drupal/core/modules/edit/edit.module

<?php

/**
 * @file
 * Provides in-place content editing functionality for fields.
 *
 * The Edit module makes content editable in-place. Rather than having to visit
 * a separate page to edit content, it may be edited in-place.
 *
 * Technically, this module adds classes and data- attributes to fields and
 * entities, enabling them for in-place editing.
 */

use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Entity\Display\EntityViewDisplayInterface;

/**
 * Implements hook_permission().
 */
function edit_permission() {
  return array(
    'access in-place editing' => array(
      'title' => t('Access in-place editing'),
    ),
  );
}

/**
 * Implements hook_page_build().
 *
 * Adds the edit library to the page for any user who has the 'access in-place
 * editing' permission.
 */
function edit_page_build(&$page) {
  if (!\Drupal::currentUser()->hasPermission('access in-place editing')) {
    return;
  }

  // In-place editing is only supported on the front-end.
  $path = \Drupal::request()->attributes->get('_system_path');
  if (path_is_admin($path)) {
    return;
  }

  $page['#attached']['library'][] = 'edit/edit';
}

/**
 * Implements hook_library_alter().
 *
 * Includes additional stylesheets defined by the admin theme to allow it to
 * customize the Edit toolbar appearance.
 *
 * An admin theme can specify CSS files to make the front-end administration
 * experience of in-place editing match the administration experience in the
 * back-end.
 *
 * The CSS files can be specified via the "edit_stylesheets" property in the
 * .info.yml file:
 * @code
 * edit_stylesheets:
 *   - css/edit.css
 * @endcode
 *
 * The library needs to be dynamically enhanced, because an admin theme normally
 * does not participate in the front-end.
 *
 * @param string $theme
 *   (optional) Internal use only. A base theme name for which to retrieve the
 *   'edit_stylesheets' property.
 *
 * @todo Remove this in favor of the 'stylesheets-additional' property proposed
 *   in https://drupal.org/node/1209958
 */
function edit_library_alter(array &$library, $name, $theme = NULL) {
  if ($name == 'edit/edit') {
    // Retrieve the admin theme.
    if (!isset($theme)) {
      $theme = Drupal::config('system.theme')->get('admin');
    }
    if ($theme && $theme_path = drupal_get_path('theme', $theme)) {
      $info = system_get_info('theme', $theme);
      // Recurse to process base theme(s) first.
      if (isset($info['base theme'])) {
        edit_library_alter($library, $name, $info['base theme']);
      }
      if (isset($info['edit_stylesheets']) && is_array($info['edit_stylesheets'])) {
        foreach ($info['edit_stylesheets'] as $path) {
          $library['css'][$theme_path . '/' . $path] = array(
            'group' => CSS_AGGREGATE_THEME,
            'weight' => CSS_THEME,
          );
        }
      }
    }
  }
}

/**
 * Implements hook_field_formatter_info_alter().
 *
 * Edit extends the @FieldFormatter annotation with the following keys:
 * - edit: currently only contains one subkey 'editor' which indicates which
 *   in-place editor should be used. Possible values are 'form', 'plain_text',
 *   'disabled' or another in-place editor other than the ones Edit module
 *   provides.
 */
function edit_field_formatter_info_alter(&$info) {
  foreach ($info as $key => $settings) {
    // Set in-place editor to 'form' if none is supplied.
    if (empty($settings['edit'])) {
      $info[$key]['edit'] = array('editor' => 'form');
    }
  }
}

/**
 * Implements hook_preprocess_HOOK() for field templates.
 */
function edit_preprocess_field(&$variables) {
  $element = $variables['element'];
  /** @var $entity \Drupal\Core\Entity\EntityInterface */
  $entity = $element['#object'];

  // Edit module only supports view modes, not dynamically defined "display
  // options" (which \Drupal\Core\Field\FieldItemListInterface::view() always
  // names the "_custom" view mode).
  // @see \Drupal\Core\Field\FieldItemListInterface::view()
  // @see https://drupal.org/node/2120335
  if ($element['#view_mode'] === '_custom') {
    return;
  }

  // Fields that are not part of the entity (i.e. dynamically injected "pseudo
  // fields") and computed fields are not editable.
  $definition = $entity->getFieldDefinition($element['#field_name']);
  if ($definition && !$definition->isComputed()) {
    $variables['attributes']['data-edit-field-id'] = $entity->getEntityTypeId() . '/' . $entity->id() . '/' . $element['#field_name'] . '/' . $element['#language'] . '/' . $element['#view_mode'];
  }
}

/**
 * Implements hook_entity_view_alter().
 */
function edit_entity_view_alter(&$build, EntityInterface $entity, EntityViewDisplayInterface $display) {
  $build['#attributes']['data-edit-entity-id'] = $entity->getEntityTypeId() . '/' . $entity->id();
}