msg_socket: allow Enum with no variant filed types

This is to allow the Enum which doesn't have filed type for all its variants
to derive the MsgOnSocket.

BUG=None
TEST=cargo test -p msg_socket

Change-Id: Iab9edda777f42e25af40e4ec0e5870401c17572b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/2143572
Reviewed-by: Zach Reizner <zachr@chromium.org>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Chuanxiao Dong <chuanxiao.dong@intel.corp-partner.google.com>

1 files changed, 5 insertions, 0 deletions

diff --git a/msg_socket/msg_on_socket_derive/msg_on_socket_derive.rs b/msg_socket/msg_on_socket_derive/msg_on_socket_derive.rs
index fd6c19a..a3c065c 100644
--- a/msg_socket/msg_on_socket_derive/msg_on_socket_derive.rs
+++ b/msg_socket/msg_on_socket_derive/msg_on_socket_derive.rs
@@ -190,6 +190,11 @@ fn define_uses_fd_for_enum(de: &DataEnum) -> TokenStream {
             variant_field_types.push(variant_field_ty);
         }
     }
+
+    if variant_field_types.len() == 0 {
+        return quote!();
+    }
+
     quote! {
         fn uses_fd() -> bool {
             #(<#variant_field_types>::uses_fd())||*