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Crash when closing tab on Windows #6

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The-Compiler opened this issue Oct 1, 2014 · 1 comment
Closed

Crash when closing tab on Windows #6

The-Compiler opened this issue Oct 1, 2014 · 1 comment
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@The-Compiler
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This is a reminder to myself - there was a crash when closing a tab on windows, I should take a closer look at that and probably do some longer tests on Linux.

@The-Compiler The-Compiler self-assigned this Oct 1, 2014
@The-Compiler The-Compiler added this to the v0.1 milestone Oct 1, 2014
@The-Compiler
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Affected commit: e6fe358

Stacktrace:

ntdll!NtWaitForMultipleObjects+a    
KERNELBASE!WaitForMultipleObjectsEx+e8    
kernel32!WaitForMultipleObjectsExImplementation+b3    
kernel32!WerpReportFaultInternal+215    
kernel32!WerpReportFault+77    
kernel32!BasepReportFault+1f    
kernel32!UnhandledExceptionFilter+1fc    
ntdll! ?? ::FNODOBFM::`string'+2365    
ntdll!_C_specific_handler+8c    
ntdll!RtlpExecuteHandlerForException+d    
ntdll!RtlDispatchException+45a    
ntdll!KiUserExceptionDispatch+2e    
Qt5WebKitWidgets!QWebPage::qt_metacall+3c8    
Qt5WebKitWidgets!QWebPage::event+3f8    
QtWebKitWidgets!PyInit_QtWebKitWidgets+1377d    
Qt5WebKitWidgets!QWebView::mouseMoveEvent+2d    
QtWebKitWidgets!PyInit_QtWebKitWidgets+1bbed    
Qt5Widgets!QWidget::event+69a    
QtWebKitWidgets!PyInit_QtWebKitWidgets+1c0dd    
Qt5Widgets!QApplicationPrivate::notify_helper+f6    
Qt5Widgets!QApplication::notify+e2d    
QtWidgets!PyInit_QtWidgets+2e7a8    
Qt5Core!QCoreApplication::notifyInternal+6f    
Qt5Widgets!QWidgetPrivate::setGeometry_sys+16cb    
Qt5Widgets!QWidgetPrivate::setGeometry_sys+2ede    
Qt5Widgets!QApplicationPrivate::notify_helper+f6    
Qt5Widgets!QApplication::notify+1eca    
QtWidgets!PyInit_QtWidgets+2e7a8    
Qt5Core!QCoreApplication::notifyInternal+6f    
Qt5Gui!QGuiApplicationPrivate::processMouseEvent+5ac    
Qt5Gui!QGuiApplicationPrivate::processWindowSystemEvent+181    
Qt5Gui!QWindowSystemInterface::sendWindowSystemEvents+73    
Qt5Core!QEventDispatcherWin32Private::QEventDispatcherWin32Private+378    
user32!UserCallWinProcCheckWow+1ad    
user32!DispatchMessageWorker+3b5    
Qt5Core!QEventDispatcherWin32::processEvents+426    
qwindows+1fcd1    
Qt5Core!QEventLoop::exec+1cd    
Qt5Core!QCoreApplication::exec+189    
QtWidgets!PyInit_QtWidgets+30b27    
python34!Py_GetProgramName+fc437    
python34!Py_GetProgramName+170125    
python34!Py_GetProgramName+172533    
python34!Py_GetProgramName+174222    
python34!Py_GetProgramName+17018b    
python34!Py_GetProgramName+172533    
python34!Py_GetProgramName+173fa6    
python34!Py_GetProgramName+174348    
python34!Py_GetProgramName+1697cf    
python34!Py_GetProgramName+fc437    
python34!Py_GetProgramName+170125    
python34!Py_GetProgramName+172533    
python34!Py_GetProgramName+173fa6    
python34!Py_GetProgramName+174297    
python34!Py_GetProgramName+17018b    
python34!Py_GetProgramName+172533    
python34!Py_GetProgramName+173fa6    
python34!Py_GetProgramName+e7197    
python34!Py_GetProgramName+b561b    
python34!Py_GetProgramName+596e3    
python34!Py_GetProgramName+5a22a    
python+11ae    
kernel32!BaseThreadInitThunk+d    
ntdll!RtlUserThreadStart+1d    

I can't say much from the stacktrace and I could never reproduce this, so I'm closing it.

