[libcalamares] Switch to using KPluginFactory

- this is not entirely straightfoward, since  we need
   different constructor arguments for the objects
   Calamares creates (no QVariantList& args, in particular).
   Implement our own registerPlugin() and createInstance()
   for that.
 - work around a bug in K_PLUGIN_FACTORY_DECLARATION_WITH_BASEFACTORY

src/libcalamares/CMakeLists.txt

@@ -44,6 +44,7 @@ set( libSources
     utils/CommandList.cpp
     utils/Dirs.cpp
     utils/Logger.cpp
+    utils/PluginFactory.cpp
     utils/Retranslator.cpp
     utils/String.cpp
     utils/UMask.cpp

src/libcalamares/utils/PluginFactory.cpp

@@ -0,0 +1,11 @@
+/* === This file is part of Calamares - <https://github.com/calamares> ===
+ *
+ *   Copyright 2019, Adriaan de Groot <groot@kde.org>
+ *
+ */
+
+#include "PluginFactory.h"
+
+CalamaresPluginFactory::~CalamaresPluginFactory()
+{
+}

src/libcalamares/utils/PluginFactory.h

@@ -28,10 +28,75 @@
 
 #define CalamaresPluginFactory_iid "io.calamares.PluginFactory"
 
+/** @brief Plugin factory for Calamares
+ *
+ * Try to re-use KPluginFactory as much as possible (since the
+ * old code for PluginFactory was a fork of an old version of
+ * exactly that).
+ *
+ * The current createInstance() method passes more arguments
+ * to the job and viewstep constructors than we want; chasing
+ * that change means modifying each Calamares module. This class
+ * implements a version of createInstance() with fewer arguments
+ * and overloads registerPlugin() to use that.
+ */
+class CalamaresPluginFactory : public KPluginFactory
+{
+    Q_OBJECT
+public:
+    explicit CalamaresPluginFactory() : KPluginFactory() {}
+    ~CalamaresPluginFactory() override;
+
+    /** @brief Create an object from the factory.
+     *
+     * Ignores all the @p args since they are not used. Calls
+     * Calamares constructors for the Jobs and ViewSteps.
+     */
+    template<class impl, class ParentType>
+    static QObject *createInstance(QWidget *parentWidget, QObject *parent, const QVariantList &args)
+    {
+        Q_UNUSED(parentWidget);
+        Q_UNUSED(args);
+        ParentType *p = nullptr;
+        if (parent) {
+            p = qobject_cast<ParentType *>(parent);
+            Q_ASSERT(p);
+        }
+        return new impl(p);
+    }
+
+    /** @brief register a plugin
+     *
+     * The Calamares version doesn't accept keywords, and uses
+     * the Calamares createInstance() version which ignores
+     * the QVariantList of arguments.
+     */
+    template<class T>
+    void registerPlugin()
+    {
+        KPluginFactory::registerPlugin<T>(QString(), &createInstance<T, QObject>);
+    }
+};
+
+/** @brief declare a Calamares Plugin Factory
+ *
+ * This would be defined as K_PLUGIN_FACTORY_DECLARATION_WITH_BASEFACTORY,
+ * except that does not actually use the base factory class that is
+ * passed in.
+ */
 #define CALAMARES_PLUGIN_FACTORY_DECLARATION(name) \
-    K_PLUGIN_FACTORY_DECLARATION_WITH_BASEFACTORY_SKEL(name,KPluginFactory,Q_PLUGIN_METADATA(IID CalamaresPluginFactory_iid))
+    class name : public CalamaresPluginFactory \
+    { \
+        Q_OBJECT \
+        Q_INTERFACES(KPluginFactory) \
+        Q_PLUGIN_METADATA(IID CalamaresPluginFactory_iid) \
+    public: \
+        explicit name(); \
+        ~name(); \
+    };
 #define CALAMARES_PLUGIN_FACTORY_DEFINITION(name, pluginRegistrations) \
-    K_PLUGIN_FACTORY_DEFINITION(name, pluginRegistrations )
+    K_PLUGIN_FACTORY_DEFINITION_WITH_BASEFACTORY(name,CalamaresPluginFactory,pluginRegistrations)
+
 
 // Q_DECLARE_INTERFACE( Calamares::PluginFactory, CalamaresPluginFactory_iid )
 

src/libcalamaresui/modulesystem/CppJobModule.cpp

@@ -49,7 +49,7 @@ CppJobModule::loadSelf()
 {
     if ( m_loader )
     {
-        PluginFactory* pf = qobject_cast< PluginFactory* >( m_loader->instance() );
+        CalamaresPluginFactory* pf = qobject_cast< CalamaresPluginFactory* >( m_loader->instance() );
         if ( !pf )
         {
             cDebug() << Q_FUNC_INFO << m_loader->errorString();

src/libcalamaresui/modulesystem/ViewModule.cpp

@@ -50,7 +50,7 @@ ViewModule::loadSelf()
 {
     if ( m_loader )
     {
-        PluginFactory* pf = qobject_cast< PluginFactory* >( m_loader->instance() );
+        CalamaresPluginFactory* pf = qobject_cast< CalamaresPluginFactory* >( m_loader->instance() );
         if ( !pf )
         {
             cWarning() << Q_FUNC_INFO << "No factory:" << m_loader->errorString();