'nix develop' with home-manager flake

I want to do development and testing on a wayland compositor that is available in unstable, but I wish to work on bleeding edge git commits of the package.

Thus, I am looking for guidance on using nix develop within the context of an existing home-manager flake. I have a flake with some overrides for dwl that draw in git versions of wlroots and dwl and I want to start a nix develop environment to work on the git dwl code.

I have read the nixos manual page for nix develop and the create/debug packages wiki entry and the ysinder blog post in addition to many pages here (discourse) and on reddit.

I have tried
nix develop nixpkgs#dwl
and while this pulls into the $PATH the necessary build tools, it leaves me with the (non-git) versions of wlroots and dwl that are present in unstable instead of the git override versions I need to compile and work on.

I have tried
nix develop /home/username/.config/home-manager#dwl
nix develop /home/username/.config/home-manager#[various permutations of username or username@host or homeConfigurations.username@host]
but I am guessing that a home-manager flake.nix is not sufficient for nix develop because all of these yield
“flake … does not provide attribute …”
“flake output attribute … is not a derivation or path”.

If I must create a new flake from scratch to use nix develop, I’ll do so, but it seems like there is a way I am simply not aware of to work on the source of the package that I already have installed.

It is likely that I am overlooking something obvious. I have a thick skin. If I am being an idiot, just tell me so, but please point me toward what I should have read.

If your flake at ~/.config/home-manager provides the package dwl with some overridden dependencies, I’d expect nix develop ~/.config/home-manager#dwl to enter a shell with those dependencies. – Your packages.x86_64-linux.dwl should evaluate to this dwl with overridden dependencies.

Whereas: nix develop nixpkgs#dwl would be a devshell for dwl from the nixpkgs flake (and wouldn’t have anything to do with ~/.config/home-manager; invoking this command wouldn’t look there for anything), and nix develop ~/.config/home-manager#username@host is looking for the devShell or package named username@host in the flake at ~/.config/home-manager, so it’s erroring out with “that output attribute is not provided”.

@rgoulter: Thank you for taking the time to read and answer.

I did try that route as well, though I did not describe it in the original post. The specific error I received when I did led me to believe I was still taking the wrong approach.

This is the home-manager flake.nix I am using:

  description = "Home Manager configuration of redacted_user";

  inputs = {
    # Specify the source of Home Manager and Nixpkgs.
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
    home-manager = {
      url = "github:nix-community/home-manager";
      inputs.nixpkgs.follows = "nixpkgs";

  outputs = { nixpkgs, home-manager, ... }:
      system = "x86_64-linux";
      pkgs = nixpkgs.legacyPackages.${system};
    in {
      homeConfigurations."redacted_user@redacted_host1" = home-manager.lib.homeManagerConfiguration {
        inherit pkgs;
        modules = [ ./redacted_host1.nix ];
        extraSpecialArgs = { hostName = "redacted_host1"; };
      homeConfigurations."redacted_user@redacted_host2" = home-manager.lib.homeManagerConfiguration {
        inherit pkgs;
        modules = [ ./redacted_host2.nix ];
        extraSpecialArgs = { hostName = "redacted_host2"; };
      homeConfigurations."redacted_user@redacted_host3" = home-manager.lib.homeManagerConfiguration {
        inherit pkgs;
        modules = [ ./redacted_host3.nix ];
        extraSpecialArgs = { hostName = "redacted_host3"; };

The overrides for dwl are within files in the import = [] set in redacted_host?.nix

nix develop ~/.config/home-manager#dwl
error: flake 'path:/home/redacted_user/.config/home-manager' does not provide attribute 'devShells.x86_64-linux.dwl', 'packages.x86_64-linux.dwl', 'legacyPackages.x86_64-linux.dwl' or 'dwl'

Right now your flake is only defining 3 outputs, which are all homeConfigurations.

With that flake.nix, it’s not possible to invoke nix develop in such a way that would get you what you want.

You need to add your overridden dwl as an output in the flake. Add something like:

packages.${system}.dwl = whatever expression you had in your imports;
1 Like

@rgoulter Thank you, again.

At that point, nothing currently in my existing flake.nix file is really of any use and the modules/imports I have written have to be re-written within the flake anyway.

It would seem that the answer to the original question

is, “yes, one must rewrite the flake from scratch. The bits already generated for home-manager cannot be used directly in nix develop.”

I have started work on doing just that and I am running into a great deal of difficulty phrasing final: prev: ... within flake.nix in a way that nix will accept, but I’ll puzzle through that.

Your experience and willingness to lend a hand here were very much appreciated.

EDIT: The above sounds like complaint. It is not. Nix is a great experience. It is like linux from the beginning was for me decades ago … and sometimes there is frustration in learning and I get to feel really stupid … like years ago. : )