Application: kcmshell5 (5.21.5)

Qt Version: 5.15.2
Frameworks Version: 5.86.0
Operating System: Linux 5.14.0-2-amd64 x86_64
Windowing System: X11
Distribution: Debian GNU/Linux bookworm/sid
DrKonqi: 5.23.0 [KCrashBackend]

-- Information about the crash:
- What I was doing when the application crashed:

When attempting to open the window decorations system settings module either via the normal system setttings application or via `kcmshell kwindecoration`, the application instantly crashes. Other settings tabs in the system settings application work without issues.

- Unusual behavior I noticed:

My whole plasma desktop installation is broken after updating debian (testing) packages. The desktop fails to start after the login splash screen and remains black. Opening ksysguard via the `Ctrl-Esc` key combinations works and from there a shell can be opened via the tools menu. Attempting to start the plasma desktop via `startplasma-x11` fails and does not bring up the desktop either. Manually starting the plasma shell via the `plasmashell` command does work and shows the toolbar and desktop widgets. Window titlebars/decorations are missing and attempting to start `kwin` fails with a segmentation fault.
The crash of the window decoration system settings module is very likely related to this, but ideally it should show an error message instead of crashing and burning.

The crash can be reproduced every time.

-- Backtrace:
Application: System Settings Module (kcmshell5), signal: Segmentation fault
Content of s_kcrashErrorMessage: std::unique_ptr<char []> = {get() = 0x0}
[KCrash Handler]
#6  0x00007f1f48c2dd00 in typeinfo for QMetaCallEvent () from /usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#7  0x00007f1f4040e513 in KDecoration2::DecorationSettings::font (this=this@entry=0x55ec05130720) at /usr/include/c++/11/bits/unique_ptr.h:173
#8  0x00007f1f4040e737 in operator() (__closure=<synthetic pointer>) at ./src/decorationsettings.cpp:19
#9  KDecoration2::DecorationSettings::DecorationSettings (this=0x55ec05130720, bridge=0x55ec04f48620, parent=<optimized out>) at ./src/decorationsettings.cpp:34
#10 0x00007f1f393f679b in QSharedPointer<KDecoration2::DecorationSettings>::create<KDecoration2::Preview::PreviewBridge*> () at /usr/include/c++/10/new:175
#11 KDecoration2::Preview::Settings::createSettings (this=0x55ec04f1e720) at ./kcmkwin/kwindecoration/declarative-plugin/previewsettings.cpp:237
#12 0x00007f1f489ca977 in QtPrivate::QSlotObjectBase::call (a=0x7fff323c7800, r=0x55ec04f1e720, this=0x55ec04f1b5a0) at ../../include/QtCore/../../src/corelib/kernel/qobjectdefs_impl.h:398
#13 doActivate<false> (sender=0x55ec04f1e720, signal_index=3, argv=0x7fff323c7800) at kernel/qobject.cpp:3886
#14 0x00007f1f47a56d4f in QQmlPropertyData::writeProperty (flags=..., value=0x7fff323c7868, target=<optimized out>, this=<optimized out>) at ../../include/QtQml/5.15.2/QtQml/private/../../../../../src/qml/qml/qqmlpropertydata_p.h:375
#15 QObjectPointerBinding::write (this=0x55ec05001c30, result=..., isUndefined=<optimized out>, flags=...) at qml/qqmlbinding.cpp:739
#16 0x00007f1f47a5848e in QQmlNonbindingBinding::doUpdate (this=0x55ec05001c30, watcher=..., flags=..., scope=...) at qml/qqmlbinding.cpp:258
#17 0x00007f1f47a56144 in QQmlBinding::update (this=0x55ec05001c30, flags=...) at qml/qqmlbinding.cpp:194
#18 0x00007f1f47a627e3 in QQmlObjectCreator::finalize (this=0x55ec04e33f40, interrupt=...) at qml/qqmlobjectcreator.cpp:1394
#19 0x00007f1f479fd69c in QQmlIncubatorPrivate::incubate (this=0x55ec04d52390, i=...) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qscopedpointer.h:116
#20 0x00007f1f479fdc27 in QQmlEnginePrivate::incubate (this=this@entry=0x55ec04dfe230, i=..., forContext=forContext@entry=0x55ec04dee3f0) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qshareddata.h:160
#21 0x00007f1f479f8c52 in QQmlComponent::create (this=<optimized out>, incubator=..., context=<optimized out>, forContext=forContext@entry=0x0) at qml/qqmlcomponent.cpp:1178
#22 0x00007f1f482155be in KDeclarative::QmlObject::completeInitialization (initialProperties=..., this=0x55ec04d5c3e0) at ./src/kdeclarative/qmlobject.cpp:307
#23 KDeclarative::QmlObject::completeInitialization (this=0x55ec04d5c3e0, initialProperties=...) at ./src/kdeclarative/qmlobject.cpp:289
#24 0x00007f1f49e57d44 in KQuickAddons::ConfigModule::mainUi (this=this@entry=0x55ec04d5c460) at ./src/quickaddons/configmodule.cpp:178
#25 0x00007f1f49ebd61c in KCModuleLoader::loadModule (mod=..., report=report@entry=KCModuleLoader::Inline, parent=0x55ec04df2f80, args=...) at ./src/kcmoduleloader.cpp:98
#26 0x00007f1f49ec8c35 in KCModuleProxyPrivate::loadModule (this=this@entry=0x55ec04d47390) at ./src/kcmoduleproxy.cpp:117
#27 0x00007f1f49ec9888 in KCModuleProxy::realModule (this=this@entry=0x55ec04df2f80) at ./src/kcmoduleproxy.cpp:59
#28 0x00007f1f49ec6a8a in KCMultiDialog::addModule (this=0x7f1f3400c130, moduleInfo=..., parentItem=0x0, args=...) at ./src/kcmultidialog.cpp:583
#29 0x000055ec042d1994 in main (_argc=<optimized out>, _argv=0x7fff323c8230) at ./kcmshell/main.cpp:307
[Inferior 1 (process 19707) detached]

Possible duplicates by query: bug 430007, bug 423234, bug 421299, bug 419428, bug 419389.

Reported using DrKonqi