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Qt: Difference between revisions

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m Fix syntax error in example code for specifying explitit Qt dependencies
 
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<code>nix-shell -p qt5Full -p qtcreator --run qtcreator</code>
<code>nix-shell -p qt5Full -p qtcreator --run qtcreator</code>


Tip: if it finds no Qt Kits, <code>rm -rf ~/.config/QtProject*</code> and start again.
Tip: if it finds no Qt Kits, <code>rm -rf ~/.config/QtProject*</code> and start again. Sometimes it finds a kit, but cannot find a suitable qt version for it, in this case you can also type <code>which qmake</code> in your nix-shell and add a new entry in the <code>QT-Versions</code> tab in <code>Tools->Options->Kits</code>.


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


{{File|shell.nix|nix|<nowiki>
<syntaxHighlight lang=nix>
# shell.nix
{ pkgs ? import <nixpkgs> {} }:
{ pkgs ? import <nixpkgs> {} }:
   pkgs.mkShell {
   pkgs.mkShell {
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                   ];
                   ];
}
}
</nowiki>}}
</syntaxHighlight>


Tip: if you want use clang-format, add '''clang-format''' to '''buildinputs''' list.
Tip: if you want use clang-format, add '''clang-format''' to '''buildinputs''' list.
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Happy qt coding :)
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:
<syntaxhighlight lang="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-${qtbase.version}" [
    qtdeclarative
  ];
in
  pkgs.mkShell {
    buildInputs = [
      qtEnv
      # pkgs.qt6.qtdeclarative depends on pkgs.libglvnd
      # Also worth noting it could be in qtEnv if preferred for "relatedness" reasons
      pkgs.libglvnd
      pkgs.qtcreator
    ];
}
</syntaxhighlight>
== Packaging ==
[https://nixos.org/manual/nixpkgs/stable/#sec-language-qt See] for the entry in the nixpkgs manual.
Qt applications can't be called with <code>callPackage</code>, since they expect more inputs. Namely <code>qtbase</code> and <code>wrapQtAppsHook</code>. Instead they should be called with <code>libsForQt5.callPackage</code>.
{{File|./build/default.nix|nix|<nowiki>
{ stdenv, lib, qtbase, wrapQtAppsHook }:
stdenv.mkDerivation {
  pname = "myapp";
  version = "1.0";
  buildInputs = [ qtbase ];
  nativeBuildInputs = [ wrapQtAppsHook ];
}
</nowiki>}}
<syntaxHighlight lang=nix>
#nix-repl
myapp = callPackage ./build/myapp/default.nix { } # Will complain it wasn't called with qtbase, etc.
myapp = libsForQt5.callPackage ./build/myapp/default.nix { } # Should work
</syntaxHighlight>
== Projects using python (e.g. PyQt5) ==
It's possible to package a program that uses internally python and Qt (like PyQt5) by providing a python executable with the appropriate libraries like that <code>myPython = python3.withPackages (pkgs: with pkgs; [ pyqt5 ]);</code>. `<code>wrapQtAppsHook</code>` even seems  to be optional when using `mkderivation` (at least this program can be run without) since anyway it does not patch scripts.
<syntaxHighlight lang=nix>
{ mkDerivation,
  lib,
  stdenv,
  fetchFromGitHub,
  jack2,
  which,
  python3,
  qtbase,
  qttools,
  wrapQtAppsHook,
  liblo,
  git,
}:
let
  myPython = python3.withPackages (pkgs: with pkgs; [ pyqt5 liblo pyliblo pyxdg ]);
in
mkDerivation rec {
  pname = "RaySession";
  version = "0.11.1";
  src = fetchFromGitHub {
    owner = "Houston4444";
    repo = pname;
    rev = "v${version}";
    sha256 = "sha256-EbDBuOcF0JQq/LOrakb040Yfrpdi3FOB1iczQTeXBkc=";
  };
  # This patch is required to be able to create a new session, but not a problem to compile and start the program
  # patches = [ ./copy_template_writable.patch ];
  # Otherwise lrelease-qt is not found:
  postPatch = ''
  substituteInPlace Makefile \
    --replace "lrelease-qt4" "${qttools.dev}/bin/lrelease" \
    --replace '$(DESTDIR)/' '$(DESTDIR)$(PREFIX)' # Otherwise problem with installing manual etc...
  '';
  nativeBuildInputs = [
    myPython
    wrapQtAppsHook # Not really useful since it will not pack scripts. And actually it seems that it's not required?
    which
    qttools
  ];
  propagatedBuildInputs = [ myPython qtbase jack2 git ];
  # Prefix must be set correctly due to sed -i "s?X-PREFIX-X?$(PREFIX)?"
  makeFlags = [ "PREFIX=$(out)" ]; # prefix does not work since due to line "install -d $(DESTDIR)/etc/xdg/"
}
</syntaxHighlight>
Call it with
<syntaxHighlight>
{ pkgs ? import <nixpkgs> {} }:
pkgs.libsForQt5.callPackage ./derivation.nix {}
</syntaxHighlight>
For actual python applications, you may also use something like that (to test) :
<syntaxHighlight>
python3.pkgs.buildPythonApplication {
  pname = "blabla";
  version = "3.32.2";
  nativeBuildInputs = [
    wrapQtAppsHook
    ...
  ];
  dontWrapQtApps = true; # wrapQtApps won't patch script anyway. TODO: save to use if it contains executables?
  # Arguments to be passed to `makeWrapper`, only used by buildPython*
  preFixup = ''
        qtWrapperArgs+=("''${gappsWrapperArgs[@]}")
        # You can manually patch scripts using: wrapQtApp "$out/bin/myapp". TODO: check when it's required.
  '';
}
</syntaxHighlight>
== Migrating apps from Qt5 to Qt6 ==
# Replace <code>libsForQt5.callPackage</code> with <code>qt6Packages.callPackage</code>
# Add the dependency [https://www.qt.io/blog/porting-from-qt-5-to-qt-6-using-qt5compat-library qt5compat]
# Hope for the best ; )
<code>qt5compat</code> is only needed for Qt5 projects, which are not-yet migrated to Qt6.
Maybe add libraries like <code>qtwayland</code>
Conditional blocks in qmake <code>*.pro</code> files
<syntaxHighlight lang=pro>
lessThan(QT_MAJOR_VERSION, 6) {
  # qt5, qt4, ...
  QT += x11extras
}
equals(QT_MAJOR_VERSION, 6) {
  # qt6
  QT += core-private
}
</syntaxHighlight>
See also:
* [https://doc.qt.io/qt-6/portingguide.html Porting to Qt 6]
* [https://stackoverflow.com/questions/18663331 How to check the selected version of Qt in a .pro file?]
== Hello world involving QML, Qt5, nix and cmake, qmake or meson ==
You can find [https://gist.github.com/tobiasBora/04d0febda0b3f09707b5e1b7b85390a5 here] a minimal example to use QML, cmake, nix and Qt5, and [https://gist.github.com/tobiasBora/6f114cca1affb5528c872ca01d7e28c1 here] is the same example with qmake instead and [https://gist.github.com/tobiasBora/812701e8741814393f3df7b23a11eb4b here] is the same with meson instead. There is nothing special to nix there, but note that if you provide the qml file using something like <code>qrc:///main.qml</code>, then you need to write a qrc file that lists all the resources that must be included in the qt resource manager. This file is then used to compile the resources and include them in the binary (you have to compile the binaries, either automatically with cmake or qmake, or manually using rcc). With cmake you compile it using <code>qt5_add_resources(SOURCES qml.qrc)</code> ([https://doc.qt.io/qt-5/qtcore-cmake-qt5-add-resources.html doc]) as illustrated in the above example (make sure to use a variable as the source and to reuse the same variable in <code>add_executable</code>).


