REPL breaks when complicated type is inferred

I was trying to investigate something about how dotty infers types that scalac infers as existential “forSome” types. Alas the REPL only shows me an error that seems to come from the code generation phase of the REPL itself.

scala> 
object foo { 
    trait ShapeLevel 
    trait FlatShapeLevel extends ShapeLevel 
    trait ColumnsShapeLevel extends FlatShapeLevel 
   
    abstract class Shape[Level <: ShapeLevel, -Mixed, Unpacked, Packed] 
    object Shape extends TupleShapeImplicits { } 
    trait TupleShapeImplicits { 
      implicit final def tuple2Shape[Level <: ShapeLevel, M1,M2, U1,U2, P1,P2](implicit u1: Shape[_ <: Level, M1, U1, P1], u2: Shape[_ <: Level, M2, U2, P2]): Shape[Level, (M1,M2), (U1,U2), (P1,P2)] = ??? 
    } 
  } 
defined module foo
scala> import foo._ 
import foo._
scala> implicit val shape: Shape[_ <: FlatShapeLevel, Int, Int, _] = null 
val shape: foo.Shape[_ <: foo.FlatShapeLevel, Int, Int, _] = null
scala> def hint = Shape.tuple2Shape(shape, shape) 
-- Error: <console>:4:4 --------------------------------------------------------
4 |(""+"def hint: foo.Shape[foo.FlatShapeLevel, (Int, Int), (Int, Int), (shape.Packed, 
  |    ^
  |    unclosed string literal
-- [E039] Syntax Error: <console>:6:1 ------------------------------------------
6 |)]\n"
  | ^
  | ';' expected, but `Packed` found

[felixmulder]

Thanks for reporting @Jasper-M! We will shortly be reimplementing the REPL from scratch. Hopefully, this won’t rear its ugly head in the new shiny version! 😃

[felixmulder]

See #3020, there was still an issue with how the types were printed.