Problem/Motivation
With the release of Symfony 4.3 the event dispatching changed: https://symfony.com/blog/new-in-symfony-4-3-simpler-event-dispatching
This already causes issues for drupal regarding the upgrade to Symfony 4.x or 5, for example in
#3055194: [Symfony 5] The signature of the "Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher::dispatch()" method should be updated to "dispatch($event, string $eventName = null)", not doing so is deprecated since Symfony 4.3. and #3055180: [META] Make Drupal 8 work with Symfony 5 (along with Symfony 3 and 4).
But Drupal isn't the only system that has to deal with that. Third party libraries drupal leverages directly or via contributed modules need to adapt to this change. Therefore the symfony project itself provides a migration path by decorating the event dispatcher with LegacyEventDispatcherProxy as described in blog post linked above.
This LegacyEventDispatcherProxy has been released as part of symfony/event-dispatcher 4.3.0.
The event-dispatcher has no dependency to any 4.3 versions of other symfony components but is backward compatible to symfony 3.4 which we use in Drupal 8:
"require-dev": {
"symfony/dependency-injection": "~3.4|~4.0",
"symfony/expression-language": "~3.4|~4.0",
"symfony/config": "~3.4|~4.0",
"symfony/http-foundation": "^3.4|^4.0",
"symfony/service-contracts": "^1.1",
"symfony/stopwatch": "~3.4|~4.0",
"psr/log": "~1.0"
},
"conflict": {
"symfony/dependency-injection": "<3.4"
},See https://github.com/symfony/event-dispatcher/blob/4.3/composer.json
But no matter how we deal with the migration within the Drupal project, we already have a critical issue.
As an example, the upcoming 5.1.0 release of the solarium library implements the migration path as recommended by the symfony project:
https://github.com/solariumphp/solarium/pull/690
This library is required by the search_api_solr module that has more than 14,000 active 8.x installations already. search_api_solr injects the Drupal event dispatcher into the solarium Solr Client.
From my point that works perfectly fine. But Drupal prohibits the update because of this version constraint:"symfony/event-dispatcher": "~3.4.0",
This version constraint is simply wrong as Drupal doesn't use the event dispatcher provided by this module but only it's EventDispatcherInterface which has been kept compatible in symfony 4.x.
So the current situation is that Drupal blocks feature and security updates of third party libraries which use symfony event dispatching and adopting to symfony event dispatching changes in the proposed and compatible way. That has to be considered as critical.
Proposed resolution
Adjust the version requirement like this:"symfony/event-dispatcher": "~3.4.0|~4.0"
Afterwards composer will resolve the correct combination of module versions without upgrading the other symfony components at all.
Drupal will still use 3.4.
Remaining tasks
Just apply the patch.
The (failing) test result of https://www.drupal.org/project/drupal/issues/3055194#comment-13221924 already proves that drupal will work perfectly fine with symfony/event-dispatcher:4.3
User interface changes
None
API changes
None
Data model changes
None
Release notes snippet
Todo, maybe not required at all.
