> I put it up on the Rust forums for comments, and got replies that I should stop doing all that fancy stuff and just use indices into arrays.[1] Or arena allocation. Things that bypass the Rust ownership system. Those approaches would probably have more bugs.

I ran into this years ago as well. It was very unsatisfying. Maybe Rust is just missing a good GC type?

It's not an allocation problem. It's a back-reference problem. When struct A owns struct B, and B needs to be able to find A, that's surprisingly difficult to set up in Rust. Even for structures where B is inside of A's struct.