Fix memory leak in QQC2

When repeatedly creating a QQuickView, loading a QML file that imports
QQC2 and deleting the view again, we would leak memory that was
allocated as a consequence of QML type registration in
initializeEngine() callbacks that were called on every iteration.

After the limitation of namespacing in the registerTypes() callback of
QML module plugins has been lifted, we can move the type registrations
into registerTypes() where they belong and which is called only once.

Change-Id: I7e314663a69fd8c8529195b56c128b61392c0042
Reviewed-by: J-P Nurmi <jpnurmi@qt.io>
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
Reviewed-by: Michael Winkelmann <michael.winkelmann@qt.io>

1 files changed, 10 insertions, 22 deletions

diff --git a/src/imports/controls/qtquickcontrols2plugin.cpp b/src/imports/controls/qtquickcontrols2plugin.cpp
index 464bbbdf..d04d3018 100644
--- a/src/imports/controls/qtquickcontrols2plugin.cpp
+++ b/src/imports/controls/qtquickcontrols2plugin.cpp
@@ -78,7 +78,6 @@ class QtQuickControls2Plugin: public QQuickStylePlugin
 public:
     QtQuickControls2Plugin(QObject *parent = nullptr);
     void registerTypes(const char *uri) override;
-    void initializeEngine(QQmlEngine *engine, const char *uri) override;
 
     QString name() const override;
     QQuickProxyTheme *createTheme() const override;
@@ -165,25 +164,6 @@ void QtQuickControls2Plugin::registerTypes(const char *uri)
     qmlRegisterType(selector.select(QStringLiteral("MenuBar.qml")), uri, 2, 3, "MenuBar");
     qmlRegisterType(selector.select(QStringLiteral("MenuBarItem.qml")), uri, 2, 3, "MenuBarItem");
     qmlRegisterUncreatableType<QQuickOverlay>(uri, 2, 3, "Overlay", QStringLiteral("Overlay is only available as an attached property."));
-}
-
-static QObject *styleSingleton(QQmlEngine *engine, QJSEngine *scriptEngine)
-{
-    Q_UNUSED(engine);
-    Q_UNUSED(scriptEngine);
-    return new QQuickDefaultStyle;
-}
-
-static QObject *colorSingleton(QQmlEngine *engine, QJSEngine *scriptEngine)
-{
-    Q_UNUSED(engine);
-    Q_UNUSED(scriptEngine);
-    return new QQuickColor;
-}
-
-void QtQuickControls2Plugin::initializeEngine(QQmlEngine *engine, const char *uri)
-{
-    QQuickStylePlugin::initializeEngine(engine, uri);
 
     const QByteArray import = QByteArray(uri) + ".impl";
     qmlRegisterModule(import, 2, QT_VERSION_MINOR - 7); // Qt 5.7->2.0, 5.8->2.1, 5.9->2.2...
@@ -198,7 +178,11 @@ void QtQuickControls2Plugin::initializeEngine(QQmlEngine *engine, const char *ur
 #if QT_CONFIG(quick_listview) && QT_CONFIG(quick_pathview)
     qmlRegisterType<QQuickTumblerView>(import, 2, 1, "TumblerView");
 #endif
-    qmlRegisterSingletonType<QQuickDefaultStyle>(import, 2, 1, "Default", styleSingleton);
+    qmlRegisterSingletonType<QQuickDefaultStyle>(import, 2, 1, "Default", [](QQmlEngine *engine, QJSEngine *scriptEngine) -> QObject* {
+            Q_UNUSED(engine);
+            Q_UNUSED(scriptEngine);
+            return new QQuickDefaultStyle;
+    });
 
     // QtQuick.Controls.impl 2.2 (Qt 5.9)
     qmlRegisterType<QQuickClippedText>(import, 2, 2, "ClippedText");
@@ -208,7 +192,11 @@ void QtQuickControls2Plugin::initializeEngine(QQmlEngine *engine, const char *ur
     // QtQuick.Controls.impl 2.3 (Qt 5.10)
     qmlRegisterType<QQuickColorImage>(import, 2, 3, "ColorImage");
     qmlRegisterType<QQuickIconImage>(import, 2, 3, "IconImage");
-    qmlRegisterSingletonType<QQuickColor>(import, 2, 3, "Color", colorSingleton);
+    qmlRegisterSingletonType<QQuickColor>(import, 2, 3, "Color", [](QQmlEngine *engine, QJSEngine *scriptEngine) -> QObject* {
+            Q_UNUSED(engine);
+            Q_UNUSED(scriptEngine);
+            return new QQuickColor;
+    });
     qmlRegisterType<QQuickIconLabel>(import, 2, 3, "IconLabel");
     qmlRegisterType<QQuickCheckLabel>(import, 2, 3, "CheckLabel");
     qmlRegisterType<QQuickMnemonicLabel>(import, 2, 3, "MnemonicLabel");