# https://stackoverflow.com/a/49216539
#
# Removes the specified compile flag from the specified target.
#   _target     - The target to remove the compile flag from
#   _flag       - The compile flag to remove
#
# Pre: apply_global_cxx_flags_to_all_targets() must be invoked.
#
macro(remove_flag_from_target _target _flag)
  get_target_property(_target_cxx_flags ${_target} COMPILE_OPTIONS)
  if(_target_cxx_flags)
    list(REMOVE_ITEM _target_cxx_flags ${_flag})
    set_target_properties(${_target}
                          PROPERTIES COMPILE_OPTIONS "${_target_cxx_flags}")
  endif()
endmacro()

#
# Removes the specified compiler flag from the specified file.
#   _target     - The target that _file belongs to
#   _file       - The file to remove the compiler flag from
#   _flag       - The compiler flag to remove.
#
# Pre: apply_global_cxx_flags_to_all_targets() must be invoked.
#
macro(remove_flag_from_file _target _file _flag)
  get_target_property(_target_sources ${_target} SOURCES)
  # Check if a sync is required, in which case we'll force a rewrite of the cache variables.
  if(_flag_sync_required)
    unset(_cached_${_target}_cxx_flags CACHE)
    unset(_cached_${_target}_${_file}_cxx_flags CACHE)
  endif()
  get_target_property(_${_target}_cxx_flags ${_target} COMPILE_OPTIONS)
  # On first entry, cache the target compile flags and apply them to each source file
  # in the target.
  if(NOT _cached_${_target}_cxx_flags)
    # Obtain and cache the target compiler options, then clear them.
    get_target_property(_target_cxx_flags ${_target} COMPILE_OPTIONS)
    set(_cached_${_target}_cxx_flags "${_target_cxx_flags}" CACHE INTERNAL "")
    set_target_properties(${_target} PROPERTIES COMPILE_OPTIONS "")
    # Apply the target compile flags to each source file.
    foreach(_source_file ${_target_sources})
      # Check for pre-existing flags set by set_source_files_properties().
      get_source_file_property(_source_file_cxx_flags ${_source_file}
                               COMPILE_FLAGS)
      if(_source_file_cxx_flags)
        separate_arguments(_source_file_cxx_flags UNIX_COMMAND
                           ${_source_file_cxx_flags})
        list(APPEND _source_file_cxx_flags "${_target_cxx_flags}")
      else()
        set(_source_file_cxx_flags "${_target_cxx_flags}")
      endif()
      # Apply the compile flags to the current source file.
      string(REPLACE ";" " " _source_file_cxx_flags_string
                     "${_source_file_cxx_flags}")
      set_source_files_properties(${_source_file} PROPERTIES COMPILE_FLAGS
                                  "${_source_file_cxx_flags_string}")
    endforeach()
  endif()
  list(FIND _target_sources ${_file} _file_found_at)
  if(_file_found_at GREATER -1)
    if(NOT _cached_${_target}_${_file}_cxx_flags)
      # Cache the compile flags for the specified file.
      # This is the list that we'll be removing flags from.
      get_source_file_property(_source_file_cxx_flags ${_file} COMPILE_FLAGS)
      separate_arguments(_source_file_cxx_flags UNIX_COMMAND
                         ${_source_file_cxx_flags})
      set(_cached_${_target}_${_file}_cxx_flags ${_source_file_cxx_flags}
          CACHE INTERNAL "")
    endif()
    # Remove the specified flag, then re-apply the rest.
    list(REMOVE_ITEM _cached_${_target}_${_file}_cxx_flags ${_flag})
    string(REPLACE ";" " " _cached_${_target}_${_file}_cxx_flags_string
                   "${_cached_${_target}_${_file}_cxx_flags}")
    set_source_files_properties(
      ${_file} PROPERTIES COMPILE_FLAGS
      "${_cached_${_target}_${_file}_cxx_flags_string}")
  endif()
endmacro()