$node->save() fails when run in post_update

I have a simple hook_post_update function which fails with the following error:

[notice] Update started: ssc_custom_post_update_9001

[error] LogicException: Render context is empty, because render() was called outside of a renderRoot() or renderPlain() call. Use renderPlain()/renderRoot() or #lazy_builder/#pre_render instead. in Drupal\Core\Render\Renderer->doRender() (line 244 of E:\www\myssc\html\core\lib\Drupal\Core\Render\Renderer.php). [error] Render context is empty, because render() was called outside of a renderRoot() or renderPlain() call. Use renderPlain()/renderRoot() or #lazy_builder/#pre_render instead. [error] Update failed: ssc_custom_post_update_9001

In ProcessBase.php line 171:

Unable to decode output into JSON: Syntax error

[ERROR] [node] [2022-03-12T04:58:35] LogicException: Render context is empty, because render() was called outside of a renderRoot() or renderPlain() call. Use renderPlain()/renderRoot() or #lazy_builder/#pre_re nder instead. in Drupal\Core\Render\Renderer->doRender() (line 244 of E:\www\myssc\html\core\lib\Drupal\C ore\Render\Renderer.php). | uid: 0 | request-uri: http://default/ | refer: | ip: 127.0.0.1 | link:
{ "0": { "ssc_custom": { "9001": { "#abort": { "success": false, "query": "Drupal\Core\Entity\EntityStorageException: Ren der context is empty, because render() was called outside of a renderRoot() or renderPlain() call. Use re nderPlain()/renderRoot() or #lazy_builder/#pre_render instead. in Drupal\Core\Ent
ity\Sql\SqlContentEntityStorage->save() (line 810 of E:\www\myssc\html\core\lib\Drupal\Core\Entity\Sql\SqlContentEntityStorage.php)." } } }, "#abort": [ "ssc_custom_post_update_9001" ] }, "drush_batch_process_finished": true }

I have stripped the code down to the bare minimum:

use Drupal\Core\Entity\EntityStorageInterface;
use Drupal\Core\Entity\EntityTypeManagerInterface;
use Drupal\node\NodeInterface;

function ssc_custom_post_update_9001(&$sandbox) {
  /** @var \Drupal\node\NodeStorageInterface $node_storage */
  $node_storage = \Drupal::entityTypeManager()->getStorage('node');

  // How many entities to processed per batch.
  $limit = 5;

  $node_ids = $node_storage->getQuery()
    ->accessCheck(FALSE)
    ->condition('type', 'article')
    ->range(0, $limit)
    ->execute();
  // Load entities.
  $nodes = $node_storage->loadMultiple($node_ids);

  /** @var \Drupal\node\NodeInterface $node */
  foreach ($nodes as $node) {
    $node->setNewRevision();
    $node->save();
  }

  $sandbox['#finished'] = 1;

}

If I run the same code directly (not from drush updb) it runs fine. Running from the admin menu "Run updates"; it also fails (so it is not a drush issue).

Commenting out the $node->save() and the error does not occur.

You can reproduce the error with Drush:

# drush php

>>> $build = ['#markup' => 'TEST'];
=> [
     "#markup" => "TEST",
   ]

>>> $rendered = \Drupal::service('renderer')->render($build);
LogicException with message 'Render context is empty, because render() was called outside of a renderRoot() or renderPlain() call. Use renderPlain()/renderRoot() or #lazy_builder/#pre_render instead.'

>>> $rendered = \Drupal::service('renderer')->renderPlain($build);
=> Drupal\Core\Render\Markup {#4668
     markup: "TEST",
   }

So as the error message says modules which hook into the node save process should use renderPlain() instead. They shouldn't assume nodes are always saved within a render context of a themed Drupal page.

Code example for rendering a view in isolation:

$build = $view->buildRenderable();
$rendered = \Drupal::service('renderer')->renderPlain($build);