Qt: Difference between revisions - Official NixOS Wiki

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== Development ==

~~If you want~~ to develop qt applications in ~~nixos~~ you ~~have to~~ use nix-shell or direnv.

{{warning|With the deprecation of <code>qt5.full</code> & <code>qt6.full</code>, for 25.11 and up (see [https://github.com/NixOS/nixpkgs/blob/32b61ba4d9088ef926dd27065daad604ca6b58aa/pkgs/development/libraries/qt-6/default.nix#L152 change]) this recommendation is outdated. For now please primarily refer to the [[#Explicit Dependencies|Explicit Dependencies]] Section below.}}

To develop Qt applications in NixOS you may use nix-shell or direnv.

For using nix-shell just run this command in the terminal:

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For using direnv, create a '''shell.nix''' file in the root of your project and paste these lines into it:

<~~syntaxHighlight~~ lang=nix>

<syntaxhighlight lang="nix"># shell.nix

# shell.nix

{ pkgs ? import <nixpkgs> {} }:

pkgs.mkShell {

buildInputs = [

pkgs.qt5.full

pkgs.qtcreator

];

}

}</syntaxhighlight>

</~~syntaxHighlight~~>

~~Tip: if you want use clang-format~~, ~~add '''clang-format''' to '''buildinputs''' list.~~

Also, create '''.envrc''' file and paste: <code>use_nix</code> into it.

~~Also~~ create '''.envrc''' file and paste: <code>use_nix</code> into it.

~~Happy qt coding :)~~

=== Explicit Dependencies ===

~~However if~~ fetching the entirety of <code>pkgs.qt6.full</code> is not appealing and you know which parts of Qt you need, your first instinct might be adding something like <code>pkgs.qt6.qtdeclarative</code> for creating QML-based Qt programs to <code>buildInputs</code>, '''however''' that will not work and you will get compile errors for missing libraries. <code>pkgs.qt6.full</code> is actually [https://github.com/NixOS/nixpkgs/blob/nixos-24.11/pkgs/development/libraries/qt-6/default.nix#L94-L144 creating an environment that contains all Qt libraries] that allows <code>qmake</code> and tools to find those libraries, so you must do the same and <code>pkgs.qt6.env</code> will help make one. For example:

If fetching the entirety of <code>pkgs.qt6.full</code> is not appealing and you know which parts of Qt you need, your first instinct might be adding something like <code>pkgs.qt6.qtdeclarative</code> for creating QML-based Qt programs to <code>buildInputs</code>, '''however''' that will not work and you will get compile errors for missing libraries. <code>pkgs.qt6.full</code> is actually [https://github.com/NixOS/nixpkgs/blob/nixos-24.11/pkgs/development/libraries/qt-6/default.nix#L94-L144 creating an environment that contains all Qt libraries] that allows <code>qmake</code> and tools to find those libraries, so you must do the same and <code>pkgs.qt6.env</code> will help make one. For example:

<~~syntaxHighlight~~ lang=nix>

<syntaxhighlight lang="nix"># shell.nix

# shell.nix

{ pkgs ? import <nixpkgs> {} }:

let

# pkgs.qt6.env already includes pkgs.qt6.qtbase

# And using `with` to prevent a lot of typing.

qtEnv = with pkgs.qt6; env "qt-custom-${qtbase.version}" {

qtEnv = with pkgs.qt6; env "qt-custom-${qtbase.version}" [

[

qtdeclarative

];

]

};

in

pkgs.mkShell {

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pkgs.qtcreator

];

}

}</syntaxhighlight>

</~~syntaxHighlight~~>

== Packaging ==

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For actual python applications, you may also use something like that (to test) :

python3.pkgs.buildPythonApplication {

pname = "blabla";

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== Troubleshooting ==

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

~~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 "" ===

~~==== qt4 ====~~

~~Qt4 depends on the environment variable <code>QT_PLUGIN_PATH</code> to find plugins. It is normally already~~

present in the environment on NixOS at least, but for example systemd user units are launched in a pretty empty environment. A solution is to use the command {{Commands|systemctl --user import-environment QT_PLUGIN_PATH}} from a sane environment. For example add it to the <code>services.xserver.displayManager.sessionCommands</code> option.

