/RestApi;Lcom/google/gwt/core/client/JavaScriptObject;Lcom/google/gwt/core/client/JavaScriptObject;)(this._api(u),i,b)},
-      put: function(u,i,b){@com.google.gerrit.client.api.ActionContext::put(Lcom/google/gerrit/client/rpc/RestApi;Lcom/google/gwt/core/client/JavaScriptObject;Lcom/google/gwt/core/client/JavaScriptObject;)(this._api(u),i,b)},
-      'delete': function(u,b){@com.google.gerrit.client.api.ActionContext::delete(Lcom/google/gerrit/client/rpc/RestApi;Lcom/google/gwt/core/client/JavaScriptObject;)(this._api(u),b)},
-    };
-
-    $wnd.Gerrit = Gerrit;
   }-*/;
 
   /** Install deprecated {@code gerrit_addHistoryHook()} function. */
@@ -119,17 +101,25 @@ public class ApiGlue {
      };
   }-*/;
 
-  private static void install(JavaScriptObject cb, JsUiPlugin p) {
+  private static void install(JavaScriptObject cb, Plugin p) throws Exception {
     try {
       pluginName = p.name();
       invoke(cb, p);
+      p._initialized();
+    } catch (Exception e) {
+      p.failure(e);
+      throw e;
     } finally {
       pluginName = null;
+      PluginLoader.loaded();
     }
   }
 
   private static final String getPluginName() {
-    return pluginName != null ? pluginName : PluginName.get();
+    if (pluginName != null) {
+      return pluginName;
+    }
+    return PluginName.fromUrl(PluginName.getCallerUrl());
   }
 
   private static final void go(String urlOrToken) {

gerrit-gwtui/src/main/java/com/google/gerrit/client/api/JsUiPlugin.java

@@ -1,24 +0,0 @@
-// Copyright (C) 2013 The Android Open Source Project
-//
-// Licensed 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 com.google.gerrit.client.api;
-
-import com.google.gwt.core.client.JavaScriptObject;
-
-class JsUiPlugin extends JavaScriptObject {
-  final native String name() /*-{ return this.name }-*/;
-
-  protected JsUiPlugin() {
-  }
-}

gerrit-gwtui/src/main/java/com/google/gerrit/client/api/Plugin.java

@@ -0,0 +1,77 @@
+// Copyright (C) 2013 The Android Open Source Project
+//
+// Licensed 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 com.google.gerrit.client.api;
+
+import com.google.gwt.core.client.JavaScriptObject;
+
+final class Plugin extends JavaScriptObject {
+  private static final JavaScriptObject TYPE = createType();
+
+  static Plugin create(String url) {
+    int s = "plugins/".length();
+    int e = url.indexOf('/', s);
+    String name = url.substring(s, e);
+    return create(TYPE, url, name);
+  }
+
+  final native String url() /*-{ return this._scriptUrl }-*/;
+  final native String name() /*-{ return this.name }-*/;
+
+  final native boolean loaded() /*-{ return this._success || this._failure != null }-*/;
+  final native Exception failure() /*-{ return this._failure }-*/;
+  final native void failure(Exception e) /*-{ this._failure = e }-*/;
+  final native boolean success() /*-{ return this._success || false }-*/;
+  final native void _initialized() /*-{ this._success = true }-*/;
+
+  private static native Plugin create(JavaScriptObject T, String u, String n)
+  /*-{ return new T(u,n) }-*/;
+
+  private static native JavaScriptObject createType() /*-{
+    function Plugin(u, n) {
+      this._scriptUrl = u;
+      this.name = n;
+    }
+    return Plugin;
+  }-*/;
+
+  static native void init() /*-{
+    var G = $wnd.Gerrit;
+    @com.google.gerrit.client.api.Plugin::TYPE.prototype = {
+      getPluginName: function(){return this.name},
+      go: @com.google.gerrit.client.api.ApiGlue::go(Ljava/lang/String;),
+      refresh: @com.google.gerrit.client.api.ApiGlue::refresh(),
+      on: G.on,
+      onAction: function(t,n,c){G._onAction(this.name,t,n,c)},
+
+      url: function (u){return G.url(this._url(u))},
+      get: function(u,b){@com.google.gerrit.client.api.ActionContext::get(Lcom/google/gerrit/client/rpc/RestApi;Lcom/google/gwt/core/client/JavaScriptObject;)(this._api(u),b)},
+      post: function(u,i,b){@com.google.gerrit.client.api.ActionContext::post(Lcom/google/gerrit/client/rpc/RestApi;Lcom/google/gwt/core/client/JavaScriptObject;Lcom/google/gwt/core/client/JavaScriptObject;)(this._api(u),i,b)},
+      put: function(u,i,b){@com.google.gerrit.client.api.ActionContext::put(Lcom/google/gerrit/client/rpc/RestApi;Lcom/google/gwt/core/client/JavaScriptObject;Lcom/google/gwt/core/client/JavaScriptObject;)(this._api(u),i,b)},
+      'delete': function(u,b){@com.google.gerrit.client.api.ActionContext::delete(Lcom/google/gerrit/client/rpc/RestApi;Lcom/google/gwt/core/client/JavaScriptObject;)(this._api(u),b)},
+
+      _loadedGwt: function(){@com.google.gerrit.client.api.PluginLoader::loaded()()},
+      _api: function(u){return @com.google.gerrit.client.rpc.RestApi::new(Ljava/lang/String;)(this._url(u))},
+      _url: function (d) {
+        var u = 'plugins/' + this.name + '/';
+        if (d && d.length > 0)
+          return u + (d.charAt(0)=='/' ? d.substring(1) : d);
+        return u;
+      },
+    };
+  }-*/;
+
+  protected Plugin() {
+  }
+}

