Function to_canonical_json 

pub fn to_canonical_json(
    table: &ParseTable,
    terminals: &[TerminalDef],
    ignore: &[String],
    start: &[String],
    options: &SaveOptions,
) -> Result<String, SaveError>

Serialize a compiled grammar to the canonical envelope, as a pretty-printed (indent-2, key-sorted) string with a trailing newline — matching the corpus fixtures’ shape and byte-stable across repeated saves.

terminals MUST be the grammar’s terminals in lexer_conf (id) order — their index is their memo id 0..N-1; rules follow at N..N+R-1 (the exact order Lark’s memo_serialize walk assigns: lexer_conf.terminals then parser_conf.rules).