How to make nix shell use my home-manager flake input?

Help
1

I have nixpkgs as a flake input to my home-manager configuration flake.

How can I configure my registry so that nix shell nixpkgs#... will use the input that is locked in my configuration flake?

3

There is a gotcha when pinning nixpkgs registry entry to a hardcoded path in the /nix/store. That is, any flakes you develop locally which reference nixpkgs indirectly via the registry will lock your store path, possibly breaking downstream consumers. Because of this, on my nixos system, I pin a nixos registry entry instead. If you are only using home-manager you could call it whatever you what, like localpkgs or something.

4

Try nix shell --inputs-from ~/.config/home-manager foobar

It won’t touch your registry though. Works just for this command.

5

The problem is relying on the registry in your flake…

The registry is nice to use on the CLI, but a footgun within a flakes input. I use flakes for 3ish years now, and am still (or even more) the opinion that we should remove flake:* input URLs and especially “implicit” inputs through the argument set.

1 Like
6

I have

nix.registry = {
       nixos = {
         from = { type = "indirect"; id = "nixos"; };
         flake = args.nixpkgs;
       };

in my hm config to avoid re-download and re-evaluation of nixpkgs every time I do a nix search nixos foobar and to avoid massive downloads on every nix shell invocation.

2 Likes
7

Can you expand on that? Are you using the flake version of home-manager? Because in my flake based config there is no args.

8

Yes, I’m using a flake based setup.

Using the HM-Module on NixOS my HM config starts with args@{ config, pkgs, ... }: and I pass nixpkgs from the system flake.

Similar on a Ubuntu machine where I have only HM-flake. I have extraSpecialArgs = { inherit (inputs) nixpkgs }; which is captured in args as above.

1 Like