feat: impure symlink

modules/impure.nix

@@ -0,0 +1,26 @@
+{
+  lib,
+  pkgs,
+  self,
+  ...
+}:
+let
+  relativePath =
+    path:
+    assert lib.types.path.check path;
+    lib.strings.removePrefix (toString self) (toString path);
+  mkImpureLink =
+    path:
+    let
+      relative = relativePath path;
+    in
+    pkgs.runCommandLocal relative { } "ln -s ${lib.escapeShellArg (impureRoot + relative)} $out";
+  impureRoot =
+    let
+      impureRoot = builtins.getEnv "IMPURE_ROOT";
+    in
+    if impureRoot == "" then throw "IMPURE_ROOT is not set" else impureRoot;
+in
+{
+  _module.args.impure = { inherit mkImpureLink; };
+}