I don't think speed of a full compile (including your dependencies) is the right thing to optimize for -- and incremental compiles don't rebuild dependencies. I

I don't think speed of a full compile (including your dependencies) is the right thing to optimize for -- and incremental compiles don't rebuild dependencies. In a project that depends on serde, for example, most compiles in an ordinary dev cycle are probably not recompiling serde. And sccache reduces the incidence of unnecessary rebuilds far further. Even clean builds tend to get through my dependencies quite quickly.