Oh wow, this is fantastic! Thanks for the tip and I'd like to thank you for all of the work you do on nix + Darwin. I'm using your `nix-env.fish` package and it's made things much easier than when I tried this setup a few years ago.
self: super {
fish = super.fish.override {
fishEnvPreinit = sourceBash: sourceBash "${self.nix}/etc/profile.d/nix-daemon.sh";
];
}