Flakelight-crossplatform

About

Simple flakelight module for adding cross-platform modules for darwin and nixos systems.

Quickstart

1. Add flakelight-crossplatform to your flakelight flake like so:

{
  inputs = {
    flakelight.url = "github:accelbread/flakelight";
    flakelight-darwin.url = "github:cmacrae/flakelight-darwin";
    flakelight-crossplatform.url = "github:rencire/flakelight-crossplatform";
  };

  outputs =
    {
      flakelight,
      flakelight-darwin,
      flakelight-crossplatform,
      ...
    }@inputs:
    flakelight ./. {
      inherit inputs;
      imports = [
        flakelight-darwin.flakelightModules.default
        flakelight-crossplatform.flakelightModules.default
      ];
    };
}

2. Add the cross-platform nix module(s) in the flake.nix, or use flakelight's folder autoload behavior and add the modules as individual files under nix/crossplatformModules folder.

Note: the interface is the same as nixosModules, except we replace nixosModule/nixosModules with crossplatformModule/crossplatformModules.

e.g. Folder structure when using flakelight's folder autoload behavior:

.
├── crossplatformModules
│   └── example.nix
├── darwin
│   └── host1
│       ├── configuration.nix
│       └── default.nix
└── nixos
    └── host2
        ├── configuration.nix
        └── default.nix

3. Import the the cross-platform modules in the darwin and nixos host configurations. e.g.

nix/darwin/host1/default.nix

{ inputs, ... }:
{
  system = "aarch64-darwin";
  modules = [
    inputs.self.crossplatformModules.example
    ./configuration.nix
  ];
}
  

nix/nixos/host2/default.nix

{ inputs, ... }:
{
  system = "x86_64-linux";
  modules = [
    inputs.self.crossplatformModules.example
    ./configuration.nix
  ];
}
  

4. Rebuild hosts

darwin-rebuild switch --flake .#host1 

nixos-rebuild switch --flake .#host2

Motivation

In my flakelight dotfiles, I have both darwin and nixos configurations defined for different macs and pcs I own. Both of these confiurations use modules defined in the folders darwinModules and nixosModules respectively.
However, I noticed that some of the configuration in the those modules can actually be shared between the two different type of systems. (e.g. settings for nix such as nix.gc.automatic, nix.settings, etc.)

Here's an example to illustrate the problem and potential solutions:

Example Problem

e.g. folder structure with duplicate module-c module:

.
├── flake.nix
└── nix
    ├── darwin
    │   └── host1
    │       ├── configuration.nix
    │       └── default.nix
    ├── darwinModules
    │   ├── module-a.nix
    │   └── module-c.nix
    ├── nixos
    │   └── host2
    │       ├── configuration.nix
    │       └── default.nix
    └── nixosModules
        ├── module-b.nix
        └── module-c.nix

nix/darwin/host1/default.nix

{ inputs, ... }:
{
  system = "aarch64-darwin";
  modules = [
    inputs.self.darwinModules.module-a
    inputs.self.darwinModules.module-c
    ./configuration.nix
  ];
}

nix/nixos/host2/default.nix

{ inputs, ... }:
{
  system = "x86_64-linux";
  modules = [
    inputs.self.nixosModules.module-b
    inputs.self.nixosModules.module-c
    ./configuration.nix
  ];
}

Potential Solution

See how inputs.self.nixosModules.example is duplicated in both the nixosModules and the darwinModules folder. First step we can try to share the common module files is to move them to a crossplatformModules folder.

Folder structure with addition of crossplatformModules folder:

.
├── flake.lock
├── flake.nix
└── nix
    ├── crossplatformModules
    │   └── module-c.nix
    ├── darwin
    │   └── host1
    │       ├── configuration.nix
    │       └── default.nix
    ├── darwinModules
    │   └── module-a.nix
    ├── nixos
    │   └── host2
    │       ├── configuration.nix
    │       └── default.nix
    └── nixosModules
        └── module-b.nix

Now, we'll have to import these via relative file paths:

nix/darwin/host1/default.nix

{ inputs, ... }:
{
  system = "aarch64-darwin";
  modules = [
    inputs.self.darwinModules.module-a
    ../../crossplatformModules/module-c.nix
    ./configuration.nix
  ];
}

nix/nixos/host2/default.nix

{ inputs, ... }:
{
  system = "x86_64-linux";
  modules = [
    inputs.self.nixosModules.module-b
    ../../crossplatformModules/module-c.nix
    ./configuration.nix
  ];
}

Pros

• Simple, no need for additional tooling

Cons

• Have to maintain relative file references
• Not as consistent with pattern of using inputs.self... for including re-usable modules.

Refining the solution

We can refine the solution to support importing with the inputs.self... convention in our host configurations.

We'll update the flake.nix to include our flakelight-crossplatform module:

{
  inputs = {
    flakelight.url = "github:accelbread/flakelight";
    flakelight-darwin.url = "github:cmacrae/flakelight-darwin";
    flakelight-crossplatform.url = "github:rencire/flakelight-crossplatform"; # Added
  };

  outputs =
    {
      flakelight,
      flakelight-darwin,
      flakelight-crossplatform, # Added
      ...
    }@inputs:
    flakelight ./. {
      inherit inputs;
      imports = [
        flakelight-darwin.flakelightModules.default
        flakelight-crossplatform.flakelightModules.default # Added
      ];
    };
}

Now we can update the host configurations:

nix/darwin/host1/default.nix

{ inputs, ... }:
{
  system = "aarch64-darwin";
  modules = [
    inputs.self.darwinModules.module-a
    inputs.self.crossplatformModules.module-c
    ./configuration.nix
  ];
}

nix/nixos/host2/default.nix

{ inputs, ... }:
{
  system = "x86_64-linux";
  modules = [
    inputs.self.nixosModules.module-b
    inputs.self.crossplatformModules.module-c
    ./configuration.nix
  ];
}

Pros

• Can follow the inputs.self... import convention in our host configurations

Cons

• Need to add a dependecny on an external flakelight module

Summary

Hopefully the above shows why I created this flakelight module. In short, the main motivation is to avoid duplication in my darwin and nixos configurations.