$ nix-shell /home/exi/git/nixpkgs --pure --dry-run -A rustNightly.cargo
these derivations will be built:
  /nix/store/vflxcakp79y9q9bmx7gvgab6dy0axl18-rustc-beta-2016-11-16-ge627a2e.drv
  /nix/store/2pmm7iksbj9wlm6jzybnaw922jvzfnyl-cargo-0.14.0.drv
  /nix/store/vjn6xsb5g2hhj09jhdsmalsbz1i02bp8-rustc-nightly-2016-11-23-gd5814b0.drv
  /nix/store/y7prm9cm9iaaxi32389v6s91yn832igk-cargo-nightly-2016-07-25-fetch.drv
build input /nix/store/r76hz6zqyrk4brjm5xvis437yjln3fzj-cargo-0.14.0 does not exist