[cormacrelf]

The most promising proposal so far is to compile proc macros to WASM. Then you precompile them to a single cross-platform WASM binary, publish those to crates.io alongside the source code, and then execute them in a sandbox. You wouldn’t see much benefit until all your chosen proc macros were available in this form, but after a while this would be great, basically no downsides. In fact you can publish proc macros this way today, IIRC with some caveats about compiler versions (?), but it’s manual and a proof of concept only so nobody has done it.

The only thing missing was effort into the idea to make it the default and able to be supported long term. You need a stable WASM ABI that won’t change across rustc versions and for someone to add a runtime to rustc.

Dtolnay (the author of the Watt concept) recently put out a message looking for help putting together an RFC. https://twitter.com/davidtolnay/status/1574913813400330241