I am currently trying for the first time to migrate from Symfony 3.4 to 4.3. I'm at the stage where I have to remove the depreciation so that I can update the dependencies via composing as the doc says I have solved all the depreciations except one that I have a little trouble here it is:
Relying on service auto-registration for type "AppBundle\Entity\AdaImporterDoc" is deprecated since Symfony 3.4 and won't be supported in 4.0. Create a service named "AppBundle\Entity\AdaImporterDoc" instead.
This is not a rare situation when upgrading to Symfony 4.
To avoid that deprecation warning message that is, in fact, a false positive (Read This), you can replicate the way Symfony 4 works, doing the following in your app/config/config.yml:
parameters:
container.autowiring.strict_mode: true
This way that 'fake' warning message will disappear and you will get real errors, if found.
If you want to know what changed on autowiring, this Strict Autowiring Mode is good place to start.