JDK 24: REPL prints warning on startup about JLineNativeLoader

[alanbur]

:
According to https://docs.scala-lang.org/overviews/jdk-compatibility/overview.html, Scala 3.6.4 is compatible with Java 24, yet:

$ scala
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:/data/opt/periscope-tools-1.1.0/scala3-3.6.4/maven2/org/scala-lang/scala3-library_3/3.6.4/scala3-library_3-3.6.4.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
WARNING: A restricted method in java.lang.System has been called
WARNING: java.lang.System::load has been called by org.jline.nativ.JLineNativeLoader in an unnamed module (file:/data/opt/periscope-tools-1.1.0/scala3-3.6.4/maven2/org/jline/jline-native/3.27.1/jline-native-3.27.1.jar)
WARNING: Use --enable-native-access=ALL-UNNAMED to avoid a warning for callers in this module
WARNING: Restricted methods will be blocked in a future release unless native access is enabled

Welcome to Scala 3.6.4 (24, Java Java HotSpot(TM) 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                                                                                                            
scala> 

[SethTisue]

it will still work, it's just printing warnings — two different ones — both of which you can safely ignore

the LazyVal thing is described at https://www.scala-lang.org/blog/next-scala-lts.html and work on it is being tracked at #9013

for the JLine one we have a Scala 2 ticket at scala/bug#13030. but it's good to have a Scala 3 ticket as well, thank you. I've changed the title of this ticket to just be about the JLine warning. there are some remarks on the Scala 2 ticket about what the root cause is and what's needed to address it

[alanbur]

Thanks for the info Seth.

I note #9013 says "problematic for various reasons (e.g. usage of a security manager, using Graal Native (#13985)).", I don't think that's an issue any more, my app is built using Native Image and I don't see that problem.

However, unfortunately these warnings are deal-breakers for me, I'm shipping a CLI utility that will require JDK24 for its next release and I can't have it spewing warnings when it runs. What I haven't figured out is if it's possible to suppress the warnings.

[SethTisue]

I can't have it spewing warnings when it runs

You shouldn't see the JLine one; that’s specific to the REPL.

(Whether you'll see the LazyVal one, I don't know; but let's keep this ticket specific to the REPL issue, please.)

[alanbur]

I've confirmed that the JLine one only seems to affect the REPL. I think I've found a workaround for the LazyVal warning, I'll add a note to #9013.

[alanbur]

This seems to suppress the warnings for the REPL:

e$ export JDK_JAVA_OPTIONS='--sun-misc-unsafe-memory-access=allow --enable-native-access=ALL-UNNAMED'
$ scala
NOTE: Picked up JDK_JAVA_OPTIONS: --sun-misc-unsafe-memory-access=allow --enable-native-access=ALL-UNNAMED
Welcome to Scala 3.6.4 (24, Java Java HotSpot(TM) 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                                                                                      
scala> 

Well, sort of works - I'm not sure where the NOTE: comes from.

[SethTisue]

I wouldn't expect that you'd need to go through JDK_JAVA_OPTIONS; I would expect scala -J --sun-misc-unsafe-memory-access=allow to work. @Gedochao seems like a bug in Scala-CLI — would you agree?

[alanbur]

This seems to work, just providing the single flag above doesn't:

$ scala -J --sun-misc-unsafe-memory-access=allow -J --enable-native-access=ALL-UNNAMED
Welcome to Scala 3.6.4 (24, Java Java HotSpot(TM) 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.
                                                                                                                                              
scala> 

[SethTisue]

Oh, weird! I was testing on JDK 25, where I see:

% scala -J --sun-misc-unsafe-memory-access=allow -J --enable-native-access=ALL-UNNAMED
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:/opt/homebrew/Cellar/scala/3.6.4/libexec/libexec/scala-cli.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
Welcome to Scala 3.6.4 (25-ea, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

Not sure how to account for the difference, unless it's the 24 vs 25 thing. (I don't have a 24 installation easily accessible at the moment.)

[alanbur]

Yeah, weird indeed. But if there's one way that works for 24 and a different way for 25, that's probably good enough for now :-)

[Gedochao]

@SethTisue I do not think it's a Scala CLI issue, the options seem to be passed correctly... let me know if there's reason to think otherwise. Might be a JDK 24 vs JDK 25 thing, indeed.

[Gedochao]

Related JEP:

• https://openjdk.org/jeps/472

JLine ticket:

• WARNING: A restricted method in java.lang.System has been called (JDK24) jline/jline3#1067