diff --git a/CMakeLists.txt b/CMakeLists.txt
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -139,8 +139,6 @@
 add_definitions(-DQT_USE_QSTRINGBUILDER)
 add_definitions(-DQT_NO_URL_CAST_FROM_STRING)
 
-remove_definitions(-DQT_NO_CAST_FROM_ASCII -DQT_STRICT_ITERATORS -DQT_NO_CAST_FROM_BYTEARRAY -DQT_NO_KEYWORDS)
-
 include(KF5PlasmaMacros.cmake)
 
 #########################################################################
diff --git a/autotests/CMakeLists.txt b/autotests/CMakeLists.txt
--- a/autotests/CMakeLists.txt
+++ b/autotests/CMakeLists.txt
@@ -2,6 +2,7 @@
 set_package_properties(Qt5Test PROPERTIES PURPOSE "Required for tests")
 
 set(EXECUTABLE_OUTPUT_PATH ${CMAKE_CURRENT_BINARY_DIR})
+remove_definitions(-DQT_NO_CAST_FROM_ASCII -DQT_STRICT_ITERATORS -DQT_NO_CAST_FROM_BYTEARRAY -DQT_NO_KEYWORDS)
 
 include(ECMMarkAsTest)
 include(ECMAddTests)
diff --git a/src/declarativeimports/calendar/calendarplugin.cpp b/src/declarativeimports/calendar/calendarplugin.cpp
--- a/src/declarativeimports/calendar/calendarplugin.cpp
+++ b/src/declarativeimports/calendar/calendarplugin.cpp
@@ -39,7 +39,7 @@
 
 void CalendarPlugin::registerTypes(const char *uri)
 {
-    Q_ASSERT(uri == QLatin1String("org.kde.plasma.calendar"));
+    Q_ASSERT(uri == QByteArray("org.kde.plasma.calendar"));
     qmlRegisterType<CalendarData>(uri, 2, 0, "CalendarData");
     qmlRegisterType<Calendar>(uri, 2, 0, "Calendar");
     qmlRegisterType<QAbstractItemModel>();
diff --git a/src/declarativeimports/calendar/eventpluginsmanager.cpp b/src/declarativeimports/calendar/eventpluginsmanager.cpp
--- a/src/declarativeimports/calendar/eventpluginsmanager.cpp
+++ b/src/declarativeimports/calendar/eventpluginsmanager.cpp
@@ -87,9 +87,9 @@
             {
                 // The currentPlugin path contains the full path including
                 // the plugin filename, so it needs to be cut off from the last '/'
-                const QStringRef pathRef = currentPlugin.leftRef(currentPlugin.lastIndexOf('/'));
+                const QStringRef pathRef = currentPlugin.leftRef(currentPlugin.lastIndexOf(QLatin1Char('/')));
                 const QString qmlFilePath = metadata.configUi;
-                return QString(pathRef % '/' % qmlFilePath);
+                return QString(pathRef % QLatin1Char('/') % qmlFilePath);
             }
             case Qt::UserRole + 1:
                 return currentPlugin;
diff --git a/src/declarativeimports/core/corebindingsplugin.cpp b/src/declarativeimports/core/corebindingsplugin.cpp
--- a/src/declarativeimports/core/corebindingsplugin.cpp
+++ b/src/declarativeimports/core/corebindingsplugin.cpp
@@ -70,10 +70,10 @@
 
 void CoreBindingsPlugin::registerTypes(const char *uri)
 {
-    Q_ASSERT(uri == QLatin1String("org.kde.plasma.core"));
+    Q_ASSERT(uri == QByteArray("org.kde.plasma.core"));
 
-    qmlRegisterUncreatableType<Plasma::Types>(uri, 2, 0, "Types", "");
-    qmlRegisterUncreatableType<Units>(uri, 2, 0, "Units", "");
+    qmlRegisterUncreatableType<Plasma::Types>(uri, 2, 0, "Types", {});
+    qmlRegisterUncreatableType<Units>(uri, 2, 0, "Units", {});
 
     qmlRegisterType<Plasma::Svg>(uri, 2, 0, "Svg");
     qmlRegisterType<Plasma::FrameSvg>(uri, 2, 0, "FrameSvg");
diff --git a/src/declarativeimports/core/datamodel.h b/src/declarativeimports/core/datamodel.h
--- a/src/declarativeimports/core/datamodel.h
+++ b/src/declarativeimports/core/datamodel.h
@@ -243,6 +243,7 @@
     QRegExp m_keyRoleFilterRE;
     QString m_sourceFilter;
     QRegExp m_sourceFilterRE;
+#warning QByteArray key?
     QMap<QString, QVector<QVariant> > m_items;
     QHash<int, QByteArray> m_roleNames;
     QHash<QString, int> m_roleIds;
diff --git a/src/declarativeimports/core/datamodel.cpp b/src/declarativeimports/core/datamodel.cpp
--- a/src/declarativeimports/core/datamodel.cpp
+++ b/src/declarativeimports/core/datamodel.cpp
@@ -55,7 +55,7 @@
     const QHash<int, QByteArray> rNames = roleNames();
     m_roleIds.reserve(rNames.count());
     for (auto i = rNames.constBegin(); i != rNames.constEnd(); ++i) {
-        m_roleIds[i.value()] = i.key();
+        m_roleIds[QString::fromUtf8(i.value())] = i.key();
     }
 
     setRoleNames(sourceModel()->roleNames());
@@ -193,7 +193,7 @@
 
     const QHash<int, QByteArray> rNames = roleNames();
     for (auto i = rNames.begin(); i != rNames.end(); ++i) {
-        hash[i.value()] = data(idx, i.key());
+        hash[QString::fromUtf8(i.value())] = data(idx, i.key());
     }
 
     return hash;
@@ -439,7 +439,7 @@
     if (m_keyRoleFilter.isEmpty()) {
         //source name in the map, linear scan
         for (int i = 0; i < m_items.value(QString()).count(); ++i) {
-            if (m_items.value(QString())[i].value<QVariantMap>().value("DataEngineSource") == sourceName) {
+            if (m_items.value(QString())[i].value<QVariantMap>().value(QStringLiteral("DataEngineSource")) == sourceName) {
                 beginRemoveRows(QModelIndex(), i, i);
                 m_items[QString()].remove(i);
                 endRemoveRows();
@@ -498,7 +498,7 @@
     if (!m_keyRoleFilter.isEmpty() && m_roleNames.value(role) == "DataEngineSource") {
         return source;
     } else {
-        return m_items.value(source).value(actualRow).value<QVariantMap>().value(m_roleNames.value(role));
+        return m_items.value(source).value(actualRow).value<QVariantMap>().value(QString::fromUtf8(m_roleNames.value(role)));
     }
 }
 
@@ -554,7 +554,7 @@
 
     const QHash<int, QByteArray> rNames = roleNames();
     for (auto i = rNames.constBegin(); i != rNames.constEnd(); ++i) {
-        map[i.value()] = data(idx, i.key());
+        map[QString::fromUtf8(i.value())] = data(idx, i.key());
     }
 
     return map;
diff --git a/src/declarativeimports/core/datasource.cpp b/src/declarativeimports/core/datasource.cpp
--- a/src/declarativeimports/core/datasource.cpp
+++ b/src/declarativeimports/core/datasource.cpp
@@ -174,7 +174,7 @@
 {
     //it can arrive also data we don't explicitly connected a source
     if (m_connectedSources.contains(sourceName)) {
-        m_data->insert(sourceName.toLatin1(), data);
+        m_data->insert(sourceName, data);
         emit dataChanged();
         emit newData(sourceName, data);
     } else if (m_dataEngine) {
diff --git a/src/declarativeimports/core/iconitem.cpp b/src/declarativeimports/core/iconitem.cpp
--- a/src/declarativeimports/core/iconitem.cpp
+++ b/src/declarativeimports/core/iconitem.cpp
@@ -175,7 +175,7 @@
 
             if (m_usesPlasmaTheme) {
                 //try as a svg icon from plasma theme
-                m_svgIcon->setImagePath(QLatin1String("icons/") + sourceString.section('-', 0, 0));
+                m_svgIcon->setImagePath(QLatin1String("icons/") + sourceString.section(QLatin1Char('-'), 0, 0));
                 m_svgIcon->setContainsMultipleImages(true);
             }
 
diff --git a/src/declarativeimports/core/tooltip.cpp b/src/declarativeimports/core/tooltip.cpp
--- a/src/declarativeimports/core/tooltip.cpp
+++ b/src/declarativeimports/core/tooltip.cpp
@@ -52,7 +52,7 @@
 
     loadSettings();
 
