Multiple imports of the same NixOS module not allowed with flake

[datafoo]

Describe the bug

Importing multiple times a given NixOS module exposed by a flake is not allowed. Nix complains about options being already declared.

Steps To Reproduce

1. Define a flake that expose a NixOS module which declare at least one option: flake.nix:

   {
     outputs = { self }: {
   
       nixosModules.debug = { config, lib, ... }:
       {
         options = {
   
           debug = {
   
             enable = lib.mkOption {
               type = lib.types.bool;
               default = false;
               description = ''
                 Whether to enable debug.
               '';
             };
           };
         };
   
         config = lib.mkIf config.debug.enable {
   
           systemd.globalEnvironment = {
             SYSTEMD_LOG_LEVEL = "debug";
           };
   
         };
       };
   
     };
   }
   

2. Define another flake that uses the previous flake: flake.nix:

   {
     inputs.nixpkgs.url = github:NixOS/nixpkgs/nixos-22.05;
     inputs.debug.url = path:/home/me/flakes/debug;
   
     outputs = inputs@{ self, nixpkgs, ... }: {
   
       nixosConfigurations.mymachine = nixpkgs.lib.nixosSystem {
         system = "x86_64-linux";
         modules =
           [ 
             (import ./configuration.nix)
           ];
         specialArgs = { inherit inputs; };
       };
   
     };
   }

   configuration.nix:

   { config, pkgs, inputs, ... }:
   
   {
     imports =
       [
         ./hardware-configuration.nix
         inputs.debug.nixosModules.debug
         inputs.debug.nixosModules.debug
       ];
   
     # here goes the rest of the config
   }

3. Build the configuration and notice the error

   $ nixos-rebuild switch --flake .#mymachine
   building the system configuration...
   error: The option `debug.enable' in `/nix/store/da9dyx30lsdgw2x2gnxkc88aq1d9fwik-source/flake.nix' is already declared in `/nix/store/da9dyx30lsdgw2x2gnxkc88aq1d9fwik-source/flake.nix'.
   (use '--show-trace' to show detailed location information)

Expected behavior

It should be allowed to import multiple times a NixOS module that declare options. It already works today unless this module is exposed by a flake.

Importing multiple times into the same module is not very useful. What is useful is to import the same module (i.e.: D) into several modules (i.e.: B, C) which are themselves imported into one final module (i.e.: A):

• A import B
• A import C
• B import D
• C import D

nix-env --version output

nix-env (Nix) 2.11.0

[SuperSandro2000]

It should be allowed to import multiple times a NixOS module that declare options. It already works today unless this modules is exposed by a flake.

Where the relative import paths the same before?

[datafoo]

I made a test with a relative import path duplicated and it was working.

[jcollie]

I worked around this by creating a new module E that imports D from a flake. Then I modify B & C to import E instead of importing D directly.

[datafoo]

ping

[TheColorman]

This is quite annoying when you have several modules with the same module dependency, and have situations where you want to import two or more of them.

[SuperSandro2000]

@fricklerhandwerk the module system is defined in nixpkgs, so we should move zhe issue to there

[datafoo]

@fricklerhandwerk the module system is defined in nixpkgs, so we should move zhe issue to there

Feel free to do so. I do not have the permission to do it myself.