add hm modules: riff

nixos/common/default.nix

@@ -1,13 +1,12 @@
 { inputs, lib, config, ... }: {
   # This file deals with everything requiring `inputs`, the rest being delagated to `common.nix`
   # this is because we can't import inputs from all contexts as that can lead to infinite recursion.
-  imports = [
-    ./common.nix
-    inputs.vault-secrets.nixosModules.vault-secrets
-  ];
+  imports = [ ./common.nix inputs.vault-secrets.nixosModules.vault-secrets ];
 
   nix.nixPath = [ "nixpkgs=${inputs.nixpkgs}" ];
-  nix.registry.nixpkgs.flake =  inputs.nixpkgs;
+  nix.registry.nixpkgs.flake = inputs.nixpkgs;
+
+  home-manager.sharedModules = [ ./hm-modules ];
 
   vault-secrets = let
     inherit (config.networking) domain hostName;

nixos/common/hm-modules/default.nix

@@ -0,0 +1,5 @@
+{ ... }: {
+  imports = [
+    ./riff.nix
+  ];
+} 

nixos/common/hm-modules/riff.nix

@@ -0,0 +1,28 @@
+{ config, pkgs, lib, inputs, ... }:
+with lib;
+let cfg = config.programs.riff;
+in {
+  options.programs.riff = {
+    enable = mkEnableOption "riff";
+    direnv = mkOption {
+      type = types.bool;
+      default = false;
+      description = ''
+        Whether to enable direnv support
+      '';
+    };
+  };
+  config = mkIf cfg.enable {
+    home.packages = [ inputs.riff.packages.${pkgs.system}.riff ];
+
+    xdg.configFile."direnv/lib/riff.sh" = mkIf cfg.direnv {
+      executable = true;
+      text = ''
+        use_riff() {
+          watch_file Cargo.toml watch_file Cargo.lock
+          eval "$(riff --offline print-dev-env)"
+        }
+      '';
+    };
+  };
+}