# binary_dir_relative_path sets outvar to
# ${CMAKE_CURRENT_BINARY_DIR}/${cur_bin_dir_relative}, but expressed relative to
# ${CMAKE_BINARY_DIR}.
#
# TODO(davidben): When we require CMake 3.20 or later, this can be replaced with
# the built-in cmake_path(RELATIVE_PATH) function.
function(binary_dir_relative_path cur_bin_dir_relative outvar)
  string(LENGTH "${CMAKE_BINARY_DIR}/" root_dir_length)
  string(SUBSTRING "${CMAKE_CURRENT_BINARY_DIR}/${cur_bin_dir_relative}" ${root_dir_length} -1 result)
  set(${outvar} ${result} PARENT_SCOPE)
endfunction()

# copy_post_build causes targets in ${ARGN} to be copied to
# ${CMAKE_CURRENT_BINARY_DIR}/${dir} after being built.
function(copy_post_build dir)
  foreach(target ${ARGN})
    add_custom_command(
      TARGET ${target}
      POST_BUILD
      COMMAND ${CMAKE_COMMAND} -E make_directory "${CMAKE_CURRENT_BINARY_DIR}/${dir}"
      COMMAND ${CMAKE_COMMAND} -E copy $<TARGET_FILE:${target}> "${CMAKE_CURRENT_BINARY_DIR}/${dir}")
  endforeach()
endfunction()