-    const QString configFile = QStandardPaths::writableLocation(QStandardPaths::GenericConfigLocation) + QLatin1Char('/') + "plasmarc";
+    const QString configFile = QStandardPaths::writableLocation(QStandardPaths::GenericConfigLocation) + QStringLiteral("/plasmarc");
     KDirWatch::self()->addFile(configFile);
     QObject::connect(KDirWatch::self(), SIGNAL(created(QString)), this, SLOT(settingsChanged()));
     QObject::connect(KDirWatch::self(), SIGNAL(dirty(QString)), this, SLOT(settingsChanged()));
diff --git a/src/declarativeimports/core/tooltipdialog.cpp b/src/declarativeimports/core/tooltipdialog.cpp
--- a/src/declarativeimports/core/tooltipdialog.cpp
+++ b/src/declarativeimports/core/tooltipdialog.cpp
@@ -57,8 +57,8 @@
     if (!m_qmlObject->rootObject()) {
         //HACK: search our own import
         foreach (const QString &path, m_qmlObject->engine()->importPathList()) {
-            if (QFile::exists(path + "/org/kde/plasma/core")) {
-                m_qmlObject->setSource(QUrl::fromLocalFile(path + "/org/kde/plasma/core/private/DefaultToolTip.qml"));
+            if (QFile::exists(path + QStringLiteral("/org/kde/plasma/core"))) {
+                m_qmlObject->setSource(QUrl::fromLocalFile(path + QStringLiteral("/org/kde/plasma/core/private/DefaultToolTip.qml")));
                 break;
             }
         }
diff --git a/src/declarativeimports/plasmacomponents/plasmacomponentsplugin.cpp b/src/declarativeimports/plasmacomponents/plasmacomponentsplugin.cpp
--- a/src/declarativeimports/plasmacomponents/plasmacomponentsplugin.cpp
+++ b/src/declarativeimports/plasmacomponents/plasmacomponentsplugin.cpp
@@ -81,16 +81,16 @@
 
 void PlasmaComponentsPlugin::registerTypes(const char *uri)
 {
-    Q_ASSERT(uri == QLatin1String("org.kde.plasma.components"));
+    Q_ASSERT(uri == QByteArray("org.kde.plasma.components"));
 
     qmlRegisterType<QMenuProxy>(uri, 2, 0, "Menu");
     qmlRegisterType<QMenuItem>(uri, 2, 0, "MenuItem");
 
     qmlRegisterType<Plasma::QRangeModel>(uri, 2, 0, "RangeModel");
 
-    qmlRegisterUncreatableType<DialogStatus>(uri, 2, 0, "DialogStatus", "");
-    qmlRegisterUncreatableType<PageOrientation>(uri, 2, 0, "PageOrientation", "");
-    qmlRegisterUncreatableType<PageStatus>(uri, 2, 0, "PageStatus", "");
+    qmlRegisterUncreatableType<DialogStatus>(uri, 2, 0, "DialogStatus", {});
+    qmlRegisterUncreatableType<PageOrientation>(uri, 2, 0, "PageOrientation", {});
+    qmlRegisterUncreatableType<PageStatus>(uri, 2, 0, "PageStatus", {});
 }
 
 #include "moc_plasmacomponentsplugin.cpp"
diff --git a/src/declarativeimports/plasmacomponents/qmenu.cpp b/src/declarativeimports/plasmacomponents/qmenu.cpp
--- a/src/declarativeimports/plasmacomponents/qmenu.cpp
+++ b/src/declarativeimports/plasmacomponents/qmenu.cpp
@@ -448,7 +448,7 @@
 
         //pre 5.8.0 QQuickWindow code is "item->grabMouse(); sendEvent(item, mouseEvent)"
         //post 5.8.0 QQuickWindow code is sendEvent(item, mouseEvent); item->grabMouse()
-        if (QVersionNumber::fromString(qVersion()) > QVersionNumber(5, 8, 0)) {
+        if (QVersionNumber::fromString(QString::fromLatin1(qVersion())) > QVersionNumber(5, 8, 0)) {
             QTimer::singleShot(0, this, ungrabMouseHack);
         } else {
             ungrabMouseHack();
diff --git a/src/declarativeimports/plasmaextracomponents/appbackgroundprovider.cpp b/src/declarativeimports/plasmaextracomponents/appbackgroundprovider.cpp
--- a/src/declarativeimports/plasmaextracomponents/appbackgroundprovider.cpp
+++ b/src/declarativeimports/plasmaextracomponents/appbackgroundprovider.cpp
@@ -41,6 +41,6 @@
 {
     Q_UNUSED(size)
     Q_UNUSED(requestedSize)
-    return QImage(m_theme->backgroundPath(id % ".png"));
+    return QImage(m_theme->backgroundPath(id % QStringLiteral(".png")));
 }
 
diff --git a/src/declarativeimports/plasmaextracomponents/fallbackcomponent.cpp b/src/declarativeimports/plasmaextracomponents/fallbackcomponent.cpp
--- a/src/declarativeimports/plasmaextracomponents/fallbackcomponent.cpp
+++ b/src/declarativeimports/plasmaextracomponents/fallbackcomponent.cpp
@@ -75,7 +75,7 @@
             resolved = m_basePath + path + key;
         } else {
 
-            resolved = QStandardPaths::locate(QStandardPaths::GenericDataLocation, m_basePath + '/' + path + key);
+            resolved = QStandardPaths::locate(QStandardPaths::GenericDataLocation, m_basePath + QLatin1Char('/') + path + key);
         }
 
         m_possiblePaths.insert(path + key, new QString(resolved));
diff --git a/src/declarativeimports/plasmaextracomponents/plasmaextracomponentsplugin.cpp b/src/declarativeimports/plasmaextracomponents/plasmaextracomponentsplugin.cpp
--- a/src/declarativeimports/plasmaextracomponents/plasmaextracomponentsplugin.cpp
+++ b/src/declarativeimports/plasmaextracomponents/plasmaextracomponentsplugin.cpp
@@ -30,13 +30,13 @@
 
 void PlasmaExtraComponentsPlugin::initializeEngine(QQmlEngine *engine, const char *uri)
 {
-    Q_ASSERT(uri == QLatin1String("org.kde.plasma.extras"));
+    Q_ASSERT(uri == QByteArray("org.kde.plasma.extras"));
     engine->addImageProvider(QStringLiteral("appbackgrounds"), new AppBackgroundProvider);
 }
 
 void PlasmaExtraComponentsPlugin::registerTypes(const char *uri)
 {
-    Q_ASSERT(uri == QLatin1String("org.kde.plasma.extras"));
+    Q_ASSERT(uri == QByteArray("org.kde.plasma.extras"));
     qmlRegisterType<FallbackComponent>(uri, 2, 0, "FallbackComponent");
 }
 
diff --git a/src/plasma/applet.cpp b/src/plasma/applet.cpp
--- a/src/plasma/applet.cpp
+++ b/src/plasma/applet.cpp
@@ -109,7 +109,7 @@
     }
     d->icon = d->appletDescription.iconName();
 
