The documentation states that invalid cache keys always throw an exception #28

Description

The documentation states that an invalid cache key throws a Psr\Cache\InvalidArgumentException:

• reference/adapter.md: "Cache keys must follow the PSR-6 rules: an empty key, or a key containing one of the reserved characters {}()/\@:, throws a Psr\Cache\InvalidArgumentException."
• reference/tasks/set_task.md: "If the input does not override the placeholder key, the empty key throws a Psr\Cache\InvalidArgumentException."

This is only true when assertions are enabled. Symfony cache adapters (ArrayAdapter, and every adapter based on AbstractAdapterTrait: filesystem, Redis, APCu...) only validate the keys with assert(): with zend.assertions=-1 (production php.ini), an empty key or a key with reserved characters is silently accepted and the item is stored.

Reproduction

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

foreach ([new ArrayAdapter(), new FilesystemAdapter('test')] as $adapter) {
    foreach (['', 'a/b'] as $key) {
        $adapter->save($adapter->getItem($key)->set('value'));
    }
}

$ php -d zend.assertions=1 test.php
Symfony\Component\Cache\Exception\InvalidArgumentException (for each adapter and key)

$ php -d zend.assertions=-1 test.php
(no exception, the items are stored and can be read back)

Found with the CI of #27 (setup-php uses the production php.ini): a test expecting the exception on an empty key failed.

Tested on main (e88cf4f), symfony/cache 7.4 / 8.1, PHP 8.5.

Proposed fix

Document that the key validation belongs to the adapter, and that Symfony adapters only reject invalid keys when assertions are enabled: in production, a placeholder key '' not overridden by the input stores / reads every item under the same empty key.

Requirements

• Documentation updates
  • Reference
  • Changelog
• Unit tests

Breaking changes

None (documentation only).