watt VS syn

The precompiled binary is not a sandboxed WASM binary. Despite the name "watt" it has nothing to do with https://github.com/dtolnay/watt . You can look at the actual code to see for yourself.

* Related: watt is one approach to pre-compile proc-macro crates using WASM.

In addition to thiserror and anyhow, our resident superhuman Rust-improving Robot, dtolnay, also developed an experiment in distributing precompiled proc macros as WebAssembly named Watt and, though I never bothered to create a Zulip account so I don't know what was said, I'm told there has been discussion around the idea of implementing something in that vein.

I think when we have Cranelift, Mold, and maybe Watt all working together then compile times will basically be a non-issue. It'll be a few years though.

Check out https://github.com/dtolnay/watt - it's a really interesting solution to the problem!

I really like the idea of Watt: https://github.com/dtolnay/watt Run macros in a wasm sandbox so they can't touch anything you don't explicitly allow.

I really wish there was more interest in getting something like Watt upstreamed.

[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.