Hiro failure when building with Qt5

[nathanzachary]

Describe the bug
The build of the hiro component fails when attempting to use the Qt5 backend instead of GTK3.

To Reproduce

1. Attempt to build ares (the hiro component, in particular) using '-DUSE_QT5'.
2. The build of hiro fails with:

CMake Error at /usr/lib64/cmake/Qt5/Qt5Config.cmake:28 (find_package):
  Could not find a package configuration file provided by "Qt5Xcb" with any
  of the following names:

    Qt5XcbConfig.cmake
    qt5xcb-config.cmake

  Add the installation prefix of "Qt5Xcb" to CMAKE_PREFIX_PATH or set
  "Qt5Xcb_DIR" to a directory containing one of the above files.  If "Qt5Xcb"
  provides a separate development package or SDK, be sure it has been
  installed.
Call Stack (most recent call first):
  hiro/cmake/os-linux.cmake:16 (find_package)
  hiro/CMakeLists.txt:13 (include)

Expected behavior
The hiro component should build with either GTK3 or Qt5.

Additional context
I am working on a CMake-based ebuild for Gentoo Linux. I haven't come across any fatal build errors when using the GTK3 backend. When using the Qt5 backend, I hit the error mentioned above. Searching through package-provided files, I don't see either of the ones mentioned above. The closest that I have found is:

/usr/lib64/cmake/Qt5XcbQpa/Qt5XcbQpaConfig.cmake

which is provided by the Gentoo packages dev-qt/qtgui:
https://packages.gentoo.org/packages/dev-qt/qtgui

Having looked through the other packages, I don't see either of those .cmake files available.

[jcm93]

The documentation does not make it as clear as it perhaps should, but the Qt5 build is not currently supported; USE_QT5 is essentially an experimental flag at present. While much of the stuff is there, some work definitely needs to be done for Qt5 to be properly supported alongside GTK3 in the new build system.

In this specific instance, though: It seems like the Qt5 installation you are building with may just lack the Xcb component, which would be required by ares if you were building the Qt backend. It could be that your Qt doesn't have any X11 backend whatsoever, or it could be that you are just missing certain development libraries. I have not looked in-depth at why or why not this component might be present on a given system.

[nathanzachary]

Thank you very much for the explanation. That actually makes it easier on me for now. I'll simply mask the Qt-based installation. If it's ready at some point, I'll update my ebuild accordingly.

Thanks again for the details, @jcm93. Have a nice day.

Cheers,
Nathan Zachary