I don’t see any obvious error. Maybe post your hardware.nix and just do trial and error, commenting out bits of the config until you can narrow down which part it’s complaining about. Hopefully someone smarter comes along though and can help pinpoint the issue.
it’s called rustc which is the actual command. However, most people use cargo which has rustc on its path.
If you’re on NixOS (and following a nixos-* channel), then you can do:
$ command-not-found rustc
The program 'rustc' is not in your PATH. It is provided by several packages.
You can make it available in an ephemeral shell by typing one of the following:
nix-shell -p mrustc-bootstrap
nix-shell -p rustc
nix-shell -p rustup