template_preprocess_file_upload_help

template_preprocess_file_upload_help(&$variables)

function template_preprocess_file_upload_help(&$variables) {
  $description = $variables['description'];
  $upload_validators = $variables['upload_validators'];
  $cardinality = $variables['cardinality'];

  $descriptions = array();

  if (!empty($description)) {
    $descriptions[] = FieldFilteredMarkup::create($description);
  }
  if (isset($cardinality)) {
    if ($cardinality == -1) {
      $descriptions[] = t('Unlimited number of files can be uploaded to this field.');
    }
    else {
      $descriptions[] = \Drupal::translation()->formatPlural($cardinality, 'One file only.', 'Maximum @count files.');
    }
  }
  if (isset($upload_validators['file_validate_size'])) {
    $descriptions[] = t('@size limit.', array('@size' => format_size($upload_validators['file_validate_size'][0])));
  }
  if (isset($upload_validators['file_validate_extensions'])) {
    $descriptions[] = t('Allowed types: @extensions.', array('@extensions' => $upload_validators['file_validate_extensions'][0]));
  }

  if (isset($upload_validators['file_validate_image_resolution'])) {
    $max = $upload_validators['file_validate_image_resolution'][0];
    $min = $upload_validators['file_validate_image_resolution'][1];
    if ($min && $max && $min == $max) {
      $descriptions[] = t('Images must be exactly <strong>@size</strong> pixels.', array('@size' => $max));
    }
    elseif ($min && $max) {
      $descriptions[] = t('Images must be larger than <strong>@min</strong> pixels. Images larger than <strong>@max</strong> pixels will be resized.', array('@min' => $min, '@max' => $max));
    }
    elseif ($min) {
      $descriptions[] = t('Images must be larger than <strong>@min</strong> pixels.', array('@min' => $min));
    }
    elseif ($max) {
      $descriptions[] = t('Images larger than <strong>@max</strong> pixels will be resized.', array('@max' => $max));
    }
  }

  $variables['descriptions'] = $descriptions;
}