filter on formfactors if set

if KDeclarative::runtimePlatform() is set, then filter applets
that have formfactors set and don't match, in order to not
show on the phone applets that are desktop only

in desktop case, list all applets, for maximum retrocompatibility,
to be reconsidered for kf6

src/plasma/pluginloader.cpp

@@ -28,6 +28,7 @@
 #include <KPluginTrader>
 #include <KPluginLoader>
 #include <kpackage/packageloader.h>
+#include <kdeclarative/kdeclarative.h>
 
 #include "config-plasma.h"
 
@@ -468,22 +469,57 @@ Package PluginLoader::loadPackage(const QString &packageFormat, const QString &s
 
 QList<KPluginMetaData> PluginLoader::listAppletMetaData(const QString &category, const QString &parentApp)
 {
+    auto platforms = KDeclarative::KDeclarative::runtimePlatform();
+    // For now desktop always lists everything
+    if (platforms.contains(QStringLiteral("desktop"))) {
+        platforms.clear();
+    }
+
     //FIXME: this assumes we are always use packages.. no pure c++
     std::function<bool(const KPluginMetaData&)> filter;
     if (category.isEmpty()) { //use all but the excluded categories
         KConfigGroup group(KSharedConfig::openConfig(), "General");
         QStringList excluded = group.readEntry("ExcludeCategories", QStringList());
 
-        filter = [excluded, parentApp](const KPluginMetaData &md) -> bool
+        filter = [excluded, parentApp, platforms](const KPluginMetaData &md) -> bool
         {
+            if (!platforms.isEmpty() && !md.formFactors().isEmpty()) {
+                bool found = false;
+                for (const auto &plat : platforms) {
+                    if (md.formFactors().contains(plat)) {
+                        found = true;
+                        break;
+                    }
+                }
+
+                if (!found) {
+                    return false;
+                }
+            }
+
             const QString pa = md.value(QStringLiteral("X-KDE-ParentApp"));
             return (parentApp.isEmpty() || pa == parentApp) && !excluded.contains(md.category());
         };
     } else { //specific category (this could be an excluded one - is that bad?)
 
-        filter = [category, parentApp](const KPluginMetaData &md) -> bool
+        filter = [category, parentApp, platforms](const KPluginMetaData &md) -> bool
         {
+            if (!platforms.isEmpty() && !md.formFactors().isEmpty()) {
+                bool found = false;
+                for (const auto &plat : platforms) {
+                    if (md.formFactors().contains(plat)) {
+                        found = true;
+                        break;
+                    }
+                }
+
+                if (!found) {
+                    return false;
+                }
+            }
+
             const QString pa = md.value(QStringLiteral("X-KDE-ParentApp"));
+
             if (category == QLatin1String("Miscellaneous")) {
                 return (parentApp.isEmpty() || pa == parentApp) && (md.category() == category || md.category().isEmpty());
             } else {