Imported From: https://issues.scala-lang.org/browse/SI-8197?orig=1
Reporter: Jarek Sacha (jpsacha)
Affected Versions: 2.11.0-M8
See #6169

@adriaanm said:
Thanks for reporting! I think this is because of the fix for #1786, and it looks related to #8198.
The fix for #1786 is useful, but it now also infers more precise bounds in expected types (it was mostly intended to have more precise types for "provided things").

I haven't checked, but is it legal in java to assign skinProperty to a variable with type javafx.scene.control.Skin<C extends Skinnable>,
where ObjectProperty<Skin<?>> skinProperty()??

Jarek Sacha (jpsacha) said:
To clarify, the bug report is in response to 2.11.0-M8 announcement requesting examples of code that does not compile but compiled with 2.10.

The code that does not compile looks like this

import scalafx.beans.property.ObjectProperty

def skin: ObjectProperty[javafx.scene.control.Skin[_]] = delegate.skinProperty

skinProperty is a JavaFX method of javafx.scene.control.Skinnable with returning type ObjectProperty<javafx.scene.control.Skin<?>>, so the type parameters do match here. I think the problem is that javafx.scene.control.Skin is defined as

Interface Skin<C extends Skinnable>

This may be a bug in JavaFX API, most likely skinProperty should be returning ObjectProperty<javafx.scene.control.Skin<C extends Skinnable>>. Or maybe it is defined as is to avoid some type parametrization cycle: Skin defined in terms Skinnable, and Skinnable in terms of Skin. This somehow type-checks in Java and Scala 2.10.
A work around, in this case, is to force type-cast:

import scalafx.beans.property.ObjectProperty

def skin: ObjectProperty[jfxsc.Skin[_ <: jfxsc.Skinnable]] = {
   val p = delegate.skinProperty
   p.asInstanceOf[javafx.beans.property.ObjectProperty[jfxsc.Skin[_ <: jfxsc.Skinnable]]]
}

though it is quite ugly.

Note that there is an implicit conversion from javafx.beans.property.ObjectProperty to scalafx.beans.property.ObjectProperty, which may or may not be involved somehow:

package scalafx.beans.property

object ObjectProperty {
  
  implicit def sfxObjectProperty2jfx[T <: Any](op: ObjectProperty[T]) = op.delegate
...
}

where op.delegate is of type {noformat}javafx.beans.property.ObjectProperty[T]{noformat}.

I did not find yet workarounds for the other compilation errors shown in the original report. The third error is a bit similar. But the second is reporting some type invariance issues, it may be a different thing.

@adriaanm said:
Thanks for the detailed follow-up! I'm working on a fix here: https://github.com/adriaanm/scala/compare/t6169

Jarek Sacha (jpsacha) said:
Do you think this fix will also resolve the second error message?

[error] D:\ScalaFX\scalafx.hg-publish\scalafx\src\main\scala\scalafx\scene\control\TableColumn.scala:100: type mismatch;
[error]  found   : javafx.event.EventType[javafx.scene.control.TableColumn.CellEditEvent[_, _]]
[error]  required: javafx.event.EventType[javafx.scene.control.TableColumn.CellEditEvent[S, T]]
[error] Note: javafx.scene.control.TableColumn.CellEditEvent[_, _] >: javafx.scene.control.TableColumn.CellEditEvent[S, T], but Java-defined class EventType is invariant in type T.
[error] You may wish to investigate a wildcard type such as `_ >: javafx.scene.control.TableColumn.CellEditEvent[S, T]`. (SLS 3.2.10)
[error]       this(new jfxsc.TableColumn.CellEditEvent(table, pos, eventType, newValue))

Stephen Compall (s11001001) said:
jpsacha: I don't think this #8198 related, but see #6169 for much further discussion. It isn't a bug in the JavaFX API, because some of the bounds that it infers yield unspeakable existential types in Java, mostly on the *Builders. With a fix for 6169, your interactions with JavaFX types should get smoother and less casty overall.

Stephen Compall (s11001001) said:
...well, except insofar as the non-F-bound case in #1786 interacts with the non-F-bound case of #6169 to cause your issues with non-F-bounded existentials, something similar would occur between #8198 and #6169, were the former fixed but not the latter.

