Change record status: 
Project: 
Introduced in branch: 
8.5.x
Introduced in version: 
8.5.0
Description: 

Drupal 8.5.x now uses a minimum of Symfony 3.4.x.

All Symfony components in Drupal 8.5.x have been updated to 3.4.x, this is the last release in the 3.x cycle for Symfony. Symfony 3.4 is a long-term support release and we expect to remain on 3.4 releases for the rest of Drupal 8's support lifetime.

The following API breaks have been identified and fixed in Drupal core:

Private/public services

As of Symfony 3.4, all services are marked as private. Normal services declared via *.services.yml files are automatically marked as public (unless explicitly declared private). Services declared via ServiceProviderInterface and ServiceModifierInterface classes should mark themselves as public if this is the intent:

  $my_service = new Definition(Foo::class);
  $my_service->setPublic(TRUE);
  $container->setDefinition('my_service', $my_service);

Deprecations

The following new deprecations occurred between symfony 3.2 and 3.4. Individual change-notices will be issued as Drupal is updated to remove interactions with these deprecated APIs.

Relevant Symfony links:

Impacts: 
Module developers
Updates Done (doc team, etc.)
Online documentation: 
Not done
Theming guide: 
Not done
Module developer documentation: 
Not done
Examples project: 
Not done
Coder Review: 
Not done
Coder Upgrade: 
Not done
Other: 
Other updates done