Tests/RunCMake/MaxRecursionDepth/variable_watch.cmake - third_party/github.com/Kitware/CMake - Git at Google

 function(update_x)
   message("${x}")
   math(EXPR y "${x} + 2")
   variable_watch(x update_x)
   set(x "${y}")
 endfunction()

 variable_watch(x update_x)
 set(x 4)
	function(update_x)
	message("${x}")
	math(EXPR y "${x} + 2")
	variable_watch(x update_x)
	set(x "${y}")
	endfunction()

	variable_watch(x update_x)
	set(x 4)