[layer-shell-qt] [Bug 524317] New: Linker error, expecting to have Qt::WaylandClient

https://bugs.kde.org/show_bug.cgi?id=524317

            Bug ID: 524317
           Summary: Linker error, expecting to have Qt::WaylandClient
    Classification: Frameworks and Libraries
           Product: layer-shell-qt
      Version First unspecified
       Reported In:
          Platform: Fedora RPMs
                OS: Linux
            Status: REPORTED
          Severity: minor
          Priority: NOR
         Component: general
          Assignee: [email protected]
          Reporter: [email protected]
  Target Milestone: ---

DESCRIPTION

So, I am trying to make an app very similar to spectacle, but for translation
of text and new words learning.

And when I am trying to compile my app with these deps (I've tried to add
Qt::WaylandClient dependency after 1st linker error, but it has'nt resolved my
issue): 

```
target_link_libraries(QBackgroundAppWithShortcutToShow
    PRIVATE
        Qt::Core
        Qt::Widgets
        Qt::DBus
        Qt::WaylandClient 
        LayerShellQt::Interface
)
```

STEPS TO REPRODUCE

1. I've tried to compile my app with LayerShellQt as a dependency. 
Cmake and 'hello world' project example:
https://github.com/Maslyna/LayerShellQtLinkerBugExample/blob/master/CMakeLists.txt 

OBSERVED RESULT

I got linker errors: 

```
/usr/bin/ld.bfd: /usr/lib64/libLayerShellQtInterface.so.6.7.4: undefined
reference to
`QtWaylandClient::QWaylandWindow::updateExposure()@Qt_6.11_PRIVATE_API'
/usr/bin/ld.bfd: /usr/lib64/libLayerShellQtInterface.so.6.7.4: undefined
reference to `typeinfo for
QtWaylandClient::QWaylandShellSurface@Qt_6.11_PRIVATE_API'
/usr/bin/ld.bfd: /usr/lib64/libLayerShellQtInterface.so.6.7.4: undefined
reference to
`QtWaylandClient::QWaylandShellIntegration::~QWaylandShellIntegration()@Qt_6.11_PRIVATE_API'
/usr/bin/ld.bfd: /usr/lib64/libLayerShellQtInterface.so.6.7.4: undefined
reference to `QtWaylandClient::QWaylandShellSurface::sendProperty(QString
const&, QVariant const&)@Qt_6.11_PRIVATE_API'
...
Basically 24 linker errors from libLayerShellQtInterface.so that are expecting
to have Qt::WaylandClientPrivate
```

EXPECTED RESULT

Successful compilation

POSSIBLE SOLUTION AND ROOT CAUSE

I think, the root cause is in 
https://invent.kde.org/plasma/layer-shell-qt/-/blob/ecebbfed0b42dbdb0dffa14e02e8ea3c345f0239/src/CMakeLists.txt 
at lines 35-36 we are declaring Qt::WaylandClientPrivate as PRIVATE:

```
target_link_libraries(LayerShellQtInterface PUBLIC Qt::Gui) 
target_link_libraries(LayerShellQtInterface PRIVATE Qt::WaylandClientPrivate
Wayland::Client PkgConfig::XKBCOMMON)
```

Since LayerShellQtInterface's own implementation depends on symbols from
libQt6WaylandClient.so - any consumer that doesn't also explicitly force-link
Qt6::WaylandClient gets this undefined reference at link time, because
"--as-needed" (Fedora's default) drops the library from the link line before it
can satisfy that transitive symbol.

Workaround that works for me:

```
target_link_libraries(QBackgroundAppWithShortcutToShow
    PRIVATE
        Qt::Core
        Qt::Widgets
        Qt::DBus
        -Wl,--no-as-needed
        Qt::WaylandClient
        -Wl,--as-needed
        LayerShellQt::Interface
)
```

SOFTWARE/OS VERSIONS

mordyntsev@fedora:~$ rpm -q layer-shell-qt qt6-qtwayland
layer-shell-qt-6.7.4-1.fc44.x86_64
qt6-qtwayland-6.11.1-1.fc44.x86_64


Operating System: Fedora Linux 44
KDE Plasma Version: 6.7.4
KDE Frameworks Version: 6.29.0
Qt Version: 6.11.1
Kernel Version: 7.1.8-200.fc44.x86_64 (64-bit)
Graphics Platform: Wayland

ADDITIONAL INFORMATION

Here's a project example, that can recreate my problem:
https://github.com/Maslyna/LayerShellQtLinkerBugExample.git

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