Multiple issues with foreign windows from QWindow::fromWinId() and QWidget::createWindowContainer()

Hello,

I've encountered many issues with foreign windows. Rather than open many tickets, I've listed them all here, especially since I can't tell if any of them have the same root cause.

I mainly tested foreign windows from Notepad.exe (Windows) and GEdit (Linux) through QWindow and QWidget classes. I briefly tried other programs too, with the same results as far as I could tell.

TEST CODE
The report below is split into 3 parts. Uncomment the code related to each part to proceed.

#include "windows.h"
#include <QApplication>
#include <QWindow>
#include <QWidget>
#include <QDebug>
#include <QTimer>

int main(int argc, char *argv[])
{
    // Windows: Find HWND by window title
    WId id = (WId)FindWindow(NULL, L"Untitled - Notepad");
    if (!id)
        return -1;

    // Linux: Find Window ID by running xwininfo externally before compiling this test
    //WId id = 0x4600085

    QApplication a(argc, argv);
    QTimer t;
    t.start(2500);

    // Part 1
    QWindow* window = QWindow::fromWinId(id);
    window->show();
    window->requestActivate();
    QObject::connect(&t, &QTimer::timeout, [=]
    {
        qDebug() << "=== Inner QWindow ===";
        qDebug() << "Geometry:" << window->geometry();
        qDebug() << "Active?:" << window->isActive();
        qDebug() << "Flags:" << window->flags();
    });

/*
    // Part 2
    QWidget* widget = QWidget::createWindowContainer(window);
    widget->show();
    QObject::connect(&t, &QTimer::timeout, [=]
    {
        qDebug() << "=== Outer QWidget ===";
        qDebug() << "Geometry:" << widget->geometry();
        qDebug() << "Active?" << widget->isActiveWindow();
        qDebug() << "Flags:" << widget->windowFlags();
    });
*/

    QObject::connect(&t, &QTimer::timeout, [=]
    {
        qDebug("\n");

/*
        // Part 3
        // Release the window after a few iterations
        static int i = 0;
        if (i++ == 3)
        {
            window->setParent(nullptr);
            window->setFlags(window->flags() | Qt::CustomizeWindowHint | Qt::WindowTitleHint);
        }
*/
    });

    return a.exec();
}

ISSUES
Part 1: Using a QWindow interface

• Incorrect geometry reported
  • (Win) window->geometry() always returns the initial geometry (from the point when window->show() was called). Moving/resizing the window does not alter the result of subsequent calls to window->geometry().
  • (Linux) window->geometry() always returns QRect(0, 0, 0x0). Moving/resizing the window has no effect.
• Incorrect "Active" status reported
  • (Win & Linux) window->isActive() always returns false, even when the window is active. window->requestActivate() has no effect.

Part 2: Embedding in a QWidget
This step seems to fix the problems in Part 1, but reveals new problems.

• Lost key/mouse input
  • (Win) The embedded window stops receiving key press and mouse wheel events (although mouse click events are still fine).

• Quirks with initial geometry
  • (Win & Linux) The window is forcibly resized to 640x480, even if the original window was not resizable. (The built-in calculator app in Windows, calc.exe, is non-resizable)
  • (Win & Linux) Initially, the inner window is not aligned properly with the outer widget. Resizing the outer widget fixes the alignment. Moving it has no effect.

Part 3: Releasing an embedded window
http://qt-project.org/doc/qt-5/qwidget.html#createWindowContainer says that QWindow::setParent() can release the window, but it doesn't quite work.

• Released but broken
  • (Win) The window is released but remains borderless (as if Qt::FramelessWindowHint was set).
    • However, window->flags() only returns 0x1|0x20 (i.e. Qt::ForeignWindow).
    • Explicitly applying Qt::WindowTitleHint etc. has no effect.