Qt: Difference between revisions

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== Troubleshooting ==

=== ~~Cannot mix incompatible~~ Qt ~~library (version 0x_____) with this library (version 0x_____)~~ ===

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

~~This is a known issue, see {{issue|30551}} for the current status.~~

~~Starting with the 19.09 release, the issue should be fixed by {{pull|65526}}~~

~~=== This application failed to start because it could not find or load the Qt platform plugin ??? in "" ===~~

~~==== qt5 ====~~

{{warning|This recommendation is deprecated for 19.09 and up, see {{issue|65399}}. Failing packages should be updated to use <code>wrapQtAppsHook</code>.}}

Qt5 seems (?) to look for plugins in the <code>PATH</code>. This will fail from a systemd user unit for example, because their path is nearly empty by default. As an example, here is a workaround to have <code>usbguard-applet</code> launched from a systemd user unit:

~~{{File|/etc/nixos/configuration.nix|nix|<nowiki>~~

~~systemd.user.services.usbguard-applet = {~~

~~description = "USBGuard applet";~~

~~partOf = [ "graphical-session.target" ];~~

~~wantedBy = [ "graphical-session.target" ];~~

~~path = [ "/run/current-system/sw/" ]; ### Fix empty PATH to find qt plugins~~

~~serviceConfig = {~~

~~ExecStart = "${pkgs.usbguard}/bin/usbguard-applet-qt";~~

};

~~</nowiki>}}~~

~~==== qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in "" ====~~

~~Here is a concrete example:~~

<pre>

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The package will need to be fixed to use [the new https://github.com/NixOS/nixpkgs/issues/65399 <code>wrapQtAppsHook</code>]. The hook wraps every qt application with adding <code>QT_PLUGIN_PATH</code> and <code>XDG_DATA_DIRS</code> as well as <code>XDG_CONFIG_DIRS</code>.See [https://github.com/NixOS/nixpkgs/blob/nixos-19.09/pkgs/development/libraries/qt-5/hooks/wrap-qt-apps-hook.sh wrap-qt-apps-hook.sh in nixpkgs]

==== Debugging methods ====

=== Debugging methods ===

As a general rule, exporting <code>QT_DEBUG_PLUGINS=1</code> make qt print where it looks for plugins.

If a plugin exists in a directory but is ignored with a message like <code>QLibraryPrivate::loadPlugin failed on "/nix/store/...-teamspeak-client-3.1.6/lib/teamspeak/platforms/libqxcb.so" : "Cannot load library /nix/store/...-client-3.1.6/lib/teamspeak/platforms/libqxcb.so: "</code> it can be that the library cannot be <code>dlopen()</code>ed because of dependencies/rpath issues and needs <code>patchelf</code>ing. Exporting <code>LD_DEBUG=libs</code> may prove helpful in this scenario.

@@ Line 193: / Line 193: @@
 == Troubleshooting ==
-=== Cannot mix incompatible Qt library (version 0x_____) with this library (version 0x_____) ===
+=== This application failed to start because it could not find or load the Qt platform plugin ??? in "" ===
-This is a known issue, see {{issue|30551}} for the current status.
-Starting with the 19.09 release, the issue should be fixed by {{pull|65526}}
-=== This application failed to start because it could not find or load the Qt platform plugin ??? in "" ===
-==== qt5 ====
 {{warning|This recommendation is deprecated for 19.09 and up, see {{issue|65399}}. Failing packages should be updated to use <code>wrapQtAppsHook</code>.}}
-Qt5 seems (?) to look for plugins in the <code>PATH</code>. This will fail from a systemd user unit for example, because their path is nearly empty by default. As an example, here is a workaround to have <code>usbguard-applet</code> launched from a systemd user unit:
-{{File|/etc/nixos/configuration.nix|nix|<nowiki>
-  systemd.user.services.usbguard-applet = {
-    description = "USBGuard applet";
-    partOf = [ "graphical-session.target" ];
-    wantedBy = [ "graphical-session.target" ];
-    path = [ "/run/current-system/sw/" ]; ### Fix empty PATH to find qt plugins
-    serviceConfig = {
-      ExecStart = "${pkgs.usbguard}/bin/usbguard-applet-qt";
-    };
-  };
-</nowiki>}}
-====  qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in "" ====
-Here is a concrete example:
 <pre>
@@ Line 226: / Line 204: @@
 The package will need to be fixed to use [the new https://github.com/NixOS/nixpkgs/issues/65399 <code>wrapQtAppsHook</code>]. The hook wraps every qt application with adding <code>QT_PLUGIN_PATH</code> and <code>XDG_DATA_DIRS</code> as well as <code>XDG_CONFIG_DIRS</code>.See [https://github.com/NixOS/nixpkgs/blob/nixos-19.09/pkgs/development/libraries/qt-5/hooks/wrap-qt-apps-hook.sh wrap-qt-apps-hook.sh in nixpkgs]
-==== Debugging methods ====
+=== Debugging methods ===
 As a general rule, exporting <code>QT_DEBUG_PLUGINS=1</code> make qt print where it looks for plugins.
 If a plugin exists in a directory but is ignored with a message like <code>QLibraryPrivate::loadPlugin failed on "/nix/store/...-teamspeak-client-3.1.6/lib/teamspeak/platforms/libqxcb.so" : "Cannot load library /nix/store/...-client-3.1.6/lib/teamspeak/platforms/libqxcb.so: "</code> it can be that the library cannot be <code>dlopen()</code>ed because of dependencies/rpath issues and needs <code>patchelf</code>ing. Exporting <code>LD_DEBUG=libs</code> may prove helpful in this scenario.