Thank you @X-Coder264.

I just noticed by accident. What is this feature for? Is there some docs?

https://symfony.com/doc/current/reference/dic_tags.html#auto-alias

That looks very confusing. What is the usecase?

For example, I work on a highly modular application that is working in different European countries (one instance of the app per country). Almost all features must be switchable (they can be enabled or disabled depending on the requrements - which we solve with Flagception), but a lot of these features also have different requirements for each country - business validation rules, export stuff (what data and in what format must be exported), stuff like fiscalization where each country has its own authority to which you have to register the invoices that you create for your customers when they pay for something on the platform (and each of them has a different API which we must consume) etc.

So all of that stuff which needs to be customized differently because it's country specific has an interface and thanks to this auto-alias feature all I have to do is change the parameter which controls the auto-aliasing in parameters.yaml to point the interface alias to the concrete implementation of that interface for that country.

Fiscalization example:

Domain\Billing\Fiscalization\AuthorityRegistratorInterface:
        tags:
            - { name: auto_alias, format: '%fiscalization_authority_registrator_class%' }

And then in parameters.yaml of the Croatian app I have:

fiscalization_authority_registrator_class: Infrastructure\Billing\Fiscalization\CroatianAuthority\AuthorityRegistrator

while for the Slovenian app it is:

fiscalization_authority_registrator_class: Infrastructure\Billing\Fiscalization\SlovenianAuthority\AuthorityRegistrator

Why not separate that via existing *_env.yaml convention? It support also routing and parameters compared services only.