I've just been experimenting with v1.9.36, and specifically, the idea that adding transit-clj as a dependency would result in a compile time speedup. So I took an existing project and made the dependencies be as follows:

[org.clojure/clojure        "1.8.0"]
[org.clojure/clojurescript  "1.9.36"]        ;; previously "1.8.40"
[com.cognitect/transit-clj "0.8.285"]        ;; not there originally

it looks like transit is used for encoding caches, so my guess would be it would only be after the initial build

Oh, right. So if you compile once. Then make a change and compile again (without having done a clean).

I am not sure, but it looks like the caching is per namespace (which is more or less per file), so a change in a namespace would invalidate the cache

For sanity purposes, all of our figwheel builds do an initial clean. So no real benefit for us then, at least in the initial build. But perhaps this improves the incremental figwheel recompilations?

figuring out all the ways all the clojurescript tooling interacts with new features in the compiler seems like a non-trivial thing

@mikethompson: if I understood right this speeds up the repl startup, not the compile time

I tried myself on http://clojurescript.io without seeing improvements, then in #C07UQ678E it was clear that when the compile time dominates you cannot appreciate the speed up