Fix QQmlTypePrivate memory leak in qmltc-generated types with extensions

Apparently registering the QQmlTypePrivate for a meta-object is not
good enough. Somehow clang's ASan failed to discover a memory leak but
gcc's ASan did not. After carefully exercising the code and a bit of
debugging, turns out we indeed not release manually created
QQmlTypePrivate objects. Do release the QQmlTypePrivate correctly now

In the process of doing so, remove now-redundant QMetaObject function
parameter

Amends 26179e693717535eeff2e7b2a6ee99dc02dcd8f9

Pick-to: 6.4
Change-Id: Ia0c808cd8a09cf996672bca9953108facfdf5d4e
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

3 files changed, 8 insertions, 12 deletions

diff --git a/src/qml/qmltc/qqmltcobjectcreationhelper.cpp b/src/qml/qmltc/qqmltcobjectcreationhelper.cpp
index 4be6ae0c9f..db8517ca70 100644
--- a/src/qml/qmltc/qqmltcobjectcreationhelper.cpp
+++ b/src/qml/qmltc/qqmltcobjectcreationhelper.cpp
@@ -10,8 +10,7 @@
 
 QT_BEGIN_NAMESPACE
 
-void qmltcCreateDynamicMetaObject(QObject *object, const QMetaObject *staticMetaObject,
-                                  const QmltcTypeData &data)
+void qmltcCreateDynamicMetaObject(QObject *object, const QmltcTypeData &data)
 {
     // TODO: when/if qmltc-compiled types would be registered via
     // qmltyperegistrar, instead of creating a dummy QQmlTypePrivate, fetch the
@@ -19,9 +18,11 @@ void qmltcCreateDynamicMetaObject(QObject *object, const QMetaObject *staticMeta
     // along with the meta object, module name and revision. all that should be
     // available ahead-of-time to qmltc.
     auto qmlTypePrivate = new QQmlTypePrivate(data.regType);
-    // place the newly created QQmlTypePrivate into the qml meta data storage so
-    // that it is properly deleted
-    QQmlMetaType::registerMetaObjectForType(staticMetaObject, qmlTypePrivate);
+
+    // tie qmlTypePrivate destruction to objects's destruction. the type's
+    // content is not needed once the associated object is deleted
+    QObject::connect(object, &QObject::destroyed,
+                     [qmlTypePrivate](QObject *) { qmlTypePrivate->release(); });
 
     // initialize QQmlType::QQmlCppTypeData
     Q_ASSERT(data.regType == QQmlType::CppType);
diff --git a/src/qml/qmltc/qqmltcobjectcreationhelper_p.h b/src/qml/qmltc/qqmltcobjectcreationhelper_p.h
index 6f81d5265d..ae4633ac43 100644
--- a/src/qml/qmltc/qqmltcobjectcreationhelper_p.h
+++ b/src/qml/qmltc/qqmltcobjectcreationhelper_p.h
@@ -118,9 +118,7 @@ struct QmltcTypeData
     }
 };
 
-Q_QML_PRIVATE_EXPORT void qmltcCreateDynamicMetaObject(QObject *object,
-                                                       const QMetaObject *staticMetaObject,
-                                                       const QmltcTypeData &data);
+Q_QML_PRIVATE_EXPORT void qmltcCreateDynamicMetaObject(QObject *object, const QmltcTypeData &data);
 
 QT_END_NAMESPACE
 
diff --git a/tools/qmltc/qmltccompilerpieces.h b/tools/qmltc/qmltccompilerpieces.h
index bc423807fb..9afc001b55 100644
--- a/tools/qmltc/qmltccompilerpieces.h
+++ b/tools/qmltc/qmltccompilerpieces.h
@@ -236,10 +236,7 @@ inline decltype(auto) QmltcCodeGenerator::generate_initCode(QmltcType &current,
     if (hasExtension) {
         current.init.body << u"{"_s;
         current.init.body << u"auto cppData = QmltcTypeData(this);"_s;
-        current.init.body
-                << QStringLiteral(
-                           "qmltcCreateDynamicMetaObject(this, &%1::staticMetaObject, cppData);")
-                           .arg(type->internalName());
+        current.init.body << u"qmltcCreateDynamicMetaObject(this, cppData);"_s;
         current.init.body << u"}"_s;
     }