Support for GWT to PolyGerrit integration plugin migration

Detect migration scenario based on UI script files to have same name and
different extensions (.html and .js).

Allow for multiple `Gerrit.install()` calls, reusing `plugin` instance
for purposes of migration.

Cleanup plugin interface between tests.

Change-Id: I1a98a2b8660ce4a1700766dc722d587817ede884

Documentation/dev-plugins.txt

@@ -2577,7 +2577,7 @@ displayed as part of the index page, if present in the manifest:
 Compiled plugins and extensions can be deployed to a running Gerrit
 server using the link:cmd-plugin-install.html[plugin install] command.
 
-Web UI plugins distributed as a single `.js` file (or `.html' file for
+Web UI plugins distributed as a single `.js` file (or `.html` file for
 Polygerrit) can be deployed without the overhead of JAR packaging. For
 more information refer to link:cmd-plugin-install.html[plugin install]
 command.

Documentation/pg-plugin-dev.txt

@@ -4,6 +4,9 @@ CAUTION: Work in progress. Hard hat area. Please
 link:https://bugs.chromium.org/p/gerrit/issues/entry?template=PolyGerrit%20plugins[send
 feedback] if something's not right.
 
+For migrating existing GWT UI plugins, please check out the
+link:pg-plugin-migration.html#migration[migration guide].
+
 [[loading]]
 == Plugin loading and initialization
 

Documentation/pg-plugin-migration.txt

@@ -0,0 +1,153 @@
+= Gerrit Code Review - PolyGerrit Plugin Development
+
+CAUTION: Work in progress. Hard hat area. Please
+link:https://bugs.chromium.org/p/gerrit/issues/entry?template=PolyGerrit%20plugins[send
+feedback] if something's not right.
+
+[[migration]]
+== Incremental migration of existing GWT UI plugins
+
+link:pg-plugin-dev.html[PolyGerrit plugin API] operates different concepts and
+provides different type of API compared to ones available to GWT
+plugins. Depending on the plugin, it might require significant modifications to
+existing UI scripts to fully take advantage of benefits PolyGerrit API
+provides.
+
+To make migration easier, PolyGerrit recommends incremental migration
+strategy. Starting with a .js file that works for GWT UI, plugin author can
+incrementally migrate deprecated APIs to new plugin API.
+
+The goal for this guide is to provide migration path from .js-based UI script to
+.html-based.
+
+NOTE: Web UI plugins distributed as a single .js file are not covered in this
+guide.
+
+Let's start with a basic plugin that has an UI module. Commonly, file tree
+should look like this:
+
+  ├── BUILD
+  ├── LICENSE
+  └── src
+      └── main
+          ├── java
+          │   └── com
+          │       └── foo
+          │           └── SamplePluginModule.java
+          └── resources
+              └── static
+                  └── sampleplugin.js
+
+For simplicity's sake, let's assume SamplePluginModule.java has following
+content:
+
+``` java
+public class SamplePluginModule extends AbstractModule {
+
+  @Override
+  protected void configure() {
+    DynamicSet.bind(binder(), WebUiPlugin.class)
+        .toInstance(new JavaScriptPlugin("sampleplugin.js"));
+  }
+}
+```
+
+=== Step 1: Create `sampleplugin.html`
+
+As a first step, create starter `sampleplugin.html` and include UI script in the
+module file.
+
+NOTE: GWT UI ignore .html since it's not supported.
+
+``` java
+  @Override
+  protected void configure() {
+    DynamicSet.bind(binder(), WebUiPlugin.class)
+        .toInstance(new JavaScriptPlugin("sampleplugin.js"));
+    DynamicSet.bind(binder(), WebUiPlugin.class)
+        .toInstance(new JavaScriptPlugin("sampleplugin.html"));
+  }
+```
+
+Here's recommended starter code for `sampleplugin.html`:
+
+NOTE: By specification, the `id` attribute of `dom-module` *must* contain a dash
+(-).
+
+``` html
+<dom-module id="sample-plugin">
+  <script>
+    Gerrit.install(plugin => {
+        // Setup block, is executed before sampleplugin.js
+
+        // Install deprecated JS APIs (onAction, popup, etc)
+        plugin.deprecated.install();
+    });
+  </script>
+
+  <script src="./sampleplugin.js"></script>
+
+  <script>
+    Gerrit.install(plugin => {
+        // Cleanup block, is executed after sampleplugin.js
+    });
+  </script>
+</dom-module>
+```
+
+Here's how this works:
+
+- PolyGerrit detects migration scenario because UI scripts have same filename
+and different extensions
+ * PolyGerrit will load `sampleplugin.html` and skip `sampleplugin.js`
+ * PolyGerrit will reuse `plugin` (aka `self`) instance for `Gerrit.install()`
+callbacks
+- `sampleplugin.js` is loaded since it's referenced in `sampleplugin.html`
+- setup script tag code is executed before `sampleplugin.js`
+- cleanup script tag code is executed after `sampleplugin.js`
+- `plugin.deprecated.install()` enables deprecated APIs (onAction(), popup(),
+etc) before `sampleplugin.js` is loaded
+
+So the purpose is to share plugin instance between .html-based and .js-based
+code, making it possible to gradually and incrementally transfer code to new API.
+
+=== Step 2: Create cut-off marker in `sampleplugin.js`
+
+Commonly, window.Polymer is being used to detect in GWT UI script if it's being
+executed inside PolyGerrit. This could be used to separate code that was already
+migrated to new APIs from the one that hasn't been migrated yet.
+
+During incremental migration, some of the UI code will be reimplemented using
+PolyGerrit plugin API. However, old code still could be required for the plugin
+to work in GWT UI.
+
+To handle this case, add following code to be the last thing in installation
+callback in `sampleplugin.js`
+
+``` js
+Gerrit.install(function(self) {
+
+  // Existing code here, not modified.
+
+  if (window.Polymer) { return; } // Cut-off marker
+
+  // Everything below was migrated to PolyGerrit plugin API.
+  // Code below is still needed for the plugin to work in GWT UI.
+});
+```
+
+=== Step 3: Migrate!
+
+The code that uses deprecated APIs should be eventually rewritten using
+non-deprecated counterparts. Duplicated pieces could be kept under cut-off
+marker to work in GWT UI.
+
+If some data or functions needs to be shared between code in .html and .js, it
+could be stored on `plugin` (aka `self`) object that's shared between both
+
+=== Step 4: Cleanup
+
+Once deprecated APIs are migrated, `sampleplugin.js` will only contain
+duplicated code that's required for GWT UI to work. With sudden but inevitable
+GWT code removal from Gerrit that file can be simply deleted, along with script
+tag loading it.

