3 files changed, 28 insertions, 5 deletions

diff --git a/crates/ra_mbe/src/mbe_expander.rs b/crates/ra_mbe/src/mbe_expander.rs
index d5189b537..1b579f319 100644
--- a/crates/ra_mbe/src/mbe_expander.rs
+++ b/crates/ra_mbe/src/mbe_expander.rs
@@ -206,8 +206,24 @@ fn match_lhs(pattern: &crate::Subtree, input: &mut TtCursor) -> Result<Bindings,
                             );
                         }
                         "vis" => {
-                            let vis = input.eat_vis().ok_or(ExpandError::UnexpectedToken)?.clone();
-                            res.inner.insert(text.clone(), Binding::Simple(vis.into()));
+                            // `vis` is optional
+                            if let Some(vis) = input.try_eat_vis() {
+                                let vis = vis.clone();
+                                res.inner.insert(text.clone(), Binding::Simple(vis.into()));
+                            } else {
+                                // FIXME: Do we have a better way to represent an empty token ?
+                                // Insert an empty subtree for empty token
+                                res.inner.insert(
+                                    text.clone(),
+                                    Binding::Simple(
+                                        tt::Subtree {
+                                            delimiter: tt::Delimiter::None,
+                                            token_trees: vec![],
+                                        }
+                                        .into(),
+                                    ),
+                                );
+                            }
                         }
 
                         _ => return Err(ExpandError::UnexpectedToken),
diff --git a/crates/ra_mbe/src/subtree_source.rs b/crates/ra_mbe/src/subtree_source.rs
index 8176296e6..3554dc110 100644
--- a/crates/ra_mbe/src/subtree_source.rs
+++ b/crates/ra_mbe/src/subtree_source.rs
@@ -319,7 +319,7 @@ fn convert_ident(ident: &tt::Ident) -> TtToken {
 
 fn convert_punct(p: &tt::Punct) -> TtToken {
     let kind = match p.char {
-        // lexer may produce combpund tokens for these ones
+        // lexer may produce compound tokens for these ones
         '.' => DOT,
         ':' => COLON,
         '=' => EQ,
diff --git a/crates/ra_mbe/src/tt_cursor.rs b/crates/ra_mbe/src/tt_cursor.rs
index 8f15d215b..d85ab43e4 100644
--- a/crates/ra_mbe/src/tt_cursor.rs
+++ b/crates/ra_mbe/src/tt_cursor.rs
@@ -149,9 +149,16 @@ impl<'a> TtCursor<'a> {
         self.eat_ident().cloned().map(|ident| tt::Leaf::from(ident).into())
     }
 
-    pub(crate) fn eat_vis(&mut self) -> Option<tt::TokenTree> {
+    pub(crate) fn try_eat_vis(&mut self) -> Option<tt::TokenTree> {
+        // `vis` matcher is optional
+        let old_pos = self.pos;
         let parser = Parser::new(&mut self.pos, self.subtree);
-        parser.parse_vis()
+
+        let res = parser.parse_vis();
+        if res.is_none() {
+            self.pos = old_pos;
+        }
+        res
     }
 
     pub(crate) fn expect_char(&mut self, char: char) -> Result<(), ParseError> {