php - Change Twig Loader order

So I've created a few twig loaders in my project for templates stored in databases. Simply having them implement LoaderInterface already automatically adds them to the default Twig\Loader\ChainLoader - however, I haven't found a way to configure the order.

When I check which loaders are in the ChainLoader, it's

LoaderA -> LoaderB -> FilesystemLoader

, but I want the order to be

FilesystemLoader -> LoaderB -> LoaderA

If I define twig.loader in my services.yaml, it always ends up with infinite recursion and nothing works. If I manually configure the calls to twig.loader.chain, I get the correct order of loaders, followed by a chainloader X, followed by the loaders in the "autoconfigured" order. Chainloader X is the same as the very ChainLoader Symfony configures, so... infinite recursion if a template is not found.

So how on earth do I tell twig which loaders to load in what order? Do I need to create a CompilerPass just for this simple requirement?

Solution:

You can alter the order by tagging the services manually, when priority is not specified it defaults to 0:

# services.yaml
    App\Twig\LoaderA:
        tags:
            - { name: 'twig.loader', priority: 2 }
    App\Twig\LoaderB:
        tags:
            - { name: 'twig.loader', priority: 1 }

If you prefer, since Symfony 5.3 (running under PHP 8), you can use PHP attributes instead.