Only validate table keys against fields when deserializing enum.

Issue #225

src/de.rs

@@ -501,14 +501,21 @@ impl<'de> de::Deserializer<'de> for StrDeserializer<'de> {
 
 struct ValueDeserializer<'a> {
     value: Value<'a>,
+    validate_struct_keys: bool,
 }
 
 impl<'a> ValueDeserializer<'a> {
     fn new(value: Value<'a>) -> ValueDeserializer<'a> {
         ValueDeserializer {
             value: value,
+            validate_struct_keys: false,
         }
     }
+
+    fn with_struct_key_validation(mut self) -> Self {
+        self.validate_struct_keys = true;
+        self
+    }
 }
 
 impl<'de> de::Deserializer<'de> for ValueDeserializer<'de> {
@@ -557,6 +564,7 @@ impl<'de> de::Deserializer<'de> for ValueDeserializer<'de> {
             }
         }
 
+        if self.validate_struct_keys {
             match &self.value.e {
                 &E::InlineTable(ref values) | &E::DottedTable(ref values) => {
                     let extra_fields = values.iter()
@@ -578,6 +586,7 @@ impl<'de> de::Deserializer<'de> for ValueDeserializer<'de> {
                 }
                 _ => {}
             }
+        }
 
         if name == spanned::NAME && fields == &[spanned::START, spanned::END, spanned::VALUE] {
             let start = self.value.start;
@@ -900,7 +909,7 @@ impl<'de> de::VariantAccess<'de> for TableEnumDeserializer<'de> {
         V: de::Visitor<'de>,
     {
         de::Deserializer::deserialize_struct(
-            ValueDeserializer::new(self.value),
+            ValueDeserializer::new(self.value).with_struct_key_validation(),
             "", // TODO: this should be the variant name
             fields,
             visitor,