1 files changed, 26 insertions, 0 deletions
diff --git a/lib/fileset/mock-splitRoot.nix b/lib/fileset/mock-splitRoot.nix
new file mode 100644
index 00000000000..3c18ab1b1af
--- /dev/null
+++ b/lib/fileset/mock-splitRoot.nix
@@ -0,0 +1,26 @@
+# This overlay implements mocking of the lib.path.splitRoot function
+# It pretends that the last component named "mock-root" is the root:
+#
+# splitRoot /foo/mock-root/bar/mock-root/baz
+# => {
+#      root = /foo/mock-root/bar/mock-root;
+#      subpath = "./baz";
+#    }
+self: super: {
+  path = super.path // {
+    splitRoot = path:
+      let
+        parts = super.path.splitRoot path;
+        components = self.path.subpath.components parts.subpath;
+        count = self.length components;
+        rootIndex = count - self.lists.findFirstIndex
+          (component: component == "mock-root")
+          (self.length components)
+          (self.reverseList components);
+        root = self.path.append parts.root (self.path.subpath.join (self.take rootIndex components));
+        subpath = self.path.subpath.join (self.drop rootIndex components);
+      in {
+        inherit root subpath;
+      };
+  };
+}