How to check if a class uses a trait in PHP?

Notice that a trait may use other traits, so the class may not be using that trait directly. And also the class may be inherited from a parent class who is the one uses the trait.

Is this a question that can be solved within several lines or I would have to do some loops?

The class_uses() function will return an array containing the names of all traits used by that class, and will work by passing it a class name or an instance.... however, you'd need to "recurse" through the inheritance tree to get all traits used, and through each trait as well

EDIT

Note that stealz at op dot pl has provided an example function showing how to do this recursion in the comments section of the linked PHP Docs page

If anyone has this problem while using the Laravel framework, that has a helper function called class_uses_recursive().

https://laravel.com/docs/8.x/helpers#method-class-uses-recursive