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Comment by alisonatwork | Hacker News Reader

I work professionally in Python these days, but I've just spent a bit of time digging into the contemporary situation because the JVM environment is much more interesting to me, and found this spec: https://build-server-protocol.github.io

Seems the Scala guys have doubled down on the "compiler as a service" approach, presumably because their compile time story continues to be painful. But also looks like the same solution is used for the VS Code Java/Gradle integration, so seems like this might be the more conventional way to go for traditional JVM projects.

For processes where the JIT takes a while to kick in, but also you don't want to waste memory keeping JVMs alive while not doing anything (and compilation could be a good example of that), I wondered if there was a way to snapshot and restore the JVM state and turns out some people are experimenting with that too: https://openjdk.org/projects/crac/

It's all neat stuff!

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> I work professionally in Python these days

Elide can run Python using GraalPy, and we want to do some similar toolchain stuff in that universe. We are working on an integration with uv. Thanks also for linking this Build Server Protocol thing -- this looks very cool, very relevant, and I don't think I've seen this yet.

> Seems the Scala guys have doubled down on the "compiler as a service" approach, presumably because their compile time story continues to be painful

I wonder if we could run the Scala compiler. Reflection is a challenge in native mode and iirc Scala is reflection heavy, but I have no idea, I've never used it myself. I'll look into this

> snapshot and restore the JVM state and turns out some people are experimenting with that too

There are many efforts in this area: CrAC, Leyden, the new JDK 24 AOT stuff, and pre-warmup stuff before that. These all do make a difference but Native Image takes AOT optimization to a whole other level and seems to perform better for quick-startup quick-shutdown cases[1].

Elide also runs JVM code via Truffle/Espresso, and we're going to need a regular JVM integration. On this side CrAC and so on will be useful to cut down on startup time

[1]: https://github.com/simonis/LeydenVsGraalNative

For scala 2 at least, the standard library is very heavy and the compiler of course relies on it. It has a god object, predef, that cascades massive classloading if you touch anything in it. As a result, it is essential for latency to keep a warm jvm up to avoid reloading it.

Incremental rebuilds can actually be not too bad in scala when a warm jvm is used for compilation as it is by sbt and other scala build tools, but sbt also by default uses the warm jvm to run in process tests. This too can be reasonably quick but leads to problems if there are any resource leaks in the user's test suite.

Thus with sbt, one must either exercise discipline and care with tests to not leak anything or you will periodically have to restart sbt, which can be very painful because it is much heavier than the already heavy scala compiler.

It's a disappointing state of affairs because while there is a lot to like about scala, it is impossible to escape the bloat. Even if you opt out of sbt, the lack of modularity in the standard library forces workarounds, such as native-image, which had its own issues (including horrific build times for making native images and weak reflection support). Even if you or your org avoids the direct pitfalls, it is likely at some point you will end up debugging a dependency that doesn't.

I personally abandoned scala due to this bloat, which was a shame because I find it to have the best combo of expressiveness and pragmatism of any established general purpose languages.

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