Quite accidentally I discovered a bug with my implementation: if a value that is also a callable is returned from a field, it will get wrapped in a Deferred wrapper and be called as a callable, instead of simply being returned as a value.

E.g.:

function test() {
    throw new RuntimeException('This is called!');
}

#[Type]
class Test {
    #[Field]
    public string $title = 'test';
}

class TestController {
    #[Query]
    public function test(): Test {
        return new Test();
    }
}

If you then run the test { title } query, instead of simply returning the {"title": "test"}, it would call the test function - because is_callable('test') returns true.

Potential fixes

This could be solved two ways:

1. remove support for callable, only leave support for actual Closure
2. keep support for callable, but make it so it wraps values in Deferred based on whether the type was specified as callable, not if the value itself is callable

This PR implements option #1. Option #2 would require some architectural changes to how GraphQLite works, way outside the scope of this feature :)