https://reviews.llvm.org/D77184 research

foo.cmake

# cmake -P foo.cmake

include(FindPythonInterp)

#set(FOO_DIR "/Users/thakis/blah")
set(FOO_DIR "/Users/thakis/blah" CACHE STRING "wsdf")

function(configure_lit_site_cfg site_in site_out)
  cmake_parse_arguments(ARG "" "" "MAIN_CONFIG;OUTPUT_MAPPING;PATHS" ${ARGN})

  #message(${FOO_DIR})
  # Walk ARG_PATHS and collect the current value of the variables in there.
  foreach(path ${ARG_PATHS})
    #message("${path}")
    list(APPEND ARG_PATH_VALUES "${${path}}")
  endforeach()
  #message("val ${ARG_PATH_VALUES}")
  #message("py ${PYTHON_EXECUTABLE}")

  set(PYTHON_EXECUTABLE ${PYTHON_EXECUTABLE})
  # This is len(ARG_PATH_VALUES) - 1, for use with foreach(RANGE) loops.
  set(arg_path_limit 0)  # XXX -1?

  if (ARG_PATH_VALUES)
    # Passing ARG_PATH_VALUES as-is to execute_process() makes cmake strip
    # empty list entries. So escape the ;s in the list and do the splitting
    # outselves. cmake has no relpath function, so use Python for that.
    string(REPLACE ";" "\\;" ARG_PATH_VALUES_ESCAPED "${ARG_PATH_VALUES}")
    execute_process(COMMAND "${PYTHON_EXECUTABLE}" "-c"
      "import os, sys; sys.stdout.write(';'.join(os.path.relpath(p, sys.argv[1]) if p else '' for p in sys.argv[2].split(';')))"
      "/Users/thakis"
      ${ARG_PATH_VALUES_ESCAPED}
      OUTPUT_VARIABLE ARG_PATH_VALUES_RELATIVE)
    #message("p ${ARG_PATHS}")
    #message("v ${ARG_PATH_VALUES}")
    #message("o ${ARG_PATH_VALUES_RELATIVE}")

    list(LENGTH ARG_PATHS len_vars)
    list(LENGTH ARG_PATH_VALUES len_values)
    list(LENGTH ARG_PATH_VALUES_RELATIVE len_rels)
    if ((NOT ${len_vars} EQUAL ${len_values}) OR
        (NOT ${len_vars} EQUAL ${len_rels}))
      message(SEND_ERROR "PATHS lengths got confused")
    endif()

    math(EXPR arg_path_limit "${len_rels} - 1")

    # Transform variables mentioned in ARG_PATHS to relative paths for
    # the configure_file() call.
    foreach(i RANGE ${arg_path_limit})
      list(GET ARG_PATHS ${i} val1)
      list(GET ARG_PATH_VALUES_RELATIVE ${i} val2)
      set(${val1} ${val2})
    endforeach()
  endif()

  message(${FOO_DIR})

  #configure_file(${site_in} ${site_out} @ONLY)

  # Restore ARG_PATHS variables to their original values.
  #foreach(i RANGE ${arg_path_limit})
    #list(GET ARG_PATHS ${i} val1)
    #list(GET ARG_PATH_VALUES ${i} val2)
    #set(${val1} ${val2})
  #endforeach()

  message(${FOO_DIR})

endfunction()



message(${FOO_DIR})
configure_lit_site_cfg(
  "asdf"
  "foo"
  PATHS
  "FOO_DIR"
  )
message(${FOO_DIR})