Crate nextjson_derive 

Zero-dependency derive macros for nextjson.

Implemented entirely with the standard proc_macro API: no syn, no quote, no proc-macro2. The input TokenStream is parsed by a hand-written recursive-descent parser into a small AST, and the output is generated as text and re-parsed.

Forward compatibility contract

A derive macro only ever receives a single item’s tokens, and this parser interprets a deliberately stable grammar subset: the item header (struct / enum + name), the generic parameter list, the where clause, and the field / variant structure, plus #[njson] / #[nextjson] / #[serde] attributes. Everything inside a field or generic type position is carried through verbatim as an opaque token sequence, so new Rust syntax that appears in type positions (new literals, impl Trait forms, associated-type paths, …) needs no parser change — it is round-tripped unchanged.

The risk of future item-level grammar changes is handled defensively: parse_input requires that every input token be consumed. If a future Rust release extends item syntax in a way this parser does not understand, the macro fails with a loud compile_error! naming the leftover tokens instead of silently generating impls from a mis-parsed subset.

Derive Macros

NsonDeserialize

Derive NextJson’s native decoding contract.

NsonSerialize

Derive NextJson’s native serialization contract and compile-time schema.