Always deterministic, composable on newer Nixpkgs

default.nix

@@ -1,13 +1,34 @@
 { lib ? import <nixpkgs/lib> }:
 let
   find-files = import ./find-files.nix { inherit lib; };
+
+  newCleanSourceWith =
+    let newSrc = lib.cleanSourceWith { filter = f: t: true; src = ./.; };
+    in (builtins.functionArgs lib.cleanSourceWith) ? name || newSrc ? name;
+
 in
 {
   inherit (find-files) gitignoreFilter;
-  
-  gitignoreSource = path: lib.cleanSourceWith {
-    name = "source";
-    filter = find-files.gitignoreFilter path;
-    src = path;
-  };
+
+  gitignoreSource =
+    if newCleanSourceWith
+    then
+      path:
+        let
+          origPath = path.origPath or path;
+        in
+        lib.cleanSourceWith {
+          name = "source";
+          filter = find-files.gitignoreFilter origPath;
+          src = path;
+        }
+    else
+      path:
+        if path ? _isLibCleanSourceWith
+        then builtins.abort "Sorry, please update your Nixpkgs if you want to use gitignoreSource on cleanSourceWith"
+        else builtins.path {
+          name = "source";
+          filter = find-files.gitignoreFilter path;
+          inherit path;
+        };
 }