-    if (args.contains("org.kde.plasma:force-create")) {
+    if (args.contains(QVariant::fromValue(QStringLiteral("org.kde.plasma:force-create")))) {
         setProperty("org.kde.plasma:force-create", true);
     }
 
diff --git a/src/plasma/containment.cpp b/src/plasma/containment.cpp
--- a/src/plasma/containment.cpp
+++ b/src/plasma/containment.cpp
@@ -423,8 +423,8 @@
         //change the group to its configloader, if any
         //FIXME: this is very, very brutal
         if (applet->configScheme()) {
-            const QString oldGroupPrefix = QString("Containments" + QString::number(currentContainment->id()) + "Applets");
-            const QString newGroupPrefix = QString("Containments" + QString::number(id()) + "Applets");
+            const QString oldGroupPrefix = QStringLiteral("Containments") + QString::number(currentContainment->id()) + QStringLiteral("Applets");
+            const QString newGroupPrefix = QStringLiteral("Containments") + QString::number(id()) + QStringLiteral("Applets");
 
             applet->configScheme()->setCurrentGroup(applet->configScheme()->currentGroup().replace(0, oldGroupPrefix.length(), newGroupPrefix));
 
diff --git a/src/plasma/containmentactions.cpp b/src/plasma/containmentactions.cpp
--- a/src/plasma/containmentactions.cpp
+++ b/src/plasma/containmentactions.cpp
@@ -125,23 +125,23 @@
         QMouseEvent *e = static_cast<QMouseEvent *>(event);
         int m = QObject::staticQtMetaObject.indexOfEnumerator("MouseButtons");
         QMetaEnum mouse = QObject::staticQtMetaObject.enumerator(m);
-        trigger += mouse.valueToKey(e->button());
+        trigger += QString::fromLatin1(mouse.valueToKey(e->button()));
         modifiers = e->modifiers();
         break;
     }
     case QEvent::Wheel: {
         QWheelEvent *e = static_cast<QWheelEvent *>(event);
         int o = QObject::staticQtMetaObject.indexOfEnumerator("Orientations");
         QMetaEnum orient = QObject::staticQtMetaObject.enumerator(o);
         trigger = QStringLiteral("wheel:");
-        trigger += orient.valueToKey(e->orientation());
+        trigger += QString::fromLatin1(orient.valueToKey(e->orientation()));
         modifiers = e->modifiers();
         break;
     }
     case QEvent::ContextMenu: {
         int m = QObject::staticQtMetaObject.indexOfEnumerator("MouseButtons");
         QMetaEnum mouse = QObject::staticQtMetaObject.enumerator(m);
-        trigger = mouse.valueToKey(Qt::RightButton);
+        trigger = QString::fromLatin1(mouse.valueToKey(Qt::RightButton));
         modifiers = Qt::NoModifier;
         break;
     }
@@ -151,8 +151,7 @@
 
     int k = QObject::staticQtMetaObject.indexOfEnumerator("KeyboardModifiers");
     QMetaEnum kbd = QObject::staticQtMetaObject.enumerator(k);
-    trigger += ';';
-    trigger += kbd.valueToKeys(modifiers);
+    trigger += QLatin1Char(';') + QString::fromLatin1(kbd.valueToKeys(modifiers));
 
     return trigger;
 }
diff --git a/src/plasma/corona.cpp b/src/plasma/corona.cpp
--- a/src/plasma/corona.cpp
+++ b/src/plasma/corona.cpp
@@ -246,7 +246,7 @@
 
 Containment *Corona::createContainment(const QString &name, const QVariantList &args)
 {
-    if (d->immutability == Types::Mutable || args.contains("org.kde.plasma:force-create")) {
+    if (d->immutability == Types::Mutable || args.contains(QVariant::fromValue(QStringLiteral("org.kde.plasma:force-create")))) {
         return d->addContainment(name, args, 0);
     }
 
@@ -364,7 +364,7 @@
     KConfigGroup config(KSharedConfig::openConfig(), "General");
 
     if (QCoreApplication::instance()) {
-        configName = QCoreApplication::instance()->applicationName() + "-appletsrc";
+        configName = QCoreApplication::instance()->applicationName() + QStringLiteral("-appletsrc");
     } else {
         configName = QStringLiteral("plasma-appletsrc");
     }
@@ -484,7 +484,7 @@
             applet->init();
             delete applet;
         }
-        applet = containment = new Containment(q, 0, id);
+        applet = containment = new Containment(q, {}, id);
         //if it's a dummy containment, just say its ui is ready, not blocking the corona
         applet->updateConstraints(Plasma::Types::UiReadyConstraint);
 
diff --git a/src/plasma/dataengine.cpp b/src/plasma/dataengine.cpp
--- a/src/plasma/dataengine.cpp
+++ b/src/plasma/dataengine.cpp
@@ -433,7 +433,7 @@
         if (!api.isEmpty()) {
             const QString path =
                 QStandardPaths::locate(QStandardPaths::GenericDataLocation,
-                                       PLASMA_RELATIVE_DATA_INSTALL_DIR "/dataengines/" + dataEngineDescription.pluginName() + '/',
+                                       QStringLiteral(PLASMA_RELATIVE_DATA_INSTALL_DIR "/dataengines/") + dataEngineDescription.pluginName(),
                                        QStandardPaths::LocateDirectory);
             package = new Package(PluginLoader::self()->loadPackage(QStringLiteral("Plasma/DataEngine"), api));
             package->setPath(path);
diff --git a/src/plasma/framesvg.cpp b/src/plasma/framesvg.cpp
--- a/src/plasma/framesvg.cpp
+++ b/src/plasma/framesvg.cpp
@@ -132,7 +132,7 @@
     } else {
         d->prefix = prefix;
         if (!d->prefix.isEmpty()) {
-            d->prefix += '-';
+            d->prefix += QLatin1Char('-');
         }
     }
     d->requestedPrefix = prefix;
diff --git a/src/plasma/packagestructure.cpp b/src/plasma/packagestructure.cpp
--- a/src/plasma/packagestructure.cpp
+++ b/src/plasma/packagestructure.cpp
@@ -116,7 +116,7 @@
     } else {
         if (!servicePrefix.isEmpty()) {
             // and now we register it as a service =)
-            QString metaPath = path + "/metadata.desktop";
+            QString metaPath = path + QStringLiteral("/metadata.desktop");
             KDesktopFile df(metaPath);
             KConfigGroup cg = df.desktopGroup();
             const QString pluginName = cg.readEntry("X-KDE-PluginInfo-Name", QString());
@@ -132,7 +132,7 @@
 
             //TODO: remove installation of the desktop file in kservices5 when possible
 
-            const QString serviceName = servicePrefix + pluginName + ".desktop";
+            const QString serviceName = servicePrefix + pluginName + QStringLiteral(".desktop");
 
             QString localServiceDirectory = QStandardPaths::writableLocation(QStandardPaths::GenericDataLocation) + QLatin1String("/kservices5/");
             if (!QDir().mkpath(localServiceDirectory)) {
@@ -148,7 +148,7 @@
                 qCDebug(LOG_PLASMA) << "Copying metadata went ok.";
                 // the icon in the installed file needs to point to the icon in the
                 // installation dir!
-                QString iconPath = path + '/' + cg.readEntry("Icon");
+                QString iconPath = path + QLatin1Char('/') + cg.readEntry("Icon");
                 QFile icon(iconPath);
                 if (icon.exists()) {
                     KDesktopFile df(service);
@@ -217,11 +217,11 @@
 KJob *PackageStructure::uninstall(Package *package, const QString &packageRoot)
 {
     if (d->internalStructure && !qobject_cast<PackageStructureWrapper *>(d->internalStructure)) {
-        QString metaPath = package->path() + "/metadata.desktop";
+        QString metaPath = package->path() + QStringLiteral("/metadata.desktop");
         KDesktopFile df(metaPath);
         KConfigGroup cg = df.desktopGroup();
         const QString pluginName = cg.readEntry("X-KDE-PluginInfo-Name", QString());
-        const QString serviceName = package->servicePrefix() + pluginName + ".desktop";
+        const QString serviceName = package->servicePrefix() + pluginName + QStringLiteral(".desktop");
 
         KJob *job = d->internalStructure->uninstall(package->d->internalPackage, packageRoot);
         if (job) {
diff --git a/src/plasma/packagestructure/packages.cpp b/src/plasma/packagestructure/packages.cpp
--- a/src/plasma/packagestructure/packages.cpp
+++ b/src/plasma/packagestructure/packages.cpp
@@ -56,7 +56,7 @@
     }
 
     KPluginMetaData md(package->metadata().metaDataFileName());
-    QString mainScript = md.value("X-Plasma-MainScript");
+    QString mainScript = md.value(QLatin1String("X-Plasma-MainScript"));
 
     if (!mainScript.isEmpty()) {
         package->addFileDefinition("mainscript", mainScript, i18n("Main Script File"));
@@ -72,7 +72,7 @@
         QMutableStringListIterator it(platform);
         while (it.hasNext()) {
             it.next();
-            it.setValue("platformcontents/" + it.value());
+            it.setValue(QStringLiteral("platformcontents/") + it.value());
         }
 
         platform.append(QStringLiteral("contents"));
diff --git a/src/plasma/pluginloader.cpp b/src/plasma/pluginloader.cpp
--- a/src/plasma/pluginloader.cpp
+++ b/src/plasma/pluginloader.cpp
@@ -182,7 +182,7 @@
 
 
     //if name wasn't a path, pluginName == name
-    const QString pluginName = name.split('/').last();
+    const auto pluginName = name.splitRef(QLatin1Char('/')).last();
 
