Comment by pornel
2 days ago
It's a "unit" in the sense of calling `rustc` once, but it's not a minimal unit of work. It's not directly comparable to what C does.
Rust has incremental compilation within a crate. It also splits optimization work into many parallel codegen units. The compiler front-end is also becoming parallel within crates.
The advantage is that there can be common shared state (equivalent of parsing C headers) in RAM, used for the entire crate. Otherwise it would need to be collected, written out to disk, and reloaded/reparsed by different compiler invocations much more often.
> Rust has incremental compilation within a crate. It also splits optimization work into many parallel codegen units.
Eh, it does, but it's not currently very good at this in my experience. Nothing unfixable AFAIK (and the parallel frontend can help (but is currently a significant regression on small crates)), but currently splitting things into smaller crates can often lead to much faster compiles.
Yes the actual implementation is far from what could be, but the argument was that it's not a language design issue, but an implementation one.
Agreed on that