Rust: Enum of Enums need to use 'untagged' serde attr

[BelfordZ]

To properly serialize/deserialize enum of enums, we should use #[serde(untagged)]

[BelfordZ]

to decide if the enum should be untagged, follow the heuristic of

"if the enum is a result of oneOf/anyOf/allOf, it should be untagged."
"if the enum is the result of type as array, it should be untagged."

[BelfordZ]

🎉 This issue has been resolved in version 1.8.0 🎉

The release is available on:

• GitHub release
• 1.8.0
• npm package (@latest dist-tag)

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