Fix crash with StackView::initialItem

The following binding

    initialView: Qt.createComponent("blah.qml")

works with QQC1 but crashes with QQC2 as soon as the garbage collector
kicks in. In QQC1 StackView was implemented in a .qml file and the
property was declared as

    property var initialItem

For such declared properties the QML engine takes care of ensuring that
the reference assigned is a strong reference towards the GC and it also
tracks the life-time of the QObject in case it's explicitly deleted by
somebody else.

In QQC2 the property continues to be documented as "var" property,
however it is implemented in C++ as QVariant property. The QVariant is
not known to the GC at all and it also doesn't do life-cycle tracking.

The C++ equivalent to "var" in QML is QJSValue, which is a strong
reference and also ends up using a QPointer internally when holding a
QObject.

Task-number: QTBUG-67118
Change-Id: I43e473c7bf2c40f9843e9d50fe4fd805b54fd256
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

1 files changed, 15 insertions, 0 deletions

diff --git a/tests/auto/controls/data/tst_stackview.qml b/tests/auto/controls/data/tst_stackview.qml
index 3c0f0273..3827354b 100644
--- a/tests/auto/controls/data/tst_stackview.qml
+++ b/tests/auto/controls/data/tst_stackview.qml
@@ -1230,4 +1230,19 @@ TestCase {
         touch.release(0, control).commit()
         verify(!ma.pressed)
     }
+
+    // Separate function to ensure that the temporary value created to hold the return value of the Qt.createComponent()
+    // call is out of scope when the caller calls gc().
+    function stackViewFactory()
+    {
+        return createTemporaryObject(stackView, testCase, {initialItem: Qt.createComponent("TestItem.qml")})
+    }
+
+    function test_initalItemOwnership()
+    {
+        var control = stackViewFactory()
+        verify(control)
+        gc()
+        verify(control.initialItem)
+    }
 }