cachix: move out of root and into profile

doc/integrations/cachix.md

@@ -1,8 +1,13 @@
 # Cachix
-The cachix directory simple captures the output of `sudo cachix use` for the
-developers personal cache, as well as the nix-community cache. You can easily
-add your own cache, assuming the template lives in /etc/nixos, by simply
-running `sudo cachix use yourcache`.
+The system will automatically pull a cachix.nix at the root if one exists.
+This is usually created automatically by a `sudo cachix use`. If your more
+inclined to keep the root clean, you can drop any generated files in the
+`cachix` directory into the `profiles/cachix` directory without further
+modification.
+
+For example, to add your own cache, assuming the template lives in /etc/nixos,
+by simply running `sudo cachix use yourcache`. Then, optionally, move
+`cachix/yourcache.nix` to `profiles/cachix/yourcache.nix`
 
 These caches are only added to the system after a `nixos-rebuild switch`, so it
 is recommended to call `cachix use nrdxp` before the initial deployment, as it

lib/devos/mkHosts.nix

@@ -63,7 +63,11 @@ let
     # Everything in `./modules/list.nix`.
     flakeModules = { imports = builtins.attrValues self.nixosModules ++ extern.modules; };
 
-    cachix = ../../cachix.nix;
+    cachix = let rootCachix = ../../cachix.nix; in
+      if builtins.pathExists rootCachix
+      then rootCachix
+      else { }
+    ;
   };
 
   specialArgs = extern.specialArgs // { suites = suites.system; };

profiles/cachix/default.nix

@@ -1,9 +1,8 @@
-# WARN: this file will get overwritten by $ cachix use <name>
 { pkgs, lib, ... }:
 let
-  folder = ./cachix;
+  folder = ./.;
   toImport = name: value: folder + ("/" + name);
-  filterCaches = key: value: value == "regular" && lib.hasSuffix ".nix" key;
+  filterCaches = key: value: value == "regular" && lib.hasSuffix ".nix" key && key != "default.nix";
   imports = lib.mapAttrsToList toImport (lib.filterAttrs filterCaches (builtins.readDir folder));
 in
 {

profiles/core/default.nix

@@ -2,6 +2,7 @@
 let inherit (lib) fileContents;
 in
 {
+  imports = [ ../cachix ];
 
   nix.systemFeatures = [ "nixos-test" "benchmark" "big-parallel" "kvm" ];