1 files changed, 13 insertions, 0 deletions

diff --git a/crates/ra_mbe/src/tt_cursor.rs b/crates/ra_mbe/src/tt_cursor.rs
index 741b5ea1c..87bcf8b0d 100644
--- a/crates/ra_mbe/src/tt_cursor.rs
+++ b/crates/ra_mbe/src/tt_cursor.rs
@@ -7,6 +7,10 @@ pub(crate) struct TtCursor<'a> {
     pos: usize,
 }
 
+pub(crate) struct TtCursorMemento {
+    pos: usize,
+}
+
 impl<'a> TtCursor<'a> {
     pub(crate) fn new(subtree: &'a tt::Subtree) -> TtCursor<'a> {
         TtCursor { subtree, pos: 0 }
@@ -157,4 +161,13 @@ impl<'a> TtCursor<'a> {
             Err(ParseError::Expected(format!("`{}`", char)))
         }
     }
+
+    #[must_use]
+    pub(crate) fn save(&self) -> TtCursorMemento {
+        TtCursorMemento { pos: self.pos }
+    }
+
+    pub(crate) fn rollback(&mut self, memento: TtCursorMemento) {
+        self.pos = memento.pos;
+    }
 }