inconsistent logic when override self type method

[ohze]

reproduction steps

• pk1/A.scala

package pk1
class A {
  protected def f(): Unit = print("A")
}

• Main.scala

import pk1.A

trait B { self: A =>
  override def f(): Unit = {
    print("B")
    self.f()
  }
}
class C extends A with B
object Main {
  def main(args: Array[String]): Unit = {
    new C().f()
  }
}

problem

• The code above run successfully

[info] running Main 
BA[success]...

• But when remove the protected modifier from A.f =>

[info] running Main 
BBB...//many Bs
[error] java.lang.StackOverflowError
...
[error] 	at scala.Predef$.print(Predef.scala:385)
[error] 	at B.f(Main.scala:5)
[error] 	at B.f$(Main.scala:4)
[error] 	at C.f(Main.scala:9)
[error] 	at B.f(Main.scala:6)
[error] 	at B.f$(Main.scala:4)
[error] 	at C.f(Main.scala:9)
...

• similar (StackOverflowError) if we move A from pkg1 to default package (same package as B)

expectation

IDK :)

[ohze]

Note: The above code is simplified from akka's:
DockerBindDnsService.atStartup override AkkaSpec.atStartup

[lrytz]

I cannot reproduce this, I get the infinite recursion with both 2.12.11 and 2.13.1 (with A.f being protected or not).

The infinite recursion seems to be the correct behavior, (self: A).f() is a virtual call.

[Jasper-M]

When I run this in the REPL I see the same as reported by ohze. On 2.11, 2.12 or 2.13.

scala> class A {
     |   protected def f(): Unit = print("A")
     | }
class A

scala> trait B { self: A =>
     |   override def f(): Unit = {
     |     print("B")
     |     self.f()
     |   }
     | }
     | class C extends A with B
     | object Main {
     |   def main(args: Array[String]): Unit = {
     |     new C().f()
     |   }
     | }
trait B
class C
object Main

scala> Main.main(Array())
BA

[lrytz]

Wow, I omitted the package declaration in A, and that makes a difference

   // access flags 0x1
   public default f()V
     GETSTATIC scala/Predef$.MODULE$ : Lscala/Predef$;
     LDC "B"
     INVOKEVIRTUAL scala/Predef$.print (Ljava/lang/Object;)V
     ALOAD 0
-    INVOKEINTERFACE B.B$$super$f ()V
+    CHECKCAST A
+    INVOKEVIRTUAL A.f ()V
     RETURN