Theme is broken on several tabs of systemsettings5

[y-usuzumi]

Describe the bug
On the Plasma 5 desktop, theme is broken on several tabs of systemsettings5. This happens on both plasma desktop 5.16.5 and 5.17.5

To Reproduce
Steps to reproduce the behavior:

1. Launch System settings
2. Switch to the "Display and Monitor" tab
3. Notice the broken theme:

Expected behavior
Theme should work properly

Additional context
If run from the terminal, the following log is displayed when switching the tab:

org.kde.kcoreaddons: Error loading plugin "kcm_kscreen" "The shared library was not found." 
Plugin search paths are ("/nix/store/dkm6jsa0apc7vlpdkslpvsxw1qr7kxh2-python3-3.7.6/lib/qt-5.12.6/plugins", "/run/wrappers/lib/qt-5.12.6/plugins", "/home/kj/.nix-profile/lib/qt-5.12.6/plugins", "/etc/profiles/per-user/kj/lib/qt-5.12.6/plugins", "/nix/var/nix/profiles/default/lib/qt-5.12.6/plugins", "/run/current-system/sw/lib/qt-5.12.6/plugins", "/nix/store/p4vbc0aqsj22f38fniixm0mc9binmal6-systemsettings-5.17.5-bin/lib/qt-5.12.6/plugins", "/nix/store/5h2d5lmhxy4b5ad6h41y8gxa5rd20q4a-plasma-workspace-5.17.5/lib/qt-5.12.6/plugins", "/nix/store/pwkk4w00kvddfyzdv9g0z0531mjv6ddj-qtlocation-5.12.6-bin/lib/qt-5.12.6/plugins", "/nix/store/kwxxwfd3vyz9aw16wyi031ll776rr7hx-libkscreen-5.17.5/lib/qt-5.12.6/plugins", "/nix/store/n1xfvr02f5l81gjap4v51jqc7dc7y8jp-kwin-5.17.5-bin/lib/qt-5.12.6/plugins", "/nix/store/rpy458gzc6rpgszwi1hpinsrv3yr3p6f-breeze-qt5-5.17.5-bin/lib/qt-5.12.6/plugins", "/nix/store/9rm257fgzpb5nhf2swhqvmh15yb4zbg1-frameworkintegration-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/3kfyqzz0chffhrlfcd3z0y03624z57aa-qtsensors-5.12.6-bin/lib/qt-5.12.6/plugins", "/nix/store/sprs2s1m8xgqf4kspl5pnwmfxf3ll0mw-ktexteditor-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/28chnah4xmkb1j9mb8b6m0cpl65qdys7-kscreenlocker-5.17.5/lib/qt-5.12.6/plugins", "/nix/store/jqnydkyplv1s0l7sqavh6qk3g3ay5lpn-plasma-framework-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/wkfp1h7xja24gw5y71ixmsj0y7zq1vic-kdelibs4support-5.66.0/lib/qt-5.12.6/plugins", "/nix/store/94wk9psqhasi9wysh96abdxnqhq08bzc-kemoticons-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/fhi739yhv9bapk09a071pi2gips3x6vy-kplotting-5.66.0/lib/qt-5.12.6/plugins", "/nix/store/462sx9hz9bij1piwbdqbj04fiaz43sw9-baloo-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/krphqcq0dv1h9psa4qwgr0lbxy6r19k3-kidletime-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/b8jwp7i8hrbdkrzd95cnv7vm0w4h3rk1-kfilemetadata-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/17j1xi89yz969vq0nh58w7xzfjdp3l64-qtmultimedia-5.12.6-bin/lib/qt-5.12.6/plugins", "/nix/store/vpclqcmcwsgxwsw2nj4d779xqva6i6i2-khtml-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/0yh5jm2488m40b4r4iwdvmgwdc05dnsq-kio-5.66.0/lib/qt-5.12.6/plugins", "/nix/store/z2l2h5idnn45ybbmpkgbnqy43jai0ni2-phonon-4.11.1/lib/qt-5.12.6/plugins", "/nix/store/25acay6sf1nc7dcal25gb9pqr9d3rp3z-kxmlgui-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/sgpsgpwkzkz61rcc5f5jlrjdy3fa37hi-ktextwidgets-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/i4kb53jjn7g1a9cbs96944mfw75igyra-kcompletion-5.66.0/lib/qt-5.12.6/plugins", "/nix/store/gjhx2ng2ggsw9lbihk59l2ynvr1b8q14-sonnet-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/zwx96j7gllhckvran7ab2fqcdxn96fv4-kiconthemes-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/6m98b8nkyvcy19i1jmzha3rf45s65wnh-kitemviews-5.66.0/lib/qt-5.12.6/plugins", "/nix/store/3vqwlbm2wl90vy91ky11wnvdmzabbv6r-kglobalaccel-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/xchw8xyppk5q750kfbaic52zq6d5ll1g-kwindowsystem-5.66.0/lib/qt-5.12.6/plugins", "/nix/store/zcnjc2dybpkdhiskgmspyk2ajd89asax-kguiaddons-5.66.0/lib/qt-5.12.6/plugins", "/nix/store/4pcp8z5hfdhs46gf1si5wpiqshxg86wb-kwidgetsaddons-5.66.0/lib/qt-5.12.6/plugins", "/nix/store/1v8ja8988gk5p5m91nnyi27pc622521z-kauth-5.66.0/lib/qt-5.12.6/plugins", "/nix/store/09v7c5gn755varmy8nm5vi1r556dkpyk-kconfigwidgets-5.66.0-dev/lib/qt-5.12.6/plugins", "/nix/store/gsrc9z7jls62kgwhyh0xxdvlb30bsysf-ki18n-5.66.0-bin/lib/qt-5.12.6/plugins", "/nix/store/pfsm8mmw5vi2b7xfavlkawl9yqal71ak-qtwayland-5.12.6-bin/lib/qt-5.12.6/plugins", "/nix/store/rp9zgzm1s5bw8545mhyihmksaxc9zfyv-qtdeclarative-5.12.6-bin/lib/qt-5.12.6/plugins", "/nix/store/55arwwspz5sjx2qc65wy66i6kkazrd74-qtsvg-5.12.6-bin/lib/qt-5.12.6/plugins", "/nix/store/6vypqvbkj9jwf4lrjmgm3p8s2xn4addp-qtbase-5.12.6-bin/lib/qt-5.12.6/plugins", "/nix/store/gbbgnr20a3wia424qrd5rrp6630pn75k-fcitx-with-plugins-4.2.9.6/lib/qt4/plugins", "/nix/store/p4vbc0aqsj22f38fniixm0mc9binmal6-systemsettings-5.17.5-bin/bin") 
The environment variable QT_PLUGIN_PATH might be not correctly set
QQmlEngine::setContextForObject(): Object already has a QQmlContext
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/Screen.qml:50: TypeError: Value is null and could not be converted to an object
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/main.qml:28: ReferenceError: units is not defined
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/main.qml:27: ReferenceError: units is not defined
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/Screen.qml:48: ReferenceError: units is not defined
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/Screen.qml:59: ReferenceError: units is not defined
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/Screen.qml:57: ReferenceError: units is not defined
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/main.qml:116: ReferenceError: units is not defined
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/main.qml:116: ReferenceError: units is not defined
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/Screen.qml:48: ReferenceError: units is not defined
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/main.qml:116: ReferenceError: units is not defined
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/OutputPanel.qml:93:12: QML RotationButton: Binding loop detected for property "height"
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/OutputPanel.qml:90:12: QML RotationButton: Binding loop detected for property "height"
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/OutputPanel.qml:87:12: QML RotationButton: Binding loop detected for property "height"
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/OutputPanel.qml:84:12: QML RotationButton: Binding loop detected for property "height"
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/Output.qml:80: ReferenceError: units is not defined
file:///nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/share/kpackage/kcms/kcm_kscreen/contents/ui/Output.qml:90: ReferenceError: units is not defined

