Issue #3416538 by rodrigoaguilera: Add suport for contact roles with static/fixed treaty

src/Plugin/Field/FieldFormatter/RoleWithTreatyEntityReferenceFormatter.php

+<?php
+
+namespace Drupal\informea_api\Plugin\Field\FieldFormatter;
+
+use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\Core\Field\Plugin\Field\FieldFormatter\EntityReferenceLabelFormatter;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Plugin implementation of the 'Role with treaty' formatter.
+ *
+ * @FieldFormatter(
+ *   id = "informea_api_role_with_treaty",
+ *   label = @Translation("[InforMEA] Role with treaty"),
+ *   field_types = {
+ *     "entity_reference",
+ *   }
+ * )
+ */
+class RoleWithTreatyEntityReferenceFormatter extends EntityReferenceLabelFormatter {
+
+  use SerializerObjectTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function defaultSettings() : array {
+    $settings = [
+      'treaties' => '',
+    ] + parent::defaultSettings();
+    $settings['link'] = FALSE;
+    return $settings;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function settingsForm(array $form, FormStateInterface $form_state) : array {
+
+    $form['treaties'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('Treaty'),
+      '#description' => $this->t('Treaty machine name.'),
+      '#default_value' => $this->getSetting('treaties'),
+      '#required' => TRUE,
+    ];
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function settingsSummary() : array {
+    $summary = [];
+
+    $summary[] = $this->t('Treaties: @treaties', ['@treaties' => $this->getSetting('treaties')]);
+
+    return $summary;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function viewElements(FieldItemListInterface $items, $langcode) : array {
+    $roles = [];
+    $elements = parent::viewElements($items, $langcode);
+    $treaties = $this->getTreaties($items);
+    foreach ($elements as $element) {
+      $roles[] = [
+        'treaty' => reset($treaties),
+        'role' => $element['#plain_text'],
+      ];
+
+    }
+    return $this->serialize($roles);
+  }
+
+  /**
+   * Get the treaties.
+   *
+   * @return array
+   *   The treaties.
+   */
+  protected function getTreaties(FieldItemListInterface $items) : array {
+    $treaties = $this->getSetting('treaties');
+    $treaties = explode(',', $treaties);
+    foreach ($treaties as &$treaty) {
+      $treaty = trim($treaty);
+    }
+    return $treaties;
+  }
+
+}