Symfony version(s) affected

<6.0.0

Description

On older, supported versions of Symfony (4.4, 5.3, and 5.4) the Psr16Cache class is not compatible with psr/simple-cache:3.0.0. Trying to use those versions together results in this error:

PHP Fatal error: Declaration of Symfony\Component\Cache\Psr16Cache::get($key, $default = null) must be compatible with Psr\SimpleCache\CacheInterface::get(string $key, mixed $default = null): mixed

Users must either upgrade to Symfony 6.0 or downgrade psr/simple-cache to 1.x or 2.x.

Composer does not currently prevent users from installing these conflicting versions. This causes application errors for users who aren't fixing transitive dependencies like psr/simple-cache to a specific version and use tools like composer update or Dependabot to upgrade those transitive dependencies.

How to reproduce

Create a composer.json file like this:

{
    "require": {
        "psr/simple-cache": "^3.0",
        "symfony/cache": "5.4.*"
    }
}

And then try running this simple PHP script:

<?php

use Symfony\Component\Cache\Adapter\ArrayAdapter;
use Symfony\Component\Cache\Psr16Cache;

require_once 'vendor/autoload.php';

$cache = new Psr16Cache(new ArrayAdapter());

The issue also occurs with symfony/cache constraints of 5.3.* and 4.4.*.

Possible Solution

I see two possible solutions:

1. Add psr/simple-cache as a non-dev dependency containing the supported version ranges; or
2. Add psr/simple-cache to the conflict section for versions >=3.0.0

Either approach would ensure that users aren't able to install incompatible versions.

Additional Context

No response