The-Compiler added a commit that referenced this issue Jun 5, 2015
Upstream changelog:

- Fix issue #6 - support PEP263 for source file encoding.
- Clarified license to be MIT like pytest-pep8 from which this is derived.
The-Compiler added a commit that referenced this issue Mar 29, 2021
This reverts commit c6cf306.

Seems to cause segfaults:

  #0  0x00007ffff5cecbcc in void doActivate<false>(QObject*, int, void**) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
  #1  0x00007ffff5be4e31 in QIODevice::channelReadyRead(int) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
  #2  0x00007fffeffccb54 in QAbstractSocketPrivate::canReadNotification() () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Network.so.5
  #3  0x00007fffeffdf061 in QReadNotifier::event(QEvent*) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Network.so.5
  #4  0x00007ffff269e43c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Widgets.so.5
  #5  0x00007ffff26a4f20 in QApplication::notify(QObject*, QEvent*) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Widgets.so.5
  #6  0x00007ffff318d0d6 in sipQApplication::notify(QObject*, QEvent*) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/QtWidgets.abi3.so
  #7  0x00007ffff5cb4808 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
  #8  0x00007ffff5d10d98 in socketNotifierSourceDispatch(_GSource*, int (*)(void*), void*) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
  #9  0x00007ffff691df9c in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
  #10 0x00007ffff6971a49 in ?? () from /usr/lib/libglib-2.0.so.0
  #11 0x00007ffff691b6f1 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
  #12 0x00007ffff5d101cc in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
  #13 0x00007ffff5cb321a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
  #14 0x00007ffff5cbc1d3 in QCoreApplication::exec() () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
The-Compiler added a commit that referenced this issue Mar 29, 2021
This reverts commit c6cf306.

Seems to cause segfaults:

  #0  0x00007ffff5cecbcc in void doActivate<false>(QObject*, int, void**) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
  #1  0x00007ffff5be4e31 in QIODevice::channelReadyRead(int) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
  #2  0x00007fffeffccb54 in QAbstractSocketPrivate::canReadNotification() () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Network.so.5
  #3  0x00007fffeffdf061 in QReadNotifier::event(QEvent*) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Network.so.5
  #4  0x00007ffff269e43c in QApplicationPrivate::notify_helper(QObject*, QEvent*) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Widgets.so.5
  #5  0x00007ffff26a4f20 in QApplication::notify(QObject*, QEvent*) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Widgets.so.5
  #6  0x00007ffff318d0d6 in sipQApplication::notify(QObject*, QEvent*) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/QtWidgets.abi3.so
  #7  0x00007ffff5cb4808 in QCoreApplication::notifyInternal2(QObject*, QEvent*) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
  #8  0x00007ffff5d10d98 in socketNotifierSourceDispatch(_GSource*, int (*)(void*), void*) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
  #9  0x00007ffff691df9c in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
  #10 0x00007ffff6971a49 in ?? () from /usr/lib/libglib-2.0.so.0
  #11 0x00007ffff691b6f1 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
  #12 0x00007ffff5d101cc in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
  #13 0x00007ffff5cb321a in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
  #14 0x00007ffff5cbc1d3 in QCoreApplication::exec() () from /home/florian/proj/qutebrowser/git/.tox/py39-pyqt515/lib/python3.9/site-packages/PyQt5/Qt5/lib/libQt5Core.so.5
The-Compiler added a commit that referenced this issue Dec 6, 2022
In bleeding tests, we started to get a segfault on the second test in
tests/unit/mainwindow/test_prompt.py, with a stacktrace like:

