REPL breaks when complicated type is inferred

[Jasper-M]

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! :)

[OlivierBlanvillain]

@felixmulder Actually I take back what I've said in #2991 (I tested with scalac repl...), this breaks the new repl in a different way:

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 object foo
scala> import foo._
scala> implicit val shape: Shape[_ <: FlatShapeLevel, Int, Int, _] = null
Exception in thread "main" java.lang.reflect.InvocationTargetException
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at dotty.tools.repl.Rendering.valueOf(Rendering.scala:56)
        at dotty.tools.repl.Rendering.renderVal(Rendering.scala:75)
        at dotty.tools.repl.ReplDriver.$anonfun$displayDefinitions$8(ReplDriver.scala:262)
        at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:234)
        at scala.collection.mutable.ResizableArray.foreach(ResizableArray.scala:59)
        at scala.collection.mutable.ResizableArray.foreach$(ResizableArray.scala:52)
        at scala.collection.mutable.ArrayBuffer.foreach(ArrayBuffer.scala:48)
        at scala.collection.TraversableLike.map(TraversableLike.scala:234)
        at scala.collection.TraversableLike.map$(TraversableLike.scala:227)
        at scala.collection.AbstractTraversable.map(Traversable.scala:104)
        at dotty.tools.repl.ReplDriver.displayMembers$1(ReplDriver.scala:262)
        at dotty.tools.repl.ReplDriver.$anonfun$displayDefinitions$15(ReplDriver.scala:289)
        at scala.Option.map(Option.scala:146)
        at dotty.tools.repl.ReplDriver.$anonfun$displayDefinitions$13(ReplDriver.scala:287)
        at dotty.tools.dotc.core.Periods.atPhase(Periods.scala:26)
        at dotty.tools.dotc.core.Phases.atPhase(Phases.scala:36)
        at dotty.tools.dotc.core.Phases.atPhase$(Phases.scala:35)
        at dotty.tools.dotc.core.Contexts$Context.atPhase(Contexts.scala:58)
        at dotty.tools.repl.ReplDriver.displayDefinitions(ReplDriver.scala:282)
        at dotty.tools.repl.ReplDriver.$anonfun$compile$2(ReplDriver.scala:219)
        at scala.util.Either.fold(Either.scala:188)
        at dotty.tools.repl.ReplDriver.compile(ReplDriver.scala:213)
        at dotty.tools.repl.ReplDriver.interpret(ReplDriver.scala:187)
        at dotty.tools.repl.ReplDriver.runUntilQuit(ReplDriver.scala:140)
        at dotty.tools.repl.Main$.main(Main.scala:6)
        at dotty.tools.repl.Main.main(Main.scala)
Caused by: java.lang.NullPointerException
        at dotty.Show$$anon$1.show(Show.scala:16)
        at dotty.Show$ShowValue$.show$extension(Show.scala:25)
        at rs$line$3$.shapeShow(rs$line$3:1)
        at rs$line$3.shapeShow(rs$line$3)
        ... 30 more
java.lang.RuntimeException: Nonzero exit code returned from runner: 1
        at scala.sys.package$.error(package.scala:27)
[trace] Stack trace suppressed: run last dotty-repl/compile:runMain for the full output.
[error] (dotty-repl/compile:runMain) Nonzero exit code returned from runner: 1
[error] Total time: 23 s, completed Aug 23, 2017 11:43:43 AM

[felixmulder]

My first guess is that there should be a null check when trying to render the rhs of the last val. I'll look into it after lunch :)

[felixmulder]

Yes, it seems like that's the issue, will fix asap

[felixmulder]

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