     // Look for C++ plugins first
     auto filter = [&pluginName](const KPluginMetaData &md) -> bool
@@ -452,7 +452,7 @@
         return Package();
     }
 
-    const QString hashkey = packageFormat + '%' + specialization;
+    const QString hashkey = packageFormat + QLatin1Char('%') + specialization;
     PackageStructure *structure = d->structures.value(hashkey).data();
 
     if (structure) {
@@ -528,7 +528,7 @@
     //NOTE: it still produces kplugininfos from KServices because some user code expects
     //info.sevice() to be valid and would crash ohtherwise
     foreach (auto& md, plugins) {
-        auto pi = md.metaDataFileName().endsWith(".json") ? KPluginInfo(md) : KPluginInfo(KService::serviceByStorageId(md.metaDataFileName()));
+        auto pi = md.metaDataFileName().endsWith(QLatin1String(".json")) ? KPluginInfo(md) : KPluginInfo(KService::serviceByStorageId(md.metaDataFileName()));
         if (!pi.isValid()) {
             qCWarning(LOG_PLASMA) << "Could not load plugin info for plugin :" << md.pluginId() << "skipping plugin";
             continue;
@@ -716,7 +716,7 @@
     if (parentApp.isEmpty()) {
         constraint = QStringLiteral("not exist [X-KDE-ParentApp]");
     } else {
-        constraint = QLatin1String("[X-KDE-ParentApp] == '") + parentApp + '\'';
+        constraint = QLatin1String("[X-KDE-ParentApp] == '") + parentApp + QLatin1Char('\'');
     }
 
     list.append(KPluginTrader::self()->query(PluginLoaderPrivate::s_dataEnginePluginDir, QStringLiteral("Plasma/DataEngine"), constraint));
@@ -735,7 +735,7 @@
     if (parentApp.isEmpty()) {
         constraint = QStringLiteral("not exist [X-KDE-ParentApp]");
     } else {
-        constraint = QLatin1String("[X-KDE-ParentApp] == '") + parentApp + '\'';
+        constraint = QLatin1String("[X-KDE-ParentApp] == '") + parentApp + QLatin1Char('\'');
     }
 
     list.append(KPluginTrader::self()->query(PluginLoaderPrivate::s_containmentActionsPluginDir, QStringLiteral("Plasma/ContainmentActions"), constraint));
diff --git a/src/plasma/private/applet_p.cpp b/src/plasma/private/applet_p.cpp
--- a/src/plasma/private/applet_p.cpp
+++ b/src/plasma/private/applet_p.cpp
@@ -174,8 +174,8 @@
     //It's valid, let's try to load the icon from within the package
     if (script) {
         //use the absolute path of the in-package icon as icon name
-        if (appletDescription.iconName().startsWith('/')) {
-            icon = package->filePath("", appletDescription.iconName().toUtf8());
+        if (appletDescription.iconName().startsWith(QLatin1Char('/'))) {
+            icon = package->filePath({}, appletDescription.iconName());
         }
     //package not valid, get rid of it
     } else {
diff --git a/src/plasma/private/componentinstaller.cpp b/src/plasma/private/componentinstaller.cpp
--- a/src/plasma/private/componentinstaller.cpp
+++ b/src/plasma/private/componentinstaller.cpp
@@ -65,7 +65,7 @@
         QWidget *parent, bool force)
 {
 #ifdef PLASMA_ENABLE_PACKAGEKIT_SUPPORT
-    QString searchString = type + '-' + name;
+    QString searchString = type + QLatin1Char('-') + name;
 
     if (!force) {
         if (d->alreadyPrompted.contains(searchString)) {
diff --git a/src/plasma/private/containment_p.cpp b/src/plasma/private/containment_p.cpp
--- a/src/plasma/private/containment_p.cpp
+++ b/src/plasma/private/containment_p.cpp
@@ -192,7 +192,7 @@
         return 0;
     }
 
-    if (q->immutability() != Types::Mutable && !args.contains("org.kde.plasma:force-create")) {
+    if (q->immutability() != Types::Mutable && !args.contains(QVariant::fromValue(QStringLiteral("org.kde.plasma:force-create")))) {
 #ifndef NDEBUG
         // qCDebug(LOG_PLASMA) << "addApplet for" << name << "requested, but we're currently immutable!";
 #endif
diff --git a/src/plasma/private/dataenginemanager.cpp b/src/plasma/private/dataenginemanager.cpp
--- a/src/plasma/private/dataenginemanager.cpp
+++ b/src/plasma/private/dataenginemanager.cpp
@@ -162,7 +162,7 @@
 void DataEngineManager::timerEvent(QTimerEvent *)
 {
 #ifndef NDEBUG
-    QString path = QStandardPaths::writableLocation(QStandardPaths::DataLocation) + QLatin1Char('/') + "plasma_dataenginemanager_log";
+    QString path = QStandardPaths::writableLocation(QStandardPaths::DataLocation) + QStringLiteral("/plasma_dataenginemanager_log");
     QFile f(path);
     if (!f.open(QIODevice::WriteOnly | QIODevice::Append | QIODevice::Text)) {
         // qCDebug(LOG_PLASMA) << "faild to open" << path;
@@ -195,7 +195,7 @@
                 out << "                       Relays: " << dc->d->relays.count() << endl;
                 QString times;
                 foreach (SignalRelay *relay, dc->d->relays) {
-                    times.append(' ').append(QString::number(relay->m_interval));
+                    times.append(QLatin1Char(' ') + QString::number(relay->m_interval));
                 }
                 out << "                       Relay Timeouts: " << times << ' '  << endl;
             }
diff --git a/src/plasma/private/storagethread.cpp b/src/plasma/private/storagethread.cpp
--- a/src/plasma/private/storagethread.cpp
+++ b/src/plasma/private/storagethread.cpp
@@ -81,14 +81,14 @@
         m_db = QSqlDatabase::addDatabase(QStringLiteral("QSQLITE"), QStringLiteral("plasma-storage-%1").arg((quintptr)this));
         const QString storageDir = QStandardPaths::writableLocation(QStandardPaths::DataLocation);
         QDir().mkpath(storageDir);
-        m_db.setDatabaseName(storageDir + QLatin1Char('/') + "plasma-storage2.db");
+        m_db.setDatabaseName(storageDir + QLatin1Char('/') + QStringLiteral("plasma-storage2.db"));
     }
 
     if (!m_db.open()) {
         qCWarning(LOG_PLASMA) << "Unable to open the plasma storage cache database: " << m_db.lastError();
     } else if (!m_db.tables().contains(caller->clientName())) {
         QSqlQuery query(m_db);
-        query.prepare(QStringLiteral("create table ") + caller->clientName() + " (valueGroup varchar(256), id varchar(256), txt TEXT, int INTEGER, float REAL, binary BLOB, creationTime datetime, accessTime datetime, primary key (valueGroup, id))");
+        query.prepare(QStringLiteral("create table ") + caller->clientName() + QStringLiteral(" (valueGroup varchar(256), id varchar(256), txt TEXT, int INTEGER, float REAL, binary BLOB, creationTime datetime, accessTime datetime, primary key (valueGroup, id))"));
         if (!query.exec()) {
             qCWarning(LOG_PLASMA) << "Unable to create table for" << caller->clientName();
             m_db.close();
@@ -122,21 +122,21 @@
         QSqlField field(QStringLiteral(":id"), QVariant::String);
         field.setValue(it.key());
         if (!ids.isEmpty()) {
-            ids.append(", ");
+            ids.append(QStringLiteral(", "));
         }
         ids.append(m_db.driver()->formatValue(field));
     }
 
-    query.prepare("delete from " + caller->clientName() + " where valueGroup = :valueGroup and id in (" + ids + ");");
+    query.prepare(QStringLiteral("delete from ") + caller->clientName() + QStringLiteral(" where valueGroup = :valueGroup and id in (") + ids + QStringLiteral(");"));
     query.bindValue(QStringLiteral(":valueGroup"), valueGroup);
 
     if (!query.exec()) {
         m_db.commit();
         emit newResult(caller, false);
         return;
     }
 