    Thread 1 "python" received signal SIGSEGV, Segmentation fault.
    0x00007ffff7b55912 in _PyFunction_Vectorcall (func=<function at remote 0x7fffc4368ca0>, stack=0x7fffd74656a8, nargsf=<optimized out>, kwnames=0x0) at Objects/call.c:341
    341	   if (((PyCodeObject *)f->fc_code)->co_flags & CO_OPTIMIZED) {
    (gdb) bt
    #0  0x00007ffff7b55912 in _PyFunction_Vectorcall (func=<function at remote 0x7fffc4368ca0>, stack=0x7fffd74656a8, nargsf=<optimized out>, kwnames=0x0) at Objects/call.c:341
    #1  0x00007ffff4e0b3f1 in PyQtSlot::call(_object*, _object*) const (this=0x555556c759c0, args=('/tmp/pytest-of-florian/pytest-70/test_simple_completion_1_next_0/test',), callable=<function at remote 0x7fffc4368ca0>)
        at ../../qpy/QtCore/qpycore_pyqtslot.cpp:247
    #2  PyQtSlot::invoke(void**, _object*, void*, bool) const (this=0x555556c759c0, qargs=<optimized out>, qargs@entry=0x7fffffff86c0, self=<optimized out>, self@entry=0x0, result=result@entry=0x0, no_receiver_check=<optimized out>)
        at ../../qpy/QtCore/qpycore_pyqtslot.cpp:159
    #3  0x00007ffff4e12213 in PyQtSlot::invoke(void**, bool) const (no_receiver_check=<optimized out>, qargs=0x7fffffff86c0, this=<optimized out>) at ../../qpy/QtCore/qpycore_pyqtslot.cpp:78
    #4  PyQtSlotProxy::unislot(void**) (qargs=0x7fffffff86c0, this=0x555557193e20) at ../../qpy/QtCore/qpycore_pyqtslotproxy.cpp:205
    #5  PyQtSlotProxy::unislot(void**) (qargs=0x7fffffff86c0, this=0x555557193e20) at ../../qpy/QtCore/qpycore_pyqtslotproxy.cpp:186
    #6  PyQtSlotProxy::qt_metacall(QMetaObject::Call, int, void**) (this=0x555557193e20, _c=<optimized out>, _id=0, _a=0x7fffffff86c0) at ../../qpy/QtCore/qpycore_pyqtslotproxy.cpp:170
    #7  0x00007ffff48bd91d in doActivate<false>(QObject*, int, void**) (sender=0x555556b3d680, signal_index=28, argv=0x7fffffff86c0) at kernel/qobject.cpp:3945
    #8  0x00007fffeff96aca in QFileSystemModel::directoryLoaded(QString const&) (this=<optimized out>, _t1=<optimized out>) at .moc/moc_qfilesystemmodel.cpp:272
    #9  0x00007ffff48b0be0 in QObject::event(QEvent*) (this=this@entry=0x555556b3d680, e=e@entry=0x7fff0c004af0) at kernel/qobject.cpp:1347
    #10 0x00007fffeff962ab in QFileSystemModel::event(QEvent*) (this=this@entry=0x555556b3d680, event=event@entry=0x7fff0c004af0) at dialogs/qfilesystemmodel.cpp:1748
    #11 0x00007ffff070995c in sipQFileSystemModel::event(QEvent*) (this=0x555556b3d680, a0=0x7fff0c004af0) at /usr/src/debug/pyqt5/PyQt5-5.15.7/build/QtWidgets/sipQtWidgetsQFileSystemModel.cpp:376
    [...]
    #23 0x00007ffff4da94ce in meth_QCoreApplication_processEvents(PyObject*, PyObject*, PyObject*) (sipArgs=<optimized out>, sipKwds=0x0) at /usr/src/debug/pyqt5/PyQt5-5.15.7/build/QtCore/sipQtCoreQCoreApplication.cpp:590
    [...]

from pytest-qt in Python:

    Current thread 0x00007fb366207740 (most recent call first):
    File ".../pytestqt/plugin.py", line 209 in _process_events
    File ".../pytestqt/plugin.py", line 171 in pytest_runtest_setup
    [...]
    File ".../pytest/src/_pytest/runner.py", line 115 in pytest_runtest_protocol
    [...]
    File ".../pytest/src/_pytest/main.py", line 317 in pytest_cmdline_main
    [...]

