Comment by kibwen

All compilers have compilation units, there's not actually much interesting about Rust here other than using the word "crate" as a friendlier term for "compilation unit".

What you may be referring to instead is Cargo's decision to re-use the notion of a crate as the unit of package distribution. I don't think this was necessarily a bad idea (it certainly made things simpler, which matters when you're bootstrapping an ecosystem), but it's true that prevailing best practices since then have led to Rust's ecosystem having comparatively larger compilation units (which itself isn't necessarily a bad thing either; larger compilation units do tend to produce faster code). I would personally like to see Cargo provide a way to decouple the unit of distribution from the unit of compilation, which would give us free parallelism (which currently today rustc needs to tease out via parallel codegen units (and the forthcoming parallel frontend)) and also assuage some of the perpetual hand-wringing about how many crates are in a dependency tree (which is exactly the wrong measure as getting upset about how many source files are in your C program). This would be a fully backwards-compatible change.