Comment moved over from facet-rs/facet#326:

My use case that the serde ecosystem is struggling with is this:

#[derive(serde_derive::Serialize, serde_derive::Deserialize)]
#[serde(tag = "type")]
enum Outer {
  OVar1,
  #[serde(untagged)]
  Inner(Inner),
}

#[derive(serde_derive::Serialize, serde_derive::Deserialize)]
#[serde(tag = "type")]
enum Inner {
  IVar1,
  IVar2,
}

Which should just work like

• Outer::OVar1 ⭤ {"type":"OVar1"}
• Outer::Inner(Inner::Ivar1) ⭤ {"type":"Ivar1"} ⭤ Inner::Ivar1
• Outer::Inner(Inner::Ivar2) ⭤ {"type":"Ivar2"} ⭤ Inner::Ivar2

But also strange things happen like [0] deserializing to Outer::OVar1.

I feel like we can do better.