Introduced by this change in pytest, which now deletes the temporary
directory after the test by default:

pytest-dev/pytest#10517

It sounds like something odd like the directory removal causing (Py)Qt
to call the lambda, but the underlying Python object already being gone
or something along those lines. With a proper Qt slot (@pyqtSlot),
PyQt seems to do the right thing, so let's just use that instead...
toofar added a commit that referenced this issue Oct 27, 2023
It all just works!

Changes from the `__main__` implementation down below:

* copy the whole resources directory instead of just the one file:
  looking at the implementation around QTWEBENGINE_RESOURCES_PATH it
  uses the main resources file to find the one directory and then loads
  the other resources from that dir. So I'm assuming it was crashing
  because it couldn't find the other resources. Stack trace was:

    #1  0x00007fffe95f1dca in content::ContentMainRunnerImpl::Initialize(content::ContentMainParams) ()
       from /usr/local/Qt-6.6.0/lib/libQt6WebEngineCore.so.6
    #2  0x00007fffe628cf09 in QtWebEngineCore::WebEngineContext::WebEngineContext() ()
       from /usr/local/Qt-6.6.0/lib/libQt6WebEngineCore.so.6
    #3  0x00007fffe628dfa4 in QtWebEngineCore::WebEngineContext::current() ()
       from /usr/local/Qt-6.6.0/lib/libQt6WebEngineCore.so.6
    #4  0x00000210b845c780 in ?? ()
    #5  0x00000210b845c780 in ?? ()
    #6  0x00007fffffffd480 in ?? ()
    #7  0x00007fffe62391bb in QtWebEngineCore::ProfileAdapter::ProfileAdapter(QString const&) ()
       from /usr/local/Qt-6.6.0/lib/libQt6WebEngineCore.so.6

* write stuff to our cache dir, not tmp ;)

I haven't actually checked this fixes an affected version of Qt (need to
rebuild or get from riverbank pypi). But I unpacked the pak file and it
has the right fake URL in it.
The-Compiler added a commit that referenced this issue Dec 7, 2023
Almost 7 years ago, it was observed that hiding the status bar causes some
websites being scrolled to the top: #2236.

Back then, it never really was clear why this happens. However, with the v3.0.0
release, we had a regression causing the same thing to happen when leaving
prompt mode: #7885.

Thanks to "git bisect", the culprit was found to be 8e152aa, "Don't give
keyboard focus to tab bar", which was a fix for #7820. However, it still wasn't
clear why this phenomenon happens.

What made things clearer to me was a combination of debugging and an old comment
by pevu: #2236 (comment)

    Chromium-browser has the same issue. When you open lipsum.com, scroll down,
    then focus the location bar (url box), then press Tab, it will jump to the
    top of the page and focus the first link. This doesn't happen when you
    switch focus using the mouse.

    It seems to be an issue of how the view containing the website is focused
    when all qutebrowser ui elements disappear.

And indeed, tabbing into the web contents from the UI elements via the tab key
in Chromium causes the website to start at the top, presumably as an
accessibility feature?

Essentially, this is also what happens in qutebrowser when an UI element is
hidden while it still has focus: In QWidget::hide() (or, rather,
QWidgetPrivate::hide_helper()), Qt moves the focus to the next widget by
calling focusPrevNextChild(true):
https://github.com/qt/qtbase/blob/v6.6.1/src/widgets/kernel/qwidget.cpp#L8259-L8271

And apparently, focusPrevNextChild() basically does the same thing as pressing
the tab key, to the point that there is some code in Qt Declarative actually
making tab keypresses out of it (which I'm still not sure is related, or maybe
just the cause of #4579):
https://github.com/qt/qtdeclarative/blob/v6.6.1/src/quickwidgets/qquickwidget.cpp#L1415-L1429

jome debugging confirms that this is exactly what happening:

1) We hide the status bar (or prompt) which has keyboard focus
2) Qt focuses the web view, which triggers the Chromium feature (?) scrolling it
   to the very top.
3) Only then, in TabbedBrowser.on_mod_left(), we noticed that the command or
   prompt mode was left, and reassign focus to the web view properly.

