The borrow checker knows nothing about your arena allocations.
That is if we are talking about the same thing!
All the borrow checker knows is there is a chunk of memory (the arena) in scope.
It works, no memory safety in the sense that you must manage your own garbage and you can reference uninitialized parts of the arena
I have found myself using arenas in Rust for managing circular references (networks with cycles) and if I were to do it again I think I would write that bit in C or unsafe Rust.
