Generated pkg-config file for Qt6 includes has incorrect file separator

[Cole Richardson]

Describe the bug
I initially encountered this issue when building GStreamer. However, I was able to reproduce it with minimal example.

I am building a static library that uses Qt6. I want my library to be consumed by upstream packages using pkg-config files. However, when I generate the pkg-config file, I get the following:

Libs: -L${libdir} -lfoo C:/Tools/Qt6.5.1/6.5.1/msvc2019_64/lib/Qt6Widgetsd.lib C:/Tools/Qt6.5.1/6.5.1/msvc2019_64/lib/Qt6Cored.lib C:/Tools/Qt6.5.1/6.5.1/msvc2019_64/lib/Qt6Guid.lib C:/Tools/Qt6.5.1/6.5.1/msvc2019_64/lib/Qt6Qmld.lib C:/Tools/Qt6.5.1/6.5.1/msvc2019_64/lib/Qt6Quickd.lib
Cflags: -I${includedir} -IC:/Tools/Qt6.5.1/6.5.1/msvc2019_64/include -IC:/Tools/Qt6.5.1/6.5.1/msvc2019_64/include\QtWidgets -DQT_WIDGETS_LIB -IC:/Tools/Qt6.5.1/6.5.1/msvc2019_64/include\QtCore -DQT_CORE_LIB -IC:/Tools/Qt6.5.1/6.5.1/msvc2019_64/include\QtGui -DQT_GUI_LIB -IC:/Tools/Qt6.5.1/6.5.1/msvc2019_64/include\QtQml -DQT_QML_LIB -IC:/Tools/Qt6.5.1/6.5.1/msvc2019_64/include\QtQuick -DQT_QUICK_LIB

Notice how the last component (include dirs in Cflags) is not using the same file separator (i.e. \ instead of /). Also, the library paths seem to be unaffected?

I am building on Windows (using msvc). However, I know from manually modifying the include directories, I can get the pkg-config file to work (e.g. manually changing the \ to / in the .pc file).

Investigation
From the implementation here: https://github.com/mesonbuild/meson/blob/master/mesonbuild/dependencies/qt.py it looks like os.path.join(...) is used for the include path but other logic is used for the library paths.

I'm not sure if this should be handled by pkg-config generation or the Qt6 module import. I believe pkg-config is expecting only Unix file separators?

To Reproduce
Install dependencies:

choco install ninja --version=1.11.1
choco install meson --version=1.4.0
choco install pkgconfiglite --version=0.28

All the files below can be put in a directory and ran (build.bat):

meson.build

project('tutorial', 'cpp')

qt6_mod = import('qt6')
qt6_dep = dependency('qt6', modules : ['Widgets', 'Core', 'Gui', 'Qml', 'Quick'],
                        required: true)

inc = include_directories('.')
foo = static_library('foo', 'lib.cpp',
    include_directories: [inc],
    override_options : ['cpp_std=c++17'],
    dependencies : [qt6_dep])

pkg = import('pkgconfig')
pkg.generate(foo)

executable('demo', 'main.cpp',
    override_options : ['cpp_std=c++17'],
    link_with : foo,
    dependencies: [qt6_dep])

main.cpp

#include "lib.hpp"

int main(int argc, char *argv[])
{
    hello(argc, argv);
}

lib.hpp

bool hello(int argc, char *argv[]);

lib.cpp

#include "lib.hpp"

#include <iostream>

#include <QApplication>

bool hello(int argc, char *argv[]) {
    std::cout << "Hello, World!" << std::endl;
    QApplication app(argc, argv);
    return app.exec();
}

build.bat

@ECHO OFF
RMDIR /S /Q builddir
MKDIR builddir
meson setup --wipe builddir\
PUSHD builddir
meson compile -v
POPD

Expected behavior
The generated pkg-config files (foo.pc) should have all Unix file separators.

system parameters

• OS: Windows 11
• Compiler: MSVC (19.36.32535 x64)
• meson --version: 1.4.0
• ninja --version: 1.11.1
• python --version: 3.11.9