Make it possible to use value form elements

src/Form/Control/Callbacks/ValueElementValueCallback.php

@@ -0,0 +1,46 @@
+<?php
+
+/*
+ * Copyright (C) 2022 SYSTOPIA GmbH
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+declare(strict_types=1);
+
+namespace Drupal\json_forms\Form\Control\Callbacks;
+
+use Drupal\Core\Form\FormStateInterface;
+
+final class ValueElementValueCallback {
+
+  /**
+   * @param array<int|string, mixed> $element
+   * @param mixed $input
+   * @param \Drupal\Core\Form\FormStateInterface $formState
+   *
+   * @return mixed
+   */
+  public static function convert(array $element, $input, FormStateInterface $formState) {
+    $value = $element['#value'] ?? $element['#default_value'] ?? NULL;
+    if (NULL === $value) {
+      // Prevent empty string as value. Drupal sets an empty string in this
+      // case if no value is set in the form state.
+      $formState->setValueForElement($element, NULL);
+    }
+
+    return $value;
+  }
+
+}

src/Form/Control/ValueArrayFactory.php

@@ -0,0 +1,61 @@
+<?php
+
+/*
+ * Copyright (C) 2022 SYSTOPIA GmbH
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+declare(strict_types=1);
+
+namespace Drupal\json_forms\Form\Control;
+
+use Assert\Assertion;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\json_forms\Form\AbstractConcreteFormArrayFactory;
+use Drupal\json_forms\Form\Control\Callbacks\ValueElementValueCallback;
+use Drupal\json_forms\Form\Control\Util\BasicFormPropertiesFactory;
+use Drupal\json_forms\Form\FormArrayFactoryInterface;
+use Drupal\json_forms\JsonForms\Definition\Control\ControlDefinition;
+use Drupal\json_forms\JsonForms\Definition\DefinitionInterface;
+
+class ValueArrayFactory extends AbstractConcreteFormArrayFactory {
+
+  public static function getPriority(): int {
+    return HiddenArrayFactory::getPriority() + 1;
+  }
+
+  /**
+   * {@inheritDoc}
+   */
+  public function createFormArray(DefinitionInterface $definition,
+    FormStateInterface $formState,
+    FormArrayFactoryInterface $formArrayFactory
+  ): array {
+    Assertion::isInstanceOf($definition, ControlDefinition::class);
+    /** @var \Drupal\json_forms\JsonForms\Definition\Control\ControlDefinition $definition */
+
+    return [
+      '#type' => 'value',
+      '#value_callback' => ValueElementValueCallback::class . '::convert',
+    ] + BasicFormPropertiesFactory::createFieldProperties($definition, $formState);
+  }
+
+  public function supportsDefinition(DefinitionInterface $definition): bool {
+    return $definition instanceof ControlDefinition
+      && 'hidden' === $definition->getOptionsValue('type')
+      && TRUE === $definition->getOptionsValue('internal');
+  }
+
+}