Resolve #3311480 "add set_attribute and add_class filters"

Closes #3311480

src/Template/AttributesFilterTrait.php

+<?php
+
+namespace Drupal\ui_patterns\Template;
+
+use Drupal\Core\Template\Attribute;
+use Drupal\Core\Template\AttributeHelper;
+
+/**
+ * Methods for the set_attribute and add_class filters.
+ *
+ * In a trait, to be usable in other places.
+ */
+trait AttributesFilterTrait {
+
+  /**
+   * Add a value into the class attributes of a given element.
+   *
+   * @param mixed $element
+   *   A render array.
+   * @param string[]|string ...$classes
+   *   The classes to add on element. Arguments can include string keys directly
+   *   or arrays of string keys.
+   *
+   * @return mixed
+   *   The element with the given class(es) in attributes or the unchanged
+   *   element if passed value is not an array.
+   *
+   * @see Drupal\Core\Template\TwigExtension::addClass()
+   */
+  public function addClass(mixed $element, ...$classes): mixed {
+    if (!\is_array($element)) {
+      return $element;
+    }
+    if ($this->arrayIsList($element)) {
+      foreach ($element as $index => $item) {
+        if (!\is_array($item)) {
+          continue;
+        }
+        $element[$index] = $this->addClass($item, ...$classes);
+      }
+      return $element;
+    }
+    $attributes = new Attribute($element['#attributes'] ?? []);
+    $attributes->addClass(...$classes);
+    $element['#attributes'] = $attributes->toArray();
+
+    // Make sure element gets rendered again.
+    unset($element['#printed']);
+
+    return $element;
+  }
+
+  /**
+   * Set attribute on a given element.
+   *
+   * @param mixed $element
+   *   A render array.
+   * @param string $name
+   *   The attribute name.
+   * @param mixed $value
+   *   (optional) The attribute value.
+   *
+   * @return mixed
+   *   The element with the given sanitized attribute's value or the unchanged
+   *   element if passed value is not an array.
+   *
+   * @see Drupal\Core\Template\TwigExtension::setAttribute()
+   */
+  public function setAttribute(mixed $element, string $name, mixed $value = NULL): mixed {
+    if (!\is_array($element)) {
+      return $element;
+    }
+    if ($this->arrayIsList($element)) {
+      foreach ($element as $index => $item) {
+        if (!\is_array($item)) {
+          continue;
+        }
+        $element[$index] = $this->setAttribute($item, $name, $value);
+      }
+      return $element;
+    }
+    $element['#attributes'] = AttributeHelper::mergeCollections(
+      $element['#attributes'] ?? [],
+      new Attribute([$name => $value])
+    );
+
+    // Make sure element gets rendered again.
+    unset($element['#printed']);
+
+    return $element;
+  }
+
+  /**
+   * Checks whether a given array is a list.
+   *
+   * Same as array_is_list() but compatible with PHP8.
+   *
+   * @param array $array
+   *   The array being evaluated.
+   *
+   * @return bool
+   *   Returns true if array is a list, false otherwise.
+   *
+   * @see https://www.php.net/manual/en/function.array-is-list.php#126794
+   */
+  private function arrayIsList(array $array): bool {
+    $i = -1;
+    foreach ($array as $k => $v) {
+      ++$i;
+      if ($k !== $i) {
+        return FALSE;
+      }
+    }
+    return TRUE;
+  }
+
+}