Serde's `ContentDeserializer` and `ContentRefDeserializer`
cannot deserialize struct enum variant associated data when
that data is encoded as a sequence. This failure leads to
errors when decoding an enum nested in another untagged
enum. For example:
#[derive(Serialize, Deserialize)]
#[serde(untagged)]
enum Foo {
A(Bar),
}
#[derive(Serialize, Deserialize)]
enum Bar {
B{f1: String},
}
let data1 = Foo::A(Bar::B{f1: "Hello".into()});
let bytes = rmp_serde::to_vec(&data1).unwrap();
let data2 = rmp_serde::from_slice::<Foo>(&bytes).unwrap();
Deserializing fails with the error `Syntax("data did not
match any variant of untagged enum Foo")`, but the
underlying failure occurs when decoding the associated data
of `Bar::B`.
This pull request fixes the issue by allowing
`ContentDeserializer` and `ContentRefDeserializer` to
deserialize sequence-encoded struct enum variant data.