gerrit-gwtui/src/main/java/com/google/gerrit/client/api/PluginLoader.java

@@ -0,0 +1,185 @@
+// Copyright (C) 2013 The Android Open Source Project
+//
+// Licensed 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 com.google.gerrit.client.api;
+
+import com.google.gerrit.client.ErrorDialog;
+import com.google.gerrit.client.Gerrit;
+import com.google.gerrit.client.rpc.NativeMap;
+import com.google.gerrit.client.rpc.Natives;
+import com.google.gwt.core.client.Callback;
+import com.google.gwt.core.client.CodeDownloadException;
+import com.google.gwt.core.client.ScriptInjector;
+import com.google.gwt.user.client.Timer;
+import com.google.gwt.user.client.Window;
+import com.google.gwt.user.client.ui.DialogBox;
+import com.google.gwtexpui.progress.client.ProgressBar;
+
+import java.util.List;
+
+/** Loads JavaScript plugins with a progress meter visible. */
+public class PluginLoader extends DialogBox {
+  private static final int MAX_LOAD_TIME_MILLIS = 5000;
+  private static PluginLoader self;
+
+  public static void load(List<String> plugins, final String token) {
+    if (plugins == null || plugins.isEmpty()) {
+      Gerrit.display(token);
+    } else {
+      self = new PluginLoader(token);
+      self.load(plugins);
+      self.startTimers();
+      self.center();
+    }
+  }
+
+  static void loaded() {
+    self.loadedOne();
+  }
+
+  private final String token;
+  private ProgressBar progress;
+  private Timer show;
+  private Timer update;
+  private Timer timeout;
+  private boolean visible;
+
+  private PluginLoader(String tokenToDisplay) {
+    super(/* auto hide */false, /* modal */true);
+    token = tokenToDisplay;
+    progress = new ProgressBar(Gerrit.C.loadingPlugins());
+
+    setStyleName(Gerrit.RESOURCES.css().errorDialog());
+    addStyleName(Gerrit.RESOURCES.css().loadingPluginsDialog());
+  }
+
+  private void load(List<String> pluginUrls) {
+    for (String url : pluginUrls) {
+      Plugin plugin = Plugin.create(url);
+      plugins().put(url, plugin);
+      ScriptInjector.fromUrl(url)
+        .setWindow(ScriptInjector.TOP_WINDOW)
+        .setCallback(new LoadCallback(plugin))
+        .inject();
+    }
+  }
+
+  private void startTimers() {
+    show = new Timer() {
+      @Override
+      public void run() {
+        setText(Window.getTitle());
+        setWidget(progress);
+        setGlassEnabled(true);
+        getGlassElement().addClassName(Gerrit.RESOURCES.css().errorDialogGlass());
+        hide(true);
+        center();
+        visible = true;
+      }
+    };
+    show.schedule(500);
+
+    update = new Timer() {
+      private int cycle;
+
+      @Override
+      public void run() {
+        progress.setValue(100 * ++cycle * 250 / MAX_LOAD_TIME_MILLIS);
+      }
+    };
+    update.scheduleRepeating(250);
+
+    timeout = new Timer() {
+      @Override
+      public void run() {
+        finish();
+      }
+    };
+    timeout.schedule(MAX_LOAD_TIME_MILLIS);
+  }
+
+  private void loadedOne() {
+    boolean done = true;
+    for (Plugin plugin : Natives.asList(plugins().values())) {
+      done &= plugin.loaded();
+    }
+    if (done) {
+      finish();
+    }
+  }
+
+  private void finish() {
+    show.cancel();
+    update.cancel();
+    timeout.cancel();
+    self = null;
+
+    if (!hadFailures()) {
+      if (visible) {
+        progress.setValue(100);
+        new Timer() {
+          @Override
+          public void run() {
+            hide(true);
+          }
+        }.schedule(250);
+      } else {
+        hide(true);
+      }
+    }
+
+    Gerrit.display(token);
+  }
+
+  private boolean hadFailures() {
+    boolean failed = false;
+    for (Plugin plugin : Natives.asList(plugins().values())) {
+      if (!plugin.success()) {
+        failed = true;
+
+        Exception e = plugin.failure();
+        String msg;
+        if (e != null && e instanceof CodeDownloadException) {
+          msg = Gerrit.M.cannotDownloadPlugin(plugin.url());
+        } else {
+          msg = Gerrit.M.pluginFailed(plugin.name());
+        }
+        hide(true);
+        new ErrorDialog(msg).center();
+      }
+    }
+    return failed;
+  }
+
+  private static native NativeMap<Plugin> plugins()
+  /*-{ return $wnd.Gerrit.plugins }-*/;
+
+  private class LoadCallback implements Callback<Void, Exception> {
+    private final Plugin plugin;
+
+    LoadCallback(Plugin plugin) {
+      this.plugin = plugin;
+    }
+
+    @Override
+    public void onSuccess(Void result) {
+    }
+
+    @Override
+    public void onFailure(Exception reason) {
+      plugin.failure(reason);
+      loadedOne();
+    }
+  }
+}

