Detect unknown struct variant fields deserializing from Value

Author: dtolnay

Diff for: src/value/de.rs

@@ -538,7 +538,7 @@ impl<'de> VariantAccess<'de> for VariantDeserializer {
         V: Visitor<'de>,
     {
         match self.value {
-            Some(Value::Object(v)) => visitor.visit_map(MapDeserializer::new(v)),
+            Some(Value::Object(v)) => visit_object(v, visitor),
             Some(other) => Err(serde::de::Error::invalid_type(
                 other.unexpected(),
                 &"struct variant",
@@ -1021,7 +1021,7 @@ impl<'de> VariantAccess<'de> for VariantRefDeserializer<'de> {
         V: Visitor<'de>,
     {
         match self.value {
-            Some(&Value::Object(ref v)) => visitor.visit_map(MapRefDeserializer::new(v)),
+            Some(&Value::Object(ref v)) => visit_object_ref(v, visitor),
             Some(other) => Err(serde::de::Error::invalid_type(
                 other.unexpected(),
                 &"struct variant",