I don't think that there are that many production level compilers that don't perform the kind of caching that you're advocating for. Part of them problem is what the language semantics are. https://www.pingcap.com/blog/rust-huge-compilation-units/ gives an example of this.

> Surely it’s possible to make a compiler that takes time proportional to how much of my code has changed, not how large the program is in total.

Language design also affects what can be done. For example Rust relies a lot on monomorphisation, which in turn makes much harder (not necessarily impossible) to do in-place patching, but a language like Java or Swift, where a lot of checks can be relegated to runtime, it becomesuch easier to do that kind of patching.

I think that there's a lot left to be done to get closer to what you want, but changing a compiler that has users in such an extensive way is a bit like changing the engine of a plane while it's flying.

But once you have your REPL prompt, it's just: edit code, test it. Revise figures out what needs recompiling and does it for you. There are some limitations, most notably, any redefinition of a struct requires a reboot, but it's a great experience.

A lot of the current work going into the Zig compiler is to greatly increase the compile time of debug builds, by cutting the LLVM dependency, and then add incremental compilation. I'm looking forward to the fruits of that labor; I don't like to wait.

My understanding is that this is how Eclipse's Java compiler works, but I'm not positive.