support for C++ applets

make possible for an applet to be implemented in c++ but still
have the qml package with the usual api, this was supposed to
be supported from the beginning.

if a c++ applet has been loaded, make available the property
plasmoid.nativeInterface to the qml part, exposing the subclasses
Applet instance with all eventual extra propertiels/slots.

if no c++ plugin is present, appletInterface will be dummy/not available

this (besides limiting a bit the qml import rabbit procreation)
makes available some things not available to normal private imports:
* access to applet config() to save more complex things compared to what kconfigxt allows
  or save/load stuff from the c++ part
* access to containment()/corona(), may be useful for containment implementations
* easier port for old very big applets such as comics/weather

Change-Id: I65117660043de3a60ad58c77b086f686683d4d8c

src/plasma/pluginloader.cpp

@@ -201,8 +201,8 @@ Applet *PluginLoader::loadApplet(const QString &name, uint appletId, const QVari
 
     QVariantList allArgs;
     allArgs << offer->storageId() << appletId << args;
-
-    if (!offer->property("X-Plasma-API").toString().isEmpty()) {
+    if (!offer->property("X-Plasma-API").toString().isEmpty() &&
+        offer->property("Library").toString().isEmpty()) {
 #ifndef NDEBUG
         // qDebug() << "we have a script using the"
         //         << offer->property("X-Plasma-API").toString() << "API";

src/scriptengines/qml/plasmoid/appletinterface.cpp

@@ -63,6 +63,7 @@ AppletInterface::AppletInterface(DeclarativeAppletScript *script, const QVariant
       m_busy(false),
       m_hideOnDeactivate(true),
       m_oldKeyboardShortcut(0),
+      m_dummyNativeInterface(0),
       m_positionBeforeRemoval(QPointF(-1, -1))
 {
     qmlRegisterType<QAction>();
@@ -118,7 +119,8 @@ AppletInterface::AppletInterface(Plasma::Applet *a, const QVariantList &args, QQ
       m_appletScriptEngine(0),
       m_backgroundHints(Plasma::Types::StandardBackground),
       m_busy(false),
-      m_hideOnDeactivate(true)
+      m_hideOnDeactivate(true),
+      m_dummyNativeInterface(0)
 {
     qmlRegisterType<QAction>();
 
@@ -585,6 +587,18 @@ void AppletInterface::setGlobalShortcut(const QKeySequence &sequence)
     applet()->setGlobalShortcut(sequence);
 }
 
+QObject *AppletInterface::nativeInterface()
+{
+    if (applet()->metaObject()->className() != "Plasma::Applet") {
+        return applet();
+    } else {
+        if (!m_dummyNativeInterface) {
+            m_dummyNativeInterface = new QObject(this);
+        }
+        return m_dummyNativeInterface;
+    }
+}
+
 QString AppletInterface::downloadPath(const QString &file)
 {
     const QString downloadDir = QStandardPaths::writableLocation(QStandardPaths::DownloadLocation) + "/Plasma/" + applet()->pluginInfo().pluginName() + '/';

src/scriptengines/qml/plasmoid/appletinterface.h

@@ -192,6 +192,11 @@ class AppletInterface : public PlasmaQuick::AppletQuickItem
      */
     Q_PROPERTY(QKeySequence globalShortcut READ globalShortcut WRITE setGlobalShortcut NOTIFY globalShortcutChanged)
 
+    /**
+     * An interface to the native C++ plasmoid, if implemented
+     */
+    Q_PROPERTY(QObject *nativeInterface READ nativeInterface CONSTANT)
+
 public:
     AppletInterface(DeclarativeAppletScript *script, const QVariantList &args = QVariantList(), QQuickItem *parent = 0);
     AppletInterface(Plasma::Applet *applet, const QVariantList &args = QVariantList(), QQuickItem *parent = 0);
@@ -318,6 +323,8 @@ public:
     QKeySequence globalShortcut() const;
     void setGlobalShortcut(const QKeySequence &keySequence);
 
+    QObject *nativeInterface();
+
 Q_SIGNALS:
     /**
      * somebody else, usually the containment sent some data to the applet
@@ -390,6 +397,7 @@ private:
     bool m_hideOnDeactivate : 1;
     //this is used to build an emacs style shortcut
     int m_oldKeyboardShortcut;
+    QObject *m_dummyNativeInterface;
 
     friend class ContainmentInterface;
     //This is used by ContainmentInterface