A tree builder without a root node is deprecated since Symfony 4.2

[belinde]

In DependencyInjection\Configuration::getConfigTreeBuilder() a TreeBuilder is istantiated without arguments, and so triggers an E_USER_DEPRECATED error on Symfony 4.2. The problem is in the first two rows of method:

        $treeBuilder = new TreeBuilder();
        $rootNode    = $treeBuilder->root('doctrine_migrations', 'array');

I think it could be safe put the parameters ALSO in the constructor, so the error is suppressed in Symfony 4.2 but the code still works for previous versions:

        $treeBuilder = new TreeBuilder('doctrine_migrations', 'array');
        if (!is_callable([$treeBuilder, 'getRootNode'])) { // hack for backward compatibility
            $rootNode = $treeBuilder->root('doctrine_migrations', 'array');
        }

In this way new versions get the arguments in the constructor, and old versions silently ignore them. I assume that getRootNode() has been introduced in the same time of the deprecation, so it could be a good and almost inexpensive check.

[greg0ire]

Can you make a PR? Here is an example: sonata-project/SonataAdminBundle#5360

[alcaeus]

Yes, a PR would be great. Please make sure to send it to the 1.3 branch as we want to fix the error not only in 2.0 (which is master) but 1.3 as well. 👍

[belinde]

I wasn't sure about the quality of the fix... Sure, I'll do tomorrow, I don't have a PC available right now.

[belinde]

In branch 1.3 the issue has been fixed in commit e16ce0c by user Chalas, in date 2018-12-01, so it has just to be merged in master.

[jwage]

This was merged to master and is in 2.0