den duplicating config value on import

[vic]

I put a minimal example up here: https://github.com/Cybolic/nix-den-double-import-demo

Awesome!, @Cybolic thank you so much, I managed to reduce it even further:

I removed your routes.nix, and here is the complete hosts.nix:

let
  once.nixos = { pkgs, ... }: {
    users.users.test-user.packages = [ pkgs.hello ];
  };
in
{
  den.hosts.x86_64-linux.test-host.users.test-user = { };
  den.default.includes = [ once ];
}

Here's the output:

vic@nargun ~/h/nix-den-double-import-demo> nix repl
Nix 2.31.2
Type :? for help.
nix-repl> :lf . 
warning: Git tree is dirty
Added 23 variables.

nix-repl> outputs.nixosConfigurations.test-host.config.users.users.test-user.packages
[
  «derivation /nix/store/dzgpbp0vp7lj7lgj26rjgmnjicq2wf4k-hello-2.12.2.drv»
  «repeated»
  «repeated»
]

This correctly reproduces the bug (even worse, in my reduced example, we have THREE packages, when there should be only one). The problem was not submodules (attrs) but arrays, den is duplicating values and they are evident at arrays.

Thanks to both of you for helping find the bug. I will open an issue!

Originally posted by @vic in #35 (reply in thread)

[vic]

@Cybolic, @mariolopjr

The PR #42 is still WIP, the nixos and macos testsuites are ok now, but some unit tests are failing due to my changes, I will fix them asap.

Changes for fix:

Our dependencies system is now separate from the actual aspect definitions.

Added a test that checks only one hello package is contributed to the config.

Basically we have more types of context now to avoid the recursion:

{ host } is for Host configuration (likely nixos/darwin)
{ host, user } is for User config (most likely homeManager)
{ home } is for standalone home-manager.

{ fromUser, toHost } is for users contributing configuration to hosts.
{ fromHost, toUser } is for hosts contributing to its users.

Using these more explicit contexts instead of how we previously only used { host, user } for the bi-directional dependencies. Fixed this.

So basically, contexts need to be exact, { host, ...} is just { host }, according to lib.functionArgs there's no way to tell them apart.

If you look at the definition of host/user/home aspects, they only include den.default.
And we have some parametric defaults that add configuration depending on context,

for example, this one just adds the host-same-class values from den.defaults into a host.

our den.default is how dependencies work via parametric functions. So, in den the argument names (the context) of configuration providers is quite important, that's how they know what kind of configuration to produce.

Here's the output of running my fork of the reproduction repository:

vic@nargun ~/h/nix-den-double-import-demo> nix eval --override-input den github:vic/den/deps --refresh .#.nixosConfigurations.test-host.config.users.users.test-user.packages
warning: not writing modified lock file of flake 'git+file:///home/vic/hk/nix-den-double-import-demo':
• Updated input 'den':
    'github:vic/den/04dfe099cc7d4f773f4fd50bdf0571791a2e9fad?narHash=sha256-pM0/ri%2B4LPrZUIv9c8Bh4%2BRyB2VMGyChXrxyIP4mbjs%3D' (2025-11-05)                          → 'github:vic/den/3dfb65c872655fe0f3853a6229ceda32cd4045ed?narHash=sha256-1UUIU8nddcNTqGr2Wz3ASVXxbBIafeU/fGSelhd1GpA%3D' (2025-11-06)
trace: [ "host" ]
trace: [ "aspect-chain" "class" ]
trace: [ "fromUser" "toHost" ]
[ «derivation /nix/store/dzgpbp0vp7lj7lgj26rjgmnjicq2wf4k-hello-2.12.2.drv» ]

[vic]

As an additional example see den._.define-user that is context generic.

[vic]

So, basically __functor = den.lib.parametric true means that the aspect does just one thing: it dispatches its includes list-of-functions according to the argument that the aspect itself was called with, and nothing more (previously it also added the aspect owned attributes, that is <aspect>.<class>.<setting> = value) now that is not a responsibility of the parametric functor. See how in dependencies.nix how static attributes set on den.default are included depending on the context.