--- a/rust/hg-core/src/lib.rs	Wed Jan 23 07:39:27 2019 -0500
+++ b/rust/hg-core/src/lib.rs	Wed Jan 23 07:47:04 2019 -0500
@@ -33,4 +33,5 @@
 #[derive(Clone, Debug, PartialEq)]
 pub enum GraphError {
     ParentOutOfRange(Revision),
+    WorkingDirectoryUnsupported,
 }