REPL: chained extension methods on opaque types can only be called once

[bishabosha]

Minimized code

Only in the REPL, it seems like calling a chain of extension methods has a strange side effect that prevents it from happening again.

First, compile this source:

// IArr.scala
package example
import scala.reflect.ClassTag

object opaques:
  opaque type IArr[+T] = Array[_ <: T]
  given arrayOps: AnyRef with
    extension [T](arr: IArr[T]) def reverse: IArr[T] =
      genericArrayOps(arr).reverse

    extension [T](arr: IArr[T]) def sorted(using math.Ordering[T]): IArr[T] =
      genericArrayOps(arr).sorted
end opaques

type IArr[+T] = opaques.IArr[T]

object IArr:
  inline def apply(inline x: Int, inline xs: Int*): IArr[Int] = Array(x, xs: _*).asInstanceOf

Then run the repl task with IArr on the classpath

scala> import example.IArr

scala> IArr(1,2,3).reverse.sorted                                                                                   
val res0: example.opaques.IArr[Int] = Array(1, 2, 3)

scala> IArr(1,2,3).reverse.sorted                                                                                   
1 |IArr(1,2,3).reverse.sorted
  |^^^^^^^^^^^^^^^^^^^^^^^^^^
  |value sorted is not a member of example.opaques.IArr[Int].
  |An extension method was tried, but could not be fully constructed:
  |
  |    genericArrayOps[T](
  |      example.opaques.arrayOps.reverse[Int](example.IArr.apply(1, [2,3 : Int]*))
  |    )

scala> 

Expectation

this is ok when they are called one after the other in a source file

[OlivierBlanvillain]

@anatoliykmetyuk Not sure who to assign this to, are you the most knowledgeable person on REPL at the moment?

[som-snytt]

The type seems to change subtly.

scala> IArray(1,2,3).reverse
val res0: opaques.IArray[Int] = Array(3, 2, 1)

scala> IArray(1,2,3).reverse
val res1: scala.opaques.IArray[Int] = Array(3, 2, 1)

Also

scala> IArray.emptyIntIArray.reverse
val res0: opaques.IArray[Int] = Array()

scala> IArray.emptyIntIArray.reverse
1 |IArray.emptyIntIArray.reverse
  |^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |value reverse is not a member of opaques.IArray[Int].
  |An extension method was tried, but could not be fully constructed:
  |
  |    opaques.arrayOps.reverse[T](IArray.emptyIntIArray)

[odersky]

Seems to work in 3.0-M3

[som-snytt]

Still broken on M3 and also current master

[success] Total time: 126 s (02:06), completed Dec 27, 2020, 9:32:57 AM
Starting scala3 REPL...
scala>

scala> IArray(1,2,3).reverse.sorted
val res0: opaques.IArray[Int] = Array(1, 2, 3)

scala> IArray(1,2,3).reverse.sorted
1 |IArray(1,2,3).reverse.sorted
  |^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |value sorted is not a member of scala.opaques.IArray[Int].
  |An extension method was tried, but could not be fully constructed:
  |
  |    copyArrayToImmutableIndexedSeq[T](
  |      opaques.arrayOps.reverse[Int](
  |        Array.apply(1, [2,3 : Int]:Int*:Int*).asInstanceOf[opaques.IArray[Int]]:
  |          IArray[Int]
  |      )
  |    )

scala>  

also per previous comment

scala> IArray(1,2,3).reverse
val res0: opaques.IArray[Int] = Array(3, 2, 1)

scala> IArray(1,2,3).reverse
val res1: scala.opaques.IArray[Int] = Array(3, 2, 1)

scala> IArray(1,2,3).reverse.sorted
1 |IArray(1,2,3).reverse.sorted
  |^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |value sorted is not a member of scala.opaques.IArray[Int].
  |An extension method was tried, but could not be fully constructed:
  |
  |    genericArrayOps[T](
  |      opaques.arrayOps.reverse[Int](
  |        Array.apply(1, [2,3 : Int]:Int*:Int*).asInstanceOf[opaques.IArray[Int]]:
  |          IArray[Int]
  |      )
  |    )

scala> (IArray(1,2,3).reverse: opaques.IArray[Int]).sorted
val res2: scala.opaques.IArray[Int] = Array(1, 2, 3)

scala> (IArray(1,2,3).reverse: scala.opaques.IArray[Int]).sorted
val res3: scala.opaques.IArray[Int] = Array(1, 2, 3)

scala> (IArray(1,2,3).reverse: IArray[Int]).sorted
val res4: scala.opaques.IArray[Int] = Array(1, 2, 3)

scala> 

[bishabosha]

This seems to be fixed for IArray since #11354 , but it can be reproduced by compiling the the old definition under a new name and adding to the classpath in the repl task

[nicolasstucki]

@bishabosha could you include the code you needed to reproduce it?

[bishabosha]

@nicolasstucki I have updated the original post

[mpilquist]

Is this the same issue or something new?

➜  cs launch scala3-repl
scala> object Foo:
     |   opaque type Bar = Int
     |   object Bar:
     |     extension (b: Bar) def flip: Bar = -b
     |     def apply(x: Int): Bar = x
     |
// defined object Foo

scala> val a = Foo.Bar(42)
val a: Foo.Bar = 42

scala> val b = a.flip
val b: Foo.Bar = -42

scala> val c = b.flip
val c: Foo.Bar = 42

scala> val d = c.flip
1 |val d = c.flip
  |        ^^^^^^
  |value flip is not a member of Foo.Bar, but could be made available as an extension method.
  |
  |The following import might fix the problem:
  |
  |  import Foo.Bar.flip
  |

scala>