~~==== 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 2: / Line 2: @@
 == Development ==
-If you want to develop qt applications in nixos you have to use nix-shell or direnv.
+{{warning|With the deprecation of <code>qt5.full</code> & <code>qt6.full</code>, for 25.11 and up (see [https://github.com/NixOS/nixpkgs/blob/32b61ba4d9088ef926dd27065daad604ca6b58aa/pkgs/development/libraries/qt-6/default.nix#L152 change]) this recommendation is outdated. For now please primarily refer to the [[#Explicit Dependencies|Explicit Dependencies]] Section below.}}
+To develop Qt applications in NixOS you may use nix-shell or direnv.
 For using nix-shell just run this command in the terminal:
@@ Line 11: / Line 13: @@
 For using direnv, create a '''shell.nix''' file in the root of your project and paste these lines into it:
-<syntaxHighlight lang=nix>
+<syntaxhighlight lang="nix"># shell.nix
-# shell.nix
 { pkgs ? import <nixpkgs> {} }:
    pkgs.mkShell {
      buildInputs = [
-                    pkgs.qt5.full
+      pkgs.qt5.full
-                    pkgs.qtcreator
+      pkgs.qtcreator
-                  ];
+    ];
-}
+}</syntaxhighlight>
-</syntaxHighlight>
-Tip: if you want use clang-format, add '''clang-format''' to '''buildinputs''' list.
+Also, create '''.envrc''' file and paste: <code>use_nix</code> into it.
-Also create '''.envrc''' file and paste: <code>use_nix</code> into it.
-Happy qt coding :)
 === Explicit Dependencies ===
-However if fetching the entirety of <code>pkgs.qt6.full</code> is not appealing and you know which parts of Qt you need, your first instinct might be adding something like <code>pkgs.qt6.qtdeclarative</code> for creating QML-based Qt programs to <code>buildInputs</code>, '''however''' that will not work and you will get compile errors for missing libraries. <code>pkgs.qt6.full</code> is actually [https://github.com/NixOS/nixpkgs/blob/nixos-24.11/pkgs/development/libraries/qt-6/default.nix#L94-L144 creating an environment that contains all Qt libraries] that allows <code>qmake</code> and tools to find those libraries, so you must do the same and <code>pkgs.qt6.env</code> will help make one. For example:
+If fetching the entirety of <code>pkgs.qt6.full</code> is not appealing and you know which parts of Qt you need, your first instinct might be adding something like <code>pkgs.qt6.qtdeclarative</code> for creating QML-based Qt programs to <code>buildInputs</code>, '''however''' that will not work and you will get compile errors for missing libraries. <code>pkgs.qt6.full</code> is actually [https://github.com/NixOS/nixpkgs/blob/nixos-24.11/pkgs/development/libraries/qt-6/default.nix#L94-L144 creating an environment that contains all Qt libraries] that allows <code>qmake</code> and tools to find those libraries, so you must do the same and <code>pkgs.qt6.env</code> will help make one. For example:
-<syntaxHighlight lang=nix>
+<syntaxhighlight lang="nix"># shell.nix
-# shell.nix
 { pkgs ? import <nixpkgs> {} }:
 let
    # pkgs.qt6.env already includes pkgs.qt6.qtbase
    # And using `with` to prevent a lot of typing.
-   qtEnv = with pkgs.qt6; env "qt-custom-${qtbase.version}" {
+   qtEnv = with pkgs.qt6; env "qt-custom-${qtbase.version}" [
-     [
+     qtdeclarative
-      qtdeclarative
+  ];
-    ]
-  };
 in
    pkgs.mkShell {
@@ Line 52: / Line 45: @@
        pkgs.qtcreator
      ];
-}
+}</syntaxhighlight>
-</syntaxHighlight>
 == Packaging ==
@@ Line 142: / Line 134: @@
 For actual python applications, you may also use something like that (to test) :
-<syntaxHighlight>
+<syntaxHighlight lang=nix>
 python3.pkgs.buildPythonApplication {
    pname = "blabla";
@@ Line 196: / Line 188: @@
 == Troubleshooting ==
-=== Cannot mix incompatible Qt library (version 0x_____) with this library (version 0x_____) ===
-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 "" ===
-==== qt4 ====
-Qt4 depends on the environment variable <code>QT_PLUGIN_PATH</code> to find plugins. It is normally already
-present in the environment on NixOS at least, but for example systemd user units are launched in a pretty empty environment. A solution is to use the command {{Commands|systemctl --user import-environment QT_PLUGIN_PATH}} from a sane environment. For example add it to the <code>services.xserver.displayManager.sessionCommands</code> option.
-==== 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 234: / Line 200: @@
 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.