REPL still prints LazyVal warnings (because of fansi+pprint)

[jrlawson]

Compiler version

3.8.2
JDK 25

Minimized example

given theMagicNumber: Int = 3

Output Error/Warning message

WARNING: A terminally deprecated method in sun.misc.Unsafe has been called
WARNING: sun.misc.Unsafe::objectFieldOffset has been called by scala.runtime.LazyVals$ (file:/home/jamielawson/.cache/coursier/arc/https/github.com/scala/scala3/releases/download/3.8.2/scala3-3.8.2-x86_64-pc-linux.tar.gz/scala3-3.8.2-x86_64-pc-linux/maven2/org/scala-lang/scala-library/3.8.2/scala-library-3.8.2.jar)
WARNING: Please consider reporting this to the maintainers of class scala.runtime.LazyVals$
WARNING: sun.misc.Unsafe::objectFieldOffset will be removed in a future release
lazy val magicNumber: Int

## Why this Error/Warning was not helpful
 
Per my understanding, this was supposed to have been fixed in scala 3.8.0. But it's still there. Supposedly will throw exceptions in JDK 26, so it needs to get resolved.


## Suggested improvement

It could be made more helpful by...
There is supposedly a fix that was introduced in scala 3.8.0. If so, the error has made its way back into scala 3.8.2. 

[tgodzik]

Thanks for reporting! I can't reproduce this problem, could you provide the full reproduction? Minimized example doesn't contain any lazy vals.

[jrlawson]

This is a full reproduction. To reproduce the error, call "scala" from the bash prompt to get the REPL. Type the scala command

given theMagicNumber: Int = 3

into the REPL. Press enter to evaluate. This is an example from the "Functional Programming Strategies" book by Noel Welsh, page 105 in the current (Jan. 21, 2026) draft. The warning message I showed in the initial report is produced. This is consistent across several different machines, all running Linux Ubuntu.

It can be seen from the warning that it is looking in the Scala 3.8.2. If I type java -version from the bash prompt I get:

java version "25.0.2" 2026-01-20 LTS

[tgodzik]

Looks like this could be an issue with repl itself, my guess is that it's because it uses the libraries from Li Haoyi, which are compiled with LTS.

[jrlawson]

My understanding is the Unsafe warning for lazy is finally settled at jdk 26 and scala 3.9 LTS. So we currently see the warning everywhere. I have a PR to strip it from test results, for example.

Discussion of 3.3 LTS #24993

In this issue tracker it is listed as "fixed" in 3.8.0. So are you saying that those claims were in error? That would be okay. It's just confusing if it wasn't actually fixed. I have seen errors in software systems that seem fixed and then return as zombies.

[jrlawson]

Looks like this could be an issue with repl itself, my guess is that it's because it uses the libraries from Li Haoyi, which are compiled with LTS.

I've seen this from within IntelliJ where IntelliJ is doing all of the config management of JDKs and Scala versions, and seen the same warning when I install the JDK and Scala environment by hand, and run my trivial example from the Scala REPL. So if the problem was believed fixed in 3.8.0, but is still manifesting in 3.8.2, it is pretty deep within the Scala ecosystem. My by-hand installation of Scala 3.8.2 is done according to the ScalaLang web page https://www.scala-lang.org/download/ using the "recommended" cs setup.

[tgodzik]

It's fixed if you don't use the REPL. Any production code should not suffer from the problem. When you run normal JVM code the repl is not involved, it's a separate artifact.

[jrlawson]

It's fixed if you don't use the REPL. Any production code should not suffer from the problem. When you run normal JVM code the repl is not involved, it's a separate artifact.

Try this from IntelliJ (no REPL involved) configured for JDK 25 and Scala 3.8.2. Pretty small example:

import scala.collection.parallel.CollectionConverters.*
@main
def main(): Unit = {
println(Seq(1,2,3,4,5,6,7,8,9,10).par.map(i=>2*i))
}

Running this from within IntelliJ you get:

WARNING: A terminally deprecated method in sun.misc.Unsafe has been called
WARNING: sun.misc.Unsafe::objectFieldOffset has been called by scala.runtime.LazyVals$ (file:/home/jamielawson/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/3.8.2/scala-library-3.8.2.jar)
WARNING: Please consider reporting this to the maintainers of class scala.runtime.LazyVals$
WARNING: sun.misc.Unsafe::objectFieldOffset will be removed in a future release
ParVector(2, 4, 6, 8, 10, 12, 14, 16, 18, 20)

Basically the same LazyVal terminally deprecated method stuff. I know par is deprecated in Scala3, but somewhere inside, Scala libraries are still calling the sun.misc.Unsafe::objectFieldOffset method, and still coughing up the warning...NO REPL INVOLVED

[bishabosha]

So the fix here for REPL is for https://github.com/com-lihaoyi/fansi and https://github.com/com-lihaoyi/pprint to recompile with the eventual 3.3.x release that supports the JDK 17 min version

or shade the sources and recompile them with the same version as the release

[tgodzik]

Are you ale to reproduce it running from command line? From sbt project for example?

[tgodzik]

import scala.collection.parallel.CollectionConverters.*

This is coming from a library compiled with an earlier Scala version, so it is using the older lazy vals. Anything compiled with previous version will suffer from that.

It's worth including all information about what dependencies you are using, since it took me a minute to see the import 😓

[jrlawson]

import scala.collection.parallel.CollectionConverters.*

This is coming from a library compiled with an earlier Scala version, so it is using the older lazy vals. Anything compiled with previous version will suffer from that.

Does this indicate that the parallel collections will no longer work in Scala 3.9/JDK 26, when JDK removes sun.misc.Unsafe::objectFieldOffset???