How to create static plugin using cmake?

[Maksym Kravchenko]

I wrote qml plugin using cmake. the source code is presented below. It works fine.
Now I want built it as static plugin . I have added next changes in project.

• add my plugin to link libraries in CMakeLists.txt

target_link_libraries(
    ${PROJECT_NAME}
    PRIVATE
        Qt5::Core
        Qt5::Quick
        Qt5::Qml
        myplugin
)

• add plugin import to main.cpp

#include <QtPlugin>
Q_IMPORT_PLUGIN(MyPlugin)

• build STATIC plugin version with QT_STATICPLUGIN difinition in my/plugin/CMakeLists.txt

add_library(
    ${PLUGIN_NAME}
    STATIC
    Plugin.h
    QuickItem.h
    Plugin.cpp
    QuickItem.cpp
    plugin.qrc
    qmldir
)

target_compile_definitions(${PLUGIN_NAME}
    PUBLIC
      QT_STATICPLUGIN
)

• change plugin to classname i n qmldir

classname Plugin

Project is built fine but I have runtime error:
QQmlApplicationEngine failed to load component
qrc:/main.qml:11 MyQuickItem is not a type

QML engine parses "import my.plugin 1.0" it's mean qmldir is found
But MyPlugin::registerTypes is never called (I think for calling this function need add classname to qmldir but unfortunately it doesn't work ). I have checked this code with Qt 5.12.4 and 5.15.1, result is same.
What else should I do?

My file system:

┣━ CMakeLists.txt
┣━ app.qrc
┣━ main.cpp
┣━ main.qml
┗━ my
    ┗━ plugin
        ┣━ CMakeLists.txt
        ┣━ MyButton.qml
        ┣━ Plugin.cpp
        ┣━ Plugin.h
        ┣━ QuickItem.cpp
        ┣━ QuickItem.h
        ┣━ plugin.qrc
        ┗━ qmldir

CMakeLists.txt:

cmake_minimum_required(VERSION 3.0)
project(app VERSION 1.0 LANGUAGES CXX)

find_package(Qt5 REQUIRED COMPONENTS Quick Core Qml)

add_executable(
    ${PROJECT_NAME}
    main.cpp
    app.qrc
)

set_target_properties(
    ${PROJECT_NAME}
    PROPERTIES
        AUTOMOC ON
        AUTORCC ON
)

target_link_libraries(
    ${PROJECT_NAME}
    PRIVATE
        Qt5::Core
        Qt5::Quick
        Qt5::Qml
)

add_subdirectory(my/plugin)

app.qrc

<RCC>
    <qresource prefix="/">
        <file>main.qml</file>
    </qresource>
</RCC>

main.cpp

#include <QGuiApplication>
#include <QQmlApplicationEngine>

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

    QGuiApplication app(argc, argv);
    QQmlApplicationEngine engine;

    engine.load(QUrl(QLatin1String("qrc:/main.qml")));
    if (engine.rootObjects().isEmpty()) {
        return -1;
    }
    return app.exec();
}

main.qml

import QtQuick.Controls 2.0
import my.plugin 1.0

ApplicationWindow {
    visible: true
    width: 640
    height: 480
    title: "Lyzer"

    // 'myplugin' C++ class
    MyQuickItem {
        id: pluginItem
        color: "green"
        width: 100
        height: 50
        anchors.centerIn: parent
    }

    // 'myplugin' QML file
    MyButton {
        anchors.top: pluginItem.bottom
        anchors.horizontalCenter: pluginItem.horizontalCenter
        width: pluginItem.width
        onClicked: {
            pluginItem.color = '#' + Math.floor(Math.random() * 0x1000000).toString(16);
        }
    }
}

CMakeLists.txt for plugin

set(PLUGIN_NAME myplugin)

add_library(
    ${PLUGIN_NAME}
    SHARED
    Plugin.h
    QuickItem.h
    Plugin.cpp
    QuickItem.cpp
    plugin.qrc
    qmldir
)

set_target_properties(
    ${PLUGIN_NAME}
    PROPERTIES
        AUTOMOC ON
        AUTORCC ON
)

target_link_libraries(
    ${PLUGIN_NAME}
    PRIVATE
        Qt5::Core
        Qt5::Quick
        Qt5::Qml
)

add_custom_command(
    TARGET ${PLUGIN_NAME}
    POST_BUILD
    COMMAND
        ${CMAKE_COMMAND} -E copy
        ${CMAKE_CURRENT_LIST_DIR}/qmldir
        $<TARGET_FILE_DIR:myplugin>/qmldir
)

MyButton.qml

import QtQuick.Controls 2.0

Button {
    text: "Click me!"
}

Plugin.cpp

#include "Plugin.h"
#include "QuickItem.h"

void MyPlugin::registerTypes(const char* uri) {
    qmlRegisterType<My::QuickItem>(uri, 1, 0, "MyQuickItem");
}

plugin.h

#pragma once

#include <QtQml/QQmlExtensionPlugin>

class MyPlugin: public QQmlExtensionPlugin {
    Q_OBJECT
    Q_PLUGIN_METADATA(IID "my.plugin/1.0")
public:
    void registerTypes(const char* uri) override;
};

QuickItem.cpp

#include "QuickItem.h"

#include <QPen>
#include <QPainter>

namespace My {
QuickItem::QuickItem(QQuickItem* parent)
    : QQuickPaintedItem(parent) {
}

QColor QuickItem::getColor() const {
    return color;
}

void QuickItem::setColor(const QColor& color) {
    if (color != this->color) {
        this->color = color;
        update();
        emit colorChanged();
    }
}

void QuickItem::paint(QPainter* painter) {
    QPen pen(color, 2);
    painter->setPen(pen);
    painter->fillRect(QRectF(0, 0, width(), height()), color);
}
}

QuickItem.h

#pragma once

#include <QtQuick/QQuickPaintedItem>
#include <QColor>

namespace My {
class QuickItem: public QQuickPaintedItem {
    Q_OBJECT
    Q_PROPERTY(QColor color READ getColor WRITE setColor NOTIFY colorChanged)
public:
    QuickItem(QQuickItem* parent = nullptr);
    QColor getColor() const;
    void setColor(const QColor &color);
    void paint(QPainter *painter) override;

signals:
    void colorChanged();

private:
    QColor color;
};
}

plugin.qrc

<RCC>
    <qresource prefix="/plugin">
        <file>MyButton.qml</file>
    </qresource>
</RCC>

qmldir

module my.plugin
plugin myplugin
MyButton 1.0 qrc:/plugin/MyButton.qml