cmake-changes in vtk9.0.1 (occt build error)

Please somebody involved in vtk-development can give a hint what cmake changes were added in vtk9.
We are running into:

CMake Error at CMakeLists.txt:730 (message):
Could not find headers of used third-party products:

with occt7.4 which worked previously with vtk8.

That variable looks like an occt variable, not VTK. Please file an issue against occt (feel free to mention me if they’re on github: @mathstuf).

thanks for the reply.
sure it is related to occt, but as the vtk-configuration worked previously it would be nice to know which parts of vtk-cmake have changed. A short hint might help to create a patch to fix the vtk configuration.

These docs should be a good start.