1 files changed, 27 insertions, 13 deletions

diff --git a/crates/mbe/src/benchmark.rs b/crates/mbe/src/benchmark.rs
index 6d81be880..503ad1355 100644
--- a/crates/mbe/src/benchmark.rs
+++ b/crates/mbe/src/benchmark.rs
@@ -40,18 +40,12 @@ fn benchmark_expand_macro_rules() {
             .into_iter()
             .map(|(id, tt)| {
                 let res = rules[&id].expand(&tt);
-                if res.err.is_some() {
-                    // FIXME:
-                    // Currently `invocation_fixtures` will generate some correct invocations but
-                    // cannot be expanded by mbe. We ignore errors here.
-                    // See: https://github.com/rust-analyzer/rust-analyzer/issues/4777
-                    eprintln!("err from {} {:?}", id, res.err);
-                }
+                assert!(res.err.is_none());
                 res.value.token_trees.len()
             })
             .sum()
     };
-    assert_eq!(hash, 66995);
+    assert_eq!(hash, 69413);
 }
 
 fn macro_rules_fixtures() -> FxHashMap<String, MacroRules> {
@@ -77,7 +71,7 @@ fn macro_rules_fixtures_tt() -> FxHashMap<String, tt::Subtree> {
         .collect()
 }
 
-// Generate random invocation fixtures from rules
+/// Generate random invocation fixtures from rules
 fn invocation_fixtures(rules: &FxHashMap<String, MacroRules>) -> Vec<(String, tt::Subtree)> {
     let mut seed = 123456789;
     let mut res = Vec::new();
@@ -86,11 +80,31 @@ fn invocation_fixtures(rules: &FxHashMap<String, MacroRules>) -> Vec<(String, tt
         for rule in &it.rules {
             // Generate twice
             for _ in 0..2 {
-                let mut subtree = tt::Subtree::default();
-                for op in rule.lhs.iter() {
-                    collect_from_op(op, &mut subtree, &mut seed);
+                // The input are generated by filling the `Op` randomly.
+                // However, there are some cases generated are ambiguous for expanding, for example:
+                // ```rust
+                // macro_rules! m {
+                //    ($($t:ident),* as $ty:ident) => {}
+                // }
+                // m!(as u32);  // error: local ambiguity: multiple parsing options: built-in NTs ident ('t') or 1 other option.
+                // ```
+                //
+                // So we just skip any error cases and try again
+                let mut try_cnt = 0;
+                loop {
+                    let mut subtree = tt::Subtree::default();
+                    for op in rule.lhs.iter() {
+                        collect_from_op(op, &mut subtree, &mut seed);
+                    }
+                    if it.expand(&subtree).err.is_none() {
+                        res.push((name.clone(), subtree));
+                        break;
+                    }
+                    try_cnt += 1;
+                    if try_cnt > 100 {
+                        panic!("invocaton fixture {} cannot be generated.\n", name);
+                    }
                 }
-                res.push((name.clone(), subtree));
             }
         }
     }