-    query.prepare("insert into " + caller->clientName() + " values(:valueGroup, :id, :txt, :int, :float, :binary, date('now'), date('now'))");
+    query.prepare(QStringLiteral("insert into ") + caller->clientName() + QStringLiteral(" values(:valueGroup, :id, :txt, :int, :float, :binary, date('now'), date('now'))"));
     query.bindValue(QStringLiteral(":valueGroup"), valueGroup);
     query.bindValue(QStringLiteral(":txt"), QVariant());
     query.bindValue(QStringLiteral(":int"), QVariant());
@@ -218,20 +218,20 @@
     //a bit redundant but should be the faster way with less string concatenation as possible
     if (params[QStringLiteral("key")].toString().isEmpty()) {
         //update modification time
-        query.prepare("update " + clientName + " set accessTime=date('now') where valueGroup=:valueGroup");
+        query.prepare(QStringLiteral("update ") + clientName + QStringLiteral(" set accessTime=date('now') where valueGroup=:valueGroup"));
         query.bindValue(QStringLiteral(":valueGroup"), valueGroup);
         query.exec();
 
-        query.prepare("select * from " + clientName + " where valueGroup=:valueGroup");
+        query.prepare(QStringLiteral("select * from ") + clientName + QStringLiteral(" where valueGroup=:valueGroup"));
         query.bindValue(QStringLiteral(":valueGroup"), valueGroup);
     } else {
         //update modification time
-        query.prepare("update " + clientName + " set accessTime=date('now') where valueGroup=:valueGroup and id=:key");
+        query.prepare(QStringLiteral("update ") + clientName + QStringLiteral(" set accessTime=date('now') where valueGroup=:valueGroup and id=:key"));
         query.bindValue(QStringLiteral(":valueGroup"), valueGroup);
         query.bindValue(QStringLiteral(":key"), params[QStringLiteral("key")].toString());
         query.exec();
 
-        query.prepare("select * from " + clientName + " where valueGroup=:valueGroup and id=:key");
+        query.prepare(QStringLiteral("select * from ") + clientName + QStringLiteral(" where valueGroup=:valueGroup and id=:key"));
         query.bindValue(QStringLiteral(":valueGroup"), valueGroup);
         query.bindValue(QStringLiteral(":key"), params[QStringLiteral("key")].toString());
     }
@@ -288,10 +288,10 @@
     QSqlQuery query(m_db);
 
     if (params[QStringLiteral("key")].toString().isEmpty()) {
-        query.prepare("delete from " + caller->clientName() + " where valueGroup=:valueGroup");
+        query.prepare(QStringLiteral("delete from ") + caller->clientName() + QStringLiteral(" where valueGroup=:valueGroup"));
         query.bindValue(QStringLiteral(":valueGroup"), valueGroup);
     } else {
-        query.prepare("delete from " + caller->clientName() + " where valueGroup=:valueGroup and id=:key");
+        query.prepare(QStringLiteral("delete from ") + caller->clientName() + QStringLiteral(" where valueGroup=:valueGroup and id=:key"));
         query.bindValue(QStringLiteral(":valueGroup"), valueGroup);
         query.bindValue(QStringLiteral(":key"), params[QStringLiteral("key")].toString());
     }
@@ -317,11 +317,11 @@
 
     QSqlQuery query(m_db);
     if (valueGroup.isEmpty()) {
-        query.prepare("delete from " + caller->clientName() + " where accessTime < :date");
+        query.prepare(QStringLiteral("delete from ") + caller->clientName() + QStringLiteral(" where accessTime < :date"));
         QDateTime time(QDateTime::currentDateTime().addSecs(-params[QStringLiteral("age")].toUInt()));
         query.bindValue(QStringLiteral(":date"), time.toTime_t());
     } else {
-        query.prepare("delete from " + caller->clientName() + " where valueGroup=:valueGroup and accessTime < :date");
+        query.prepare(QStringLiteral("delete from ") + caller->clientName() + QStringLiteral(" where valueGroup=:valueGroup and accessTime < :date"));
         query.bindValue(QStringLiteral(":valueGroup"), valueGroup);
         QDateTime time(QDateTime::currentDateTime().addSecs(-params[QStringLiteral("age")].toUInt()));
         query.bindValue(QStringLiteral(":date"), time.toTime_t());
diff --git a/src/plasma/private/theme_p.cpp b/src/plasma/private/theme_p.cpp
--- a/src/plasma/private/theme_p.cpp
+++ b/src/plasma/private/theme_p.cpp
@@ -58,8 +58,8 @@
       buttonColorScheme(QPalette::Active, KColorScheme::Button, KSharedConfigPtr(0)),
       viewColorScheme(QPalette::Active, KColorScheme::View, KSharedConfigPtr(0)),
       complementaryColorScheme(QPalette::Active, KColorScheme::Complementary, KSharedConfigPtr(0)),
-      defaultWallpaperTheme(DEFAULT_WALLPAPER_THEME),
-      defaultWallpaperSuffix(DEFAULT_WALLPAPER_SUFFIX),
+      defaultWallpaperTheme(QStringLiteral(DEFAULT_WALLPAPER_THEME)),
+      defaultWallpaperSuffix(QStringLiteral(DEFAULT_WALLPAPER_SUFFIX)),
       defaultWallpaperWidth(DEFAULT_WALLPAPER_WIDTH),
       defaultWallpaperHeight(DEFAULT_WALLPAPER_HEIGHT),
       pixmapCache(0),
@@ -151,10 +151,10 @@
 #ifndef NDEBUG
                 // qCDebug(LOG_PLASMA) << "using theme for app" << app;
 #endif
-                groupName.append('-').append(app);
+                groupName.append(QLatin1Char('-')).append(app);
             }
         }
-        cfg = KConfigGroup(KSharedConfig::openConfig(themeRcFile), groupName);
+        cfg = KConfigGroup(KSharedConfig::openConfig(QFile::decodeName(themeRcFile)), groupName);
     }
 
     return cfg;
@@ -179,10 +179,10 @@
             KDirWatch::self()->removeFile(themeMetadataPath);
         }
         if (isRegularTheme) {
-            themeMetadataPath = QStandardPaths::locate(QStandardPaths::GenericDataLocation, QLatin1Literal(PLASMA_RELATIVE_DATA_INSTALL_DIR "/desktoptheme/") % themeName % QLatin1Literal("/metadata.desktop"));
+            themeMetadataPath = QStandardPaths::locate(QStandardPaths::GenericDataLocation, QStringLiteral(PLASMA_RELATIVE_DATA_INSTALL_DIR "/desktoptheme/") % themeName % QStringLiteral("/metadata.desktop"));
             const auto *iconTheme = KIconLoader::global()->theme();
             if (iconTheme) {
-                iconThemeMetadataPath = iconTheme->dir() + "index.theme";
+                iconThemeMetadataPath = iconTheme->dir() + QStringLiteral("index.theme");
             }
 
             Q_ASSERT(!themeMetadataPath.isEmpty() || themeName.isEmpty());
@@ -236,7 +236,7 @@
             // the cache should be dropped; we need a way to detect system color change when the
             // application is not running.
             // check for expired cache
-            const QString cacheFilePath = QStandardPaths::writableLocation(QStandardPaths::GenericCacheLocation) + '/' + cacheFile + QLatin1String(".kcache");
+            const QString cacheFilePath = QStandardPaths::writableLocation(QStandardPaths::GenericCacheLocation) + QLatin1Char('/') + cacheFile + QLatin1String(".kcache");
             if (!cacheFilePath.isEmpty()) {
                 const QFileInfo cacheFileInfo(cacheFilePath);
                 const QFileInfo metadataFileInfo(themeMetadataPath);
@@ -272,7 +272,7 @@
             }
         }
 
-        const QString svgElementsFile = QStandardPaths::writableLocation(QStandardPaths::GenericCacheLocation) + '/' + svgElementsFileName;
+        const QString svgElementsFile = QStandardPaths::writableLocation(QStandardPaths::GenericCacheLocation) + QLatin1Char('/') + svgElementsFileName;
         svgElementsCache = KSharedConfig::openConfig(svgElementsFile, KConfig::SimpleConfig);
         QString currentIconThemePath;
         const auto *iconTheme = KIconLoader::global()->theme();
@@ -485,7 +485,7 @@
 
     QFont font = QGuiApplication::font();
     elements[QStringLiteral("%fontsize")] = QStringLiteral("%1pt").arg(font.pointSize());
-    elements[QStringLiteral("%fontfamily")] = font.family().split('[').first();
+    elements[QStringLiteral("%fontfamily")] = font.family().splitRef(QLatin1Char('[')).first().toString();
     elements[QStringLiteral("%smallfontsize")] = QStringLiteral("%1pt").arg(QFontDatabase::systemFont(QFontDatabase::SmallestReadableFont).pointSize());
 
