Feel free to show me the PR’s that have have been rejected that would have solved the problem. Or if you think it’s easy, feel free to make that PR yourself.
As the quote goes, “There are two hard problems in programming: cache invalidation, naming things, and off-by-one errors”. This is cache invalidation.
Cache invalidation is not always that hard. For example pure functions are more or less trivial to cache, and you don't even have to do any explicit invalidation. Perhaps do some LRU type pruning if the disk starts to fill up.
I know next to nothing about Julia's internals, but given packages like Revise.jl, PackageCompiler.jl and SnoopCompile.jl are even possible, I don't think it can be that hard. Dumb caching should be a lot easier than any of these.
I may well be wrong, and that nobody has done this yet is a hint to me being wrong. But I think another scenario may be that Julia ecosystem is so hung up on REPLs and notebooks that this case just gets no attention. And very few non REPL-or-notebook people hang around long enough to get to know the internals at all. Maybe I'm just desperate enough?
There's also another possibility, which may sound bizarre but I think is possible. At some level people who come from scripting language background think that long compile times is a sign of a "real language". This is somewhat prevalent in e.g. Javascript scene, where more and more byzantine compilation systems are introduced for a language (or platform) that works just fine without compilation (or can do very fast on-the-fly "AOT" if needed).