Extend macro machinery to expand macros in types

Reapplied the changes from 7aafe24139
to a clean branch of master

src/libsyntax/ext/expand.rs

@@ -1552,6 +1552,35 @@ fn expand_and_rename_method(sig: ast::MethodSig, body: P<ast::Block>,
     }, rewritten_body)
 }
 
+pub fn expand_type(t: P<ast::Ty>, fld: &mut MacroExpander) -> P<ast::Ty> {
+    let t = match t.node.clone() {
+        ast::Ty_::TyMac(mac) => {
+            let expanded_ty = match expand_mac_invoc(mac, t.span,
+                                                     |r| r.make_ty(),
+                                                     mark_ty,
+                                                     fld) {
+                Some(ty) => ty,
+                None => {
+                    return DummyResult::raw_ty(t.span);
+                }
+            };
+
+            // Keep going, outside-in.
+            //
+            let fully_expanded = fld.fold_ty(expanded_ty);
+            fld.cx.bt_pop();
+
+            fully_expanded.map(|t| ast::Ty {
+                id: ast::DUMMY_NODE_ID,
+                node: t.node,
+                span: t.span,
+            })
+        }
+        _ => t
+    };
+    fold::noop_fold_ty(t, fld)
+}
+
 /// A tree-folder that performs macro expansion
 pub struct MacroExpander<'a, 'b:'a> {
     pub cx: &'a mut ExtCtxt<'b>,
@@ -1602,6 +1631,10 @@ impl<'a, 'b> Folder for MacroExpander<'a, 'b> {
             .into_iter().map(|i| i.expect_impl_item()).collect()
     }
 
+    fn fold_ty(&mut self, ty: P<ast::Ty>) -> P<ast::Ty> {
+        expand_type(ty, self)
+    }
+
     fn new_span(&mut self, span: Span) -> Span {
         new_span(self.cx, span)
     }
@@ -1748,6 +1781,10 @@ fn mark_impl_item(ii: P<ast::ImplItem>, m: Mrk) -> P<ast::ImplItem> {
         .expect_one("marking an impl item didn't return exactly one impl item")
 }
 
+fn mark_ty(ty: P<ast::Ty>, m: Mrk) -> P<ast::Ty> {
+    Marker { mark: m }.fold_ty(ty)
+}
+
 /// Check that there are no macro invocations left in the AST:
 pub fn check_for_macros(sess: &parse::ParseSess, krate: &ast::Crate) {
     visit::walk_crate(&mut MacroExterminator{sess:sess}, krate);