Compiler should provide better error messages when using unsupported JDK version

[WojciechMazur]

Latest release of JDK 21 might be a time when more and more people might want to migrate to latest Java version. However, if we'd try to do so, we might get a very nasty error.

Compiler version

3.3.0 (fixed in 3.3.1 for JDK 21, however the issue would still be present in future JDK's if more assumptions of classfile format are violated)

Minimized code

import java.nio.file.StandardOpenOption

@main def Test = {
  val x =  StandardOpenOption.CREATE
}

Output

>scalac main.scala
error while loading StandardOpenOption,
class file /modules/java.base/java/nio/file/StandardOpenOption.class is broken, reading aborted with class java.lang.RuntimeException
bad constant pool index: 0 at pos: 1200
-- [E008] Not Found Error: main.scala:4:30 -------------------------------------
4 |  val x =  StandardOpenOption.CREATE
  |           ^^^^^^^^^^^^^^^^^^^^^^^^^
  |   value CREATE is not a member of object java.nio.file.StandardOpenOption
2 errors found

Expectation

Compiler should provide better error messages when using unsupported JDK version, eg. what is the latest supported version and which version was found in the classfile along with a possible way to mitigate this issue, eg. please try to use the latest version the Scala compiler

[SethTisue]

agree. a language newcomer on Discord was bitten by this today

[SethTisue]

another user bitten today

[bishabosha]

So we could add another constant in ClassfileConstants, and check it when we parse the header?

[bishabosha]

Alternatively only when there is an error from reading a classfile, then we add an addendum to say that the version was unexpected, so could be the reason?