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Details

Type: Bug
Resolution: Fixed
Priority: P1: Critical
Fix Version/s: 6.7.0 Beta2, 6.7, 6.8.0 FF
Affects Version/s: 6.7
Component/s: QML: Declarative and Javascript Engine
Labels:
None
Environment:
Fedora 39

Commits:
933f80f34 (dev), 18aeb7177 (6.7), 5eba40805 (dev), 3668db06e (6.7)

Description

KDE Plasma's systemsettings application fails to load QML-based modules using Qt 6.7 due to the following QML error:

qrc:/kcm/kcm_landingpage/main.qml:18 Type KCM.SimpleKCM unavailable
qrc:/qt/qml/org/kde/kcmutils/SimpleKCM.qml:33 Type Kirigami.ScrollablePage unavailable
qrc:/qt/qml/org/kde/kirigami/ScrollablePage.qml:68 Type Kirigami.Page unavailable
qrc:/qt/qml/org/kde/kirigami/Page.qml:237 Type Kirigami.PageRow unavailable
qrc:/qt/qml/org/kde/kirigami/PageRow.qml:180 Type OverlayDrawer unavailable
file:///home/nico/kde/usr/qml/org/kde/kirigami/OverlayDrawer.qml:22 Type KT.OverlayDrawer unavailable
file:///home/nico/kde/usr/qml/org/kde/kirigami/templates/OverlayDrawer.qml:120 Cannot assign object of type "IconPropertiesGroup" to property of type "IconPropertiesGroup_QMLTYPE_55*" as the former is neither the same as the latter nor a sub-class of it.

This seems to be due to its somewhat complex architecture: There is a QML-based sidebar (using QQuickWidget) in a QMainWindow. The QML code is added via qt_add_qml_module. The actual module content is in another QQuickWidget, loaded from a plugin that ships the QML code via qrc but not using qt_add_qml_module.

Additionally both import components from Kirigami. Kirigami uses the qmlRegisterType(QUrl ...) function to register its controls. The combination of these factors makes the bug appear.

https://invent.kde.org/nicolasfella/qml-test is a minimal example showing the problem. Loading the second component fails with

qrc:/qt/qml/org/kde/systemsettings/Main.qml:4 Type Comps.OverlayDrawer unavailable file:///home/nico/qml-test/OverlayDrawer.qml:4 Cannot assign object of type "IconPropertiesGroup" to property of type "IconPropertiesGroup_QMLTYPE_1*" as the former is neither the same as the latter nor a sub-class of it.

This is tested with current 6.7 branch (qtbase 32fa63f650be5b2d5d2c219d9150f994c761bd75, qtdeclarative ac0bbf86c979ab3faef102890ceaceb0378f8ed4). It worked fine with Qt 6.6 and previous