gerrit-gwtui/src/main/java/com/google/gerrit/client/api/PluginName.java

@@ -31,14 +31,29 @@ import com.google.gwt.core.client.impl.StackTraceCreator;
 class PluginName {
   private static final String UNKNOWN = "<unknown>";
 
-  static String get() {
-    return GWT.<PluginName> create(PluginName.class).guessName();
+  private static String baseUrl() {
+    return GWT.getHostPageBaseURL() + "plugins/";
   }
 
-  String guessName() {
+  static String getCallerUrl() {
+    return GWT.<PluginName> create(PluginName.class).findCallerUrl();
+  }
+
+  static String fromUrl(String url) {
+    String baseUrl = baseUrl();
+    if (url != null && url.startsWith(baseUrl)) {
+      int s = url.indexOf('/', baseUrl.length());
+      if (s > 0) {
+        return url.substring(baseUrl.length(), s);
+      }
+    }
+    return UNKNOWN;
+  }
+
+  String findCallerUrl() {
     JavaScriptException err = makeException();
     if (hasStack(err)) {
-      return PluginNameMoz.guessName(err);
+      return PluginNameMoz.getUrl(err);
     }
 
     String baseUrl = baseUrl();
@@ -46,19 +61,12 @@ class PluginName {
     for (int i = trace.length - 1; i >= 0; i--) {
       String u = trace[i].getFileName();
       if (u != null && u.startsWith(baseUrl)) {
-        int s = u.indexOf('/', baseUrl.length());
-        if (s > 0) {
-          return u.substring(baseUrl.length(), s);
-        }
+        return u;
       }
     }
     return UNKNOWN;
   }
 
-  private static String baseUrl() {
-    return GWT.getHostPageBaseURL() + "plugins/";
-  }
-
   private static StackTraceElement[] getTrace(JavaScriptException err) {
     StackTraceCreator.fillInStackTrace(err);
     return err.getStackTrace();
@@ -72,21 +80,22 @@ class PluginName {
 
   /** Extracts URL from the stack frame. */
   static class PluginNameMoz extends PluginName {
-    String guessName() {
-      return guessName(makeException());
+    String findCallerUrl() {
+      return getUrl(makeException());
     }
 
-    static String guessName(JavaScriptException e) {
+    private static String getUrl(JavaScriptException e) {
       String baseUrl = baseUrl();
       JsArrayString stack = getStack(e);
       for (int i = stack.length() - 1; i >= 0; i--) {
         String frame = stack.get(i);
         int at = frame.indexOf(baseUrl);
         if (at >= 0) {
-          int s = frame.indexOf('/', at + baseUrl.length());
-          if (s > 0) {
-            return frame.substring(at + baseUrl.length(), s);
+          int end = frame.indexOf(':', at + baseUrl.length());
+          if (end < 0) {
+            end = frame.length();
           }
+          return frame.substring(at, end);
         }
       }
       return UNKNOWN;

gerrit-gwtui/src/main/java/com/google/gerrit/client/gerrit.css

@@ -431,6 +431,11 @@ a:hover {
   font-size: 15px;
   font-family: verdana;
 }
+.loadingPluginsDialog {
+  background: #fff;
+  color: #000;
+  width: auto;
+}
 
