2.12 emits static forwarder for bridge method in mirror class

[lrytz]

trait A { def f: Object = null }
object B extends A { override def f: String = "b" }

With 2.12.5, asm gives

  // access flags 0x9
  public static f()Ljava/lang/String;
    GETSTATIC B$.MODULE$ : LB$;
    INVOKEVIRTUAL B$.f ()Ljava/lang/String;

  // access flags 0x9
  public static f()Ljava/lang/Object;
    GETSTATIC B$.MODULE$ : LB$;
    INVOKEVIRTUAL B$.f ()Ljava/lang/Object;

In 2.11, we don't get the static forwarder for the bridge method. Luckily, javac picks one of the two (the more specific), but IntelliJ seems to complain.

https://discuss.lightbend.com/t/http-get-is-ambiguous-from-java/571/12

[lrytz]

Turns out this is an older bug, also in 2.11. Making A a class instead of a trait:

class A { def f: Object = null }
object B extends A { override def f: String = "b" }

Gives two static forwarders in B.class.

The difference in 2.12 is: if A is a trait, in 2.11, method A.f is abstract, and no forwarder is added. In 2.12 (with default methods), A.f is concrete, and a frowarder is added.

We use this for member lookup (simplified of real):

scala> enteringJVM(symbolOf[B.type].info.membersBasedOnFlags(reflect.internal.Flags.BRIDGE, reflect.internal.Flags.METHOD)).filter(_.name.toString == "f").foreach(s => println((s, s.info, s.owner, s.debugFlagString)))
(method f,=> String,object B,<method> override)
(method f,=> Object,class A,<method> <triedcooking>)

[lrytz]

Seems I can just do the member lookup in an earlier phase where we don't have bridges yet.

[SethTisue]

scala/scala#6531

[johanandren]

Yay, thank you!