avoid copying nixpkgs to the store

README.md

@@ -132,7 +132,7 @@ drowse.instantiate (finalAttrs: {
       version = "${finalAttrs.version}";
     }
   '';
-  env.NIX_PATH = "nixpkgs=${path}";
+  env.NIX_PATH = "nixpkgs=${nixpkgs}";
   dontUnpack = true;
 })
 ```
@@ -147,7 +147,7 @@ drowse.mkDynamicDerivation {
   version = "0.3.3";
 
   nativeBuildInputs = [ nix ];
-  env.NIX_PATH = "nixpkgs=${path}";
+  env.NIX_PATH = "nixpkgs=${nixpkgs}";
 
   buildCommand = ''
     drv=$(nix-instantiate --expr "(import <nixpkgs> { }).nix-init")

src/__pathToString.nix

@@ -0,0 +1,15 @@
+# avoid copying stuff to the store when possible
+
+{ lib }:
+
+path:
+
+if !lib.isDerivation path && lib.isStorePath path then
+  let
+    str = toString path;
+  in
+  builtins.appendContext str {
+    ${str}.path = true;
+  }
+else
+  "${path}"

src/callPackage.nix

@@ -40,7 +40,7 @@ lib.extendMkDerivation {
       '';
 
       env = {
-        NIX_PATH = "nixpkgs=${path}";
+        NIX_PATH = "nixpkgs=${super.pathToString path}";
       }
       // env;
 

src/crate2nix.nix

@@ -73,7 +73,7 @@ lib.extendMkDerivation {
       '';
 
       env = {
-        NIX_PATH = "nixpkgs=${path}";
+        NIX_PATH = "nixpkgs=${super.pathToString path}";
       }
       // env;