Except for the most trivial programs, clap should not make a factor of 10 difference, especially for incremental builds. For serde, I can see it if you use it

Except for the most trivial programs, clap should not make a factor of 10 difference, especially for incremental builds. For serde, I can see it if you use it a lot. There is an experiment to try to cache the macro expansion results to not need to run macro expansion during incremental builds. For full rebuilds, there is an in-work PR to decouple serde's traits from the derive so deserializers can be built in parallel to the rest of your serde code. There is also an RFC for declarative derives. Likely, serde won't be able to use it immediately but we'd like to get it to the point that serde can, getting rid of some big dependencies.