 
 /** Screen **/

gerrit-plugin-gwt-archetype/src/main/resources/archetype-resources/src/main/java/client/HelloPlugin.java

@@ -14,7 +14,7 @@
 
 package ${package}.client;
 
-import com.google.gerrit.plugin.client.Plugin;
+import com.google.gerrit.plugin.client.PluginEntryPoint;
 import com.google.gwt.event.dom.client.ClickEvent;
 import com.google.gwt.event.dom.client.ClickHandler;
 import com.google.gwt.user.client.ui.Button;
@@ -27,10 +27,10 @@ import ${package}.HelloMenu;
 /**
  * HelloWorld Plugin.
  */
-public class HelloPlugin extends Plugin {
+public class HelloPlugin extends PluginEntryPoint {
 
   @Override
-  public void onModuleLoad() {
+  public void onPluginLoad() {
     // Create the dialog box
     final DialogBox dialogBox = new DialogBox();
 

gerrit-plugin-gwtui/src/main/java/com/google/gerrit/plugin/client/Plugin.java

@@ -1,4 +1,4 @@
-// Copyright (C) 2012 The Android Open Source Project
+// Copyright (C) 2013 The Android Open Source Project
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -14,21 +14,46 @@
 
 package com.google.gerrit.plugin.client;
 
-import com.google.gwt.core.client.EntryPoint;
+import com.google.gwt.core.client.GWT;
+import com.google.gwt.core.client.JavaScriptObject;
 
 /**
- * Base class for writing Gerrit Web UI plugins
+ * Wrapper around the plugin instance exposed by Gerrit.
  *
- * Writing a plugin:
- * <ol>
- * <li>Declare subtype of Plugin</li>
- * <li>Bind WebUiPlugin to GwtPlugin implementation in Gerrit-Module</li>
- * </ol>
+ * Listeners for events generated by the main UI must be registered
+ * through this instance.
  */
-public abstract class Plugin implements EntryPoint {
-  public native static void go(String t)
-  /*-{ $wnd.Gerrit.go(t) }-*/;
+public final class Plugin extends JavaScriptObject {
+  private static final Plugin self = install(
+      GWT.getModuleBaseURL() + GWT.getModuleName() + ".nocache.js");
 
-  public native static void refresh()
-  /*-{ $wnd.Gerrit.refresh() }-*/;
+  /** Obtain the plugin instance wrapper. */
+  public static Plugin get() {
+    return self;
+  }
+
+  /** Installed name of the plugin. */
+  public final String getName() {
+    return getPluginName();
+  }
+
+  /** Installed name of the plugin. */
+  public final native String getPluginName()
+  /*-{ return this.getPluginName() }-*/;
+
+  /** Navigate the UI to the screen identified by the token. */
+  public final native void go(String token)
+  /*-{ return this.go(token) }-*/;
+
+  /** Refresh the current UI. */
+  public final native void refresh()
+  /*-{ return this.refresh() }-*/;
+
+  protected Plugin() {
+  }
+
+  native void _initialized() /*-{ this._success = true }-*/;
+  native void _loaded() /*-{ this._loadedGwt() }-*/;
+  private static native final Plugin install(String u)
+  /*-{ return $wnd.Gerrit.installGwt(u) }-*/;
 }

gerrit-plugin-gwtui/src/main/java/com/google/gerrit/plugin/client/PluginEntryPoint.java

@@ -0,0 +1,44 @@
+// Copyright (C) 2012 The Android Open Source Project
+//
+// Licensed 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 com.google.gerrit.plugin.client;
+
+import com.google.gwt.core.client.EntryPoint;
+
+/**
+ * Base class for writing Gerrit Web UI plugins
+ *
+ * Writing a plugin:
+ * <ol>
+ * <li>Declare subtype of Plugin</li>
+ * <li>Bind WebUiPlugin to GwtPlugin implementation in Gerrit-Module</li>
+ * </ol>
+ */
+public abstract class PluginEntryPoint implements EntryPoint {
+  /**
+   * The plugin entry point method, called automatically by loading
+   * a module that declares an implementing class as an entry point.
+   */
+  public abstract void onPluginLoad();
+
+  public final void onModuleLoad() {
+    Plugin self = Plugin.get();
+    try {
+      onPluginLoad();
+      self._initialized();
+    } finally {
+      self._loaded();
+    }
+  }
+}