Issue #3450518: Add a generic trait for logic to convert references into Urls in LinkWidget

Closes #3450518

core/lib/Drupal/Core/Render/Element/UriValidationTrait.php

+<?php
+
+namespace Drupal\Core\Render\Element;
+
+use Drupal\Core\Entity\Element\EntityAutocomplete;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a trait for uri validation and management.
+ *
+ * This trait is useful to validate URIs entered form elements and transform
+ * them back to human readable strings when used as from element default value.
+ */
+trait UriValidationTrait {
+
+  /**
+   * Form element validation handler for the 'uri' element.
+   *
+   * Disallows saving inaccessible or untrusted URLs.
+   */
+  public static function validateUriElement($element, FormStateInterface $form_state, $form) {
+    $uri = static::getUserEnteredStringAsUri($element['#value']);
+    $form_state->setValueForElement($element, $uri);
+
+    // If getUserEnteredStringAsUri() mapped the entered value to an 'internal:'
+    // URI , ensure the raw value begins with '/', '?' or '#'.
+    // @todo '<front>' is valid input for BC reasons, may be removed by
+    //   https://www.drupal.org/node/2421941
+    if (parse_url($uri, PHP_URL_SCHEME) === 'internal' && !in_array($element['#value'][0], [
+      '/',
+      '?',
+      '#',
+    ], TRUE) && !str_starts_with($element['#value'], '<front>')) {
+      $form_state->setError($element, new TranslatableMarkup('Manually entered paths should start with one of the following characters: / ? #'));
+      return;
+    }
+  }
+
+  /**
+   * Gets the user-entered string as a URI.
+   *
+   * The following two forms of input are mapped to URIs:
+   * - entity autocomplete ("label (entity id)") strings: to 'entity:' URIs;
+   * - strings without a detectable scheme: to 'internal:' URIs.
+   *
+   * This method is the inverse of ::getUriAsDisplayableString().
+   *
+   * @param string $string
+   *   The user-entered string.
+   *
+   * @return string
+   *   The URI, if a non-empty $uri was passed.
+   *
+   * @see static::getUriAsDisplayableString()
+   */
+  protected static function getUserEnteredStringAsUri($string) {
+    // By default, assume the entered string is a URI.
+    $uri = trim($string);
+
+    // Detect entity autocomplete string, map to 'entity:' URI.
+    $entity_id = EntityAutocomplete::extractEntityIdFromAutocompleteInput($string);
+    if ($entity_id !== NULL) {
+      // @todo Support entity types other than 'node'. Will be fixed in
+      //   https://www.drupal.org/node/2423093.
+      $uri = 'entity:node/' . $entity_id;
+    }
+    // Support linking to nothing.
+    elseif (in_array($string, ['<nolink>', '<none>', '<button>'], TRUE)) {
+      $uri = 'route:' . $string;
+    }
+    // Detect a schemeless string, map to 'internal:' URI.
+    elseif (!empty($string) && parse_url($string, PHP_URL_SCHEME) === NULL) {
+      // @todo '<front>' is valid input for BC reasons, may be removed by
+      //   https://www.drupal.org/node/2421941
+      // - '<front>' -> '/'
+      // - '<front>#foo' -> '/#foo'
+      if (str_starts_with($string, '<front>')) {
+        $string = '/' . substr($string, strlen('<front>'));
+      }
+      $uri = 'internal:' . $string;
+    }
+
+    return $uri;
+  }
+
+  /**
+   * Gets the URI without the 'internal:' or 'entity:' scheme.
+   *
+   * The following two forms of URIs are transformed:
+   * - 'entity:' URIs: to entity autocomplete ("label (entity id)") strings;
+   * - 'internal:' URIs: the scheme is stripped.
+   *
+   * This method is the inverse of ::getUserEnteredStringAsUri().
+   *
+   * @param string $uri
+   *   The URI to get the displayable string for.
+   *
+   * @return string
+   *
+   * @see static::getUserEnteredStringAsUri()
+   */
+  protected static function getUriAsDisplayableString($uri) {
+    $scheme = parse_url($uri, PHP_URL_SCHEME);
+
+    // By default, the displayable string is the URI.
+    $displayable_string = $uri;
+
+    // A different displayable string may be chosen in case of the 'internal:'
+    // or 'entity:' built-in schemes.
+    if ($scheme === 'internal') {
+      $uri_reference = explode(':', $uri, 2)[1];
+
+      // @todo '<front>' is valid input for BC reasons, may be removed by
+      //   https://www.drupal.org/node/2421941
+      $path = parse_url($uri, PHP_URL_PATH);
+      if ($path === '/') {
+        $uri_reference = '<front>' . substr($uri_reference, 1);
+      }
+
+      $displayable_string = $uri_reference;
+    }
+    elseif ($scheme === 'entity') {
+      [$entity_type, $entity_id] = explode('/', substr($uri, 7), 2);
+      // Show the 'entity:' URI as the entity autocomplete would.
+      // @todo Support entity types other than 'node'. Will be fixed in
+      //   https://www.drupal.org/node/2423093.
+      if ($entity_type == 'node' && $entity = \Drupal::entityTypeManager()
+        ->getStorage($entity_type)
+        ->load($entity_id)) {
+        $displayable_string = EntityAutocomplete::getEntityLabels([$entity]);
+      }
+    }
+    elseif ($scheme === 'route') {
+      $displayable_string = ltrim($displayable_string, 'route:');
+    }
+
+    return $displayable_string;
+  }
+
+}