--- /dev/null
+<?php
+
+namespace Drupal\file\Plugin\Field\FieldFormatter;
+
+use Drupal\Core\Field\FieldDefinitionInterface;
+use Drupal\Core\Field\FieldItemInterface;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Formatter to render a filename as file extension.
+ *
+ * @FieldFormatter(
+ * id = "file_extension",
+ * label = @Translation("File extension"),
+ * field_types = {
+ * "string"
+ * }
+ * )
+ */
+class FileExtensionFormatter extends BaseFieldFileFormatterBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ public static function defaultSettings() {
+ $settings = parent::defaultSettings();
+
+ $settings['extension_detect_tar'] = FALSE;
+ return $settings;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public function settingsForm(array $form, FormStateInterface $form_state) {
+ $form = parent::settingsForm($form, $form_state);
+ $form['extension_detect_tar'] = [
+ '#type' => 'checkbox',
+ '#title' => $this->t('Include tar in extension'),
+ '#description' => $this->t("If the part of the filename just before the extension is '.tar', include this in the extension output."),
+ '#default_value' => $this->getSetting('extension_detect_tar'),
+ ];
+ return $form;
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ protected function viewValue(FieldItemInterface $item) {
+ $filename = $item->value;
+ if (!$this->getSetting('extension_detect_tar')) {
+ return pathinfo($filename, PATHINFO_EXTENSION);
+ }
+ else {
+ $file_parts = explode('.', basename($filename));
+ if (count($file_parts) > 1) {
+ $extension = array_pop($file_parts);
+ $last_part_in_name = array_pop($file_parts);
+ if ($last_part_in_name === 'tar') {
+ $extension = 'tar.' . $extension;
+ }
+ return $extension;
+ }
+ }
+ }
+
+ /**
+ * {@inheritdoc}
+ */
+ public static function isApplicable(FieldDefinitionInterface $field_definition) {
+ // Just show this file extension formatter on the filename field.
+ return parent::isApplicable($field_definition) && $field_definition->getName() === 'filename';
+ }
+
+}