2 files changed, 24 insertions, 10 deletions

diff --git a/crates/ra_mbe/src/lib.rs b/crates/ra_mbe/src/lib.rs
index 2c75b7b4f..989308626 100644
--- a/crates/ra_mbe/src/lib.rs
+++ b/crates/ra_mbe/src/lib.rs
@@ -42,7 +42,7 @@ pub use crate::syntax_bridge::{ast_to_token_tree, token_tree_to_ast_item_list};
 /// be very confusing is that AST has almost exactly the same shape as
 /// `tt::TokenTree`, but there's a crucial difference: in macro rules, `$ident`
 /// and `$()*` have special meaning (see `Var` and `Repeat` data structures)
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub struct MacroRules {
     pub(crate) rules: Vec<Rule>,
 }
@@ -56,13 +56,13 @@ impl MacroRules {
     }
 }
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub(crate) struct Rule {
     pub(crate) lhs: Subtree,
     pub(crate) rhs: Subtree,
 }
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub(crate) enum TokenTree {
     Leaf(Leaf),
     Subtree(Subtree),
@@ -70,7 +70,7 @@ pub(crate) enum TokenTree {
 }
 impl_froms!(TokenTree: Leaf, Subtree, Repeat);
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub(crate) enum Leaf {
     Literal(Literal),
     Punct(Punct),
@@ -79,37 +79,37 @@ pub(crate) enum Leaf {
 }
 impl_froms!(Leaf: Literal, Punct, Ident, Var);
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub(crate) struct Subtree {
     pub(crate) delimiter: Delimiter,
     pub(crate) token_trees: Vec<TokenTree>,
 }
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub(crate) struct Repeat {
     pub(crate) subtree: Subtree,
     pub(crate) kind: RepeatKind,
     pub(crate) separator: Option<char>,
 }
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub(crate) enum RepeatKind {
     ZeroOrMore,
     OneOrMore,
     ZeroOrOne,
 }
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub(crate) struct Literal {
     pub(crate) text: SmolStr,
 }
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub(crate) struct Ident {
     pub(crate) text: SmolStr,
 }
 
-#[derive(Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, PartialEq, Eq)]
 pub(crate) struct Var {
     pub(crate) text: SmolStr,
     pub(crate) kind: Option<SmolStr>,
diff --git a/crates/ra_mbe/src/mbe_expander.rs b/crates/ra_mbe/src/mbe_expander.rs
index 2dd97b665..2dafd68f6 100644
--- a/crates/ra_mbe/src/mbe_expander.rs
+++ b/crates/ra_mbe/src/mbe_expander.rs
@@ -155,7 +155,14 @@ fn match_lhs(pattern: &crate::Subtree, input: &mut TtCursor) -> Result<Bindings,
                 _ => return Err(ExpandError::UnexpectedToken),
             },
             crate::TokenTree::Repeat(crate::Repeat { subtree, kind: _, separator }) => {
+                // Dirty hack to make macro-expansion terminate.
+                // This should be replaced by a propper macro-by-example implementation
+                let mut limit = 128;
                 while let Ok(nested) = match_lhs(subtree, input) {
+                    limit -= 1;
+                    if limit == 0 {
+                        break;
+                    }
                     res.push_nested(nested)?;
                     if let Some(separator) = *separator {
                         if !input.is_eof() {
@@ -196,7 +203,14 @@ fn expand_tt(
         crate::TokenTree::Repeat(repeat) => {
             let mut token_trees = Vec::new();
             nesting.push(0);
+            // Dirty hack to make macro-expansion terminate.
+            // This should be replaced by a propper macro-by-example implementation
+            let mut limit = 128;
             while let Ok(t) = expand_subtree(&repeat.subtree, bindings, nesting) {
+                limit -= 1;
+                if limit == 0 {
+                    break;
+                }
                 let idx = nesting.pop().unwrap();
                 nesting.push(idx + 1);
                 token_trees.push(t.into())