Rewrite with of "onAction = _ => println("x")" with "-source:3.7-migration" leads to invalid code

[jpsacha]

Compiler version

"3.7.0-RC3"

Minimized code

This is the working code that I can minimize to. The code compiles file, but scalac option -source:3.7-migration generates invalid code

Original file file: ScalaFXHelloWorld.scala:

import scalafx.application.JFXApp3
import scalafx.geometry.Insets
import scalafx.scene.Scene
import scalafx.scene.control.Button
import scalafx.scene.layout.HBox

object ScalaFXHelloWorld extends JFXApp3:

  override def start(): Unit =
    stage = new JFXApp3.PrimaryStage:
      title = "ScalaFX Hello World"
      scene = new Scene:
        content = new HBox:
          padding = Insets(21)
          children +=
            new Button:
              text = "Print Hello World!"
              onAction = _ => println("Hello World!")

File build.sbt

scalaVersion := "3.7.0-RC3"

libraryDependencies +=   "org.scalafx"   %% "scalafx"   % "23.0.1-R34"

scalacOptions ++= Seq(
  "-rewrite",
  "-source:3.7-migration",
)

// Fork a new JVM for 'run' and 'test:run' to avoid JavaFX double initialization problems
fork := true

Output

When the code is build a warning is issued, but code copiles:

[warn] -- Warning: C:\tmp\myscalafxproj\src\main\scala\my\scalafx\ScalaFXHelloWorld.scala:20:27
[warn] 20 |              onAction = _ => println("Hello World!")                                                                                                                                                           
[warn]    |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                                                                                                           
[warn]    |Implicit parameters should be provided with a `using` clause.                                                                                                                                                   
[warn]    |This code can be rewritten automatically under -rewrite -source 3.7-migration.                                                                                                                                  
[warn]    |To disable the warning, please use the following option:                                                                                                                                                        
[warn]    |  "-Wconf:msg=Implicit parameters should be provided with a `using` clause:s"                                                                                                                                   
[info] [patched file C:\tmp\myscalafxproj\src\main\scala\my\scalafx\ScalaFXHelloWorld.scala]
[warn] one warning found                                                                                                

The rewritten code, the last line changed, using was added:

package my.scalafx

import scalafx.application.JFXApp3
import scalafx.geometry.Insets
import scalafx.scene.Scene
import scalafx.scene.control.Button
import scalafx.scene.layout.HBox

object ScalaFXHelloWorld extends JFXApp3:

  override def start(): Unit =
    stage = new JFXApp3.PrimaryStage:
      title = "ScalaFX Hello World"
      scene = new Scene:
        content = new HBox:
          padding = Insets(21)
          children +=
            new Button:
              text = "Print Hello World!"
              onAction = using _ => println("Hello World!")

This code will no longer compile.

Expectation

Re-generated code compiles without errors

See also: scalafx/scalafx#421

A simple SBT project is attaches

[jpsacha]

myscalafxproj.zip

[som-snytt]

This duplicates #22731 but with the twist that the application is an assignment.

That is an unusual signature, so I don't know what the check should do.

class C:
  def x: Runnable = ???
  def x_=(implicit r: Runnable): Unit = ()

@main def test = println:
  val c = C()
  c.x = { () => () }
  c.x_={ () => () }
  c.x_=(using () => ())

[som-snytt]

Closing as duplicate because I see the fix already does the reasonable thing (nothing) except for the reasonable case of a regular method call with parens.

This is the patched:

  c.x = { () => () }
  c.x = () => ()
  c.x_={() => ()}
  c.x_=(using () => ())

[som-snytt]

I intended to add that it would be nice not to warn about assignment.

8 |  c.x = { () => () }
  |        ^^^^^^^^^^^^
  |Implicit parameters should be provided with a `using` clause.

It would be nicer not to have an implicit parameter for an assignment method.

[jpsacha]

@som-snytt there is still the same problem in 3.7.0-RC4. Code generated by "-rewrite -source 3.7-migration" is invalid and will not compile

[som-snytt]

@jpsacha I think 3.7.0 branch requires backporting from main (which is future 3.7.1). During RC release process, probably they balance risk and urgency to decide whether to do that.

on github, clicking on the commit shows what branch(es) it is on.