Not possible to keep an editable ComboBox's Popup open while typing in the TextField

#include <QtWidgets>

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

    QMainWindow mainWindow;

    QWidget *widget = new QWidget;

    QHBoxLayout *hBoxLayout = new QHBoxLayout(widget);

    QComboBox *comboBox = new QComboBox(widget);
    comboBox->setEditable(true);

    const QVector<QString> contents = { "Apple", "Banana", "Coconut" };
    auto *model = new QStandardItemModel(contents.size(), 1);
    for (int row = 0; row < contents.size(); ++row) {
        const auto &modelData = contents.at(row);
        auto *item = new QStandardItem(modelData);
        model->setItem(row, 0, item);
    }
    comboBox->setModel(model);
    comboBox->completer()->setCompletionMode(QCompleter::PopupCompletion);

    hBoxLayout->addWidget(comboBox);

    mainWindow.setCentralWidget(widget);
    mainWindow.centralWidget()->setLayout(hBoxLayout);

    mainWindow.resize(400, 400);
    mainWindow.show();

    return app.exec();
}