@adriaanm said:
I can confirm the first error is due to #6169. The other two are separate :(

@adriaanm said (edited on Feb 6, 2014 6:32:35 PM UTC):
note to self: can this subsume the fix for #1786

@adriaanm said:
Jarek, could you give the latest nightly a shot? I hope we've fixed/reverted the existential regressions :)

Jarek Sacha (jpsacha) said:
I assume that I can compile with the latest nightly using

sbt> ++2.11.0-SNAPSHOT
sbt> compile

Looks that is is using 2.11.0-20140213.015456-546. Still similar errors:

...
[info] downloading http://repo1.maven.org/maven2/org/scala-lang/scala-reflect/2.10.0/scala-reflect-2.10.0.jar ...
[info]  [SUCCESSFUL ] org.scala-lang#scala-reflect;2.10.0!scala-reflect.jar (6573ms)
[info] downloading https://oss.sonatype.org/content/repositories/snapshots/org/scala-lang/scala-reflect/2.11.0-SNAPSHOT/scala-reflect-2.11.0-20140213.015456-546.jar ...
[info]  [SUCCESSFUL ] org.scala-lang#scala-reflect;2.11.0-SNAPSHOT!scala-reflect.jar (9448ms)
[info] Done updating.
[info] 'compiler-interface' not yet compiled for Scala 2.11.0-20140212-225812-2240464dea. Compiling...
[info]   Compilation completed in 11.462 s
[error] D:\scalafx.hg\scalafx\src\main\scala\scalafx\scene\control\TableColumn.scala:100: type mismatch;
[error]  found   : javafx.event.EventType[javafx.scene.control.TableColumn.CellEditEvent[_, _]]
[error]  required: javafx.event.EventType[javafx.scene.control.TableColumn.CellEditEvent[S, T]]
[error] Note: javafx.scene.control.TableColumn.CellEditEvent[_, _] >: javafx.scene.control.TableColumn.CellEditEvent[S, T], but Java-defined class EventType is invariant in type T.
[error] You may wish to investigate a wildcard type such as `_ >: javafx.scene.control.TableColumn.CellEditEvent[S, T]`. (SLS 3.2.10)
[error]       this(new jfxsc.TableColumn.CellEditEvent(table, pos, eventType, newValue))
[error]                                                            ^
[error] D:\scalafx.hg\scalafx\src\main\scala\scalafx\scene\web\WebEvent.scala:69: type mismatch;
[error]  found   : scalafx.event.EventType[javafx.scene.web.WebEvent[_]]
[error]  required: javafx.event.EventType[javafx.scene.web.WebEvent[T]]
[error]   def this(source: Any, eventType: EventType[jfxsw.WebEvent[_]], data: T) = this(new jfxsw.WebEvent(source, eventType, data))
[error]                                                                                                             ^
[error] two errors found

@adriaanm said:
Thanks, looks like we made some progress. I'll look into the remaining ones tomorrow.

Jarek Sacha (jpsacha) said:
With latest nightly 20140214.015224-547, I no longer have errors reported above. I still have one regression:

[error] D:\scalafx.hg\scalafx-demos\src\main\scala\scalafx\controls\SplitMenuButtonDemo.scala:48: ambiguous reference to overloaded definition,
[error] both constructor SplitMenuButton in class SplitMenuButton of type (items: scalafx.scene.control.MenuItem*)scalafx.scene.control.SplitMenuButton
[error] and  constructor SplitMenuButton in class SplitMenuButton of type (delegate: javafx.scene.control.SplitMenuButton)scalafx.scene.control.SplitMenuButton
[error] match argument types ()
[error]           new SplitMenuButton {
[error]               ^
[error] one error found

@adriaanm said (edited on Feb 15, 2014 4:05:13 AM UTC):
Could you explain how this is supposed to typecheck?

 new SplitMenuButton {
            text = "SplitMenuButton 1"
            onAction = {ae: ActionEvent => {println(ae.eventType + " occurred on SplitMenuButton")}}
            items = List(
              new MenuItem("MenuItem A") {
                onAction = {ae: ActionEvent => {println(ae.eventType + " occurred on Menu Item A")}}
              },
              new MenuItem("MenuItem B")
            )
          },

@adriaanm said:
In other words, a self-contained repro would really help -- running out of time for the RC deadline. Thanks for all your help so far!