In step 2), before this change, Qt happened to focus the tab bar (before we set
the focus manually to the web contents), and thus this didn't happen.
Not sure why it didn't focus the tab bar when we hid the status bar (maybe
because how our widget hierarchy works with TabbedBrowser?).

Python stacktrace of hiding prompt:

    Traceback (most recent call first):
    <built-in method hide of DownloadFilenamePrompt object at remote 0x7fffb8bc65f0>
    File ".../qutebrowser/mainwindow/prompt.py", line 204, in _on_mode_left
        self.show_prompts.emit(None)
    File ".../qutebrowser/keyinput/modeman.py", line 434, in leave
        self.left.emit(mode, self.mode, self._win_id)
    File ".../qutebrowser/keyinput/modeman.py", line 445, in mode_leave
        self.leave(self.mode, 'leave current')

C++ stacktrace, with the focus change presumably being passed of to Chromium
here: https://github.com/qt/qtwebengine/blob/dev/src/core/render_widget_host_view_qt_delegate_client.cpp#L714

    #0  QtWebEngineCore::RenderWidgetHostViewQtDelegateClient::handleFocusEvent(QFocusEvent*) () at /usr/src/debug/qt6-webengine/qtwebengine-everywhere-src-6.6.0/src/core/render_widget_host_view_qt_delegate_client.cpp:708
    #1  QtWebEngineCore::RenderWidgetHostViewQtDelegateClient::handleFocusEvent(QFocusEvent*) () at /usr/src/debug/qt6-webengine/qtwebengine-everywhere-src-6.6.0/src/core/render_widget_host_view_qt_delegate_client.cpp:705
    #2  0x00007fffe5fea70c in QtWebEngineCore::RenderWidgetHostViewQtDelegateClient::forwardEvent(QEvent*) () at /usr/src/debug/qt6-webengine/qtwebengine-everywhere-src-6.6.0/src/core/render_widget_host_view_qt_delegate_client.cpp:300
    #3  0x00007fffe4dd5c79 in QQuickItem::event(QEvent*) (this=0x555556b6cd20, ev=0x7fffffffa320) at /usr/src/debug/qt6-declarative/qtdeclarative-everywhere-src-6.6.0/src/quick/items/qquickitem.cpp:8871
    #4  0x00007ffff1f7318b in QApplicationPrivate::notify_helper(QObject*, QEvent*) (this=<optimized out>, receiver=0x555556b6cd20, e=0x7fffffffa320)
        at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qapplication.cpp:3290
    #5  0x00007ffff295e4a7 in  () at /usr/lib/python3.11/site-packages/PyQt6/QtWidgets.abi3.so
    #6  0x00007ffff59626d8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) (receiver=0x555556b6cd20, event=0x7fffffffa320) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/corelib/kernel/qcoreapplication.cpp:1118
    #7  0x00007ffff596271d in QCoreApplication::sendEvent(QObject*, QEvent*) (receiver=<optimized out>, event=<optimized out>) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/corelib/kernel/qcoreapplication.cpp:1536
    #8  0x00007fffe4f33f15 in QQuickDeliveryAgentPrivate::setFocusInScope(QQuickItem*, QQuickItem*, Qt::FocusReason, QFlags<QQuickDeliveryAgentPrivate::FocusOption>)
        (this=<optimized out>, scope=<optimized out>, item=<optimized out>, reason=<optimized out>, options=...) at /usr/src/debug/qt6-declarative/qtdeclarative-everywhere-src-6.6.0/src/quick/util/qquickdeliveryagent.cpp:439
    #9  0x00007fffe4dd348a in QQuickItem::setFocus(bool, Qt::FocusReason) (this=0x555556b724d0, focus=<optimized out>, reason=Qt::TabFocusReason) at /usr/include/qt6/QtCore/qflags.h:73
    #10 0x00007fffe4e7239b in QQuickWindow::focusInEvent(QFocusEvent*) (this=<optimized out>, ev=<optimized out>) at /usr/src/debug/qt6-declarative/qtdeclarative-everywhere-src-6.6.0/src/quick/items/qquickwindow.cpp:231
    #11 0x00007ffff1fc3a05 in QWidget::event(QEvent*) (this=0x555556457b50, event=0x7fffffffa770) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qwidget.cpp:9111
    #12 0x00007ffff1f7318b in QApplicationPrivate::notify_helper(QObject*, QEvent*) (this=<optimized out>, receiver=0x555556457b50, e=0x7fffffffa770)
        at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qapplication.cpp:3290
    #13 0x00007ffff295e4a7 in  () at /usr/lib/python3.11/site-packages/PyQt6/QtWidgets.abi3.so
    #14 0x00007ffff59626d8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) (receiver=0x555556457b50, event=0x7fffffffa770) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/corelib/kernel/qcoreapplication.cpp:1118
    #15 0x00007ffff596271d in QCoreApplication::sendEvent(QObject*, QEvent*) (receiver=<optimized out>, event=<optimized out>) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/corelib/kernel/qcoreapplication.cpp:1536
    #16 0x00007ffff1f7f1b2 in QApplicationPrivate::setFocusWidget(QWidget*, Qt::FocusReason) (focus=0x555556457b50, reason=<optimized out>) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qapplication.cpp:1538
    #17 0x00007ffff1fca29d in QWidget::setFocus(Qt::FocusReason) (this=0x555556b1ceb0, reason=<optimized out>) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qwidget.cpp:6580
    #18 0x00007ffff1fb4f1b in QWidget::focusNextPrevChild(bool) (this=<optimized out>, next=<optimized out>) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qwidget.cpp:6844
    #19 0x00007ffff298d0ac in  () at /usr/lib/python3.11/site-packages/PyQt6/QtWidgets.abi3.so
    #20 0x00007ffff298d0ac in  () at /usr/lib/python3.11/site-packages/PyQt6/QtWidgets.abi3.so
    #21 0x00007ffff298d0ac in  () at /usr/lib/python3.11/site-packages/PyQt6/QtWidgets.abi3.so
    #22 0x00007ffff1fbdb76 in QWidgetPrivate::hide_helper() (this=this@entry=0x55555646a360) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qwidget.cpp:8271
    #23 0x00007ffff1fbf158 in QWidgetPrivate::setVisible(bool) (this=0x55555646a360, visible=<optimized out>) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qwidget.cpp:8447
    [...]