Metadata

[root@DCHORUS-LEGION-NIXOS:~]# nix-shell -p nix-info --run "nix-info -m"
 - system: `"x86_64-linux"`
 - host os: `Linux 5.4.17, NixOS, 20.03pre212208.8130f3c1c2b (Markhor)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.3.2`
 - channels(root): `"nixos-20.03pre212208.8130f3c1c2b"`
 - channels(kj): `""`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

[peterhoeg]

It's because the proper theme is not selected for the qtquickcontrol2 parts of settings. The same problem applies to all the kirigami based applications (discover as an example).

The workaround:

QT_QUICK_CONTROLS_STYLE=org.kde.desktop systemsettings5

However, when I do this some parts of the settings application will segfault.

You can also pick another theme from this list - https://doc.qt.io/qt-5/qtquickcontrols2-styles.html

imagine looks decent:

QT_QUICK_CONTROLS_STYLE=imagine systemsettings5

But in any case, it's a problem that plasma doesn't set this correctly and of course that we get segfaults when using the proper theme.

Cc: @ttuegel

[peterhoeg]

What you are seeing is technically not a broken theme. It's the default qtquickcontrols2 theme.

[eliasp]

Switching to another style didn't really help here - KCMs are still utterly broken (e.g. display KCM doesn't load the QML for positioning the displays).

