Synth method generation failed on invalid value class

[dos65]

Compiler crashes on synthetic methods generation on value class with more that one parameter

class A(a:Int, b:Int) extends AnyVal 

error while transforming (a: Int, b: Int) extends AnyVal() { 
  private[this] val a: Int
  private[this] val b: Int
}
error while transforming @scala.annotation.internal.SourceFile("/home/dos65/projects/tmp/dotty_samples/3.scala") final class A(a: Int, b: Int)
   extends
 AnyVal() { 
  private[this] val a: Int
  private[this] val b: Int
}
error while transforming package <empty> {
  @scala.annotation.internal.SourceFile("/home/dos65/projects/tmp/dotty_samples/3.scala") final class A(a: Int, b: Int)
     extends
   AnyVal() { 
    private[this] val a: Int
    private[this] val b: Int
  }
  final lazy module val A: A$ = new A$()
  final module class A$() extends Object() { this: A.type =>}
}

exception occurred while compiling /home/dos65/projects/tmp/dotty_samples/3.scala
Exception in thread "main" java.lang.AssertionError: assertion failed
	at scala.Predef$.assert(Predef.scala:151)
	at dotty.tools.dotc.transform.SyntheticMethods.dotty$tools$dotc$transform$SyntheticMethods$$valueHashCodeBody$1(SyntheticMethods.scala:141)
	at dotty.tools.dotc.transform.SyntheticMethods$$anonfun$syntheticRHS$1$1.apply(SyntheticMethods.scala:87)
	at dotty.tools.dotc.transform.SyntheticMethods$$anonfun$syntheticRHS$1$1.apply(SyntheticMethods.scala:87)
	at dotty.tools.dotc.ast.tpd$.polyDefDef(tpd.scala:200)
	at dotty.tools.dotc.ast.tpd$.DefDef(tpd.scala:170)
	at dotty.tools.dotc.transform.SyntheticMethods.syntheticDef$1(SyntheticMethods.scala:96)
	at dotty.tools.dotc.transform.SyntheticMethods.dotty$tools$dotc$transform$SyntheticMethods$$syntheticDefIfMissing$1(SyntheticMethods.scala:70)
	at dotty.tools.dotc.transform.SyntheticMethods$$anonfun$syntheticMethods$1.apply(SyntheticMethods.scala:190)
	at dotty.tools.dotc.transform.SyntheticMethods$$anonfun$syntheticMethods$1.apply(SyntheticMethods.scala:190)
	at scala.collection.immutable.List.flatMap(List.scala:327)
	at dotty.tools.dotc.transform.SyntheticMethods.syntheticMethods(SyntheticMethods.scala:190)
	at dotty.tools.dotc.transform.SyntheticMethods.addSyntheticMethods(SyntheticMethods.scala:195)
	at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:215)
	at dotty.tools.dotc.ast.Trees$Instance$TreeMap.transform(Trees.scala:1149)
	at dotty.tools.dotc.transform.MacroTransform$Transformer.transform(MacroTransform.scala:55)
	at dotty.tools.dotc.transform.PostTyper$PostTyperTransformer.transform(PostTyper.scala:242)

Currently value class checking is in RefChecks, should it be moved on Typer?
@smarter

[felixmulder]

ping: @DarkDimius, @odersky

[odersky]

I think it makes sense to do this in typer.

[DarkDimius]

Instead of putting more stuff into typer, I'd propose to move such checks into InfoTransformer of RefChecks.