Kibwen is saying that there was an idea to have `fn drop(&mut x)` from Drop trait become `fn drop_own(&own x)`. Then `&own` would do mutation and drop the owner of the reference. A regular &mut reference shouldn't do that outside of `drop(&mut x)`.
That's the destructor function, that is written by you and called by Rust before actually destroying something. The function that you want to look at is [1].
If you read the docs at your link it even says:
> This method is called implicitly when the value goes out of scope, and cannot be called explicitly (this is compiler error E0040).
> However, the mem::drop function in the prelude can be used to call the argument’s Drop implementation.
By the way the implementation of the function drop is just an empty function [2]; that's enough as local variables are destroyed on function return.
Mutable reference is a "borrow" which means you take a value from an owner and promise to return it back, and you cannot destroy a thing that you must return.
The drop function being talked about here is the one I pointed to, not the one you pointed to. The Drop trait is built into the language (as a lang item), std::mem::drop is just a regular old function.
Not inherently, sure. But ultimately this is far afield of what I was trying to say, which is that the signature being discussed of being changed from &mut T to &owned T is the one from the Drop trait. That’s it.