lxqt-panel crashes on startup if statusnotifier is enabled (possibly related to Qt 5.10-beta3)

[berolinux]

lxqt-panel crashes on startup -- I didn't get to debug this a lot yet, so I'm not sure whether or not this is related to the fact that I'm using Qt 5.10-beta3 (current Plasma works fine with that version of Qt, but that doesn't necessarily mean it's bug-free).

Error messages and backtrace:
(0x7fffffffd530) Warning: QObject::connect: signal not found in LXQt::Settings
(0x7fffffffd530) Warning: QObject::connect: signal not found in GlobalKeyShortcut::Action
(0x7fffffffd530) Warning: QObject::connect: signal not found in GlobalKeyShortcut::Action
(0x7fffffffd530) Warning: QObject::connect: signal not found in LXQt::Settings
(0x7fffffffd530) Warning: QObject::connect: signal not found in LXQt::Settings
(0x7fffffffd530) Warning: QFSFileEngine::open: No file name specified
(0x7fffffffd530) Debug: XdgDesktopFile "/usr/share/applications/qupzilla.desktop" is not valid
(0x7fffffffd530) Warning: QFSFileEngine::open: No file name specified
(0x7fffffffd530) Debug: XdgDesktopFile "/usr/share/applications/openmandriva-drakconf.desktop" is not valid
(0x7fffffffd530) Warning: QObject::connect: signal not found in LXQt::Settings
(0x7fffffffd530) Warning: QObject::connect: signal not found in LXQt::Settings
(0x7fffffffd530) Warning: QObject::connect: signal not found in LXQt::Settings

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7aac6f8 in QLayout::setEnabled(bool) ()
from /usr/lib64/libQt5Widgets.so.5
(gdb) bt
#0 0x00007ffff7aac6f8 in QLayout::setEnabled(bool) ()
from /usr/lib64/libQt5Widgets.so.5
#1 0x0000000000495bac in StatusNotifierWidget::realign() ()
#2 0x000000000049553c in StatusNotifierWidget::StatusNotifierWidget(ILXQtPanelPlugin*, QWidget*) ()
#3 0x000000000048f607 in StatusNotifier::StatusNotifier(ILXQtPanelPluginStartupInfo const&) ()
#4 0x00000000004b6f95 in ?? ()
#5 0x00000000004b6fe6 in ?? ()
#6 0x000000000045c1ff in Plugin::loadLib(ILXQtPanelPluginLibrary const*) ()
#7 0x000000000045b3a5 in Plugin::Plugin(LXQt::PluginInfo const&, LXQt::Settings*, QString const&, LXQtPanel*) ()
#8 0x000000000044de5c in PanelPluginsModel::loadPlugin(LXQt::PluginInfo const&, QString const&) ()
#9 0x000000000044d92c in PanelPluginsModel::loadPlugins(QStringList const&) ()
#10 0x000000000044cf34 in PanelPluginsModel::PanelPluginsModel(LXQtPanel*, QString const&, QStringList const&, QObject*) ()
#11 0x000000000045252c in LXQtPanel::loadPlugins() ()
#12 0x00000000004510ec in LXQtPanel::LXQtPanel(QString const&, LXQt::Settings*, QWidget*) ()
#13 0x000000000045814e in LXQtPanelApplication::addPanel(QString const&) ()
#14 0x0000000000457873 in LXQtPanelApplication::LXQtPanelApplication(int&, char**) ()
#15 0x000000000044cea4 in main ()

System Information

• Distribution & Version: OpenMandriva cooker snapshot
• Kernel: 4.13.11
• Qt Version: 5.10-beta3
• liblxqt Version: 0.12.0
• Package version: 0.12.0

[berolinux]

It's definitely related to the statusnotifier plugin -- everything works as expected (minus the statusnotifier, obviously) if I rm /usr/share/lxqt/lxqt-panel/statusnotifier.desktop

[tsujan]

I'm not sure whether or not this is related to the fact that I'm using Qt 5.10-beta3

Did you recompile everything against Qt 5.10-beta3?

[berolinux]

Looking at it a bit more, this is a really odd issue:
In StatusNotifierWidget::realign(), qobject_cast<LXQt::GridLayout*>(this->layout()) returns a null pointer. If I replace qobject_cast with reinterpret_cast (yes, not exactly a nice thing to do...), everything works as expected.

I did recompile everything against 5.10-beta3.

[berolinux]

Crude but effective workaround

lxqt-panel-0.12.0-workaround-statusnotifier-crash.patch.txt

[tsujan]

If I replace qobject_cast with reinterpret_cast (yes, not exactly a nice thing to do...), everything works as expected.

Maybe the beta version of Qt isn't ready for use yet. We have to wait until a stable Qt 5.10 comes out.

[berolinux]

This does look like a bug in qobject_cast -- but that makes it surprising that Plasma seems to work without issues using the same Qt

[tsujan]

If it is a bug and if it persists in the stable version, it'll give us a headache again. We can't do anything until a stable Qt is released.

[yan12125]

Got Qt 5.10.0 beta 4 from Arch's packages. Running lxqt-panel (which is built against Qt 5.9.2) looks fine. statusnotifier passes smoke test, too.

I may try to rebuild the whole LXQt with 5.10.0 beta 4 and see if there's a difference.

[tsujan]

Definitely not the case with stable Qt5.10.