Force Plasma style for QQC2 in applets

Summary:
using the qml url interceptor, rewrite imports in order
to load always the plasma styled qqc2 controls in plasmoids
and plasma views. As is per-engine, is possible to load
controls with qstyle theme in configuration dialogs
and plasma style in plasmoids.

Note: this replaces just the style org.kde.desktop
to Plasma and not every style (so with Material
set as QT_QUICK_CONTROLS_STYLE environment variable
plasma would load controls with material style) because
we can control both org.kde.desktop and Plasma styles:
they must have the same subdirectories as unlike files,
their existence is checked before the rewrite (in our case,
 "private"), so in order to work they must exist in both
styles

Test Plan:
a qqc2 button in a plasmoid has the plasma style, in
a config dialog has the qwidget style. rewrite works
only from org.kde.desktop to Plasma and not from other
styles, due to the existence of the "private" subdirectory

Reviewers: #plasma, davidedmundson

Reviewed By: #plasma, davidedmundson

Subscribers: davidedmundson, plasma-devel, #frameworks

Tags: #plasma, #frameworks

Differential Revision: https://phabricator.kde.org/D6964

src/plasmaquick/appletquickitem.cpp

@@ -65,6 +65,7 @@ void AppletQuickItemPrivate::init()
     qmlObject = new KDeclarative::QmlObjectSharedEngine(q);
     if (!qmlObject->engine()->urlInterceptor()) {
         PackageUrlInterceptor *interceptor = new PackageUrlInterceptor(qmlObject->engine(), KPackage::Package());
+        interceptor->setForcePlasmaStyle(true);
         qmlObject->engine()->setUrlInterceptor(interceptor);
     }
 }

src/plasmaquick/packageurlinterceptor.cpp

@@ -45,6 +45,7 @@ public:
     KPackage::Package package;
     QStringList allowedPaths;
     QQmlEngine *engine;
+    bool forcePlasmaStyle = false;
 
     //FIXME: those are going to be stuffed here and stay..
     // they should probably be removed when the last applet of that type is removed
@@ -81,9 +82,23 @@ QStringList PackageUrlInterceptor::allowedPaths() const
     return d->allowedPaths;
 }
 
+bool PackageUrlInterceptor::forcePlasmaStyle() const
+{
+    return d->forcePlasmaStyle;
+}
+
+void PackageUrlInterceptor::setForcePlasmaStyle(bool force)
+{
+    d->forcePlasmaStyle = force;
+}
+
 QUrl PackageUrlInterceptor::intercept(const QUrl &path, QQmlAbstractUrlInterceptor::DataType type)
 {
     //qDebug() << "Intercepted URL:" << path << type;
+
+    if (d->forcePlasmaStyle && path.path().contains("Controls.2/org.kde.desktop/")) {
+        return QUrl::fromLocalFile(path.path().replace(QLatin1String("Controls.2/org.kde.desktop/"), QLatin1String("Controls.2/Plasma/")));
+    }
     QString pkgRoot;
     KPackage::Package package;
     if (d->package.isValid()) {

src/plasmaquick/packageurlinterceptor.h

@@ -55,6 +55,9 @@ public:
     void removeAllowedPath(const QString &path);
     QStringList allowedPaths() const;
 
+    bool forcePlasmaStyle() const;
+    void setForcePlasmaStyle(bool force);
+
     QUrl intercept(const QUrl &path, QQmlAbstractUrlInterceptor::DataType type) Q_DECL_OVERRIDE;
 
     static inline QByteArray prefixForType(QQmlAbstractUrlInterceptor::DataType type, const QString &fileName)

src/plasmaquick/view.cpp

@@ -191,6 +191,7 @@ View::View(Plasma::Corona *corona, QWindow *parent)
     const auto pkg = corona->kPackage();
     if (pkg.isValid()) {
         PackageUrlInterceptor *interceptor = new PackageUrlInterceptor(engine(), pkg);
+        interceptor->setForcePlasmaStyle(true);
         engine()->setUrlInterceptor(interceptor);
 
         KDeclarative::KDeclarative kdeclarative;