support `default impl` for specialization

this commit implements the first step of the `default impl` feature:
all items in a `default impl` are (implicitly) `default` and hence
specializable.
In order to test this feature I've copied all the tests provided for the
`default` method implementation (in run-pass/specialization and
compile-fail/specialization directories) and moved the `default` keyword
from the item to the impl.
See referenced issue for further info

1 files changed, 8 insertions, 1 deletions

diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index f39399a62e8..58cf50cdc00 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -897,9 +897,16 @@ pub fn noop_fold_item_kind<T: Folder>(i: ItemKind, folder: &mut T) -> ItemKind {
         ItemKind::DefaultImpl(unsafety, ref trait_ref) => {
             ItemKind::DefaultImpl(unsafety, folder.fold_trait_ref((*trait_ref).clone()))
         }
-        ItemKind::Impl(unsafety, polarity, generics, ifce, ty, impl_items) => ItemKind::Impl(
+        ItemKind::Impl(unsafety,
+                       polarity,
+                       defaultness,
+                       generics,
+                       ifce,
+                       ty,
+                       impl_items) => ItemKind::Impl(
             unsafety,
             polarity,
+            defaultness,
             folder.fold_generics(generics),
             ifce.map(|trait_ref| folder.fold_trait_ref(trait_ref.clone())),
             folder.fold_ty(ty),