Issue #2702401: Add integration for the user entity type

src/Form/UserInlineForm.php

+<?php
+
+namespace Drupal\inline_entity_form\Form;
+
+use Drupal\Core\Entity\EntityInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Render\Element;
+use Drupal\user\AccountForm;
+
+/**
+ * User inline form handler.
+ */
+class UserInlineForm extends EntityInlineForm {
+
+  protected ?AccountForm $accountForm;
+
+  protected ?FormStateInterface $accountFormState;
+
+  public function getEntityTypeLabels() {
+    return [
+      'singular' => $this->entityType->getSingularLabel(),
+      'plural' => $this->entityType->getPluralLabel(),
+    ];
+  }
+
+  public function entityForm(array $entity_form, FormStateInterface $form_state) {
+    $user_form_object = $this->getUserFormObject($entity_form['#entity'], $form_state, $entity_form['#form_mode']);
+
+    // Copy user base fields items into the main entity form object.
+    $user_form = $user_form_object->form($entity_form, $form_state);
+    foreach (Element::children($user_form) as $field_name) {
+      $entity_form[$field_name] = $user_form[$field_name];
+    }
+
+    return parent::entityForm($entity_form, $form_state);
+  }
+
+  /**
+   * Builds an updated entity object based upon the submitted form values.
+   */
+  protected function buildEntity(array $entity_form, EntityInterface $entity, FormStateInterface $form_state) {
+    /** @var \Drupal\user\UserInterface $entity */
+    parent::buildEntity($entity_form, $entity, $form_state);
+
+    $this->accountFormState = clone $form_state;
+    $this->accountFormState->setValues($form_state->getValue($entity_form['#parents'])['account']);
+
+    $user_entity = $this->accountForm->buildEntity($entity_form, $this->accountFormState);
+    foreach ($user_entity->getFields() as $field_name => $field_value) {
+      $entity->set($field_name, $field_value->getValue());
+    }
+
+    // Uncomment to allow resubmitting the form without having to face
+    // integrity constraint error on every submit.
+    // $entity->setEmail(uniqid() . '@example.com');
+  }
+
+  /**
+   * Internal helper.
+   *
+   * Returns handler for the user form.
+   *
+   * @param \Drupal\Core\Entity\ContentEntityInterface $entity
+   *   User account entity.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   Current form state.
+   * @param string $form_mode
+   *   User form mode (usually it's "register").
+   *
+   * @return \Drupal\Core\Form\FormInterface
+   *   User account form.
+   */
+  protected function getUserFormObject(
+    EntityInterface $entity,
+    FormStateInterface $form_state,
+    string $form_mode
+  ): AccountForm {
+    /** @var \Drupal\user\RegisterForm $user_form_object */
+    $this->accountForm = $this->entityTypeManager->getFormObject($entity->getEntityTypeId(), $form_mode);
+    $this->accountForm->setEntity($entity);
+
+    $form_display = $this->getFormDisplay($entity, $form_mode);
+    $this->accountForm->setFormDisplay($form_display, $form_state);
+
+    return $this->accountForm;
+  }
+
+}