Remove scope placeholders from the crate root.

src/libsyntax/ext/expand.rs

@@ -191,8 +191,15 @@ pub fn new(cx: &'a mut ExtCtxt<'b>,
     fn expand_crate(&mut self, mut krate: ast::Crate) -> ast::Crate {
         let err_count = self.cx.parse_sess.span_diagnostic.err_count();
 
-        let items = Expansion::Items(SmallVector::many(krate.module.items));
-        krate.module.items = self.expand(items).make_items().into();
+        let mut krate_item = placeholder(ExpansionKind::Items, ast::DUMMY_NODE_ID)
+            .make_items().pop().unwrap().unwrap();
+        krate_item.node = ast::ItemKind::Mod(krate.module);
+        let krate_item = Expansion::Items(SmallVector::one(P(krate_item)));
+
+        krate.module = match self.expand(krate_item).make_items().pop().unwrap().unwrap().node {
+            ast::ItemKind::Mod(module) => module,
+            _ => unreachable!(),
+        };
         krate.exported_macros = mem::replace(&mut self.cx.exported_macros, Vec::new());
 
         for def in &mut krate.exported_macros {
@@ -596,6 +603,10 @@ fn fold_item(&mut self, item: P<ast::Item>) -> SmallVector<P<ast::Item>> {
                 })
             }
             ast::ItemKind::Mod(ast::Mod { inner, .. }) => {
+                if item.ident == keywords::Invalid.ident() {
+                    return noop_fold_item(item, self);
+                }
+
                 let mut module = (*self.cx.current_expansion.module).clone();
                 module.mod_path.push(item.ident);