Mark newtype wrappers as #[serde(transparent)]

[ahl]

In JSON, the difference between a newtype that's transparent or not is unobservable--they both render to the same serialized output. This is not true of other serializations and--more critically--not true of other implementations of serde::Serializer.

In particular, I encountered this in oxidecomputer/progenitor#1017 where I observed that the serde_urlencoded::Serializer freaks out about our newtype wrappers. Perhaps this freak out is reasonable because the intended representation matches with the intention of transparent.

Consider the case where I noticed this: struct Name(String). Name wraps a String and imposes constraints on it. It deserializes from a string and its intended serialization is a string--the newtype wrapper is purely a type for enforcing constraints when creating or manipulating the type. This hasn't bit us before, but marking these newtypes as transparent seems like the right thing to do.

[hawkw]

This seems like the right thing to do to me!