#include <iostream>

#include <QApplication>
#include <QHBoxLayout>
#include <QLineEdit>
#include <QMainWindow>
#include <QTimer>
#include <QWidget>

class LineEditContainer : public QWidget
{
public:
    LineEditContainer(QWidget *parent = nullptr)
        : QWidget(parent)
    {
        auto *layout = new QHBoxLayout(this);
        line_edit = new QLineEdit(this);
        layout->addWidget(line_edit);
        setFocusProxy(line_edit);
    }

    QLineEdit *line_edit;
};

class MainWindow : public QMainWindow
{
public:
    MainWindow(QWidget *parent = nullptr)
        : QMainWindow(parent)
    {
        auto *main = new QWidget();
        auto *layout = new QHBoxLayout(main);
        layout->setSpacing(100);

        auto *container1 = new LineEditContainer();
        layout->addWidget(container1);
        std::cerr << "edit1:                            " << container1->line_edit << std::endl;

        main->setFixedSize(500, 200);
        main->setFocusPolicy(Qt::ClickFocus);
        main->setFocusProxy(container1);

        setCentralWidget(main);

        QTimer::singleShot(1000, [=]() {
            auto *container2 = new LineEditContainer();
            layout->addWidget(container2);
            std::cerr << "edit2:                            " << container2->line_edit << std::endl;

            std::cerr << "QApplication focus widget before: " << qApp->focusWidget() << std::endl;
            std::cerr << "QMainWindow focus widget before : " << focusWidget() << std::endl;
            main->setFocusProxy(container2);
            std::cerr << "QApplication focus widget after : " << qApp->focusWidget() << std::endl;
            std::cerr << "QMainWindow focus widget after  : " << focusWidget() << std::endl;

            // container2->line_edit is focus_widget, but keyboard events go to container1->line_edit.
            // The visual focus state is very wrong.
        });
    }
};

int main(int argc, char *argv[])
{
    std::cerr << "Qt version: " << QT_VERSION_STR << std::endl;
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}