How to integrate nix-homebrew into den?

[bennyandresen]

I'm lost on how to set den up with nix-homebrew support. I'm very intrigued and there is lots of documentation and code but I'm quite overwhelmed.

This is how one is supposed to integrate it into the flake.nix regular nix-darwin style:

darwinConfigurations."my-laptop" = nix-darwin.lib.darwinSystem {
      modules = [
      configuration
      nix-homebrew.darwinModules.nix-homebrew
      { nix-homebrew = {
          enable = true;
          enableRosetta = true;
          user = "benny";
          taps = {
            "homebrew/homebrew-core" = homebrew-core;
            "homebrew/homebrew-cask" = homebrew-cask;
          };
	  # declarative taps
          mutableTaps = false;
        }; }
      # nix-homebrew / nix-darwin tap awareness
      ({ config, ... }: {
        homebrew.taps = builtins.attrNames config.nix-homebrew.taps;
      })
      ];
    };

I don't know where the equivalent of the darwinSystem with the modules variable is in a den architecture.

Thanks in advance for any advice.

[vic]

Hey @bennyandresen,

Our default template is a good start, you only need to have a nix-darwin input somewhere.

Here is where the darwinConfiguration is being created, Den automatically detects how to build the OS based on your host system.

So, following our default-template example, the darwin host is named apple. To enable nix-homebrew you would create a module that enhances the apple aspect:

{ inputs, ... }:
{ 
  den.aspects.apple = {
    darwin = {
      # everything inside here is a nix-darwin module, so basically anything you did before
      # when creating darwinConfiguration manually can be added here.
      # like any darwin module, you can import other modules. All these are from your code:
      imports = [
        inputs.nix-homebrew.darwinModules.nix-homebrew
        { nix-homebrew = {
            enable = true;
            enableRosetta = true;
            user = "benny";
            taps = {
              "homebrew/homebrew-core" = homebrew-core;
              "homebrew/homebrew-cask" = homebrew-cask;
            };
	    # declarative taps
            mutableTaps = false;
          }; }
        # nix-homebrew / nix-darwin tap awareness
        ({ config, ... }: {
          homebrew.taps = builtins.attrNames config.nix-homebrew.taps;
        })
      ];
    };
  };
}

Just make sure you also have a flake-file.inputs.nix-homebrew.url set somewhere.

Hope that helps, thanks for trying Den :)

[bennyandresen]

Unfortunately that doesn't help. When I set flake-file.inputs.nix-homebrew.url in the modules/inputs.nix how does it magically turn into nix-homebrew inside the modules/aspects/apple.nix? Don't I need to reference inputs or rather inputs.flake-file.inputs.nix-homebrew? I tried it and I also tried setting flake-file.inputs.nix-homebrew.url within the same modules/aspects/apple.nix file and still I couldn't reference it without getting an evaluation error.

My nix-fu seems to be too weak to intuitively get den, I'm sorry.

(I also called nix run .#write-flake after each input change.)

[bennyandresen]

I've shared my in-progress repository here:
https://github.com/bennyandresen/den-experiment

Maybe this will help understanding where I'm stuck. I appreciate the help as I'm conceptually totally on board with den

[vic]

There's no magic, your intuition is correct, if you add the flake-file.inputs.nix-homebrew.url, after running nix run .#write-flake, then you access it via inputs.nix-homebrew (NOT inputs.flake-file.inputs.nix-homebrew that does not exist), inputs come from your flake manifest. So there's no magic regarding how inputs are read.

Anything that you previously did in a nix-darwin setup, translates directly into Den:

{ inputs, ... }: {
  den.aspects.myhost.darwin = {
    # here nothing changes.
    imports = [ inputs.nix-homebrew.blabla ];
  };
}

Maybe I should just used a short example like this, instead of trying to paste your previous code to make the answer clear.

Also, looking at your repo, I'd recommend not using huge modules, try instead having many files, each of them can contribute to the same aspect, each of them focused on adding something to the aspect, this way you can incrementally add features, and can better iterate instead of messing around with a huge file where everything can get wrong at once.

# modules/enable-homebrew.nix
{ inputs, ... }:
{
  den.aspects.myhost.darwin = { 
    imports = [ inputs.nix-homebrew.blabla ];
    nix-homebrew.enable = true;
  };
}

# modules/homebrew-taps.nix
{
  den.aspects.myhost.darwin = { 
    # more stuff here
  };
}

this way you incrementally enhance your host aspect, once an small step works you add a file to get into the next one.

[bennyandresen]

Yes, thank you. This helped! I will split up my modules, I just wanted to do a straight port of my freshly created already working nix-darwin and home-manager flake setup and then embrace the den way afterwards when I have a stable base.

[bennyandresen]

Now I'm getting another issue and I think it's caused by den. Could it be that nix-homebrew and den have a weird interaction? I get the error that I have to force nix-homebrew.package because it gets set multiple times.

So right now, based on the den-experiments trunk commit I'm the import gets evaluated 4 times and when I play around a bit to force it to build a darwinConfiguration I also see an issue that my all my defined Casks, taps, brews gets repeated 4 times in the generated Brewfile. Very weird behavior. (This does not happen in the above shared flake.nix)

       error: The option `nix-homebrew.package' is defined multiple times while it's expected to be unique.

       Definition values:
       - In `/nix/store/cvnyla998cadqapqq9cbbcjp9a5cf828-source/modules/aspects/benny.nix, via option den.aspects.benny.darwin':
           {
             lastModified = 1761551821;
             lastModifiedDate = "20251027075701";
             name = "brew-4.6.19";
             narHash = "sha256-N3Zj73TAxclhLGgADbPVwcVrhYIBKUgAxjfQuOXre6s=";
           ...
       - In `/nix/store/cvnyla998cadqapqq9cbbcjp9a5cf828-source/modules/aspects/benny.nix, via option den.aspects.benny.darwin':
           {
             lastModified = 1761551821;
             lastModifiedDate = "20251027075701";
             name = "brew-4.6.19";
             narHash = "sha256-N3Zj73TAxclhLGgADbPVwcVrhYIBKUgAxjfQuOXre6s=";
           ...
       - In `/nix/store/cvnyla998cadqapqq9cbbcjp9a5cf828-source/modules/aspects/benny.nix, via option den.aspects.benny.darwin':
           {
             lastModified = 1761551821;
             lastModifiedDate = "20251027075701";
             name = "brew-4.6.19";
             narHash = "sha256-N3Zj73TAxclhLGgADbPVwcVrhYIBKUgAxjfQuOXre6s=";
           ...
       - In `/nix/store/cvnyla998cadqapqq9cbbcjp9a5cf828-source/modules/aspects/benny.nix, via option den.aspects.benny.darwin':
           {
             lastModified = 1761551821;
             lastModifiedDate = "20251027075701";
             name = "brew-4.6.19";
             narHash = "sha256-N3Zj73TAxclhLGgADbPVwcVrhYIBKUgAxjfQuOXre6s=";
           ...
       Use `lib.mkForce value` or `lib.mkDefault value` to change the priority on any of these definitions.

[vic]

I will take a look at your repo later today, thanks for the report.

[vic]

@bennyandresen, hm, I'm having a hard-time following with all that code in the repo and was not able to find where you had to use lib.mkForce, but everything in your repo seems good to me. I cloned your repo and run inside GH Actions (my changes here) and it succeeds! building both your host and the standalone-home-manager you have.

If you are still getting the error, it would be best to create a bug reproduction repository and share that with me. (See instructions in contributing). Try keeping it to the absolutely minimal that I can also test.