Should Generate warnings when synchronized on `AnyVal`

[He-Pin]

Compiler version

3.2.2

Minimized code

1.synchronized{}

Output

Expectation

generate some warning as https://openjdk.org/jeps/390

[liang3zy22]

This issue also exists with scala 2.13.10.

[som-snytt]

That is due to boxing conversion.

g does not compile in Scala 2, but in Scala 3 is accepted, as though written A.synchronized.

class A(val s: String) extends AnyVal {
  //def f = eq("hello, world")  // missing argument list for method eq in object Predef

  def g = synchronized { println("hello, world") }
}

The error on f is charming. I was expecting it to use (Predef: AnyRef).eq and was hoping for a warning.

Since this ticket is an enhancement, I created a separate issue for the missing error.

[scala-center-bot]

This issue was picked for the Issue Spree No. 32 of 20 June 2023 which takes place in 7 days. @mbovel, @diogocanut, @jmesyou, @michaelpigg will be working on it. If you have any insight into the issue or guidance on how to fix it, please leave it here.

[mbovel]

See synchronized method documentation.

[mbovel]

I don't know good ressources about autoboxing in Scala, but the one for Java might be worth reading: https://docs.oracle.com/javase/tutorial/java/data/autoboxing.html.

[michaelpigg]

It's not clear to me what phase of the compiler is relevant to this issue. I was thinking initially the parser, but maybe it's at erasure after the tree shows it converted to a BoxedUnit?