Disable optimizations for some build-time crates

[lnicola]

This speeds up a release build on my laptop from 4m 13s to 3m 33s. It's a bit disappointing, but we don't get perfect parallelism during the build. The non-RA dependencies finish building around 72s as opposed to 112s.

[matklad]

bors r+

Thanks for looking into this @lnicola !

[bors]

Build succeeded

• Rust (macos-latest)
• Rust (ubuntu-latest)
• Rust (windows-latest)
• TypeScript

[Mark-Simulacrum]

Out of interest, did we check that this doesn't slow down subsequent (incremental) builds? Or, if so, by how much?

[lnicola]

I didn't check. Are you thinking that the proc macros got slower, or is there another reason why incremental builds should be affected?

[Mark-Simulacrum]

Procedural macros are evaluated on all compilations in any built crate (i.e., incremental does not apply). Depending on the relative speed up given by optimizations of those proc macro crates, this could have an impact. It would be good to check this, I think.

Edit: to be clear, incremental compilation being on or not should have no major effect on results here -- I recommend turning it off for easier measurement though.

[lnicola]

Procedural macros are evaluated on all compilations in any built crate

Got it, thanks.

So a way to test this would be to disable incremental compilation, clean the output of every crate in rust-analyzer (I wish there was a cargo clean --no-deps), then build it again. The effect might be more noticeable on debug builds, so we could actually turn build-time crate optimizations for the dev profile instead.

[Mark-Simulacrum]

Sure. My recommendation is that you probably want to have a "commonly edited file" and do something like this:

CARGO_INCREMENTAL=0 cargo build
touch path/to/normal/file.rs
CARGO_INCREMENTAL=0 cargo build # timing here is most interesting