For some reason the 'Open With' dialog opened by KMail triggers the
following crash for me:
#0 0x0000555568ea4220 in ?? ()
#1 0x00007ffff549bd60 in QObject::connect(QObject const*, char const*, QObject const*, char const*, Qt::ConnectionType) () from /usr/lib/libQt5Core.so.5
#2 0x00007ffff71287f4 in KLineEdit::setCompletionObject (this=0x555568ee8c00, comp=0x555568ea1320, handle=<optimized out>)
at /home/milian/projects/kf5/src/frameworks/kcompletion/src/klineedit.cpp:1514
#3 0x00007ffff7113d35 in KComboBox::setLineEdit (this=0x555568ea3ba0, edit=0x555568ee8c00) at /home/milian/projects/kf5/src/frameworks/kcompletion/src/kcombobox.cpp:325
#4 0x00007ffff784ef63 in KOpenWithDialogPrivate::init (this=0x7fff70240440,
_text="<qt>Select the program you want to use to open the file<br/>DebuggingProfilingWindows-2017-WK50.pdf</qt>", _value="")
at /home/milian/projects/kf5/src/frameworks/kio/src/widgets/kopenwithdialog.cpp:601
#5 0x00007ffff784f93c in KOpenWithDialog::KOpenWithDialog (this=0x7fffffffba50, _urls=QList<QUrl> = {...}, _text=..., _value="", parent=<optimized out>)
at /home/milian/projects/kf5/src/frameworks/kio/src/widgets/kopenwithdialog.cpp:531
#6 0x00007ffff7862b51 in KRun::displayOpenWithDialog (lst=QList<QUrl> = {...}, window=0x55555599a690, tempFiles=tempFiles@entry=true, suggestedFileName="",
asn=<QArrayData::shared_null+24> "") at /home/milian/projects/kf5/src/frameworks/kio/src/widgets/krun.cpp:267
Guard against it by using a QPointer to check whether the completion
object gets destroyed before we want to use it again.
Sadly WebEngine in KMail prevents me from using Valgrind, so I have
not yet figured out where exactly the deletion is coming from. That
said, this fix should make this working again with minimal impact.