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Manpage #8

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The-Compiler opened this issue Oct 1, 2014 · 0 comments
Closed

Manpage #8

The-Compiler opened this issue Oct 1, 2014 · 0 comments
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@The-Compiler
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component: docs Issues related to the documentation. good first issue Issues which are likely to be a good fit for first-time contributors.
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v0.1

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@The-Compiler
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The manpage probably needs some love (and reviewing according to manpage standards) before v0.1
@The-Compiler The-Compiler added enhancement component: docs Issues related to the documentation. labels Oct 1, 2014
@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 The-Compiler added the good first issue Issues which are likely to be a good fit for first-time contributors. label Oct 1, 2014
The-Compiler pushed a commit that referenced this issue Apr 9, 2015
@nicoddemus
Moving logging and QApplication to conftest
751b62e 
As discussed in #8
@yantar92 yantar92 mentioned this issue Jan 31, 2017
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This was referenced May 24, 2018
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@toshism toshism mentioned this issue Aug 25, 2020
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The-Compiler added a commit that referenced this issue Mar 29, 2021
@The-Compiler
Revert "ipc: Remove _old_socket handling"
85f17ca 
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
@The-Compiler
Revert "ipc: Remove _old_socket handling"
6fe5414 
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
@franzhuang franzhuang mentioned this issue Oct 6, 2021
Closed
The-Compiler added a commit that referenced this issue Dec 6, 2022
@The-Compiler
Use a proper @pyqtSlot for FilenamePrompt
7b90fd3 
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...
Closed
The-Compiler added a commit that referenced this issue Dec 7, 2023
@The-Compiler
Explicitly handle focus before hiding UI elements
7593d01 
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
@The-Compiler
Explicitly handle focus before hiding UI elements
6aa19eb 
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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