On a second though, the actual error seems to be elsewhere, so still can use proper indexing
[package]
name = "hwphysics"
version = "0.1.0"
authors = ["Hedgewars Project"]
edition = "2018"
[dependencies]
fpnum = { path = "../fpnum" }
integral-geometry = { path = "../integral-geometry" }
land2d = { path = "../land2d" }