readTree uses the output attribute set of default.nix as the value for
nixos.socrates, which disables me from resolving nixos.socrates.rebuild since
there is no rebuild attribute in the output attribute set from default.nix.
If I rename default.nix -> configuration.nix, I can resolve
nixos.socrates.{configuration,hardware,rebuild}.
Nix complains that `nixos.socrates` is not a function but a set. By adding
`{ ... }:` to the top of the file, I'm hoping to change it from a set to a
function.
When I build socrates using `sudo nixos-rebuild [...] switch`, my
`nixos-config` (i.e. <briefcase/nixos/socrates/default.nix>) is a simple Nix
anonymous function. Typically readTree populates my pkgs, briefcase, depot
function parameters with <nixpkgs>, <briefcase>, <depot>, but `nixos-rebuild` is
unaware of `readTree`.
For now I'm manually importing these dependencies, and I'm leaving a TODO to
reconsider switching to the `{ pkgs, briefcase, ... }` style when I better
understand NixOS.