cc @joachifm

Thank you but I've decided against doing this: see e.g., #31470 (comment) and #32642 (comment)

@joachifm the comments claim that this is not a problem one NixOS. However, I am running NixOS, did install the package using nix-env, and still I see this problem unless I correct it as I am doing in this patch. Clearly there's something else wrong.

Grepping for QT_QPA_PLATFORM_PLUGIN_PATH in nixpkgs suggests a couple other packages doing this as well.

cc @ttuegel

Grepping for QT_QPA_PLATFORM_PLUGIN_PATH in nixpkgs suggests a couple other packages doing this as well.

I see, but note that many anti-patterns propagate via copy-n-paste. I'll defer to the qt maintainers on this one.

Grepping for QT_QPA_PLATFORM_PLUGIN_PATH in nixpkgs suggests a couple other packages doing this as well.

Please don't do this; the result will be an application that may work under some desktop environments but not others.

Clearly there's something else wrong.

To begin with: What version of NixOS are you running? What version of Qt is installed in your system profile? What version of Qt is installed in your user profile?

@ttuegel @joachifm thanks. I am running NixOS 17.09. I have KDE Plasma 5 as my desktop environment installed in my system profile, and that's about as much QT I have installed explicitly. Do I need to install something else?

@ttuegel: Sorry to piggyback on this, but I have the same problem with Krita, where I can't run it on Travis CI (required for build to convert .kra files to .png) without setting QT_QPA_PLATFORM_PLUGIN_PATH in a wrapper: https://github.com/yegortimoshenko/zhenya-slim-theme/blob/8c3f85a394024398767ad1d09fff29ae21084d05/default.nix

I would really like to drop it from the build system and move it into Nixpkgs. It can be reproduced on any Linux machine that has Nix installed: nix-shell -p krita --pure --run krita. I get:

This application failed to start because it could not find or load the Qt platform plugin "xcb"
in "".

What is the current way around this? Setting it in shellHook? Can it be fixed for all Qt apps?

What is the current way around this? Setting it in shellHook? Can it be fixed for all Qt apps?

Yes, you could set it in shellHook. Ultimately, though, I think I just need to go in and revert the changes that made Qt applications sensitive to their environment: things were broken then, but I got fewer complaints and maintainers weren't piling broken workarounds onto their packages.

If revert will result in breakage, I'd rather have Krita broken in nix-shell rather than anywhere else.

If revert will result in breakage, I'd rather have Krita broken in nix-shell rather than anywhere else.

The current situation is: Qt applications are broken in nix-shell, but work if the user installs them following the instructions. But integration plugins (themes, non-standard input methods, etc.) work! Of course, that hardly matters if the application doesn't run. And if the maintainer sets QT_QPA_PLATFORM_PLUGIN_PATH, integration probably breaks anyway.

The alternative is: Qt applications work everywhere, but integration plugins (themes, input methods) may be broken if the package maintainer and user don't follow instructions. This is essentially the state of affairs with GTK 3, and everybody seems happy enough with that.

In that light, the alternative seems strictly less broken than the current state of affairs, and anyway I cannot keep fielding the same bug reports over and over and over.

@ttuegel @joachifm without this change, what are the instructions for running QT apps that have this problem without requiring some nix-shell wrapping for them? I agree with @yegortimoshenko that I'd rather have this broken in nix-shell than anywhere else, it's quite sad that these applications can't be installed through nix-env anymore.

I agree with @yegortimoshenko that I'd rather have this broken in nix-shell than anywhere else, it's quite sad that these applications can't be installed through nix-env anymore.

I don't understand; Qt applications do work in nix-env, they are broken in nix-shell.

@ttuegel check this out:

k@z1 ~ $ env |grep QT
QTWEBKIT_PLUGIN_PATH=/etc/per-user-pkgs/k/lib/mozilla/plugins/:/home/k/.nix-profile/lib/mozilla/plugins/:/nix/var/nix/profiles/default/lib/mozilla/plugins/:/run/current-system/sw/lib/mozilla/plugins/

QT_PLUGIN_PATH=/etc/per-user-pkgs/k/lib/qt4/plugins:/etc/per-user-pkgs/k/lib/kde4/plugins:/home/k/.nix-profile/lib/qt4/plugins:/home/k/.nix-profile/lib/kde4/plugins:/nix/var/nix/profiles/default/lib/qt4/plugins:/nix/var/nix/profiles/default/lib/kde4/plugins:/run/current-system/sw/lib/qt4/plugins:/run/current-system/sw/lib/kde4/plugins

k@z1 ~ $ nix-env -iA nixpkgs-unstable.electrum
installing ‘electrum-3.0.5’

k@z1 ~ $ electrum
This application failed to start because it could not find or load the Qt platform plugin "xcb"
in "".

Reinstalling the application may fix this problem.
Aborted

@ttuegel could it be that you already have QT_QPA_PLATFORM_PLUGIN_PATH defined in your environment somehow, and that's why it's working for you? If so, is it a good idea to have that environment variable defined with the same value for all QT applications, rather than defining it per package? I would guess no…

Fwiw, on non-NixOS hosts I've had to set those variables and LD_LIBRARY_PATH myself to run QT5 apps from nixpkgs (via nix-env or otherwise).

I just tried adding this to my configuration.nix:

environment.variables.QT_QPA_PLATFORM_PLUGIN_PATH = 
    "${pkgs.qt5.qtbase.bin}/lib/qt-${pkgs.qt5.qtbase.qtCompatVersion}/plugins/platforms";

However, electrum still complaints about not being able to find the necessary plugin. Presumably because I'm running NixOS 17.09, whose pkgs.qt5 is a different version from the one in nixpkgs unstable where I'm getting electrum from (which makes total sense, but also means that this QT program still doesn't run unless I override QT_QPA_PLATFORM_PLUGIN_PATH locally as originally suggested in this pull-request 😢).