rust-serde

Add #[serde(deny_unknown_fields)] to the struct so a misspelled key fails at parse time with an error naming the field and byte offset. Without it, serde silently discards unknown keys and the intended field keeps its default value.

Use #[serde(rename = "new_name", alias = "old_name")]. rename sets the written spelling while alias keeps the old spelling accepted on read, so old payloads keep parsing until every writer is upgraded.

Internal tagging with #[serde(tag = "type")] is the usual choice for JSON because the tag reads naturally and the payload stays flat. Use external tagging when the type must also go through binary formats like postcard or bincode, which reject the other representations at runtime.

By default serde_json::Number holds only i64, u64, or f64, so an integer outside that range parses into Value as an f64 and loses digits. Parse into the typed field instead, or enable the arbitrary_precision feature to store digits as text.

No, serde documents the combination as unsupported. The deny rule fires first and the flatten map never receives anything, returning an unknown field error. Pick either the catch-all map or the strict schema, not both.

Positional binary formats cannot represent flatten, internally or adjacently tagged enums, untagged enums, or skip_serializing_if; these compile but fail at runtime. Use external tagging, no flatten, and version the whole payload for postcard or bincode.