Fix assertion ICE

Author: fee1-dead

compiler/rustc_typeck/src/check/method/mod.rs

@@ -454,7 +454,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         };
         let def_id = method_item.def_id;
         let generics = tcx.generics_of(def_id);
-        assert_eq!(generics.params.len(), 0);
+        assert_eq!(generics.params.len(), 1); // no generics except for constness
 
         debug!("lookup_in_trait_adjusted: method_item={:?}", method_item);
         let mut obligations = vec![];