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Separating flake inputs in multiple files (lemmy.blahaj.zone)

submitted 2 days ago* (last edited 1 day ago) by claymorwan@lemmy.blahaj.zone to c/nix@programming.dev

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I'm starting to have a lot of flake inputs in my flake.nix file, and it's starting to get really cluttered. I'm wondering if there's a way to separate my inputs into multiple files so it looks cleaner. I've tried to look it up but couldn't really find anything abt it

Edit: Well as it turns out it's not something possible yet, apparently the flake.nix file isn't parsed like regular nix files and doesn't support stuff like import

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[–] hallettj@leminal.space 2 points 2 days ago* (last edited 1 day ago) (2 children)

I think you can use import to load the expression from each file, and the // operator to combine imported attribute sets. Like this:

Edit: This doesn't work - see replies

# flake.nix
{
  inputs =
    import ./inputs/nixpkgs.nix //
    import ./inputs/nix-index.nix;

  # ...
}

# inputs/nixpkgs.nix
{
  nixpkgs.url = "github:nixos/nixpkgs/nixos-25.11";
  nixpkgs-unstable.url = "github:nixos/nixpkgs/nixos-unstable";
}

# inputs/nix-index.nix
{
  nix-index-database = {
    url = "github:Mic92/nix-index-database";
    inputs.nixpkgs.follows = "nixpkgs";
  };
}

[–] claymorwan@lemmy.blahaj.zone 2 points 1 day ago (1 children)

I followed how u did it but it doesn't seem to work, i keep getting hit with this error:

error: expected a set but got a thunk at /home/claymorwan/.dotfiles/NixOS/flake.nix:4:3

[–] hallettj@leminal.space 1 points 1 day ago* (last edited 1 day ago) (1 children)

Whoops! Guess I was wrong. After some experimenting it looks like the flake system parses, but does not evaluate flake.nix to read inputs. I also experimented with string concatenation, and that failed with the same error:

nixpkgs.url = "github:nixos/nixpkgs" ++ "/nixos-25.05"; # error: expected a string or path, but got a thunk

A "thunk" is an expression whose evaluation has been delayed. It's a key piece of lazy evaluation. Remember that every expression in Nix is lazily evaluated.

It looks only literal attribute set, string, and path expressions will work in inputs. I think that means it is not possible to split inputs over multiple files.

[–] claymorwan@lemmy.blahaj.zone 2 points 1 day ago

yea i think it may just not be possible yet, looking it up more i've seen people talking abt how a big con of flakes is that flake.nix is not parsed like regular nix files. I'm not sure why they made it work like that but it gets changed eventually cuz that's really too bad we can't do things as simple as imports

[–] Klaymore@sh.itjust.works 2 points 1 day ago (1 children)

One note about // is that it doesn't deep combine attribute sets, so if you set the .url in one and .inputs.nixpkgs.follows in another then it will only use the second one. I don't think that matters here but it's tripped me up before. I think lib.mkMerge is the deep recursive alternative.

[–] hallettj@leminal.space 2 points 1 day ago* (last edited 1 day ago)

Good point! But I think lib.mkMerge only merges options in a module system like the ones used in NixOS, Home Manager, and flake-parts configs. In this situation I think the function to use would be lib.attrsets.recursiveUpdate