help with port using CMakeLists

[Gary Aitken]

11.2-RELEASE-p4 FreeBSD 11.2-RELEASE-p4

Up until now, (I think) I've been able to:
   cd /usr/ports/foo/bar
   make
   make install
   modify port
   make deinstall
   make
   make reinstall

However, I'm not sure I've ever done this with a build based on CMakeLists.

working with
   cad/freecad
source files in
   /usr/ports/cad/freecad-dev/work/FreeCAD-a14af0f/src/Gui
objs appear to be in
   /usr/ports/cad/freecad-dev/work/.build/src/Gui/CMakeFiles/FreeCADGui.dir

If I modify a source file, then type "make" from /usr/ports/cad/freecad,
there is not a new .o in the above object directory.
If I remove work/.build_done.FreeCAD._user_local it still isn't generated.

What's the magic formula?  I don't see any new files anywhere.

Thanks,
Gary