I appreciate this detailed explanation! To preface, I took on macro expansion caching because it was a clear solution for the slow builds I saw in some projects (taking the "project-specific" approach I mentioned in the blog). That said, my medium-term vision for CodeRemote isn't to develop a superior closed-source Rust compiler fork; instead, it is to provide remote tooling for faster development (i.e. bring small dev teams' tooling up closer to Google's level):

(a) pre-configured build servers, so a developer doesn't need to be equipped with the latest Mac to be functional

(b) shared cache within a developer team

I'd love to hear your thoughts on this goal! Does some aspect address a development pain point of yours? I also want to address your points above, and I agree with lots of them:

1. I agree that especially in the wider Rust community, closed source is not a long-term solution. For what it's worth, I have been considering making the source available -- though likely not with a super copyleft license, at least initially. Do you think making the source available would alleviate people's safety concerns?

2. I have thought about the mold/sold linker quite a bit, especially because the author changed his license on sold from a commercial license to MIT. And defaults are indeed very powerful (this is discussed in a recent change to strip debug info by default, https://kobzol.github.io/rust/cargo/2024/01/23/making-rust-b...) because most people aren't bothered to (or don't know to) change them. Generally one expects the defaults to be the best for the general case, but this is decidedly not true for Rust compiler settings.

I think there may be a difference, though, between catering to the general public and catering to specific users/clients. For the folks where link time is truly atrocious, I assume they make the effort to use mold (though again, there is good reason to be skeptical given that sold switched to an MIT license). I assume a similar willingness if/when someone's macro expansions are slow.

3. You're right, this macro caching feature is not complex! I'm sure someone like bjorn3 could code it up rather quickly. It does me no good trying to solo out-perform the rustc experts. But I think there is a lack of people improving the Rust dev experience. That's where I want to operate.