Symfony version(s) affected

>=7.4

Description

The Vary header(s), defined with the @Cache attributes are ignored when used in conjunction with the feature set_locale_from_accept_language.
However, the documentation doesn't mention any impact on Vary response header enabling this feature:

If this option is set to true, the Request locale will automatically be set to the value of the Accept-Language HTTP header.

When the _locale request attribute is passed, the Accept-Language header is ignored.

The possible cause is at this line, looks like the Symfony\Component\HttpKernel\EventListener\CacheAttributeListener listener overwrites the Vary header(s) passed by @Cache attributes, instead of adding to it — which may break expected behavior when custom Vary headers are required.

How to reproduce

./src/Controller/TestController.php

<?php

namespace App\Controller;

use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\HttpKernel\Attribute\Cache;

class TestController
{
    #[Cache(vary: ['X-Custom-Header'], public: true)]
    public function __invoke(): Response
    {
        return new Response('Hello world');
    }
}

./config/packages/framework.yaml

framework:
    set_locale_from_accept_language: true

curl --location 'http://localhost:8000/test'

Vary response header: Accept-Language

Possible Solution

No response

Additional Context

No response