Always generate companion object for value class, even with illegal params

Author: odersky

compiler/src/dotty/tools/dotc/ast/Desugar.scala

@@ -723,10 +723,7 @@ object desugar {
       else if (companionMembers.nonEmpty || companionDerived.nonEmpty || isEnum)
         companionDefs(anyRef, companionMembers)
       else if (isValueClass)
-        impl.constr.vparamss match {
-          case (_ :: Nil) :: _ => companionDefs(anyRef, Nil)
-          case _ => Nil // error will be emitted in typer
-        }
+        companionDefs(anyRef, Nil)
       else Nil
 
     enumCompanionRef match {

tests/pos/i7819.scala

@@ -0,0 +1 @@
+class Foo()(val x: Any) extends AnyVal