Struggling to set up a Qt devshell

Help
1

I’m attempting to compile a Qt example project (Document Viewer | Qt 6.11, source download documentviewer « demos « examples - qt/qtdoc.git - Qt Documentation), but I can’t figure out how to set up a shell with the proper libraries. I’m making my shell with

{

    inputs.nixpkgs.url = "github:nixos/nixpkgs?ref=25.11";

    outputs = { self, nixpkgs }:
    let
        pkgs = import nixpkgs { system = "x86_64-linux"; };
        qtEnv = with pkgs.qt6; env "qt-custom-${qtbase.version}" [
            qtdeclarative
            qtbase
        ];
    in
    {

        devShells.x86_64-linux.default = pkgs.mkShell {
            buildInputs = [
                qtEnv
                pkgs.libglvnd
            ];
            shellHook = ''
                echo entered dev shell
            '';
        };
    };

}

This is a flake form of the shell.nix from Qt - Official NixOS Wiki.

My build process is:

nix develop
qmake -project
qmake
make

make fails with the output:

g++ -c -pipe -O2 -Wall -Wextra -fPIC -D_REENTRANT -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -I. -I. -I/nix/store/zp6r9bxds1hldvkx1vbrk0d1ady17zhh-qtbase-6.10.1/include -I/nix/store/zp6r9bxds1hldvkx1vbrk0d1ady17zhh-qtbase-6.10.1/include/QtGui -I/nix/store/zp6r9bxds1hldvkx1vbrk0d1ady17zhh-qtbase-6.10.1/include/QtCore -I. -I/nix/store/7s6lgprlql0y0pfshsdyp7alxcc2x8kp-qt-custom-6.10.1/mkspecs/linux-g++ -o abstractviewer.o app/abstractviewer.cpp
app/abstractviewer.cpp:7:10: fatal error: QApplication: No such file or directory
    7 | #include <QApplication>
      |          ^~~~~~~~~~~~~~
compilation terminated.
make: *** [Makefile:1958: abstractviewer.o] Error 1

Qtbase should include QApplication (I think?), so it should be there somewhere in the environment. I’ve looked at the source for qt6.env, but I honestly can’t figure what what it’s doing. Most of the existing examples I can find use qt6.full or qt5.full, which was removed in 25.11.

Edit: I just noticed that QApplication is a part of Qt Widgets, not Qt Core, so it makes sense it’s not being found (at least in the expression in the makefile). Where on Earth is Qt Widgets packaged? I searched in nixpkgs and grepped around nixpkgs/pkgs/development/libraries/qt-6/, but Qt Widgets doesn’t appear anywhere in there, as far as I can tell.

1 Like
2

Your qmake project.pro file got overridden by qmake’s generator. For your project to compile, that file should include the widgets library. Something like QT += widgets. I don’t know why qmake failed to register widgets as a dependency, but if you add it manually, then run qmake and make again, it should compile.

EDIT: According to QT’s documentation they mention it is very likely the generated project file needs to be edited. So that is probably why. It only generates a basic project configuration

3

This was a stupid mistake on my part. I should’ve been using cmake. (I assumed that qmake used cmake internally…). Part of learning, right?

Anyways, for future reference, this flake creates an appropriate shell:

{

    inputs.nixpkgs.url = "github:nixos/nixpkgs?ref=25.11";

    outputs = { self, nixpkgs }:
    let
        pkgs = import nixpkgs { system = "x86_64-linux"; };
        qtEnv = with pkgs.qt6; env "qt-custom-${qtbase.version}" [
            qtdeclarative
            qtbase
            qttools
            wrapQtAppsHook
        ];
    in
    {

        devShells.x86_64-linux.default = pkgs.mkShell {
            buildInputs = [
                pkgs.cmake
                qtEnv
                pkgs.libglvnd
            ];
            shellHook = ''
                echo entered dev shell
            '';
        };
    };

}

cmake finds the appropriate libraries in that shell.

EDIT:
I was having trouble getting the built executable to load the Wayland plugin, so I forwent the strange qtEnv expression I got from the wiki. I didn’t want to follow the Nix package approach since I’m using this to learn, not just to make a working package. This is my new flake:

{

    inputs.nixpkgs.url = "github:nixos/nixpkgs?ref=25.11";

    outputs = { self, nixpkgs }:
    let
        pkgs = import nixpkgs { system = "x86_64-linux"; };
    in
    {

        devShells.x86_64-linux.default = pkgs.mkShell {
            buildInputs = [
                pkgs.cmake
                pkgs.libglvnd
                pkgs.kdePackages.qtdeclarative
                pkgs.kdePackages.qtbase
                pkgs.kdePackages.qttools
                pkgs.kdePackages.wrapQtAppsHook
                pkgs.kdePackages.qt3d
                pkgs.kdePackages.qtquick3d
                pkgs.kdePackages.qtwayland
                pkgs.kdePackages.qtbase
                pkgs.kdePackages.qtnetworkauth
                pkgs.kdePackages.qtscxml
                pkgs.kdePackages.qtsvg
                pkgs.kdePackages.qtwayland
                pkgs.kdePackages.qtwebengine
                pkgs.kdePackages.qt5compat
                pkgs.kdePackages.qtmultimedia
                pkgs.kdePackages.qtshadertools
            ];
            shellHook = ''
                echo entered dev shell
            '';
        };
    };

}

It’s a little messy. I’ll clean it up in the future. (There are a bunch of unnecessary dependencies in there; I just copied and pasted a large list of dependencies from the Digikam package.)
To get the Wayland plugin working, I wrap the built executable with wrapQtApp as in Running locally built Qt apps - #2 by wamserma.

I hope some of this is useful to someone in the future. The documentation is a little arcane.