Rust trait bound by supertrait with itself as generic parameter - rust

Question

When working with a trait hierarchy, I got into the following problem: A trait (that is used as a trait object) should define a function that returns its own type. Of course, Self cannot be used since it would be different for each subtype. Instead, the trait should return the type of the trait object, like:
trait MySpecialTrait {
fn clone(&self) -> Box<dyn MySpecialTrait>;
}
So far, this works. But now I want to extract this functionality in its own generic supertrait to be able to write generic code that only relies on the supertrait properties, like this:
trait Cloneable<Output: ?Sized> {
fn clone(&self) -> Box<Output>;
}
trait MySpecialTrait: Cloneable<dyn MySpecialTrait> {
fn something(&self);
}
fn clone_all<T>(data: &Vec<Box<T>>) -> Vec<Box<T>>
where T: ?Sized + Cloneable<T>
{
data.iter().map(|x|x.clone()).collect()
}
But this code yields the following error:
error[E0391]: cycle detected when computing the supertraits of `MySpecialTrait`
--> src\main.rs:28:1
|
28 | trait MySpecialTrait: Cloneable<dyn MySpecialTrait> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: ...which again requires computing the supertraits of `MySpecialTrait`, completing the cycle
note: cycle used when collecting item types in top-level module
--> src\main.rs:28:1
|
28 | trait MySpecialTrait: Cloneable<dyn MySpecialTrait> {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Using associated types like this does not change anything:
trait Cloneable {
type Output;
fn clone(&self) -> Box<Self::Output>;
}
trait MySpecialTrait: Cloneable<Output = dyn MySpecialTrait> {
fn something(&self);
}
Can someone explain to me why there is a cycle? I understand that in the general case of trait A: B the supertraits of B have to be known to calculate the supertraits of A, so
trait A: B {}
trait B: A {}
cannot work. But in this case, MySpecialTrait is only referenced in the generic type arguments, so why is it required to compute the supertraits of Cloneable<dyn MySpecialTrait>?
Apart from that, is there are workaround for this problem?
Edit
I do not want clone_all to work only with all concrete subtypes of Cloneable<T>, but also with all trait types, e.g. I want to call clone_all with an argument of type Vec<Box<dyn MySpecialTrait>>.