qmlsc compilation fails for qmlRegisterSingletonInstance

[robgu]

Hello,

Recently I've been testing the qmlsc compilation. I'm currently facing a problem of a piece of QML code not being compiled by qmlsc. Note, that when executed it still works, but I want to find out how to do it "properly".

I need to share a c++ side created instance of an object with QML, so I followed the usage given for QQmlEngine::qmlRegisterSingletonInstance.
For that I created a simple project (all source files below) that has a simple DummyData class storing some text. An instance of that class is created in the main (before creating QQmlEngine) and registered using
qmlRegisterSingletonInstance with URI "MyTest.Test.Dummy", version 1.0, and type name "DD". I then import the "MyTest.Test.Dummy 1.0" in the qml and call for DD properties.
This works fine, however, when compiling the QML code I get the following 3 warnings (which, AFAIK, prevent the full qml to cpp compilation):

[10/19 1,4/sec] Generating .rcc/qmlcache/appSingletonTest_Main_qml.cpp
Warning: Main.qml:2:1: Warnings occurred while importing module "MyTest.Test.Dummy": [import]
import MyTest.Test.Dummy 1.0
^^^^^^
---
Warning: Failed to import MyTest.Test.Dummy. Are your import paths set up properly? [import]
---

Warning: Main.qml:13:15: Unqualified access [unqualified]
        text: DD.dummyText
              ^^
Warning: Main.qml:13:15: Could not compile binding for text: Cannot access value for name DD [compiler]
        text: DD.dummyText
              ^^

How can I resolve these warnings and take advantage of the full QML compilation?
FYI: I'm using Qt6.5.5

Source files:
DummyData.h

#ifndef DUMMYDATA_H
#define DUMMYDATA_H

#include <QObject>

class DummyData : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QString dummyText READ dummyText WRITE setDummyText NOTIFY dummyTextChanged FINAL)

public:
    explicit DummyData(QObject *parent = nullptr);

    QString dummyText() const;
    void setDummyText(const QString &newDummyText);

signals:
    void dummyTextChanged();

private:
    QString m_dummyText;
};

#endif // DUMMYDATA_H

DummyData.cpp

#include "DummyData.h"

DummyData::DummyData(QObject *parent)
    : QObject{parent}
{}

QString DummyData::dummyText() const
{
    return m_dummyText;
}

void DummyData::setDummyText(const QString &newDummyText)
{
    if (m_dummyText == newDummyText)
        return;
    m_dummyText = newDummyText;
    emit dummyTextChanged();
}

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include "DummyData.h"

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QScopedPointer<DummyData> dd(new DummyData);
    dd->setDummyText("my test text");
    qmlRegisterSingletonInstance("MyTest.Test.Dummy", 1, 0, "DD", dd.get());

    QQmlApplicationEngine engine;
    QObject::connect(
        &engine,
        &QQmlApplicationEngine::objectCreationFailed,
        &app,
        []() { QCoreApplication::exit(-1); },
        Qt::QueuedConnection);
    engine.loadFromModule("SingletonTest", "Main");

    return app.exec();
}

Main.qml

import QtQuick
import MyTest.Test.Dummy 1.0

Window {
    width: 640
    height: 480
    visible: true
    title: qsTr("Hello World")

    Text {
        id: text1
        anchors.centerIn: parent
        text: DD.dummyText
    }
}

CMakeLists.txt

cmake_minimum_required(VERSION 3.16)

project(SingletonTest VERSION 0.1 LANGUAGES CXX)

set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 6.5 REQUIRED COMPONENTS Quick)

qt_standard_project_setup(REQUIRES 6.5)

qt_policy(SET QTP0001 NEW)

qt_add_executable(appSingletonTest
    main.cpp
)

qt_add_qml_module(appSingletonTest
    URI SingletonTest
    VERSION 1.0
    QML_FILES
        Main.qml
        SOURCES DummyData.h DummyData.cpp
)

# Qt for iOS sets MACOSX_BUNDLE_GUI_IDENTIFIER automatically since Qt 6.1.
# If you are developing for iOS or macOS you should consider setting an
# explicit, fixed bundle identifier manually though.
set_target_properties(appSingletonTest PROPERTIES
#    MACOSX_BUNDLE_GUI_IDENTIFIER com.example.appSingletonTest
    MACOSX_BUNDLE_BUNDLE_VERSION ${PROJECT_VERSION}
    MACOSX_BUNDLE_SHORT_VERSION_STRING ${PROJECT_VERSION_MAJOR}.${PROJECT_VERSION_MINOR}
    MACOSX_BUNDLE TRUE
    WIN32_EXECUTABLE TRUE
)

target_link_libraries(appSingletonTest
    PRIVATE Qt6::Quick
)

include(GNUInstallDirs)
install(TARGETS appSingletonTest
    BUNDLE DESTINATION .
    LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
    RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
)

[robgu]

Yes and no.
No: I did not solve it the way I have imagined it.
Yes: I changed DummyData to be QML_SINGLETON and use QQmlEngine::singletonInstance to get the pointer to the instance in the C++ code.

[Antony007]

Did you solve it?

[robgu]

Yes and no.
No: I did not solve it the way I have imagined it.
Yes: I changed DummyData to be QML_SINGLETON and use QQmlEngine::singletonInstance to get the pointer to the instance in the C++ code.