== Troubleshooting ==
== Troubleshooting ==
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This is a known issue, see {{issue|30551}} for the current status.
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 "" ===
=== This application failed to start because it could not find or load the Qt platform plugin ??? in "" ===
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==== qt5 ====
==== 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:
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>
{{File|/etc/nixos/configuration.nix|nix|<nowiki>
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Here is a concrete example:  
Here is a concrete example:  


{{File|||
<pre>
qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""
qt.qpa.plugin: Could not find the Qt platform plugin "xcb" in ""
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.}}
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.
 
</pre>
One solution is to run a command like
{{Commands|<nowiki>env QT_PLUGIN_PATH=/nix/store/d7q3q6wmfccss8gcp09r33xg0wkbz9gb-qtbase-5.11.0-bin/lib/qt-5.11/plugins/ some_qt_app</nowiki>}}


Another is to set the variable in a shell.nix file like the following {{File|shell.nix|nix|<nowiki>
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]
with import </nowiki><nixpkgs><nowiki> {};
 
stdenv.mkDerivation {
  name = "qt-somethingorother";
 
  buildInputs = [
    pkgs.somePackage
    ];
  QT_PLUGIN_PATH = qt5.qtbase.bin + "/" + qt5.qtbase.qtPluginPrefix;
  }
</nowiki>}} to be run with {{Commands|nix-shell shell.nix}}


==== Debugging methods ====
==== Debugging methods ====
Retrieved from "https://wiki.nixos.org/wiki/Qt"