Error on node revision view page

Problem/Motivation

When you enabled revisions on a node type and you want to view that revision you will get a fatal error / WSOD, e.g. /node/1234/revisions/12345/view

The reason is that

$node = \Drupal::routeMatch()->getParameter('node')

returns a string with the node id instead of the node object. Therefore the $node->getType() call fails. It's reported in Drupal core at #2730631: Upcast node and node_revision parameters of node revision routes.

Steps to reproduce

Proposed resolution

To avoid the problem wrap it into a condition.

if ($node = \Drupal::routeMatch()->getParameter('node')) {
    if ($node instanceof NodeInterface) {
      $suggestions[] = 'page__node__' . $node->getType();
    }
  }

If the suggestion is also relevant for the revision page, then you might want to load the full node object.

if ($node = \Drupal::routeMatch()->getParameter('node')) {
    if ($revision_id = \Drupal::routeMatch()->getParameter('node_revision')) {
      if ($node_revision = \Drupal::entityTypeManager()->getStorage('node')->loadRevision($revision_id)) {
        $node = $node_revision;
      }
    }
    if ($node instanceof NodeInterface) {
      $suggestions[] = 'page__node__' . $node->getType();
    }
  }

Remaining tasks

User interface changes

API changes

Data model changes