Explicitly handle focus before hiding UI elements #8024
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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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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)
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:
to the very top.
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:
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
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