[PyQt] Travis and PyQt 5.12: xcb plugin can't be loaded

[Florian Bruhin]

Hi,

Just in case anyone else runs into this as well:

After upgrading to the PyQt 5.12 wheel on Travis, I got an abort() when
trying to create a QApplication:

  qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in ".../site-packages/PyQt5/plugins/platforms" even though it was found.
  This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

After debugging this via QT_DEBUG_PLUGINS=1, I found out the xcb plugin
couldn't be loaded due to a missing libxkbcommon-x11.so.0.

This can be fixed by telling Travis to install it:

  addons:
    apt:
      packages:
      - libxkbcommon-x11-0

Still I wonder where that new dependency is coming from - I guess that's
a change in Qt? That library isn't required with 5.11:

  $ ldd ./PyQt5-5.11.3-5.11.2-cp35.cp36.cp37.cp38-abi3-manylinux1_x86_64/PyQt5/Qt/plugins/platforms/libqxcb.so | grep libxkb
  (no output)

But it is with 5.12:

  $ ldd ./PyQt5-5.12-5.12.1_a-cp35.cp36.cp37.cp38-abi3-manylinux1_x86_64/PyQt5/Qt/plugins/platforms/libqxcb.so | grep libxkb
	libxkbcommon-x11.so.0 => /usr/lib/libxkbcommon-x11.so.0 (0x00007f52361a2000)
	libxkbcommon.so.0 => /usr/lib/libxkbcommon.so.0 (0x00007f5236160000)

Florian

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