syn VS cargo-expand

[2] https://github.com/dtolnay/syn/issues/782

It looks to me like you are trying to make a syntax tree generic over arities. I suggest you take a look at the Expr enum in syn, its variant structs, and the ast_enum_of_structs_impl macro, which is a macro that implements a trait over different Expr variants with different fields.

Rust makes this project easy by providing the syn crate (parsing and formatting) and WASM (for interactivity). Source code lives at https://github.com/CarlKCarlK/rust-ast-explorer. Contributions welcome.

Perhaps there should, but if you look at the commit history you'll see that syn is maintained almost entirely by dtolnay (https://github.com/dtolnay/syn/graphs/contributors). Furthermore, with Rust continually adding new syntax that needs to be supported, syn can't be easy to maintain and most of the effort probably goes into making it work at all rather than optimisations.

It's been superseded by https://github.com/dtolnay/cargo-expand

Try installing cargo expand, it's useful to see how macros eventually get expanded. For example, if you run cargo expand on the following code

You can use cargo expand to see what your code expands to: https://github.com/dtolnay/cargo-expand

Not too familiar with macros but does cargo-expand do what you want or did you mean something else?

Yes. You can use Tools > Expand Macro on the playground or install and run cargo-expand to see what the macro expands to. It just adds a & before the argument.

cargo expand

Along with what others are saying, there is also cargo expand which can show you what code a macro generates

Something that may help you understand code with magic proc macros is this utility. It's basically a wrapper around a Rust compiler flag that allows you to expand macros for a file.

You can use https://github.com/dtolnay/cargo-expand to examine how it works.