Hi,
It seems that UWidgetLayoutLibrary as well as UWidgetBlueprintLibrary are not part of the public API of the UMG Module.
You can access their headers and use the type, but it will fail on Link time because the implementation is not available.
I did a workaround and copied and modified the implementation of the one needed function of UWidgetLayoutLibrary in my own class. It’s dirty, but at least it works. I’d be happy to know a better way anyway. In my case I needed the current Viewport Scale in C++ (as I move some functionality from Widget Blueprint into code)
ciao