On this page the links to chacha and hc128 does not point to an actual page: https://docs.rs/rand/0.6.0/rand/rngs/struct.StdRng.html

Also https://rust-random.github.io/book/guide-rngs.html this page mentions chacha and other rngs and seems to imply they are in the rngs module, but I cant find it there or anywhere else.