#+title: Nix Configuration
#+setupfile: headers
#+property: header-args:emacs-lisp  :lexical t :exports none :tangle no

* Nix Configuration
Something that I want to enable everywhere is, first and foremost, the
support for Nix commands and Nix flakes. I also want to make sure I
can use some caches, also known as substituters, including one of mine
from Cachix, to avoid compiling stuff as much as possible.

So first, here are my caches with their public key.

#+name: substituters
| Substituter's URL                            | Public Key                                                              |
|----------------------------------------------+-------------------------------------------------------------------------|
| https://phundrak.cachix.org?priority=10      | =phundrak.cachix.org-1:osJAkYO0ioTOPqaQCIXMfIRz1/+YYlVFkup3R2KSexk==      |
| https://nix-community.cachix.org?priority=20 | =nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs== |
| https://cache.nixos.org?priority=40          | =cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY==          |

#+name: substituters-urls
#+begin_src emacs-lisp :var subs=substituters :cache yes
(mapconcat (lambda (sub) (format "\"%s\"" (car sub))) subs "\n")
#+end_src

#+RESULTS[99d05698d7e8ca90b34823f4dd4858224be8d007]: substituters-urls
: "https://phundrak.cachix.org?priority=10"
: "https://nix-community.cachix.org?priority=20"
: "https://cache.nixos.org?priority=40"

#+name: substituters-keys
#+begin_src emacs-lisp :var subs=substituters :cache yes
(require 's)
(mapconcat (lambda (sub) (format "\"%s\""
                            (s-chop-prefix "=" (s-chop-suffix "=" (cadr sub)))))
           subs
           "\n")
#+end_src

#+RESULTS[6f5e709a7b1c1dd55e4187dfaf8be945138c68ec]: substituters-keys
: "phundrak.cachix.org-1:osJAkYO0ioTOPqaQCIXMfIRz1/+YYlVFkup3R2KSexk="
: "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
: "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="

This results in the following substituters and trusted public keys.
#+name: config-vars
#+begin_src nix :noweb yes
substituters = [
  <<substituters-urls()>>
];
trustedPublicKeys = [
  <<substituters-keys()>>
];
#+end_src

Now, we can declare the rest of the file. You’ll see, it repeats
itself a bit.

#+begin_src nix :tangle yes
let
  cacheSettings = rec {
    <<config-vars>>
    commonConf = {
      extra-trusted-public-keys = trustedPublicKeys;
      extra-substituters = substituters;
      extra-experimental-features = ["nix-command" "flakes"];
      http-connections = 128;
    };
  };
in {
  flake-file.nixConfig = cacheSettings;
  flake.nixConfig = cacheSettings;
  flake.modules.nixos.nix-cache-settings = {
    nix.settings = {
      inherit (cacheSettings) substituters;
      trusted-public-keys = cacheSettings.trustedPublicKeys;
      experimental-features = ["nix-command" "flakes"];
      http-connections = 128;
    };
  };
}
#+end_src