case class with NoStackTrace won't compile with

[bblfish]

Compiler version

3.0.2
3.1.0-RC2
running on Java 17

Minimized code

I get this error when running the command line with 3.0.2 but also when compiling my project
in SBT with 3.1.0-RC2.

$ scala -version                                                                           127 ↵
Scala compiler version 3.0.2 -- Copyright 2002-2021, LAMP/EPFL
$ scala -Yexplicit-nulls                                                                   127 ↵
scala> import scala.util.control.NoStackTrace

scala> case class ParseException(line: Int, character: Int, message: String) extends NoStackTrace
-- Error:
1 |case class ParseException(line: Int, character: Int, message: String) extends NoStackTrace
  |           ^
  |class ParseException cannot be defined due to a conflict between its parents when
  |implementing a super-accessor for fillInStackTrace in trait NoStackTrace:
  |
  |1. One of its parent (NoStackTrace) contains a call super.fillInStackTrace in its body,
  |   and when a super-call in a trait is written without an explicit parent
  |   listed in brackets, it is implemented by a generated super-accessor in
  |   the class that extends this trait based on the linearization order of
  |   the class.
  |2. Because Throwable comes before NoStackTrace in the linearization
  |   order of ParseException, and because Throwable overrides fillInStackTrace,
  |   the super-accessor in ParseException is implemented as a call to
  |   super[Throwable].fillInStackTrace.
  |3. However,
  |   (): Throwable | Null (the type of super[Throwable].fillInStackTrace in ParseException)
  |   is not a subtype of
  |   (): Throwable (the type of fillInStackTrace in trait NoStackTrace).
  |   Hence, the super-accessor that needs to be generated in ParseException
  |   is illegal.
  |
  |Here are two possible ways to resolve this:
  |
  |1. Change the linearization order of ParseException such that
  |   NoStackTrace comes before Throwable.
  |2. Alternatively, replace super.fillInStackTrace in the body of trait NoStackTrace by a
  |   super-call to a specific parent, e.g. super[Throwable].fillInStackTrace

Output

// TODO add output here

Expectation

[bblfish]

Workaround by passing "writeableStackTrace=false"

case class ParseException(line: Int, character: Int, messageStr: String)
	extends Throwable(messageStr,null,  true,  false)

[odersky]

Nice puzzler! @noti0na1 do you want to take a look?

[noti0na1]

Sure. It looks like a issue related to overriding?

The overriding in explicit nulls is still broken, I'm working it recently.