1 files changed, 7 insertions, 1 deletions
diff --git a/src/librustc_data_structures/unify/mod.rs b/src/librustc_data_structures/unify/mod.rs
index a899bbacc03..7582b7ff61d 100644
--- a/src/librustc_data_structures/unify/mod.rs
+++ b/src/librustc_data_structures/unify/mod.rs
@@ -339,5 +339,11 @@ impl<'tcx,K,V> UnificationTable<K>
     pub fn probe(&mut self, a_id: K) -> Option<V> {
         self.get(a_id).value.clone()
     }
-}
 
+    pub fn unsolved_variables(&mut self) -> Vec<K> {
+        self.values
+            .iter()
+            .filter_map(|vv| if vv.value.is_some() { None } else { Some(vv.key()) })
+            .collect()
+    }
+}