Deserializer::deserialize_struct is incorrect

[Mingun]

During investigation of correct serde deserializers behavior I found, that postcard implements struct deserialization incorrectly:

• first of all, it deserializes structs using Visitor::visit_seq:
  

  postcard/src/de/deserializer.rs

  Lines 500 to 510 in a095b49

  	fn deserialize_struct<V>(
  	self,
  	_name: &'static str,
  	fields: &'static [&'static str],
  	visitor: V,
  	) -> Result<V::Value>
  	where
  	V: Visitor<'de>,
  	{
  	self.deserialize_tuple(fields.len(), visitor)
  	}

  
  That method is intended only to provide data for sequential types. To provide data for map types you should call visit_map which would use a special deserializer to deserialize keys
• it uses fields.len() as expected tuple size, which is not correct if some fields has aliases. You are never known the count of fields in a struct.

[jamesmunns]

This is potentially correct, though postcard generally doesn't support many of the serde attributes such as alias, external tagging, etc.

If there is a better way to handle this if we'd like to disregard these attributes, I'm defintiely interested!

Thanks for the report.