add support for smfh impure mode

default.nix

@@ -92,6 +92,20 @@ in
         '';
       };
       enable = mkEnableOption "Arbitrary Symlink Manager";
+      impure = mkOption {
+        type = bool;
+        default = false;
+        description = ''
+          Expand ~ and environment variables in paths, similar to if you were in a shell.
+        '';
+      };
+      variables = mkOption {
+        type = attrsOf str;
+        default = { };
+        description = ''
+          A set of environment variables to use in the deployment.
+        '';
+      };
     };
     files = mkOption {
       description = "Files to link";
@@ -146,6 +160,7 @@ in
         text = (
           builtins.toJSON {
             inherit files;
+            inherit (config.envionrment.arbys) impure;
             clobber_by_default = config.environment.arbys.clobber;
             version = 1;
           }
@@ -195,6 +210,7 @@ in
               "arbys-copy.service"
             ];
             after = [ "arbys-prep.service" ];
+            environment = config.environment.arbys.variables;
             script =
               let
                 linker = lib.getExe (pkgs.smfh or (pkgs.callPackage ./smfh.nix { }));