Function lex_error 

pub fn lex_error(ls: &mut LexState, msg: &[u8], token: i32) -> LuaError

Build a syntax error, optionally annotated with the offending token text.

Corresponds to the static lexerror function in llex.c. In C this is l_noret (diverges via luaD_throw); in Rust it returns a LuaError value that callers wrap in Err(...).

C source

//   msg = luaG_addinfo(ls->L, msg, ls->source, ls->linenumber);
//   if (token)
//     luaO_pushfstring(ls->L, "%s near %s", msg, txtToken(ls, token));
//   luaD_throw(ls->L, LUA_ERRSYNTAX);
// }