We fix this problem by explicitly handling focus before hiding the UI elements.
This is done with a new TabbedBrowser.on_release_focus() slot, which is bound to
signals emitted just before things are hidden: The existing Command.hide_cmd()
for the status bar, and a new release_focus() signal for prompts.

Additionally, we make sure to not double-handle hiding in the statusbar
code when it's already handled separately for comamnd mode.

Unfortunately, no tests for this, as application window focus is required to
reproduce the issue. In theory, a test in scroll.feature could be added though,
which loads simple.html, scrolls down, shows/hides a prompt or the status bar,
and then checks the vertical scroll position is != 0.

Fixes #2236
Fixes #7885
The-Compiler added a commit that referenced this issue Dec 7, 2023
Almost 7 years ago, it was observed that hiding the status bar causes some
websites being scrolled to the top: #2236.

Back then, it never really was clear why this happens. However, with the v3.0.0
release, we had a regression causing the same thing to happen when leaving
prompt mode: #7885.

Thanks to "git bisect", the culprit was found to be 8e152aa, "Don't give
keyboard focus to tab bar", which was a fix for #7820. However, it still wasn't
clear why this phenomenon happens.

What made things clearer to me was a combination of debugging and an old comment
by pevu: #2236 (comment)

> Chromium-browser has the same issue. When you open lipsum.com, scroll down,
> then focus the location bar (url box), then press Tab, it will jump to the
> top of the page and focus the first link. This doesn't happen when you
> switch focus using the mouse.
>
> It seems to be an issue of how the view containing the website is focused
> when all qutebrowser ui elements disappear.

And indeed, tabbing into the web contents from the UI elements via the tab key
in Chromium causes the website to start at the top, presumably as an
accessibility feature?

