brand_new_Cargo.toml

[package]
name = "brand_new"
version = "0.0.1"

[dependencies]
ring = "0.16"

brand_new_src_main.rs

fn main() {}

Cargo.toml

[workspace]
members = [
    "brand_new",
    "old_rusty",
]

old_rusty_Cargo.toml

[package]
name = "old_rusty"
version = "0.0.1"

[dependencies]
ring = "0.13"

old_rusty_src_main.rs

fn main() {}