do the coerce_unsized check last

it’s probably the most expensive checks, so this way we avoid doing it
if another check fails first

Author: mikeyhew

src/librustc/traits/object_safety.rs

@@ -289,13 +289,6 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
 
         let sig = self.fn_sig(method.def_id);
 
-        let receiver_ty = sig.skip_binder().inputs()[0];
-
-        if !self.receiver_is_coercible(method, receiver_ty) {
-            return Some(MethodViolationCode::UncoercibleReceiver);
-        }
-
-
         for input_ty in &sig.skip_binder().inputs()[1..] {
             if self.contains_illegal_self_type_reference(trait_def_id, input_ty) {
                 return Some(MethodViolationCode::ReferencesSelf);
@@ -322,6 +315,12 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
             return Some(MethodViolationCode::WhereClauseReferencesSelf(span));
         }
 
+        let receiver_ty = sig.skip_binder().inputs()[0];
+
+        if !self.receiver_is_coercible(method, receiver_ty) {
+            return Some(MethodViolationCode::UncoercibleReceiver);
+        }
+
         None
     }