Treat unmatched non-exhaustive remote variant as serde(skip)

serde/src/private/ser.rs

@@ -1370,3 +1370,16 @@ impl Serialize for AdjacentlyTaggedEnumVariant {
         serializer.serialize_unit_variant(self.enum_name, self.variant_index, self.variant_name)
     }
 }
+
+// Error when Serialize for a non_exhaustive remote enum encounters a variant
+// that is not recognized.
+pub struct CannotSerializeVariant<T>(pub T);
+
+impl<T> Display for CannotSerializeVariant<T>
+where
+    T: Debug,
+{
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        write!(formatter, "enum variant cannot be serialized: {:?}", self.0)
+    }
+}