tops and bottoms#

this document outlines things that i learned from various sources and some pure guesswork

To learn Nix is to learn to suffer, and to learn the way of numbing the pain

— Cassie circa. 2023

overriding packages#

the pill confused me and i thought i had to make overlays to do overrides but no

in packages (i.e. environment.systemPackages), just do

#-------8<-Snip-------
environment = {
  systemPackages = with pkgs; [
    (discord.override {withOpenASAR = true;})
    ()
  ];
};
#-------Snip->8-------

This works as well

security.sudo.package = (pkgs.sudo.override {withInsults = true;});

overlays#

overlays are useful when you want to refer to a package globally.

the gist of overlays is as thus:

overlay is just final: pref: {} functions where dumbed down idea is that you do pkg = prev.pkg.override and refer to everything else from final

idea is like final = prev // overlay(prev, final) (it's a recursive definition)

(poorly made) example overlays can be found here

currently in-use and slightly better overlays can be found in this repo! head over to /overlays to see them.

note: replace self: super: with final: prev: for consistency

concept and content by @natsukagami

extra opts#

a way of passing additional options globally to modules is by using extraOpts.

in nix flakes, this is accomplished by using specialArgs in nixosSystem.

for example, check out this line in our flake.nix:

https://github.com/soopyc/nix-on-koumakan/blob/492dfaa01808c2aa5dbb2d8223163e92bcef673b/flake.nix#L22-L28

this avoids the horror of import ../../../utils/bar.nix;

refer to nixpkgs:nixos/lib/eval-config.nix and nixpkgs:lib/modules.nix#122 for more info

pointers by @natsukagami

@ (at) syntax#

very simple.

args@{a, b, c, ...}: {
  # args.a and a are the same
  some = "value";
}

nginx regex location#

{
  locations."~ \.php$".extraConfig = ''
    # balls
  '';
}

from nixos wiki

adding a package with an overlay to a package set#

for package sets with a scope, you will have to do something like

final: prev: {
  nimPackages = prev.nimPackages.overrideScope (final': prev': {
    sha1 = final'.callPackage ./sha1.nix {};
    oauth = final'.callPackage ./oauth.nix {};
  });
}

There's an alternative method that i used to use here:

https://github.com/soopyc/nix-on-koumakan/blob/30e65402d22b000a3b5af6c9e5ea48a2b58a54e0/overlays/nim/oauth/default.nix

however i do not think that's the best way lol

Common pitfalls#

importing nixpkgs with an empty attrset#

ever had this in your flake.nix

{
  outputs = { nixpkgs, ... }@inputs: let
    pkgs = import nixpkgs {};
    lib = nixpkgs.lib;
  in {
    # ...
  };
}

... and got fucked with this?

error:
       … while checking flake output 'nixosConfigurations'

         at /nix/store/lz2ra1180qfffmpwg41jpyg1z602qdgx-source/flake.nix:50:5:

           49|   in {
           50|     nixosConfigurations = {
             |     ^
           51|       koumakan = (import ./systems/koumakan { inherit pkgs lib inputs; });

       … while checking the NixOS configuration 'nixosConfigurations.koumakan'

         at /nix/store/lz2ra1180qfffmpwg41jpyg1z602qdgx-source/flake.nix:51:7:

           50|     nixosConfigurations = {
           51|       koumakan = (import ./systems/koumakan { inherit pkgs lib inputs; });
             |       ^
           52|     };

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: attribute 'currentSystem' missing

       at /nix/store/5c0k827yjq7j24qaq8l2fcnsxp7nv8v1-source/pkgs/top-level/impure.nix:17:43:

           16|   # (build, in GNU Autotools parlance) platform.
           17|   localSystem ? { system = args.system or builtins.currentSystem; }
             |                                           ^
           18|

just don't!!!11 remove the pkgs definition. (note that this only applies to pkgs = import nixpkgs {};)

explanation

you shouldn't ever really import nixpkgs with an empty attrset either

that causes it to fall back on guessing your system using builtins.currentSystem, which is impure and so not allowed in pure evaluation mode

— @getchoo

Useful links#

Builtin stdlib functions search engine: https://noogle.dev/