self.associated_item can return none

self.associated_item can return none, replace unwrap with '?' and bubble up None value instead of panicking

diff --git a/src/librustc_typeck/check/method/mod.rs b/src/librustc_typeck/check/method/mod.rs
index 11448750618e218252dd96cb040609c91127dac6..3fd61dbb97d94463e01aaf4701c536c8681b05fe 100644 (file)
--- a/src/librustc_typeck/check/method/mod.rs
+++ b/src/librustc_typeck/check/method/mod.rs
@@ -290,7 +290,7 @@ pub fn lookup_method_in_trait(&self,
         // type parameters or early-bound regions.
         let tcx = self.tcx;
         let method_item =
-            self.associated_item(trait_def_id, m_name, Namespace::Value).unwrap();
+            self.associated_item(trait_def_id, m_name, Namespace::Value)?;
         let def_id = method_item.def_id;
         let generics = tcx.generics_of(def_id);
         assert_eq!(generics.params.len(), 0);