polygerrit-ui/app/elements/plugins/gr-plugin-host/gr-plugin-host.js

@@ -30,8 +30,9 @@
 
     _configChanged(config) {
       const plugins = config.plugin;
-      const jsPlugins = plugins.js_resource_paths || [];
       const htmlPlugins = plugins.html_resource_paths || [];
+      const jsPlugins = this._handleMigrations(plugins.js_resource_paths || [],
+          htmlPlugins);
       const defaultTheme = config.default_theme;
       if (defaultTheme) {
         // Make theme first to be first to load.
@@ -42,6 +43,17 @@
       this._importHtmlPlugins(htmlPlugins);
     },
 
+    /**
+     * Omit .js plugins that have .html counterparts.
+     * For example, if plugin provides foo.js and foo.html, skip foo.js.
+     */
+    _handleMigrations(jsPlugins, htmlPlugins) {
+      return jsPlugins.filter(url => {
+        const counterpart = url.replace(/\.js$/, '.html');
+        return !htmlPlugins.includes(counterpart);
+      });
+    },
+
     /**
      * @suppress {checkTypes}
      * States that it expects no more than 3 parameters, but that's not true.

polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-js-api-interface_test.html

@@ -70,6 +70,13 @@ limitations under the License.
       plugin = null;
     });
 
+    test('reuse plugin for install calls', () => {
+      let otherPlugin;
+      Gerrit.install(p => { otherPlugin = p; }, '0.1',
+          'http://test.com/plugins/testplugin/static/test.js');
+      assert.strictEqual(plugin, otherPlugin);
+    });
+
     test('url', () => {
       assert.equal(plugin.url(), 'http://test.com/plugins/testplugin/');
       assert.equal(plugin.url('/static/test.js'),

polygerrit-ui/app/elements/shared/gr-js-api-interface/gr-public-js-api.js

@@ -18,6 +18,11 @@
     console.warn('Plugin API method ' + (opt_name || '') + ' is not supported');
   };
 
