evaluation warning: Package 'a-0' in /nix/store/eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee-default.nix:15 has the following problem: deprecated: Package a is deprecated and superseeded by b. See https://nixos.org/manual/nixpkgs/unstable#sec-problems
warning: you did not specify '--add-root'; the result might be removed by the garbage collector
