What's the intended use for flakes in system configuration?

[hugosenari]

@dawbs

Before that point they are just needless overhead?

Not a needless overhead, pinning is important.

@dawbs

I am in for the minute and it seems like pinning etc aren’t much use in this scenario anyway?

Without pinning, your versions are not defined in your repository, if you lose your computer tomorrow, and reinstall your config in another machine, and have different behaviors (software versions). If you have more than one machine, the same issue.

Flakes is the official pinning method after channels and defining hashes in your code, it is experimental, but half community are using .

I think (subjective opinion) that flake is the easier way to do pinning.

@dawbs

The one thing that flakes seem to do better (different?) is the inputs and outputs part to put some kind of contract of expectations around a fragment, but that seems like it’s just not normally done with modules?

Is not a requirement, but I use the flake “contract” (sometimes called schema) with modules

    nixosModules.I.imports =  [ ./hugosenari/default.nix ];
    nixosModules.os.imports = [ ./cfg.nix ./cache ./networking.nix ];
    nixosModules.BO.imports = [ self.nixosModules.os self.nixosModules.I ./bo ];
    nixosModules.HP.imports = [ self.nixosModules.os self.nixosModules.I ./hp ];
    nixosModules.T1.imports = [ self.nixosModules.os self.nixosModules.I ./t1 ];

    nixosConfigurations.BO  = mylib.os self.nixosModules.BO;
    nixosConfigurations.HP  = mylib.os self.nixosModules.HP;
    nixosConfigurations.T1  = mylib.os self.nixosModules.T1;

I could create a BO.nix module and use imports there

@dawbs

Modules are really just a lightweight thing to allow you to break up a file and have nix merge them all into a single blob for evaluation?

Not just but yes.

Nix Modules is a framework for templating information with merge and type validation, is a “contract framework”, “Nix Schema” (like json schema).
I like to think it has 3 parts:

1. options: contract definition, defines what kind of information we need (like someone creating the form).
2. config: information definition (like someone filling the form). You and I, setting our OS config.
3. config¹: use the information (single blob of evaluation) to create a config file or package. Again, is the community, but can be anyone.

¹ Is easy to make a confusion within 2 and 3 because they have same name, 2 is you defining information, 3 is someone using the single blob of evaluation (usaully to set 2).

example (source):

{ pkgs, lib, config, ...}:
             # ^- 3 the blob
{
  # 1 starts --------------------------------------------
  options.nixos-boot = {
    enable = lib.mkOption {
      default = false;
      type    = lib.type.bool;
    };
    theme  = lib.mkOption {
      default = "default";
      type    = lib.types.enum [ "load_unload" "default" ];
    };
    bgColor.red = lib.mkOption {
      default = 255;
      type    = lib.types.ints.between 0 255;
    };
    # ...
  };
  # 1 ends -----------------------------------------------

  # 2 starts ---------------------------------------------
  config.boot.plymouth = lib.mkIf config.nixos-boot.enable {
                                # ^----- 3 the blob -----^
    themePackages = [ pkgs.nixos-boot ];
    enable = true;
    theme  = config.nixos-boot.theme;
           # ^---- 3  the blob ----^
  };
  # ...
  # 2 ends -----------------------------------------------
}

With that our user (maybe we or another module creator) can set nixos-boot.enable, nixos-boot.theme and nixos-boot.bgColor.red, because of 1. And since we are referencing it (3) to set 2, it will enable plymouth for us, set its theme. But could be used to create a file or a package.

@dawbs

but am I right to think that no matter how you structure things, without flakes there is just one giant evaluation at the end?

NixOS is just a giant evaluation of Nix Modules at end, so with or without flakes, yes.

There are other cool features for packages in flakes, like run, build and shell, templates.
Example: GeNix7000: Nix Project Logo Generator - #17 by hugosenari