[2.13.9] Can't reference `sun.` package classes with `-release` option

[xuwei-k]

Reproduction steps

class A {
  classOf[sun.misc.Unsafe]
}

Problem

Java 8 without -release option

Success

$ java -version
openjdk version "1.8.0_332"
OpenJDK Runtime Environment (Zulu 8.62.0.19-CA-macos-aarch64) (build 1.8.0_332-b09)
OpenJDK 64-Bit Server VM (Zulu 8.62.0.19-CA-macos-aarch64) (build 25.332-b09, mixed mode)
$ scala -version
Scala code runner version 2.13.9 -- Copyright 2002-2022, LAMP/EPFL and Lightbend, Inc.
$ scalac A.scala 
A.scala:2: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
  classOf[sun.misc.Unsafe]
         ^
1 warning

Java 8 with -release:8 option

Success

$ scalac -release:8 A.scala
A.scala:2: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
  classOf[sun.misc.Unsafe]
         ^
1 warning

Java 11 without -release option

Success

$ java -version
openjdk version "11.0.16" 2022-07-19 LTS
OpenJDK Runtime Environment Zulu11.58+15-CA (build 11.0.16+8-LTS)
OpenJDK 64-Bit Server VM Zulu11.58+15-CA (build 11.0.16+8-LTS, mixed mode)
$ scala -version
Scala code runner version 2.13.9 -- Copyright 2002-2022, LAMP/EPFL and Lightbend, Inc.
$ scalac A.scala           
A.scala:2: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
  classOf[sun.misc.Unsafe]
         ^
1 warning

Java 11 with -release:11 option

Success

$ java -version 
openjdk version "11.0.16" 2022-07-19 LTS
OpenJDK Runtime Environment Zulu11.58+15-CA (build 11.0.16+8-LTS)
OpenJDK 64-Bit Server VM Zulu11.58+15-CA (build 11.0.16+8-LTS, mixed mode)
$ scala -version
Scala code runner version 2.13.9 -- Copyright 2002-2022, LAMP/EPFL and Lightbend, Inc.
$ scalac -release:11 A.scala
A.scala:2: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
  classOf[sun.misc.Unsafe]
         ^
1 warning

Java 11 with -release:8 option

Failure !?

$ java -version            
openjdk version "11.0.16" 2022-07-19 LTS
OpenJDK Runtime Environment Zulu11.58+15-CA (build 11.0.16+8-LTS)
OpenJDK 64-Bit Server VM Zulu11.58+15-CA (build 11.0.16+8-LTS, mixed mode)
$ scala -version            
Scala code runner version 2.13.9 -- Copyright 2002-2022, LAMP/EPFL and Lightbend, Inc.
$ scalac -release:8 A.scala 
A.scala:2: error: not found: value sun
  classOf[sun.misc.Unsafe]
          ^
1 error

Java 11 with -target:jvm-1.8 option

Success

$ java -version                
openjdk version "11.0.16" 2022-07-19 LTS
OpenJDK Runtime Environment Zulu11.58+15-CA (build 11.0.16+8-LTS)
OpenJDK 64-Bit Server VM Zulu11.58+15-CA (build 11.0.16+8-LTS, mixed mode)
$ scala -version                
Scala code runner version 2.13.9 -- Copyright 2002-2022, LAMP/EPFL and Lightbend, Inc.
$ scalac -target:jvm-1.8 A.scala
A.scala:2: warning: a pure expression does nothing in statement position; multiline expressions may require enclosing parentheses
  classOf[sun.misc.Unsafe]
         ^
warning: 1 deprecation; re-run with -deprecation for details
2 warnings

[lrytz]

It's the same with Scala 2.13 and Scala 3. When using Java 11 with -release:8, the ct.sym file that's put on the classpath (instead of rt.jar) contains Java 8 symbols, but only the official JDK. So sun is missing. (That's what I remember, maybe someone has a good reference here.)

[lrytz]

It's the same with Scala 2.13

Sorry, that didn't make sense. But the behavior is already in 2.13.8

➜ sandbox sv 2.13.8 -release 8 -e "classOf[sun.misc.Unsafe]"
/var/folders/8d/8tnybb497mbgq2v08vgcr5c80000gn/T/scalacmd9807037385199816981.scala:1: error: not found: value sun
classOf[sun.misc.Unsafe]
        ^

[som-snytt]

Maybe the point is to undeprecate -target? Or is there a convenient -classpath idiom?

[SethTisue]

Does javac -release behave the same way?

[SethTisue]

Maybe the point is to undeprecate -target?

Huh?

[som-snytt]

-target says "emit class file of version N, but I want to use arbitrary classes from the JDK and take my chances".

If that is a reasonable use case, then either undeprecate the compiler option or make it easy to put certain packages of compelling utility on the class path when using -release.

[lrytz]

Does javac -release behave the same way?

yes, with javac --release 8, sun.misc.Unsafe is not visible

[SethTisue]

If javac is the same, then I think we should just close this ticket.

[SethTisue]

make it easy to put certain packages of compelling utility on the class path when using -release

If anyone figures out what incantation is currently needed, please share!

(What do javac users do in this case? I did a bit of Googling for prior art but failed to find something, but maybe I didn't try hard enough.)

[He-Pin]

@SethTisue @som-snytt cc

https://github.com/akka/akka/blob/a6863e9ed5378d52cb16f386db4e137f0a02c170/project/JdkOptions.scala#L47-L58

 selectOptions( 
   targetSystemJdk, 
   jdk8home, 
   fullJavaHomes, 
   Seq(if (scalaVersion.startsWith("3.")) "-Xtarget:8" else "-target:jvm-1.8"), 
   // '-release 8' is not enough, for some reason we need the 8 rt.jar 
   // explicitly. To test whether this has the desired effect, compile 
   // akka-remote and check the invocation of 'ByteBuffer.clear()' in 
   // EnvelopeBuffer.class with 'javap -c': it should refer to 
   //""java/nio/ByteBuffer.clear:()Ljava/nio/Buffer" and not 
   // "java/nio/ByteBuffer.clear:()Ljava/nio/ByteBuffer". Issue #27079 
   (java8home: File) => Seq("-release", "8", "-javabootclasspath", java8home + "/jre/lib/rt.jar")) 

akka/akka#27079