+  /**
+   * Hash of loaded and installed plugins, name to Plugin object.
+   */
+  const plugins = {};
+
   const stubbedMethods = ['_loadedGwt', 'screen', 'settingsScreen', 'panel'];
   const GWT_PLUGIN_STUB = {};
   for (const name of stubbedMethods) {
@@ -76,6 +81,20 @@
   // http://www.gwtproject.org/doc/latest/DevGuideCodingBasicsJSNI.html
   window.$wnd = window;
 
+  function getPluginNameFromUrl(url) {
+    const base = Gerrit.BaseUrlBehavior.getBaseUrl();
+    const pathname = url.pathname.replace(base, '');
+    // Site theme is server from predefined path.
+    if (pathname === '/static/gerrit-theme.html') {
+      return 'gerrit-theme';
+    } else if (!pathname.startsWith('/plugins')) {
+      console.warn('Plugin not being loaded from /plugins base path:',
+          url.href, '— Unable to determine name.');
+      return;
+    }
+    return pathname.split('/')[2];
+  }
+
   function Plugin(opt_url) {
     this._domHooks = new GrDomHooksManager(this);
 
@@ -84,26 +103,14 @@
           'Unable to determine name.');
       return;
     }
-
-    const base = Gerrit.BaseUrlBehavior.getBaseUrl();
-
-    this._url = new URL(opt_url);
-    const pathname = this._url.pathname.replace(base, '');
-    // Site theme is server from predefined path.
-    if (pathname === '/static/gerrit-theme.html') {
-      this._name = 'gerrit-theme';
-    } else if (!pathname.startsWith('/plugins')) {
-      console.warn('Plugin not being loaded from /plugins base path:',
-          this._url.href, '— Unable to determine name.');
-      return;
-    }
-    this._name = pathname.split('/')[2];
-
     this.deprecated = {
       install: deprecatedAPI.install.bind(this),
       popup: deprecatedAPI.popup.bind(this),
       onAction: deprecatedAPI.onAction.bind(this),
     };
+
+    this._url = new URL(opt_url);
+    this._name = getPluginNameFromUrl(this._url);
   }
 
   Plugin._sharedAPIElement = document.createElement('gr-js-api-interface');
@@ -265,6 +272,17 @@
 
   const Gerrit = window.Gerrit || {};
 
+  // Provide reset plugins function to clear installed plugins between tests.
+  const app = document.querySelector('#app');
+  if (!app) {
+    // No gr-app found (running tests)
+    Gerrit._resetPlugins = () => {
+      for (const k of Object.keys(plugins)) {
+        delete plugins[k];
+      }
+    };
+  }
+
   // Number of plugins to initialize, -1 means 'not yet known'.
   Gerrit._pluginsPending = -1;
 
@@ -296,15 +314,15 @@
       return;
     }
 
-    // TODO(andybons): Polyfill currentScript for IE10/11 (edge supports it).
     const src = opt_src || (document.currentScript &&
          (document.currentScript.src || document.currentScript.baseURI));
-    const plugin = new Plugin(src);
+    const name = getPluginNameFromUrl(new URL(src));
+    const plugin = plugins[name] || new Plugin(src);
     try {
       callback(plugin);
+      plugins[name] = plugin;
     } catch (e) {
-      console.warn(plugin.getPluginName() + ' install failed: ' +
+      console.warn(`${name} install failed: ${e.name}: ${e.message}`);
-          e.name + ': ' + e.message);
     }
     Gerrit._pluginInstalled();
   };

polygerrit-ui/app/test/common-test-setup.html

@@ -44,6 +44,21 @@ limitations under the License.
     return promise;
   };
 </script>
+<script>
+  (function() {
+    setup(() => {
+      if (!window.Gerrit) { return; }
+      Gerrit._pluginsPending = -1;
+      Gerrit._allPluginsPromise = undefined;
+      if (Gerrit._resetPlugins) {
+        Gerrit._resetPlugins();
+      }
+      if (Gerrit._endpoints) {
+        Gerrit._endpoints = new GrPluginEndpoints();
+      }
+    });
+  })();
+</script>
 <link rel="import"
     href="../bower_components/iron-test-helpers/iron-test-helpers.html" />
 <link rel="import" href="test-router.html" />