How to launch .desktop files properly?

[Lubos Lunak]

 Hello,

 specifically in this case, how should ksmserver properly launch autostart 
apps, when they are specified by their .desktop files?

 When the autostart launching code was moved from klauncher to ksmserver by 
[1], it replaced the launching by simply using QProcess, which caused a 
number of problems such as not parsing the Exec line properly (fixed by [2]), 
ksmserver discarded all stderr of launched apps instead of them going to 
~/.xsession-errors, and launched apps getting killed by SIGPIPE under 
specific circumstances. I got bitten by these and simply fixed it with [3] by 
using KRun::runApplication(), as AFAIK that is the proper way to launch 
something using a .desktop file. Seeing that others had these problems as 
well (the bugreports mentioned in the commit message for [3]), I backported 
it after some time. And, after 5.9.5 got out, bug #379254 ([4]) has been 
reported, about desktop startup taking too long. It turns out that some 
distros ship broken autostart .desktop files, KRun shows a blocking error 
dialog (under ksplash) and that blocks the whole startup. To make this even 
worse, it's not very obvious why the error shows up, and even if it were, 
kcm_autostart actually completely ignores global autostart files.

 Now, does somebody know how this should be done properly? QProcess has poor 
defaults for fire-and-forget launching of apps (bye-bye stderr, hello 
SIGPIPE). KProcess is better, but there's still a lot of what KRun/klauncher 
do that would need to be copy&pasted: All the .desktop file parsing and 
KProcess setting up, kdeinit, KAuthorized, X-KDE-RunOnDiscreteGpu. Not that I 
know if all of this matters much nowadays, but if it wasn't needed, then why 
KRun still does it, and one way or another all the manual setup would be 
lame. I've also looked at KToolInvocation::startServiceByDesktopPath(), which 
talks to klauncher directly, but there I'm not sure what the status with 
klauncher is (I mean, if the autostart code hadn't been moved, there wouldn't 
be any of this), and also while the function is technically not deprecated, 
its documentation has @deprecated suggesting to use QProcess (ugh) or KRun.

 So I guess that leaves KRun and just making sure it optionally doesn't show 
the blocking dialog, such as adding "QString* error = nullptr"? Or does 
somebody have a better idea? And if not, is it ok to just commit this change 
to kio repository, or are there nowadays any special rules for library 
commits now that there are zillion git repos?


[1] 
https://cgit.kde.org/plasma-workspace.git/commit/ksmserver?id=d9883511c92e448b3441d994170fa1d43eea4ff2
[2] 
https://cgit.kde.org/plasma-workspace.git/commit/ksmserver?id=889be45e893425273d545a73edc42c4bbead446d
[3] 
https://cgit.kde.org/plasma-workspace.git/commit/ksmserver?id=0377d6a992725e0b0b469b87d17343fa3730b829
[4] https://bugs.kde.org/show_bug.cgi?id=379254

-- 
 Lubos Lunak