Resizing an undocked QDockWidget from the top-right causes the vertical resize direction to invert.

#include <QApplication>
#include <QMainWindow>
#include <QDockWidget>
#include <QLabel>
#include <Qt>

class MinimalDockApp : public QMainWindow {
public:
    MinimalDockApp(QWidget *parent = nullptr) : QMainWindow(parent) {
        setWindowTitle("Minimal QDockWidget App");
        setGeometry(100, 100, 400, 300); // x, y, width, height

        // Optional: central widget
        // setCentralWidget(new QLabel("Central Widget (Optional)"));

        // Create a QDockWidget
        QDockWidget *dockWidget = new QDockWidget("My Dock", this);
        dockWidget->setFeatures(
            QDockWidget::DockWidgetClosable |
            QDockWidget::DockWidgetMovable |
            QDockWidget::DockWidgetFloatable
        );

        // Content for the dock
        QLabel *dockContent = new QLabel("Hello from Dock!");
        dockContent->setAlignment(Qt::AlignCenter);

        dockWidget->setWidget(dockContent);

        // Add dock widget to the main window
        addDockWidget(Qt::LeftDockWidgetArea, dockWidget);
    }
};

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);
    MinimalDockApp window;
    window.show();
    return app.exec();
}

# The name of your project
TEMPLATE = app
TARGET = minimaldockapp

# The version of Qt to use — explicitly targeting Qt 6
CONFIG += qt warn_on c++17

# Specify required Qt modules
QT += widgets

# Include paths – make sure qmake can find your Qt 6 headers
INCLUDEPATH += /usr/include/qt6
INCLUDEPATH += /usr/include/qt6/QtWidgets
INCLUDEPATH += /usr/include/qt6/QtCore

# If you have Qt 6 in a non-standard lib directory, add it like this:
# QMAKE_LIBDIR += /usr/lib/qt6

# Source files
SOURCES += main.cpp

# If you had separate header files or UI forms, you would list them:
# HEADERS += myclass.h
# FORMS += form.ui

# Optionally, enforce C++17 explicitly
QMAKE_CXXFLAGS += -std=c++17