Essentially, this is also what happens in qutebrowser when an UI element is
hidden while it still has focus: In QWidget::hide() (or, rather,
QWidgetPrivate::hide_helper()), Qt moves the focus to the next widget by
calling focusPrevNextChild(true):
https://github.com/qt/qtbase/blob/v6.6.1/src/widgets/kernel/qwidget.cpp#L8259-L8271

And apparently, focusPrevNextChild() basically does the same thing as pressing
the tab key, to the point that there is some code in Qt Declarative actually
making tab keypresses out of it (which I'm still not sure is related, or maybe
just the cause of #4579):
https://github.com/qt/qtdeclarative/blob/v6.6.1/src/quickwidgets/qquickwidget.cpp#L1415-L1429

Some debugging confirms that this is exactly what happening:

1) We hide the status bar (or prompt) which has keyboard focus
2) Qt focuses the web view, which triggers the Chromium feature (?) scrolling it
   to the very top.
3) Only then, in TabbedBrowser.on_mod_left(), we noticed that the command or
   prompt mode was left, and reassign focus to the web view properly.

In step 2), before this change, Qt happened to focus the tab bar (before we set
the focus manually to the web contents), and thus this didn't happen.
Not sure why it didn't focus the tab bar when we hid the status bar (maybe
because how our widget hierarchy works with TabbedBrowser?).

Python stacktrace of hiding prompt:

    Traceback (most recent call first):
    <built-in method hide of DownloadFilenamePrompt object at remote 0x7fffb8bc65f0>
    File ".../qutebrowser/mainwindow/prompt.py", line 204, in _on_mode_left
        self.show_prompts.emit(None)
    File ".../qutebrowser/keyinput/modeman.py", line 434, in leave
        self.left.emit(mode, self.mode, self._win_id)
    File ".../qutebrowser/keyinput/modeman.py", line 445, in mode_leave
        self.leave(self.mode, 'leave current')

C++ stacktrace, with the focus change presumably being passed of to Chromium
here: https://github.com/qt/qtwebengine/blob/dev/src/core/render_widget_host_view_qt_delegate_client.cpp#L714

