scala-cli eagerly sets -release / -java-output-version, which prevents compiling on new Java versions

[lrytz]

scala-cli compile always sets -release N (aka -java-output-version on Scala 3) where N is the Java version.

This prevents compiling on a Java version which is not yet known to the compiler:

➜ sandbox cat A.scala
class A { java.io.IO.print(1) }

➜ sandbox scala compile --server=false -S 3 A.scala
23 is not a valid choice for -java-output-version
  scalac -help  gives more information
Compilation failed

I can manually set an older -release version, but then new API is not available:

➜ sandbox scala compile --server=false -S 3 A.scala -O -release -O 22
-- [E008] Not Found Error: /Users/luc/code/scala/scala13/sandbox/A.scala:1:18 --
1 |class A { java.io.IO.print(1) }
  |          ^^^^^^^^^^
  |          value IO is not a member of java.io
1 error found
Compilation failed

Invoking the compiler manually works, the compiler writes the classfile using the default version 52 (corresponds to Java 8):

➜ sandbox java -cp $(cs fetch -p org.scala-lang::scala3-compiler:3.5.0) dotty.tools.dotc.Main -usejavacp A.scala
➜ sandbox asm A.class && cat A.asm
// class version 52.0 (52)
// access flags 0x21
public class A {

  // compiled from: A.scala
...

@Gedochao mentioned that the flag might have been added due to some interaction with bloop (cc @kasiaMarek, @tgodzik)

[kasiaMarek]

The flag is not added for bloop, bloop handles adding this flag on its own. It is added when server=false.

scala-cli/modules/build/src/main/scala/scala/build/Build.scala

Lines 865 to 867 in 052ed4d

	val releaseFlagVersion =
	if (options.useBuildServer.getOrElse(true)) None
	else releaseFlag(options, compilerJvmVersionOpt, logger).map(_.toString)

Probably we could avoid adding it if scala compiler jdk matches required jdk, but checking the jvm version for simple compiler seems to be missing an implementation:

scala-cli/modules/build/src/main/scala/scala/build/compiler/SimpleScalaCompiler.scala

Lines 23 to 24 in 052ed4d

	def jvmVersion: Option[Positioned[Int]] =
	None // ??? TODO

[lrytz]

Ah, I'm indeed using --server=false

bloop handles adding this flag on its own

So is also setting -release? Then maybe it was done for consistency with bloop?

What is the "required jdk" you mention?

[kasiaMarek]

What is the "required jdk" you mention?

I just mean the one Scala CLI calculates from options like jvm xx.