Factor out value deserializers

src/json/de.rs

@@ -603,26 +603,8 @@ impl<'a, Iter> de::MapVisitor for MapVisitor<'a, Iter>
     fn missing_field<V>(&mut self, _field: &'static str) -> Result<V, Error>
         where V: de::Deserialize,
     {
-        // See if the type can deserialize from a unit.
-        struct UnitDeserializer;
-
-        impl de::Deserializer for UnitDeserializer {
-            type Error = Error;
-
-            fn visit<V>(&mut self, mut visitor: V) -> Result<V::Value, Error>
-                where V: de::Visitor,
-            {
-                visitor.visit_unit()
-            }
-
-            fn visit_option<V>(&mut self, mut visitor: V) -> Result<V::Value, Error>
-                where V: de::Visitor,
-            {
-                visitor.visit_none()
-            }
-        }
-
-        Ok(try!(de::Deserialize::deserialize(&mut UnitDeserializer)))
+        let mut de = de::value::ValueDeserializer::deserializer(());
+        Ok(try!(de::Deserialize::deserialize(&mut de)))
     }
 }
 

src/json/error.rs

@@ -145,6 +145,22 @@ impl error::FromError<io::Error> for Error {
     }
 }
 
+impl error::FromError<de::value::Error> for Error {
+    fn from_error(error: de::value::Error) -> Error {
+        match error {
+            de::value::Error::SyntaxError => {
+                de::Error::syntax_error()
+            }
+            de::value::Error::EndOfStreamError => {
+                de::Error::end_of_stream_error()
+            }
+            de::value::Error::MissingFieldError(field) => {
+                de::Error::missing_field_error(field)
+            }
+        }
+    }
+}
+
 impl de::Error for Error {
     fn syntax_error() -> Error {
         Error::SyntaxError(ErrorCode::ExpectedSomeValue, 0, 0)