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Type: Suggestion
Resolution: Unresolved
Priority: P2: Important
Fix Version/s: 6.5
Affects Version/s: None
Component/s: Documentation, QML: Compiler
Labels:
- Reported_by_support_standard

The code below produces the warning,

Warning: main.qml:8:24: Could not compile binding for color: return type QColor cannot be resolved [compiler]

To fix this warning, we need to add DEPENDENCIES QtQuick to our QML module, as explained at https://www.qt.io/blog/compiling-qml-to-c-making-types-visible This information should be part of the official documentation too.

Code

// mysingleton.h
#include <QObject>
#include <QQmlEngine>
#include <QColor>

class MySingleton : public QObject
{
    Q_OBJECT
    QML_ELEMENT
    QML_SINGLETON

public:
    MySingleton(QObject* parent = nullptr) : QObject(parent) {}
    Q_INVOKABLE QColor backgroundColor() const { return Qt::green; }
};

// main.qml
import QtQuick
import ColorCompilationStudy

Window {
    width: 640
    height: 480
    visible: true
    color: MySingleton.backgroundColor()
}

// CMakeLists.txt
cmake_minimum_required(VERSION 3.16)

project(ColorCompilationStudy VERSION 0.1 LANGUAGES CXX)

set(CMAKE_AUTOMOC ON)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

find_package(Qt6 6.2 COMPONENTS Quick REQUIRED)

qt_add_executable(appColorCompilationStudy
    main.cpp
)

qt_add_qml_module(appColorCompilationStudy
    URI ColorCompilationStudy
    VERSION 1.0
    AUTO_RESOURCE_PREFIX 
    QML_FILES main.qml
    SOURCES mysingleton.h
#    DEPENDENCIES QtQuick

### How can I know that adding "QtQuick" as a DEPENDENCY lets qmlsc resolve QColor?
)

target_link_libraries(appColorCompilationStudy
    PRIVATE Qt6::Quick)

Possible solution
Perhaps at the top of the class reference, similar to the Header/CMake/qmake details required to use the class in C++?