According to nix-env -q, I have 0 pkgs in my environment, so nothing there should mess with me here...

Seeing The environment variable QT_PLUGIN_PATH might be not correctly set reminds me quite a bit of #27050
My $QT_PLUGIN_PATH contains 138 items - I wonder whether we're hitting some limit here which might cause this?

[eliasp]

There are a few things which strike me as weird...
kcmshell5 kscreen complains about not being able to find kcm_kscreen.so and hints at a probably misconfigured $QT_PLUGIN_PATH environment variable, but the paths displayed after the error message don't seem to originate from the values in $QT_PLUGIN_PATH.

kcmshell5 kscreen seems to be right, that none of the printed paths contains kcm_kscreen.so:

$ kcmshell5 kscreen 1>/dev/null 2>&1 | grep 'Plugin search paths are' | cut -d\( -f2 | cut -d\) -f1 | sed -e 's|, |\n|g' | sed -e 's|^"||g' -e 's|"$||g' | xargs -I {} find {}/ -type f -name kcm_kscreen.so
find: ‘/run/wrappers/lib/qt-5.12.6/plugins/’: No such file or directory
find: ‘/home/eliasp/.nix-profile/lib/qt-5.12.6/plugins/’: No such file or directory
find: ‘/etc/profiles/per-user/eliasp/lib/qt-5.12.6/plugins/’: No such file or directory
find: ‘/nix/var/nix/profiles/default/lib/qt-5.12.6/plugins/’: No such file or directory

The same goes for $QT_PLUGIN_PATH - none of the entries seems to provide kcm_kscreen.so:

$ echo $QT_PLUGIN_PATH | sed 's|:|\n|g' | sort | xargs -I {} find {}/ -type f -name kcm_kscreen.so
find: ‘/etc/profiles/per-user/eliasp/lib/kde4/plugins/’: No such file or directory
find: ‘/etc/profiles/per-user/eliasp/lib/qt4/plugins/’: No such file or directory
find: ‘/home/eliasp/.nix-profile/lib/kde4/plugins/’: No such file or directory
find: ‘/home/eliasp/.nix-profile/lib/qt4/plugins/’: No such file or directory
find: ‘/nix/var/nix/profiles/default/lib/kde4/plugins/’: No such file or directory
find: ‘/nix/var/nix/profiles/default/lib/qt4/plugins/’: No such file or directory
find: ‘/run/current-system/sw/lib/kde4/plugins/’: No such file or directory
find: ‘/run/current-system/sw/lib/qt4/plugins/’: No such file or directory

Looking at /nix/store, the following possible matches are currently present:

find /nix/store/*-kscreen-*/lib/qt-*/plugins/ -type f -name kcm_kscreen.so  
/nix/store/17iyjhqrgxq63wmzz76vp9q3b9x2lg3p-kscreen-5.16.5/lib/qt-5.12.6/plugins/kcm_kscreen.so
/nix/store/24vyflvrgxi5h5mxlbgcncskmanj1381-kscreen-5.16.5/lib/qt-5.12.6/plugins/kcm_kscreen.so
/nix/store/2jp445v9xr214wgb3rjh4ix1xmy2ysr3-kscreen-5.16.5/lib/qt-5.12.6/plugins/kcm_kscreen.so
/nix/store/53w8y9xj5rvlz9rq5hmlh9alqdcgi69w-kscreen-5.14.5/lib/qt-5.12/plugins/kcm_kscreen.so
/nix/store/5m7zscnx24777xzj9zi26q4pfgplrxhi-kscreen-5.16.5/lib/qt-5.12.3/plugins/kcm_kscreen.so
/nix/store/8a3mwspiivlb6w08srjj4l4517m74f6g-kscreen-5.16.5/lib/qt-5.12.6/plugins/kcm_kscreen.so
/nix/store/djyvdkqxnj8j044lnnwvcixq15qb44k5-kscreen-5.17.5/lib/qt-5.12.6/plugins/kcms/kcm_kscreen.so
/nix/store/f5n1ybbzjrnllfiv8rvmr4z884znxkra-kscreen-5.16.5/lib/qt-5.12.6/plugins/kcm_kscreen.so
/nix/store/i7gilrkxnvmp7g0njg8bv5g9w2g6yic5-kscreen-5.14.5/lib/qt-5.12/plugins/kcm_kscreen.so
/nix/store/k7q9g6l0qd13dbqa0h35ffmwfg11apg2-kscreen-5.16.5/lib/qt-5.12.5/plugins/kcm_kscreen.so
/nix/store/nplwcwlgiw0dmh70qvakqcghvkis1nh4-kscreen-5.14.5/lib/qt-5.12/plugins/kcm_kscreen.so
/nix/store/rlm403l4qnb2y4cwfrnjvcvyga2vy5w6-kscreen-5.16.5/lib/qt-5.12.6/plugins/kcm_kscreen.so
/nix/store/wcixgs1y0xkap5am9k47jq1zjv2bqqnr-kscreen-5.16.5/lib/qt-5.12.5/plugins/kcm_kscreen.so
/nix/store/xw2avh713pa6gxpfpz4mhq8sgid5cylf-kscreen-5.14.5/lib/qt-5.12/plugins/kcm_kscreen.so
/nix/store/y34p9zp8q677qs5n26y9ax0kxba20ypj-kscreen-5.16.5/lib/qt-5.12.6/plugins/kcm_kscreen.so
/nix/store/y97p4yqkxyyc0yqlc1n2cpwcw22z4n0h-kscreen-5.14.5/lib/qt-5.12/plugins/kcm_kscreen.so

