"cannot resolve reference to type" when type member of self-type appears in method type

[andreaTP]

Compiler version

3.0.0-M3

Minimized code

I haven't managed to minimize the problem but is reproducible here:
https://github.com/akka/akka/tree/repro-scala3

sbt -Dakka.build.scalaVersion=3.0 akka-actor/compile

Output

[error] -- Error: /Users/andreatp/workspace/tmp/akka/akka-actor/src/main/scala/akka/event/ActorClassificationUnsubscriber.scala:61:6 
[error] 61 |      bus.unsubscribe(actor)
[error]    |      ^
[error]    |cannot resolve reference to type (ActorClassificationUnsubscriber.this.bus : 
[error]    |  akka.event.ManagedActorClassification
[error]    |).Subscriber
[error]    |the classfile defining the type might be missing from the classpath
[error] one error found

Expectation

Compiles as with scalac 2.12 - 2.13

[griggt]

Minimized:

trait ActorRef

trait ActorEventBus {
  type Subscriber = ActorRef
}

trait ManagedActorClassification { this: ActorEventBus =>
  def unsubscribe(subscriber: Subscriber, from: Any): Unit
  def unsubscribe(subscriber: Subscriber): Unit
}

class Unsubscriber(bus: ManagedActorClassification) {
  def test(a: ActorRef): Unit = bus.unsubscribe(a)
}

Output from Scala compiler version 3.0.0-RC1-bin-SNAPSHOT-git-8d3275c:

cannot take signature of MethodType(List(subscriber), List(TypeRef(TermRef(ThisType(TypeRef(ThisType(TypeRef(NoPrefix,module class <empty>)),class Unsubscriber)),val bus),Subscriber)), TypeRef(TermRef(ThisType(TypeRef(NoPrefix,module class <root>)),object scala),class Unit))
-- Error: i11226.scala:13:32 ---------------------------------------------------
13 |  def test(a: ActorRef): Unit = bus.unsubscribe(a)
   |                                ^
   |cannot resolve reference to type (Unsubscriber.this.bus : ManagedActorClassification).Subscriber
   |the classfile defining the type might be missing from the classpath

[smarter]

@odersky Should we disallow references to members of the self-type in the types of public methods?

[griggt]

Without the overload, the error is

-- [E007] Type Mismatch Error: i11226.scala:12:48 ------------------------------
12 |  def test(a: ActorRef): Unit = bus.unsubscribe(a)
   |                                                ^
   |                              Found:    (a : ActorRef)
   |                              Required: Unsubscriber.this.bus.Subscriber

[FlorianCassayre]

I came across this bug today, here is the minimization I came up with:

trait A {
  class T()
}
trait B {
  this: A =>
  def f(a: Int = 0): Any
}
trait C extends B {
  this: A =>
  def f(t: T): Any
}

Interestingly, removing the default value solves the problem.

[smarter]

This might be the same bug as #15030

[cchantep]

The issue seems still there is one form or another.
Since 3.3.0 up to 3.4.1 this code can no longer be compiled and the compiler crashes with the following error.

cannot resolve reference to type reactivemongo.api.collections.GenericCollectionWithCommands[P]#pack.type.Writer

The following declaration seems like a possible workaround.

private[api] trait GenericCollectionWithCommands[P <: SerializationPack] {
  //self: GenericCollection[P] =>

  // Workaround for self-type issue with Scala 3
  // https://github.com/scala/scala3/issues/11226
  protected def selfCollection: GenericCollection[P]

[odersky]

It's different from #15030.