     QHash<QString, QString>::const_iterator it = elements.constBegin();
@@ -845,7 +845,7 @@
         apiMinor = 0;
         apiRevision = 0;
         if (!apiVersion.isEmpty()) {
-            QVector<QStringRef> parts = apiVersion.splitRef('.');
+            QVector<QStringRef> parts = apiVersion.splitRef(QLatin1Char('.'));
             if (!parts.isEmpty()) {
                 apiMajor = parts.value(0).toInt();
             }
diff --git a/src/plasma/private/timetracker.cpp b/src/plasma/private/timetracker.cpp
--- a/src/plasma/private/timetracker.cpp
+++ b/src/plasma/private/timetracker.cpp
@@ -51,7 +51,7 @@
         QJsonDocument doc;
         doc.setArray(array);
 
-        QFile f(QStringLiteral("/tmp/debug-")+qgetenv("USER")+".json");
+        QFile f(QStringLiteral("/tmp/debug-") + QString::fromUtf8(qgetenv("USER")) + QStringLiteral(".json"));
         bool b = f.open(QFile::WriteOnly);
         Q_ASSERT(b);
         f.write(doc.toJson());
@@ -96,15 +96,15 @@
 
 void TimeTracker::init()
 {
-    m_history.events.append(TimeEvent { QDateTime::currentDateTime(), QStringLiteral("constructed %1 %2").arg(parent()->metaObject()->className(), parent()->objectName()) });
+    m_history.events.append(TimeEvent { QDateTime::currentDateTime(), QStringLiteral("constructed %1 %2").arg(QString::fromUtf8(parent()->metaObject()->className()), parent()->objectName()) });
 
     QMetaMethod propChange = metaObject()->method(metaObject()->indexOfSlot("propertyChanged()"));
     Q_ASSERT(propChange.isValid() && metaObject()->indexOfSlot("propertyChanged()")>=0);
 
     QObject* o = parent();
     for (int i = 0, pc = o->metaObject()->propertyCount(); i<pc; ++i) {
         QMetaProperty prop = o->metaObject()->property(i);
-        m_history.initial[prop.name()] = prop.read(o);
+        m_history.initial[QString::fromUtf8(prop.name())] = prop.read(o);
 
         if (prop.hasNotifySignal())
             connect(o, prop.notifySignal(), this, propChange);
@@ -133,7 +133,7 @@
             QString val;
             QDebug d(&val);
             d << prop.read(parent());
-            m_history.events.append(TimeEvent { QDateTime::currentDateTime(), QStringLiteral("property %1 changed to %2").arg(prop.name(), val.trimmed())});
+            m_history.events.append(TimeEvent { QDateTime::currentDateTime(), QStringLiteral("property %1 changed to %2").arg(QString::fromUtf8(prop.name()), val.trimmed())});
         }
     }
 }
diff --git a/src/plasma/service.cpp b/src/plasma/service.cpp
--- a/src/plasma/service.cpp
+++ b/src/plasma/service.cpp
@@ -198,7 +198,7 @@
         return;
     }
 
-    const QString path = QStandardPaths::locate(QStandardPaths::GenericDataLocation, PLASMA_RELATIVE_DATA_INSTALL_DIR "/services/" + d->name + ".operations");
+    const QString path = QStandardPaths::locate(QStandardPaths::GenericDataLocation, QStringLiteral(PLASMA_RELATIVE_DATA_INSTALL_DIR "/services/") + d->name + QStringLiteral(".operations"));
 
     if (path.isEmpty()) {
 #ifndef NDEBUG
diff --git a/src/plasma/svg.cpp b/src/plasma/svg.cpp
--- a/src/plasma/svg.cpp
+++ b/src/plasma/svg.cpp
@@ -309,7 +309,7 @@
     if (elementsWithSizeHints.isEmpty()) {
         // Fetch all size hinted element ids from the theme's rect cache
         // and store them locally.
-        QRegExp sizeHintedKeyExpr(CACHE_ID_NATURAL_SIZE("(\\d+)-(\\d+)-(.+)", status, ratio));
+        QRegExp sizeHintedKeyExpr(CACHE_ID_NATURAL_SIZE(QStringLiteral("(\\d+)-(\\d+)-(.+)"), status, ratio));
 
         foreach (const QString &key, cacheAndColorsTheme()->listCachedRectKeys(path)) {
             if (sizeHintedKeyExpr.exactMatch(key)) {
@@ -347,8 +347,8 @@
             }
 
             if (bestFit.isValid()) {
-                actualElementId = QString::number(bestFit.width()) % '-' %
-                                  QString::number(bestFit.height()) % '-' % elementId;
+                actualElementId = QString::number(bestFit.width()) % QLatin1Char('-') %
+                                  QString::number(bestFit.height()) % QLatin1Char('-') % elementId;
             }
         }
     }
@@ -456,7 +456,7 @@
     //qCDebug(LOG_PLASMA) << path << "**";
 
     QString styleSheet = cacheAndColorsTheme()->d->svgStyleSheet(colorGroup, status);
-    styleCrc = qChecksum(styleSheet.toUtf8(), styleSheet.size());
+    styleCrc = qChecksum(styleSheet.toUtf8().constData(), styleSheet.size());
 
     QHash<QString, SharedSvgRenderer::Ptr>::const_iterator it = s_renderers.constFind(styleCrc + path);
 
diff --git a/src/plasma/theme.cpp b/src/plasma/theme.cpp
--- a/src/plasma/theme.cpp
+++ b/src/plasma/theme.cpp
@@ -202,9 +202,7 @@
 QString Theme::wallpaperPath(const QSize &size) const
 {
     QString fullPath;
-    QString image = d->defaultWallpaperTheme;
-
-    image.append("/contents/images/%1x%2").append(d->defaultWallpaperSuffix);
+    QString image = d->defaultWallpaperTheme + QStringLiteral("/contents/images/%1x%2") + d->defaultWallpaperSuffix;
     QString defaultImage = image.arg(d->defaultWallpaperWidth).arg(d->defaultWallpaperHeight);
 
     if (size.isValid()) {
@@ -356,7 +354,7 @@
 
     //Name starting by _ means the element is empty and we're asked for the size of
     //the whole image, so the whole image is never invalid
-    if (element.indexOf('_') <= 0) {
+    if (element.indexOf(QLatin1Char('_')) <= 0) {
         return false;
     }
 
diff --git a/src/plasmapkg/main.cpp b/src/plasmapkg/main.cpp
--- a/src/plasmapkg/main.cpp
+++ b/src/plasmapkg/main.cpp
@@ -77,7 +77,7 @@
             params[typeIndex + 1] = typeFromLegacy(params.value(typeIndex + 1));
         } else {
             //user passed --type=typeName
-            typeIndex = params.indexOf(QRegularExpression("--type=.*"));
+            typeIndex = params.indexOf(QRegularExpression(QStringLiteral("--type=.*")));
             if (typeIndex > -1) {
                 params[typeIndex] = QStringLiteral("--type=") + typeFromLegacy(params.value(typeIndex).replace(QStringLiteral("--type="), QString()));
             }
diff --git a/src/plasmaquick/appletquickitem.cpp b/src/plasmaquick/appletquickitem.cpp
--- a/src/plasmaquick/appletquickitem.cpp
+++ b/src/plasmaquick/appletquickitem.cpp
@@ -186,7 +186,7 @@
 void AppletQuickItemPrivate::propagateSizeHint(const QByteArray &layoutProperty)
 {
     if (ownLayout && representationLayout) {
-        ownLayout->setProperty(layoutProperty, representationLayout->property(layoutProperty));
+        ownLayout->setProperty(layoutProperty.constData(), representationLayout->property(layoutProperty.constData()));
     }
 }
 