Jarek Sacha (jpsacha) said (edited on Feb 15, 2014 5:11:30 AM UTC):
I am not sure what you mean above by 'type check'. It is important to add "import scalafx.Includes._" that pulls a lot of implicit that may "type check" the code above, for instance, for assignment "onAction = {ae: ActionEvent => ...}"

new SplitMenuButton() should get a default constructor parameter supplied (delegate = new jfxsc.SplitMenuButton()).

Sorry I an not able to provide a reduced example. In simple examples similar code with one of the constructor had a default parameter and other has a has a T* argument compiles fine. There looks to be something more involved here. I look more tomorrow. Some other way of simplifying this is below.

A thing that may help is that if I use scalafx library (build for 2.10) but 2.11.0-M8 compiler and try to instantiate SplitMenuButton

import scalafx.scene.control.SplitMenuButton

class A { 
  val a = new SplitMenuButton()
}

I get similar error

[error] ....scala:6: ambiguous reference to overloaded definition,
[error] both constructor SplitMenuButton in class SplitMenuButton of type (items: scalafx.scene.control.MenuItem*)scalafx.scene.control.SplitMenuButton
[error] and  constructor SplitMenuButton in class SplitMenuButton of type (delegate: javafx.scene.control.SplitMenuButton)scalafx.scene.control.SplitMenuButton
[error] match argument types ()
[error]   val a = new SplitMenuButton
[error]           ^
[error] one error found

Just for a reference SBT setup looks like this:

scalaVersion := "2.11.0-M8"

libraryDependencies += "org.scalafx" % "scalafx_2.10" % "1.0.0-M7"

resolvers += "Sonatype OSS Snapshots" at "https://oss.sonatype.org/content/repositories/snapshots"

scalacOptions ++= Seq("-unchecked", "-deprecation", "–explaintypes", "–Xlint")

unmanagedJars in Compile += Attributed.blank(file(System.getenv("JAVA_HOME") + "/jre/lib/jfxrt.jar"))

I need to run, I will try to attach a sample project tomorrow.

@adriaanm said:
minimized:

Welcome to Scala version 2.11.0-M8 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_65).
Type in expressions to have them evaluated.
Type :help for more information.

scala> class Foo(val x: String = "a") {
     |   def this(bla: Int*) {
     |     this("a")
     |   }
     | }
defined class Foo

scala> new Foo
<console>:10: error: ambiguous reference to overloaded definition,
both constructor Foo in class Foo of type (bla: Int*)Foo
and  constructor Foo in class Foo of type (x: String)Foo
match argument types ()
              new Foo
              ^

Welcome to Scala version 2.10.4-RC1 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_65).
Type in expressions to have them evaluated.
Type :help for more information.

scala> class Foo(val x: String = "a") {
     |   def this(bla: Int*) {
     |     this("a")
     |   }
     | }
defined class Foo

scala> new Foo
res0: Foo = Foo@77892f2c

@adriaanm said:
Looks related to #4728

@adriaanm said:
Git bisect says it regressed in scala/scala@6c7e6eb

@adriaanm said:
Which overload do you expect to be picked?

@adriaanm said:
scala/scala#3562

@paulp said:
Great commit message though.

@adriaanm said:
The commit in which it "regressed" merely revealed an existing flaw by cleaning up the rest of the logic. I'm commenting over at the PR what I think should've been the real fix, but I'm not sure we should go there days before RC1.

@adriaanm said:
EDIT: it's mostly spec exegesis, I think the PR I submitted is an accurate fix. Clarifying with scala/scala-dist#132

@retronym said:
Followup: scala/scala#3572

Jarek Sacha (jpsacha) said:
ScalaFX now compiles and runs with 2.11.0-SNAPSHOT (20140222) !!!
Thanks guys :)

@adriaanm said:
Thank you for reporting, minimizing and testing!!

@adriaanm said:
Better fix at scala/scala#3583

I don't expect this to break scalafx since we put in a regression test, but please let me know if somehow it breaks anything for you.

Jarek Sacha (jpsacha) said:
ScalaFX runs with 2.11.0-20140226.015145-560, though I am not sure if scala/scala#3583 is in it already.

@adriaanm said:
Yep. Thanks for confirming!