    #0  QtWebEngineCore::RenderWidgetHostViewQtDelegateClient::handleFocusEvent(QFocusEvent*) () at /usr/src/debug/qt6-webengine/qtwebengine-everywhere-src-6.6.0/src/core/render_widget_host_view_qt_delegate_client.cpp:708
    #1  QtWebEngineCore::RenderWidgetHostViewQtDelegateClient::handleFocusEvent(QFocusEvent*) () at /usr/src/debug/qt6-webengine/qtwebengine-everywhere-src-6.6.0/src/core/render_widget_host_view_qt_delegate_client.cpp:705
    #2  0x00007fffe5fea70c in QtWebEngineCore::RenderWidgetHostViewQtDelegateClient::forwardEvent(QEvent*) () at /usr/src/debug/qt6-webengine/qtwebengine-everywhere-src-6.6.0/src/core/render_widget_host_view_qt_delegate_client.cpp:300
    #3  0x00007fffe4dd5c79 in QQuickItem::event(QEvent*) (this=0x555556b6cd20, ev=0x7fffffffa320) at /usr/src/debug/qt6-declarative/qtdeclarative-everywhere-src-6.6.0/src/quick/items/qquickitem.cpp:8871
    #4  0x00007ffff1f7318b in QApplicationPrivate::notify_helper(QObject*, QEvent*) (this=<optimized out>, receiver=0x555556b6cd20, e=0x7fffffffa320)
        at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qapplication.cpp:3290
    #5  0x00007ffff295e4a7 in  () at /usr/lib/python3.11/site-packages/PyQt6/QtWidgets.abi3.so
    #6  0x00007ffff59626d8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) (receiver=0x555556b6cd20, event=0x7fffffffa320) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/corelib/kernel/qcoreapplication.cpp:1118
    #7  0x00007ffff596271d in QCoreApplication::sendEvent(QObject*, QEvent*) (receiver=<optimized out>, event=<optimized out>) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/corelib/kernel/qcoreapplication.cpp:1536
    #8  0x00007fffe4f33f15 in QQuickDeliveryAgentPrivate::setFocusInScope(QQuickItem*, QQuickItem*, Qt::FocusReason, QFlags<QQuickDeliveryAgentPrivate::FocusOption>)
        (this=<optimized out>, scope=<optimized out>, item=<optimized out>, reason=<optimized out>, options=...) at /usr/src/debug/qt6-declarative/qtdeclarative-everywhere-src-6.6.0/src/quick/util/qquickdeliveryagent.cpp:439
    #9  0x00007fffe4dd348a in QQuickItem::setFocus(bool, Qt::FocusReason) (this=0x555556b724d0, focus=<optimized out>, reason=Qt::TabFocusReason) at /usr/include/qt6/QtCore/qflags.h:73
    #10 0x00007fffe4e7239b in QQuickWindow::focusInEvent(QFocusEvent*) (this=<optimized out>, ev=<optimized out>) at /usr/src/debug/qt6-declarative/qtdeclarative-everywhere-src-6.6.0/src/quick/items/qquickwindow.cpp:231
    #11 0x00007ffff1fc3a05 in QWidget::event(QEvent*) (this=0x555556457b50, event=0x7fffffffa770) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qwidget.cpp:9111
    #12 0x00007ffff1f7318b in QApplicationPrivate::notify_helper(QObject*, QEvent*) (this=<optimized out>, receiver=0x555556457b50, e=0x7fffffffa770)
        at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qapplication.cpp:3290
    #13 0x00007ffff295e4a7 in  () at /usr/lib/python3.11/site-packages/PyQt6/QtWidgets.abi3.so
    #14 0x00007ffff59626d8 in QCoreApplication::notifyInternal2(QObject*, QEvent*) (receiver=0x555556457b50, event=0x7fffffffa770) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/corelib/kernel/qcoreapplication.cpp:1118
    #15 0x00007ffff596271d in QCoreApplication::sendEvent(QObject*, QEvent*) (receiver=<optimized out>, event=<optimized out>) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/corelib/kernel/qcoreapplication.cpp:1536
    #16 0x00007ffff1f7f1b2 in QApplicationPrivate::setFocusWidget(QWidget*, Qt::FocusReason) (focus=0x555556457b50, reason=<optimized out>) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qapplication.cpp:1538
    #17 0x00007ffff1fca29d in QWidget::setFocus(Qt::FocusReason) (this=0x555556b1ceb0, reason=<optimized out>) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qwidget.cpp:6580
    #18 0x00007ffff1fb4f1b in QWidget::focusNextPrevChild(bool) (this=<optimized out>, next=<optimized out>) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qwidget.cpp:6844
    #19 0x00007ffff298d0ac in  () at /usr/lib/python3.11/site-packages/PyQt6/QtWidgets.abi3.so
    #20 0x00007ffff298d0ac in  () at /usr/lib/python3.11/site-packages/PyQt6/QtWidgets.abi3.so
    #21 0x00007ffff298d0ac in  () at /usr/lib/python3.11/site-packages/PyQt6/QtWidgets.abi3.so
    #22 0x00007ffff1fbdb76 in QWidgetPrivate::hide_helper() (this=this@entry=0x55555646a360) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qwidget.cpp:8271
    #23 0x00007ffff1fbf158 in QWidgetPrivate::setVisible(bool) (this=0x55555646a360, visible=<optimized out>) at /usr/src/debug/qt6-base/qtbase-everywhere-src-6.6.0/src/widgets/kernel/qwidget.cpp:8447
    [...]

We fix this problem by explicitly handling focus before hiding the UI elements.
This is done with a new TabbedBrowser.on_release_focus() slot, which is bound to
signals emitted just before things are hidden: The existing Command.hide_cmd()
for the status bar, and a new release_focus() signal for prompts.

Additionally, we make sure to not double-handle hiding in the statusbar
code when it's already handled separately for comamnd mode.

Unfortunately, no tests for this, as application window focus is required to
reproduce the issue. In theory, a test in scroll.feature could be added though,
which loads simple.html, scrolls down, shows/hides a prompt or the status bar,
and then checks the vertical scroll position is != 0.

Fixes #2236
Fixes #7885
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