@@ -524,7 +524,7 @@
             reason = d->applet->launchErrorMessage();
         } else if (d->applet->kPackage().isValid()) {
             foreach (QQmlError error, d->qmlObject->mainComponent()->errors()) {
-                reason += error.toString() + '\n';
+                reason += error.toString() + QLatin1Char('\n');
             }
             reason = i18n("Error loading QML file: %1", reason);
         } else {
diff --git a/src/plasmaquick/configmodel.cpp b/src/plasmaquick/configmodel.cpp
--- a/src/plasmaquick/configmodel.cpp
+++ b/src/plasmaquick/configmodel.cpp
@@ -236,7 +236,7 @@
     {
         const QString source = d->categories.at(index.row())->source();
         // Quick check if source is an absolute path or not
-        if (d->appletInterface && !source.isEmpty() && !(source.startsWith('/') && source.endsWith(QLatin1String("qml")))) {
+        if (d->appletInterface && !source.isEmpty() && !(source.startsWith(QLatin1Char('/')) && source.endsWith(QLatin1String("qml")))) {
             if(!d->appletInterface.data()->kPackage().isValid())
                 qWarning() << "wrong applet" << d->appletInterface.data()->pluginMetaData().name();
             return QUrl::fromLocalFile(d->appletInterface.data()->kPackage().filePath("ui", source));
diff --git a/src/plasmaquick/configview.cpp b/src/plasmaquick/configview.cpp
--- a/src/plasmaquick/configview.cpp
+++ b/src/plasmaquick/configview.cpp
@@ -97,9 +97,9 @@
     kdeclarative.setDeclarativeEngine(q->engine());
     const QString rootPath = applet.data()->pluginMetaData().value(QStringLiteral("X-Plasma-RootPath"));
     if (!rootPath.isEmpty()) {
-        kdeclarative.setTranslationDomain("plasma_applet_" + rootPath);
+        kdeclarative.setTranslationDomain(QStringLiteral("plasma_applet_") + rootPath);
     } else {
-        kdeclarative.setTranslationDomain("plasma_applet_" + applet.data()->pluginMetaData().pluginId());
+        kdeclarative.setTranslationDomain(QStringLiteral("plasma_applet_") + applet.data()->pluginMetaData().pluginId());
     }
     kdeclarative.setupBindings();
 
diff --git a/src/plasmaquick/containmentview.cpp b/src/plasmaquick/containmentview.cpp
--- a/src/plasmaquick/containmentview.cpp
+++ b/src/plasmaquick/containmentview.cpp
@@ -208,7 +208,7 @@
     if (corona->kPackage().isValid()) {
         const auto info = corona->kPackage().metadata();
         if (info.isValid()) {
-            setTranslationDomain("plasma_shell_" + info.pluginId());
+            setTranslationDomain(QStringLiteral("plasma_shell_") + info.pluginId());
         } else {
             qWarning() << "Invalid corona package metadata";
         }
diff --git a/src/plasmaquick/packageurlinterceptor.cpp b/src/plasmaquick/packageurlinterceptor.cpp
--- a/src/plasmaquick/packageurlinterceptor.cpp
+++ b/src/plasmaquick/packageurlinterceptor.cpp
@@ -96,18 +96,19 @@
 {
     //qDebug() << "Intercepted URL:" << path << type;
 
-    if (d->forcePlasmaStyle && path.path().contains("Controls.2/org.kde.desktop/")) {
+    if (d->forcePlasmaStyle && path.path().contains(QLatin1String("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()) {
         package = d->package;
     } else {
         foreach (const QString &base, QStandardPaths::standardLocations(QStandardPaths::GenericDataLocation)) {
-            pkgRoot = QFileInfo(base + "/plasma/plasmoids/").canonicalFilePath();
+            pkgRoot = QFileInfo(base + QStringLiteral("/plasma/plasmoids/")).canonicalFilePath();
             if (!pkgRoot.isEmpty() && path.path().startsWith(pkgRoot)) {
-                const QString pkgName = path.path().mid(pkgRoot.length() + 1).split('/').first();
+                const QString pkgName = path.path().midRef(pkgRoot.length() + 1).split(QLatin1Char('/')).first().toString();
+#warning FIX double look-up
                 if (PackageUrlInterceptorPrivate::s_packages.contains(pkgName)) {
                     package = PackageUrlInterceptorPrivate::s_packages.value(pkgName);
                 } else {
diff --git a/src/plasmaquick/private/packages.cpp b/src/plasmaquick/private/packages.cpp
--- a/src/plasmaquick/private/packages.cpp
+++ b/src/plasmaquick/private/packages.cpp
@@ -91,7 +91,7 @@
         QMutableStringListIterator it(platform);
         while (it.hasNext()) {
             it.next();
-            it.setValue("platformcontents/" + it.value());
+            it.setValue(QStringLiteral("platformcontents/") + it.value());
         }
 
         platform.append(QStringLiteral("contents"));
diff --git a/src/plasmaquick/view.cpp b/src/plasmaquick/view.cpp
--- a/src/plasmaquick/view.cpp
+++ b/src/plasmaquick/view.cpp
@@ -196,7 +196,7 @@
         KDeclarative::KDeclarative kdeclarative;
         kdeclarative.setDeclarativeEngine(engine());
         //binds things like kconfig and icons
-        kdeclarative.setTranslationDomain("plasma_shell_" + pkg.metadata().pluginId());
+        kdeclarative.setTranslationDomain(QStringLiteral("plasma_shell_") + pkg.metadata().pluginId());
         kdeclarative.setupBindings();
     } else {
         qWarning() << "Invalid home screen package";
diff --git a/src/scriptengines/qml/plasmoid/appletinterface.cpp b/src/scriptengines/qml/plasmoid/appletinterface.cpp
--- a/src/scriptengines/qml/plasmoid/appletinterface.cpp
+++ b/src/scriptengines/qml/plasmoid/appletinterface.cpp
@@ -643,30 +643,31 @@
 
 QString AppletInterface::downloadPath() const
 {
-    const QString downloadDir = QStandardPaths::writableLocation(QStandardPaths::DownloadLocation) + "/Plasma/" + applet()->pluginMetaData().pluginId() + '/';
+    const QString downloadDir = QStandardPaths::writableLocation(QStandardPaths::DownloadLocation) + QStringLiteral("/Plasma/") + applet()->pluginMetaData().pluginId() + QLatin1Char('/');
 
     if (!QFile::exists(downloadDir)) {
-        QDir dir(QChar('/'));
+        QDir dir({ QLatin1Char('/') });
         dir.mkpath(downloadDir);
     }
 
     return downloadDir;
 }
 
 QStringList AppletInterface::downloadedFiles() const
 {
-    const QString downloadDir = QStandardPaths::writableLocation(QStandardPaths::DownloadLocation) + "/Plasma/" + applet()->pluginMetaData().pluginId() + '/';
+    const QString downloadDir = QStandardPaths::writableLocation(QStandardPaths::DownloadLocation) + QStringLiteral("/Plasma/") + applet()->pluginMetaData().pluginId() + QLatin1Char('/');
     QDir dir(downloadDir);
     return dir.entryList(QDir::Files | QDir::NoSymLinks | QDir::Readable);
 }
 
 void AppletInterface::executeAction(const QString &name)
 {
     if (qmlObject()->rootObject()) {
         const QMetaObject *metaObj = qmlObject()->rootObject()->metaObject();
-        QString actionMethodName = QString("action_" + name);
-        if (metaObj->indexOfMethod(QMetaObject::normalizedSignature((actionMethodName + "()").toLatin1())) != -1) {
-            QMetaObject::invokeMethod(qmlObject()->rootObject(), actionMethodName.toLatin1(), Qt::DirectConnection);
+        const QByteArray actionMethodName = "action_" + name.toUtf8();
+        const QByteArray actionFunctionName = actionMethodName + QByteArray("()");
+        if (metaObj->indexOfMethod(QMetaObject::normalizedSignature(actionFunctionName.constData()).constData()) != -1) {
+            QMetaObject::invokeMethod(qmlObject()->rootObject(), actionMethodName.constData(), Qt::DirectConnection);
         } else {
             QMetaObject::invokeMethod(qmlObject()->rootObject(), "actionTriggered", Qt::DirectConnection, Q_ARG(QVariant, name));
         }
diff --git a/src/scriptengines/qml/plasmoid/containmentinterface.cpp b/src/scriptengines/qml/plasmoid/containmentinterface.cpp
--- a/src/scriptengines/qml/plasmoid/containmentinterface.cpp
+++ b/src/scriptengines/qml/plasmoid/containmentinterface.cpp
@@ -102,13 +102,13 @@
         }
 
         if (defaults.isValid()) {
-            KPackage::Package pkg = KPackage::PackageLoader::self()->loadPackage("KPackage/GenericQML");
-            pkg.setDefaultPackageRoot("plasma/packages");
+            KPackage::Package pkg = KPackage::PackageLoader::self()->loadPackage(QStringLiteral("KPackage/GenericQML"));
+            pkg.setDefaultPackageRoot(QStringLiteral("plasma/packages"));
 
             if (defaults.isValid()) {
                 pkg.setPath(defaults.readEntry("ToolBox", "org.kde.desktoptoolbox"));
             } else {
-                pkg.setPath("org.kde.desktoptoolbox");
+                pkg.setPath(QStringLiteral("org.kde.desktoptoolbox"));
             }
 