• Where do the outdated paths in kcmshell5 and $QT_PLUGIN_PATH come from? Some of those don't even exist and nothing in my user's profile seems to add them!
• Why is there a mismatch between the path built-in to kcmshell5 and $QT_PLUGIN_PATH?

[eliasp]

…and it looks like we're actually dealing with 2 separate issues here and you were right @peterhoeg - trying to inject a correct path into QT_PLUGIN_PATHS silences the error msgs about not being able to find kcm_kscreen.so, but the rendering issues persist:

QT_PLUGIN_PATH=$(dirname $(nix eval --raw nixpkgs.kscreen)/lib/qt-5*/plugins/kcms/kcm_kscreen.so):${QT_PLUGIN_PATH} kcmshell5 kscreen

[ttuegel]

But in any case, it's a problem that plasma doesn't set this correctly and of course that we get segfaults when using the proper theme.

@peterhoeg Do you have any idea how Plasma is supposed to set this? I don't see reference to QT_QUICK_CONTROLS_STYLE in any obvious place. The segfault with the theme set is likely due to some plugin mismatch.

[ttuegel]

The segfault with the theme set is likely due to some plugin mismatch.

This part is easy: we haven't actually packaged kdeFrameworks.qqc2-desktop-style, as required by plasma-desktop and others!

[peterhoeg]

It looks like we have 3 issues:

1. systemsettings crashes due to missing plugins, ie: incorrect QT_PLUGIN_PATH

2. entries in QT_PLUGIN_PATH are duplicated

$ echo $QT_PLUGIN_PATH | tr ':' "\n" | wc -l
90

$ echo $QT_PLUGIN_PATH | tr ':' "\n" | sort -u | wc -l
49

3. qqc2-desktop is not packaged (and used) to provide default look and feel of qtquick2 components: https://www.archlinux.org/packages/extra/x86_64/qqc2-desktop-style/ But despite showing on the arch package as being a dependency of plasma-integration, our plasma-integration package doesn't use it for anything. See the wip pr.

[peterhoeg]

Cherry-picking the commit from #80521 and setting QT_QUICK_CONTROLS_STYLE=Plasma makes it work for me.

Why we have to set that variable, I cannot say. If somebody else can confirm that it fixes it for them, we can fix the nixos module as a workaround.

[peterhoeg]

Are you sure it's #80521? Looks completely unrelated to me.

#80521 is indeed the right one.

[schmittlauch]

@peterhoeg At a quick glance it looks like #80521 hasn't yet been backported to stable. Are there still plans to do so?

[peterhoeg]

Backported - I guess we can close this now.

[solson]

How are we supposed to get the fix? For me (on nixos-unstable), it still looks like the widgets in the original post:

With a manually-specified QT_QUICK_CONTROLS_STYLE=Plasma it applies a native widget look, but it's broken in a different way (see "Orientation"):

Am I missing something, or can we reopen this issue?

[eliasp]

Am I missing something, or can we reopen this issue?

Same for me - re-opening for now.

[peterhoeg]

Are you guys still seeing this? The only time I've seen anything remotely similar over these last few months, is in case of nixos-rebuild switch where plasma or qt versions have been changed. A reboot/logout always solved it.

[WizardUli]

Are you guys still seeing this? The only time I've seen anything remotely similar over these last few months, is in case of nixos-rebuild switch where plasma or qt versions have been changed. A reboot/logout always solved it.

Its still there and always has been since I've started using NixOS a ~month ago but I'm on nixos stable 20.09.

[solson]

This appears to be totally fixed for me on nixos-unstable:

I'll close the issue for now — please speak up if the issue still affects you on the latest nixos-unstable. Presumably, the fix should hit the next stable release in March, as well.

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/kde-widgets-look-off-on-a-freshly-installed-nixos/13098/2

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/who-uses-nixos-with-kde/18212/41