[PATCH 4/4] rust/qemu-api-macros: make derive(Object) friendly when missing parent

[marcandre . lureau]

From: Marc-André Lureau <marcandre.lur...@redhat.com>

Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
---
 rust/qemu-api-macros/src/lib.rs | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/rust/qemu-api-macros/src/lib.rs b/rust/qemu-api-macros/src/lib.rs
index b525d89c09..a614741889 100644
--- a/rust/qemu-api-macros/src/lib.rs
+++ b/rust/qemu-api-macros/src/lib.rs
@@ -85,7 +85,15 @@ fn derive_object_or_error(input: DeriveInput) -> 
Result<proc_macro2::TokenStream
     is_c_repr(&input, "#[derive(Object)]")?;
 
     let name = &input.ident;
-    let parent = &get_fields(&input, "#[derive(Object)]")?[0].ident;
+    let parent = &get_fields(&input, "#[derive(Object)]")?
+        .get(0)
+        .ok_or_else(|| {
+            Error::new(
+                input.ident.span(),
+                "#[derive(Object)] requires a parent field",
+            )
+        })?
+        .ident;
 
     Ok(quote! {
         ::qemu_api::assert_field_type!(#name, #parent,
-- 
2.50.1