             PlasmaQuick::PackageUrlInterceptor *interceptor = dynamic_cast<PlasmaQuick::PackageUrlInterceptor *>(qmlObject()->engine()->urlInterceptor());
@@ -121,7 +121,7 @@
                     QObject *containmentGraphicObject = qmlObject()->rootObject();
 
                     QVariantHash toolboxProperties;
-                    toolboxProperties["parent"] = QVariant::fromValue(this);
+                    toolboxProperties[QStringLiteral("parent")] = QVariant::fromValue(this);
                     QObject *toolBoxObject = qmlObject()->createObjectFromSource(QUrl::fromLocalFile(pkg.filePath("mainscript")), 0, toolboxProperties);
                     if (toolBoxObject && containmentGraphicObject) {
                         containmentGraphicObject->setProperty("toolBox", QVariant::fromValue(toolBoxObject));
@@ -447,8 +447,8 @@
     qDebug() << "Arrived mimeData" << mimeData->urls() << mimeData->formats() << "at" << x << ", " << y;
 
     if (mimeData->hasFormat(QStringLiteral("text/x-plasmoidservicename"))) {
-        QString data = mimeData->data(QStringLiteral("text/x-plasmoidservicename"));
-        const QStringList appletNames = data.split('\n', QString::SkipEmptyParts);
+        QString data = QString::fromUtf8( mimeData->data(QStringLiteral("text/x-plasmoidservicename")) );
+        const QStringList appletNames = data.split(QLatin1Char('\n'), QString::SkipEmptyParts);
         foreach (const QString &appletName, appletNames) {
             qDebug() << "adding" << appletName;
 
@@ -519,7 +519,7 @@
         } else if (seenPlugins.count() == 1) {
             selectedPlugin = seenPlugins.constBegin().key();
             Plasma::Applet *applet = createApplet(selectedPlugin, QVariantList(), QRect(x, y, -1, -1));
-            setAppletArgs(applet, pluginFormats[selectedPlugin], mimeData->data(pluginFormats[selectedPlugin]));
+            setAppletArgs(applet, pluginFormats[selectedPlugin], QString::fromUtf8(mimeData->data(pluginFormats[selectedPlugin])));
         } else {
             QMenu *choices = nullptr;
             if (!dropJob) {
@@ -545,7 +545,7 @@
                 connect(action, &QAction::triggered, this, [this, x, y, mimeData, action]() {
                     const QString selectedPlugin = action->data().toString();
                     Plasma::Applet *applet = createApplet(selectedPlugin, QVariantList(), QRect(x, y, -1, -1));
-                    setAppletArgs(applet, selectedPlugin, mimeData->data(selectedPlugin));
+                    setAppletArgs(applet, selectedPlugin, QString::fromUtf8(mimeData->data(selectedPlugin)));
                 });
 
                 actionsToPlugins.insert(action, info.pluginId());
@@ -657,7 +657,7 @@
                     dropJob->setApplicationActions(dropActions);
                 }
                 const QString &packagePath = tjob->url().toLocalFile();
-                connect(installPlasmaPackageAction, &QAction::triggered, this, [this, tjob, posi, packagePath]() {
+                connect(installPlasmaPackageAction, &QAction::triggered, this, [this, posi, packagePath]() {
                     using namespace KPackage;
                     PackageStructure *structure = PackageLoader::self()->loadPackageStructure(QStringLiteral("Plasma/Applet"));
                     Package package(structure);
@@ -763,7 +763,7 @@
                     dropActions << action;
                     actionsToWallpapers.insert(action, info.pluginId());
                     const QUrl url = tjob->url();
-                    connect(action, &QAction::triggered, this, [this, action, url]() {
+                    connect(action, &QAction::triggered, this, [this, url]() {
                         //set wallpapery stuff
                         if (m_wallpaperInterface && url.isValid()) {
                             m_wallpaperInterface->setUrl(url);
@@ -1041,7 +1041,7 @@
 
     //pre 5.8.0 QQuickWindow code is "item->grabMouse(); sendEvent(item, mouseEvent)"
     //post 5.8.0 QQuickWindow code is sendEvent(item, mouseEvent); item->grabMouse()
-    if (QVersionNumber::fromString(qVersion()) > QVersionNumber(5, 8, 0)) {
+    if (QVersionNumber::fromString(QLatin1String(qVersion())) > QVersionNumber(5, 8, 0)) {
         QTimer::singleShot(0, this, ungrabMouseHack);
     }
     else {
diff --git a/src/scriptengines/qml/plasmoid/wallpaperinterface.cpp b/src/scriptengines/qml/plasmoid/wallpaperinterface.cpp
--- a/src/scriptengines/qml/plasmoid/wallpaperinterface.cpp
+++ b/src/scriptengines/qml/plasmoid/wallpaperinterface.cpp
@@ -197,13 +197,13 @@
 
 bool WallpaperInterface::supportsMimetype(const QString &mimetype) const
 {
-    return KPluginMetaData::readStringList(m_pkg.metadata().rawData(), "X-Plasma-DropMimeTypes").contains(mimetype);
+    return KPluginMetaData::readStringList(m_pkg.metadata().rawData(), QStringLiteral("X-Plasma-DropMimeTypes")).contains(mimetype);
 }
 
 void WallpaperInterface::setUrl(const QUrl &url)
 {
     if (m_qmlObject->rootObject()) {
-        QMetaObject::invokeMethod(m_qmlObject->rootObject(), QStringLiteral("setUrl").toLatin1(), Qt::DirectConnection, Q_ARG(QVariant, QVariant::fromValue(url)));
+        QMetaObject::invokeMethod(m_qmlObject->rootObject(), "setUrl", Qt::DirectConnection, Q_ARG(QVariant, QVariant::fromValue(url)));
     }
 }
 
@@ -254,7 +254,8 @@
 void WallpaperInterface::executeAction(const QString &name)
 {
     if (m_qmlObject->rootObject()) {
-        QMetaObject::invokeMethod(m_qmlObject->rootObject(), QString("action_" + name).toLatin1(), Qt::DirectConnection);
+        const QByteArray actionName("action_" + name.toUtf8());
+        QMetaObject::invokeMethod(m_qmlObject->rootObject(), actionName.constData(), Qt::DirectConnection);
     }
 }
 
diff --git a/tests/dpi/main.cpp b/tests/dpi/main.cpp
--- a/tests/dpi/main.cpp
+++ b/tests/dpi/main.cpp
@@ -33,7 +33,7 @@
     Plasma::DPITest app(argc, argv, parser);
 
     const QString description = i18n("DPI test app");
-    const char version[] = "2.0";
+    const QString version = QStringLiteral("2.0");
 
     app.setApplicationVersion(version);
     parser->addVersionOption();
diff --git a/tests/kplugins/main.cpp b/tests/kplugins/main.cpp
--- a/tests/kplugins/main.cpp
+++ b/tests/kplugins/main.cpp
@@ -30,7 +30,7 @@
     Plasma::PluginTest app(argc, argv, parser);
 
     const QString description = i18n("Plugin test app");
-    const char version[] = "2.0";
+    const QString version = QStringLiteral("2.0");
 
     app.setApplicationVersion(version);
     parser->addVersionOption();
diff --git a/tests/testengine/testengine.cpp b/tests/testengine/testengine.cpp
--- a/tests/testengine/testengine.cpp
+++ b/tests/testengine/testengine.cpp
@@ -127,7 +127,7 @@
     // QVariant::RectF
     setData(dsn, QStringLiteral("QRectF"), QVariant(QRectF(1.2, 3.4, 5.6, 7.8)));
     // QVariant::RegExp
-    setData(dsn, QStringLiteral("QRegExp"), QVariant(QRegExp("^KDE4$")));
+    setData(dsn, QStringLiteral("QRegExp"), QVariant(QRegExp(QStringLiteral("^KDE4$"))));
     // QVariant::Region
     setData(dsn, QStringLiteral("QRegion"), QVariant(QRegion(10, 20, 30, 40)));
     // QVariant::Size