Move to a profile-based configuration where common

This patch makes it so common configuration is now located in shared/
and each host basically just becomes a bunch of import statements.

The exception here is host-specific configuration like the `*.linus.onl`
that live inside `hosts/ahmed/`.

Specifically I have:

- moved common configuration `shared/{nixos,home-manager,nix-darwin}`.
- moved `hosts/common.nix` to `shared/nixos/common-{nix,shell}-settings.nix`.
- split `hosts/muhammed/{dev-utils,neovim}` into per-language
  configuration.

This patch was done in preparation for the arrival of a new host, which
will need to share a lot of configuration with Muhammed.

1 files changed, 60 insertions, 0 deletions

diff --git a/shared/nixos/common-nix-settings/default.nix b/shared/nixos/common-nix-settings/default.nix
new file mode 100644
index 0000000..b5c0a02
--- /dev/null
+++ b/shared/nixos/common-nix-settings/default.nix
@@ -0,0 +1,60 @@
+# This module sets common settings related to Nix such as enabling flakes and
+# using overlays everywhere..
+#
+# NOTE: Even though this lives under `shared/nixos` the configuration in here
+# should also be compatible with nix-darwin!!
+{
+  pkgs,
+  lib,
+  config,
+  flakeInputs,
+  flakeOutputs,
+  ...
+}:
+lib.mkMerge [
+  {
+    # Enable de facto stable features.
+    nix.settings.experimental-features = ["nix-command" "flakes"];
+
+    nixpkgs.overlays = [
+      # Use local overlays.
+      flakeOutputs.overlays.additions
+      flakeOutputs.overlays.modifications
+
+      # Add unstable nixpkgs.
+      (final: prev: {unstable = flakeInputs.nixpkgs-unstable.legacyPackages.${pkgs.system};})
+    ];
+
+    # I'm not *that* vegan.
+    nixpkgs.config.allowUnfree = true;
+
+    # This will add each flake input as a registry
+    # To make nix3 commands consistent with your flake
+    nix.registry = lib.mapAttrs (_: value: {flake = value;}) flakeInputs;
+
+    nix.nixPath =
+      [
+        # Use overlays from this repo for building system configuration as well as system-wide.
+        # See: https://nixos.wiki/wiki/Overlays#Using_nixpkgs.overlays_from_configuration.nix_as_.3Cnixpkgs-overlays.3E_in_your_NIX_PATH
+        "nixpkgs-overlays=${flakeInputs.self}/overlays/compat.nix"
+
+        # This will additionally add out inputs to the system's legacy channels
+        # Making legacy nix commands consistent as well, awesome!
+      ]
+      ++ lib.mapAttrsToList (key: value: "${key}=${value.to.path}") config.nix.registry;
+
+    # Add shell-utilities which are only relevant if Nix is enabled.
+    environment.systemPackages = with pkgs; [
+      # For running programs easily.
+      nix-index # Also includes nix-locate
+      flakeInputs.comma.packages.${system}.default
+
+      # For editing secrets.
+      flakeInputs.agenix.packages.${system}.default
+    ];
+  }
+  (lib.mkIf pkgs.stdenv.isLinux {
+    # There is not nix-darwin equivalent to this NixOS option.
+    nix.enable = true;
+  })
+]