flake: add default modules

[musjj]

Add default attributes for nixosModules, homeModules, darwinModules and nixOnDroidModules, following the standard convention.

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• Commit messages adhere to Stylix commit conventions
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• Changes have been tested locally
• Changes have been tested in testbeds
• Each commit in this PR is suitable for backport to the current stable branch

[musjj]

@awwpotato
Hey, what's the reason behind your thumbs down? Would appreciate it if you can elaborate.

[trueNAHO]

Proposal sounds good to me. However, we might want to consider also updating the code and the documentation to recommend this more conventional module output.

I renamed commit "flake: add default module outputs" 1 to "flake: add default module outputs to align with ecosystem conventions" 2 and added commit 3 ("treewide: use default module outputs").

[awwpotato]

awwpotato Hey, what's the reason behind your thumbs down? Would appreciate it if you can elaborate.

sorry for thumbs downing without an explanation, I didn't have time to write an comment at the time but wanted to express my disagreement with this pr.

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There isn't really a standard convention for naming of nixos/home-manager/etc outputs. Sure many projects include both nixosModules.<name> and nixosModules.default but many also don't. Personally I feel like duplicating all the modules under default is unnecessary.

In terms of the documentation I'm strongly against using default. Take "to get the NixOS module as the nixosModules.default" for example, using nixosModules.stylix is much clearer here. What is nixosModules.default? What does the module contain? It's not immediately apparent when using default.

[trueNAHO]

There isn't really a standard convention for naming of nixos/home-manager/etc outputs. Sure many projects include both nixosModules.<name> and nixosModules.default but many also don't. Personally I feel like duplicating all the modules under default is unnecessary.

In terms of the documentation I'm strongly against using default. Take "to get the NixOS module as the nixosModules.default" for example, using nixosModules.stylix is much clearer here. What is nixosModules.default? What does the module contain? It's not immediately apparent when using default.

Personally, following the inputs.${input}.${output}.default naming convention itself is not the main motivation. Rather, that the project name is not repeated:

•  imports = [
  -  inputs.nixvim.homeModules.nixvim
  -  inputs.stylix.homeModules.stylix
  +  inputs.nixvim.homeModules.default
  +  inputs.stylix.homeModules.default
   ];

• # No one should probably do this, but it somewhat illustrates the point.
  imports =
    map
    (input: input.default)
    [inputs.nixvim.homeModules inputs.stylix.homeModules];

The inputs.${input}.${output} output being an attribute set makes sense when having multiple outputs, but it seems redundant with only one output. Considering the flake scheme needs to be generic, it makes sense for it use an attribute set.

I think this boils down to how much we bother following "standards". Might be worth looking into how other projects handle this, regarding whether to declare the default output and whether to use the default output in the documentation.

Keep in mind that we already declare inputs.stylix.devShells.${system}.default, although this convention is "real" since nix actually implements it by being able to replace nix develop .#default with just nix develop.

[musjj]

There isn't really a standard convention for naming of nixos/home-manager/etc outputs

This isn't really true:

• Rename defaultX flake outputs to X.default NixOS/nix#5532

The standard is that there used to be singular and plural outputs like nixosModules and nixosModule. But this was considered inconsistent, so now the singular output is coalesced into the plural output as the default attribute.

This standard can be seen in practice with e.g. nix build . which will build the current flake's packages.<system>.default.

Of course, no tooling currently directly interacts with nixosModules.default because they can only be accessed manually in code. But some proposals are already looking to change this:

• imports preprocessing function NixOS/nixpkgs#196584

Take "to get the NixOS module as the nixosModules.default"

This is only a problem when isolated like this, but they are never written this way neither in documentation nor real user code. But this actually illustrates a different problem, this form is ambiguous with or without default: whose nixosModules is it again?

Might be worth looking into how other projects handle this

Most modules I'm using (or have used it the past) have already adopted this convention:

• home-manager
• disko
• sops-nix
• agenix
• nixvim
• nvf
• impermanence
• nix-flatpak
• declarative-flatpak
• catppuccin/nix

Not all of them uses the default attribute in the documentation, but all of them do have the default attribute present in both nixosModules and/or homeModules.

The only one I personally know that is still left behind is nix-index-database, but I have already have an active PR for that.

[vidhanio]

I think that adding the default output but not updating documentation from using stylix is a good idea. New users looking for the default output (like me) won't be surprised by the lack of its existence, and users who were already using stylix won't find the documentation/"convention" change jarring.

[awwpotato]

based on the further discussion I support merging "flake: add default module outputs to align with ecosystem conventions" but not "treewide: use default module outputs"

[trueNAHO]

based on the further discussion I support merging "flake: add default module outputs to align with ecosystem conventions" but not "treewide: use default module outputs"

Should we also revert .default uses (instead of .stylix) in the code (not the documentation)?

I dropped commit "treewide: use default module outputs" for now.