Teach parser to understand fake anonymous enum syntax

Parse `-> Ty | OtherTy`.
Parse type ascription in top level patterns.

src/types.rs

@@ -839,7 +839,9 @@ impl Rewrite for ast::Ty {
                 })
             }
             ast::TyKind::CVarArgs => Some("...".to_owned()),
-            ast::TyKind::Err => Some(context.snippet(self.span).to_owned()),
+            ast::TyKind::AnonEnum(_) | ast::TyKind::Err => {
+                Some(context.snippet(self.span).to_owned())
+            }
             ast::TyKind::Typeof(ref anon_const) => rewrite_call(
                 context,
                 "typeof",