set(oldname "${CMAKE_CURRENT_BINARY_DIR}/input")
set(newname "${CMAKE_CURRENT_BINARY_DIR}/output")
file(MAKE_DIRECTORY "${oldname}")
file(COPY_FILE "${oldname}" "${newname}" RESULT result)
message(STATUS "file(COPY_FILE) failed with result: ${result}")
if(EXISTS "${newname}")
  message(FATAL_ERROR "The new name exists:\n ${newname}")
endif()