Added CacheInterface stub

[YspMark]

Closes #235

[lookyman]

The callable annotation has to have parentheses for parameters, event if there are none. Like this callable(): T.

However, in this case the callback actually optionally accepts Psr\Cache\CacheItemInterface as the first (and only) parameter.

Also, the parameter is annotated as callable|CallbackInterface in Symfony. So I think we need to add a second stub for the CallbackInterface, with templated __invoke method, and the one for CacheInterface's $callback needs to be annotated something like this: @param \Symfony\Contracts\Cache\CallbackInterface<T>|callable(\Psr\Cache\CacheItemInterface=): T $callback.

Finally, please add some tests.

[lookyman]

\Psr\Cache\CacheItemInterface=, notice the = at the end. See https://phpstan.org/writing-php-code/phpdoc-types#callables.

For the Parameter $callback of method Symfony\Contracts\Cache\CacheInterface::get() has invalid type Psr\Cache\CacheItemInterface. error, we need to actually add the Psr\Cache\CacheItemInterface stub as well. It should be sufficient for it to be an empty class. We only need to know the class, we don't care about methods. See https://phpstan.org/user-guide/stub-files, Why is PHPStan complaining about “Class not found” in a stub file?

[YspMark]

Thanks for the feedback, I was not familiar with the = optional notation, actually thought it was a typo.

[ondrejmirtes]

Can you please write some tests in https://github.com/phpstan/phpstan-symfony/blob/master/tests/Type/Symfony/ExtensionTest.php to verify this signature works as expected? More info here: https://phpstan.org/developing-extensions/testing#type-inference

[ondrejmirtes]

The case with \Symfony\Contracts\Cache\CallbackInterface<T> should also be tested.

[ondrejmirtes]

Thank you.