Typechecker inferencing orphan type T

[rcano]

Code to reproduce it https://gist.github.com/rcano/14c1b3af9bec4b9dadbc7ba2fd097fd3
(Note, requires javafx which comes bundled with Oracle's JDK or you can install with to openjdk)

The error looks like this:

error when pickling type T
error when pickling type javafx.scene.control.ComboBox[T]
error when pickling tree javafx.scene.control.ComboBox[T]
error when pickling tree val cb: javafx.scene.control.ComboBox[T] = 
  Dsl.BorderPaneBuilder(this).right[javafx.scene.control.ComboBox[T]](
    Dsl.combobox[T](Test.this.planets: Planet*)
  )
error when pickling tree (planets: scala.collection.Seq[Planet] @scala.annotation.internal.Repeated())
   extends
 javafx.scene.layout.BorderPane() { $: Test => 
  private[this] val planets: scala.collection.Seq[Planet] @Repeated
  val cb: javafx.scene.control.ComboBox[T] = 
    Dsl.BorderPaneBuilder(this).right[javafx.scene.control.ComboBox[T]](
      Dsl.combobox[T](Test.this.planets: Planet*)
    )
  Test.this.cb.getSelectionModel().selectLast()
}
error when pickling tree @scala.annotation.internal.SourceFile(
  "/home/randa/Development/testdotty/src/main/scala/Main.scala"
) class Test(
  planets: scala.collection.Seq[Planet] @scala.annotation.internal.Repeated()
) extends javafx.scene.layout.BorderPane() { $: Test => 
  private[this] val planets: scala.collection.Seq[Planet] @Repeated
  val cb: javafx.scene.control.ComboBox[T] = 
    Dsl.BorderPaneBuilder(this).right[javafx.scene.control.ComboBox[T]](
      Dsl.combobox[T](Test.this.planets: Planet*)
    )
  this.cb.getSelectionModel().selectLast()
}
error when pickling tree package <empty> {
  import javafx.scene.Node
  import javafx.scene.control._
  import javafx.scene.layout._
  import Dsl._
  @scala.annotation.internal.SourceFile(
    "/home/randa/Development/testdotty/src/main/scala/Main.scala"
  ) class Test(
    planets: scala.collection.Seq[Planet] @scala.annotation.internal.Repeated()
  ) extends javafx.scene.layout.BorderPane() { $: Test => 
    private[this] val planets: scala.collection.Seq[Planet] @Repeated
    val cb: javafx.scene.control.ComboBox[T] = 
      Dsl.BorderPaneBuilder(this).right[javafx.scene.control.ComboBox[T]](
        Dsl.combobox[T](Test.this.planets: Planet*)
      )
    this.cb.getSelectionModel().selectLast()
  }
}

The orphan type T gets leaked even to the "presentation compiler" exposed through the language server.

[smarter]

Thanks for the report! I managed to reduce the testcase further:

class Inv[T]

class Test {
  implicit class Wrong(test: Test) {
    def right: Any = ???
  }
  implicit class Right(test: Test) {
    def right(node: Any): Any = ???
  }

  def inv[T](x: T): Inv[T] = ???

  this.right(inv(1))
}

[smarter]

this.right(inv(1)) is typechecked inside a FunProto#typedArgs, this is very reminiscent of #1460. In general the way FunProto deals with caches and contexts is very dubious, I tried to fix it in #2922 but that's not enough.