Custom Rust in Nix Shell

default.nix

let
  rust-overlay = import (builtins.fetchTarball {
    url = "https://github.com/oxalica/rust-overlay/archive/master.tar.gz";
    # Optionally pin to specific commit:
    # url = "https://github.com/oxalica/rust-overlay/archive/COMMIT_HASH.tar.gz";
  });
in
with import <nixpkgs> { overlays = [ rust-overlay ]; };
mkShell {
  buildInputs = [
    bashInteractive
    # rust-bin.nightly.latest.default # or any other
    (rust-bin.fromRustupToolchainFile ./rust-toolchain.toml)
  ];
}

echo "use nix" >> .envrc
direnv allow