[mmastrac]

Can you (err... buildcache) cache Rust proc-macros? I've been battling this with sccache and I'm now maintaining a 10-patch deep stack for the next.js build CI.

Windows builds were ridiculously poor on cache hits rates too because of non-determinism that was not able to figure out.

I'd be happy to test it out.

[estebank]

There was an experimental PR that treats proc macros as idempotent with the corresponding colpike speed up. I don't know what happened with it, and stabilization required a lot of design work to not break backcompat. But this is something in the team's radar.

[staticassertion]

Would it be possible to do somethign like editions for proc macros, or have crates establish "this is a v2 proc macro" or something? There are a lot of things I'd love to see change in a v2 but it'd all be breaking.

[estebank]

Yes, I think here are workable designs.

[mmastrac]

Do you have a link for this one? Would love to see it.

[estebank]

This is not the one I remember but another one that does part of what I'm describing.

https://github.com/rust-lang/rust/pull/145354

[NooneAtAll3]

what do you mean by idempotent and colpike?

[estebank]

Idempotent as in if the token stream in the input doesn't change, the cached result of the previous macro expansion is used during incremental, instead of being pessimistic and rerunning the macro.

Colpike as in compile typo.