@Override
  @ApiStatus.Internal
  public int @NotNull [] onlyInternalFileIds() {
    if (idSet != null) {
      return idSet.toIntArray();
    }
    if (fileIds != null) {
      return fileIds.stream().toArray();
    }
    return weirdFiles
      .stream()
      .filter(f -> f instanceof VirtualFileWithId)
      .mapToInt(f -> ((VirtualFileWithId)f).getId())
      .toArray();
  }
@Override
  @ApiStatus.Internal
  public int @NotNull [] onlyInternalFileIds()