Symfony version(s) affected

5.4

Description

I'm trying to decouple the cache dir from the build dir. I want to keep the build dir in the project under var/cache, but move the runtime cache directory outside the project.

Since the parameter kernel.build_dir and the Kernel-method getBuildDir have been introduced, I just changed those methods.
The problem is, if the new cache dir and the project share the same root directory, the parameter kernel.cache_dir won't stay absolute, but instead be changed to be calculated dynamically.

My use case is, that I'm trying to pack a symfony console application as a phar. I want to keep the warmed cache inside the phar, while using a cache directory in /tmp path. This breaks during the build process using https://github.com/box-project/box, because box moves the files into an own temp-directory, before warming the cache.

I can think of some workarounds, but I still think this is a bug here.

How to reproduce

It's pretty simple to reproduce without a reproducer-repository.

Create a new skeleton-project somewhere in your home-directory, eg. /home/app/project. Minimal installation is enough.
Create a directory for the cache, eg. home/app/cache.

Change the Kernel in src/Kernel.php to look like this:

<?php

namespace App;

use Symfony\Bundle\FrameworkBundle\Kernel\MicroKernelTrait;
use Symfony\Component\HttpKernel\Kernel as BaseKernel;

class Kernel extends BaseKernel
{
    use MicroKernelTrait;

    public function getCacheDir(): string
    {
        // hardcoded for simplicity reasons, make sure to change if your path is different
        return '/home/app/cache';
    }

    public function getBuildDir(): string
    {
        return parent::getCacheDir();
    }
}

Run bin/console cache:clear.

Now have a look at the App_KernelDevDebugContainer.php file in var/cache/dev/Container<hash>. Look into the method getDefaultParameters.

The parameter kernel.cache_dir will now be defined as (\dirname(__DIR__, 5).'/cache') instead of /home/app/cache.

Possible Solution

I found that this happens in the dependency injection component, specifically in this method:

https://github.com/symfony/dependency-injection/blob/dc25cfd99efda595f83a703e642b2db666b7adda/Dumper/PhpDumper.php#L2117-L2149

Unfortunately I really have no idea what's the best way to fix the issue. I think there should be a check somewhere, if the directory is actually inside the project directory, before using the dirname notation instead of the absolute path.

Additional Context

No response